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Garage base - Stuart Woodrow - Mar 28th 2001 | ||||
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I have laid my own garage base using a barrow mix supplier, my problem is that this dealer has not put enough concrete in the mix and the top in parts is quite loose if you rub your foot over it.
Is there a way of making the surface hard or will I have to put another lare of concrete over the top? |
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Tony McCormack - Mar 27th 2001 | ||||
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The first thing I would suggest is that you get the concrete supplier back to see what they have to say about the sub-standard concrete. If this base has been down for more than 7 days, you should NOT be able to scuff the top surface, full stop!
This phenomenon is not always because of inadequate cement content; it can be caused by contamination of the concrete, or exposure to heavy rain and/or frosts, but whatever, I would get the contractor back and pressurise them to replace it at their own expense. Other than with freshly poured concrete, there is no magic ingredient you can apply to the surface that will render it hard enough for your purposes. If you get nowhere with your supplier, you might be able to scabble off the loose surface material and replace it with a 25mm thick screed of a granolithic mortar, bonded to the underlying concrete. See the concretes page for more info on granolithic mortars. |
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Geo-textiles - John at Aintree Paving - Mar 29th 2001 | ||||
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If money was no object then would you put a membrane under your crusher run as an added protection on a driveway to stop the sub base sinking into the subsoil?
You say in your notes that they form little use beneath a driveway but I suspect you only mean a gravel drive. I see it as a selling point when pricing up a job and surely a driveway would never settle if its layers cant go anywhere. |
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Tony McCormack - Apr 2nd 2001 | ||||
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It all depends on the competence of the sub-grade. For most domestic driveways, be they blockwork, gravel, bitmac or anything else, there is not usually any need for a geo-membrane unless the sub-grade is particularly weak, there are pernicious weeds, such as Japanese Knotweed (Polygonum japonicum), or other extreme circumstances.
Geo-membranes should never be used as a substitute for sound preparation. On good ground, if I had the choice between increasing the thickness of a sub-base to, say, 150mm from 100m, or using a geo-membrane, I'd go for the thickness increase everytime. |
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Distance below DPC - Patrick Regan - Apr 2nd 2001 | ||||
| Someone has told me that I need my driveway to be 7 inches below my damp proof course. Is this a regulation or is it just good practice? | |||||
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Tony McCormack - Apr 2nd 2001 | ||||
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It should be 6 inches - 150mm below dpc. It is a regulation for new properties, but a very, very strong recommendation for existing properties. If your paving is NOT 150mm below dpc, a good surveyor will pick up on this when (if) you come to sell the property and it could cause problems with the sale. Worse than that, it can cause problems with damp in the walls, primarily because of splash-back from the paving breaching the dpc.
Don't risk it - you only need to lay good paving once, so do it right! |
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Patrick Regan - Apr 6th 2001 | ||||
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Thanks for the response, one more question though...
Does this apply to Decking? What are the regs regarding decking? |
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Tony McCormack - Apr 9th 2001 | ||||
| There are no regs regarding timber decking and dpc. It's assumed that the decking is an open structure and will not represent a damp hazard. | |||||
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Crumbling mortar - Dave Godes - Apr 30th 2001 | ||||
| I've been hand-mixing mortar for a stone wall. The problem is that after about a day the mortar has crumbled, or is easily crumbled by hand. What am I doing wrong? Am I adding too much/little water to the mix? | |||||
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Tony McCormack - Apr 30th 2001 | ||||
| What mix are you using? That is, what proportion of sand and cement, and are you using any additives? | |||||
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- Dave Godes - Apr 30th 2001 | ||||
| I'm using a premixed mortar (Quikrete brand), no additives. I've tried to mix it (i.e., add water) to achieve a consistency such that "peaks" remain in the mixing tub and about 1/2 inch of mortar will remain on the trowel if held in a near-vertical position. | |||||
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Tony McCormack - Apr 30th 2001 | ||||
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Is that a UK brand or are you overseas?
Pre-packed mortars have a finite shelf life. What you describe sounds like a perished (ie, knackered, useless, gone off) mortar. |
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- Dave Godes - Apr 30th 2001 | ||||
| I'm in the US. I'll check and see if there's a date on it. Thanks a lot for your help...I guess I'll go buy some new mortar this week. | |||||
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Tony McCormack - May 1st 2001 | ||||
| That'll be why I've never heard of that product! Would you not be better off buying sand and cement and making up your own mortar as it's needed, rather than buying a pre-pack? Pre-packs are approximately 3 times the price of self-mix mortars here in the UK. | |||||
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Brick wall footing questions - Alan Simpson - May 3rd 2001 | ||||
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I asked you some questions about a brick wall last year. I was hesitant to ask you more (fearing wearing out my welcome), but then I saw a page on your site about some diy work that someone had done using your help and thought maybe you wouldn't mind. I'll take pictures as I go along.
So... I have some questions about the concrete foundation for a brick garden wall. (1) the wall is going to come right to the rear of the house (a Victorian mid-terrace). I was going to leave a small gap (5-10mm between the house and the footing). What should I use to fill this? It's below the dpc of the house, so I shouldn't have to worry about damp, but I just want to be careful. (2) you suggested that I align the movement joints with the piers. I am going to have to ask a stupid question. What did you mean by this? Do you mean having the movement joint at one of the edges of each pier? E.g.,
-|----------------------|-------- So that the joint is just along the left edge of the two shown piers (apologies for the ASCII "art"). Or did you mean something completely different? I was also thinking of something like the following:
-| |--------|----------| |------ where the movement joint is halfway between the piers. I was speculating that having the pier in the middle of each length of brick might provide more "balanced" support. Does that make any sense or I am just talking rubbish? (3) If I did follow my suggestion of having the pier halfway along each length of brickwork, then I wouldn't have piers at either end of the entire wall.Would this be ok? Or do I really need a pier at each end to ensure long-term stability of the wall? I think that is all the questions I have in order to lay my concrete footing, which I am hoping to do during the last bank holiday weekend in May. Thanks again for all the information that you have provided |
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Tony McCormack - Apr 2nd 2001 | ||||
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Alan wrote....
(1) the wall is going to come right to the rear of the house (a Victorian mid-terrace). I was going to leave a small gap (5-10mm between the house and the footing). What should I use to fill this? Rather than leave a gap, you should form a movement joint by using a piece of Flexcell or similar compressible board between the footting and the existing wall.(2) you suggested that I align the movement joints with the piers. I am going to have to ask a stupid question. What did you mean by this? Do you mean having the movement joint at one of the edges of each pier? It's a long time since we discussed this last, but, IIRC, I think I meant that the movement joints could be incorporated midway between piers.If I did follow my suggestion of having the pier halfway along each length of brickwork, then I wouldn't have piers at either end of the entire wall. Would this be ok? Or do I really need a pier at each end to ensure long-term stability of the wall? It all depends on the size of the wall. You really ought to consult a structural engineer for any wall greater than 1200mm in height, as my speciality is paving rather than wall-building. |
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Steve Stiansen - May 8th 2001 | ||||
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I would think the best answer to your question would be a real world example.
Think of how a bridge is built.....They build columns, then span the road surface between the two columns, usually putting expansion joint at that point. A good example would be to take a 3 blocks of wood and place them 5 meters apart. Now, if you have 2 5 meter long boards, would you place them so that each board would span from one block to the next, or would you take one, teter-totter it on the middle one, and then cut the other one in half and place it on the two ends maybe screwing it together then at each joint. The answer is simple, you would span the two boards from block to block and not cut one in half. The wall is much like a bridge, spanning between the two pillars. Each pillar, over time, will eventually begin to heave/sink, moving independenty of each other. Thats why you need joints AT the pillars, not in the middle. As for the ends, I would definitely say yes, have pillars. Again think of a bridge, and how the ends are set on a foundation (this time the side of a river/culvert/etc not a pillar) you need the support on each end, or the wall will sink there and crack at the next pillar or inbetween. The wall is basically a 'bridge' from pillar to pillar. Thats the way I think about it. Hopefully I helped some and didn't confuse the daylights out of you. |
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Excavation beside my house - Alan Simpson - May 13th 2001 | ||||
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I have a question about how deep down I should dig.
There are only 3 courses of brick between the slate dpc in my house and the footing of the wall. I thought that I should keep 6" between the dpc and the final surface of the patio that I am making (yes, Tony, in addition to the wall, there is also a patio ). That suggests that I should excavate to the level of the top of the footing. But then something else just came to mind: drainage. Aren't I supposed to keep a 1:80 slope. Along one wall of the house, this is amounts to 1.5". Along the other side more like 3". So this suggests digging to a significant depth (if 1.5-3" is significant) below the level of the footing all around the extension. My gut tells me that this is bad. My gut also wonders whether even excavating to the top of the footing is ok, although I console it by telling it that there will be 40mm of compacted grit sand. Any advice on these matters? |
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Tony McCormack - May 15th 2001 | ||||
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Hi again Alan,
the recommendations I give for patio construction are not always possible and this seems to be one of these instances. The footings you mention seem to be inordinately shallow for which there must be a good reason, unless they are non-load-bearing walls, such as garden walls, or, as I've seen on far too many occasions, they are 'Friday Afternoon' foundations, slapped in for a conservatory by some bodger builder. 
The 150mm below dpc is a good recommendation but not always possible or feasible and so you have to use your discretion. I would, perhaps, elevate the patio to 125mm below dpc rather than expose the foundations of a wall, but, without being completely familiar with your site, it's not possible for me to say exactly what I would do. Keep the bedding to a minimum, say 35mm, or even 30mm if you're only using decorative patio flags and there will be no vehicular traffic. The paving should slope away from the wall, so you should find that at, say, 500mm out from the wall where you're clear of the footing, you can revert to a fuller construction method. |
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FYI: was "Excavation beside my house" - Alan Simpson - May 15th 2001 | ||||
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The walls in question (and a few more as well) are the external walls of a Victorian mid-terraced house built in the 1880's. It
is the standard type building of that sort with the usual "extension" on the back that was built at the same time.
In the rear wall of the main portion of the house, there is definitely the slate dpc, then three courses of bricks and then one single footing course of brick that is a spreader course. It projects out about 1/2 brick on each side. I'm not sure where the slate dpc is in the rear extension, although I'm guessing it runs at the same level. The only thing with this though is that the floor is at a lower level than in the main portion of the house, so how all the wooden sub-structure of the extension once was all above the dpc, I don't know. And now there is a concrete floor in the rear extension, so I can't really investigate. Also, from my excavations at the rear, it seems that there is a portion of one of the extension walls without this footing course. Strange. But then so are the odd-shaped brick foundations adjacent to part of the rear wall of the extension (but which doesn't show on any of the early Ordnance Survey maps of the area, although the outdoor w/c's of my neighbours' houses do show on such maps). Anyway, that was my babbly FYI message. Wish me luck, I FINALLY pour the concrete foundation for the wall during the coming long weekend. Once again, your site and your e-mail messages have been a TREMENDOUS help. I'll remember to take before, during and after pictures for you, if you are interested. |
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Tony McCormack - May 15th 2001 | ||||
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Definitely want to see pictures, Alan.
Good luck with the pour - don't forget to let us know how it goes! |
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- Alan Simpson - May 20th 2001 | ||||
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The aggregate, sand and cement are coming on Tuesday (and lucky me, I live in a terraced house).
Today, I am finishing off the excavation: putting stakes in place to mark the level of the cement, making sure that the bottom is the same depth all along, But there are several places where the clay is VERY sloppy. And this has me worried. Especially when I realised today that I uniformly dug about 18" deep instead of 15", as I intended. Even more worrying is the fact that the water table is fairly high here and that when I pulled out one of the pegs for the old fence, I could see water at the bottom and hear water sloshing about as I walked on the disturbed clay surrounding the hole. Should I be worried about this sloppy clay and how (possibly) close to the water table the base of my excavation is? Should I add some hardcore to give an extra few inches of "stable" base for the concrete foundation? (the right answer to that question at this stage in the works is hopefully "No" ) Maybe I should make the concrete foundation wider (it is current 450mm for a double-skinned wall)? Or maybe use a footing course of bricks for the very first course? Both of these sound like they might help to distribute the weight better. Or maybe I am just panicking. But I just want to make sure that the wall is done as well as possible.
One final question....
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Tony McCormack - May 21st 2001 | ||||
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Alan asked...
Should I be worried about this sloppy clay and how (possibly) close to the water table the base of my excavation is? The sloppy clay *must* be removed before you place the concrete. Don't worry about the water table as long a syou are not below it.Should I add some hardcore to give an extra few inches of "stable" base for the concrete foundation? Not really.Maybe I should make the concrete foundation wider (it is current 450mm for a double-skinned wall)? That would not help the situation.Or maybe use a footing course of bricks for the very first course? Eh?I have used staking pegs [...] Any thoughts about how to easily get these up when they have served their purpose? Yank them out before the concrete sets. As soon as the concrete is in place and has been levelled, wriggle the pegs free and chuck them out, then re-settle the concrete in the disturbed area.At least you've got the weather for it! |
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- Alan Simpson - May 22nd 2001 | ||||
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Mucho thanks for that. It has helped calm my troubled mind (as has a good night's sleep ).
Just a few questions about removing the sloppy clay. It appears to be sloppy for some distance (several inches at least from the old fence pegs that I have pulled up today and yesterday) below the current level. What do I do if it just continues to be sloppy? There is a length of about 50 cm where it is sloppy at the surface and another 7-10 metres surrounding there (I haven't actually measured it) where there is water below the surface. This is the area of my on-again/off-again moat since the autumn. Might the water-levels continue to sink with more seasonable rainfall? Or is that just wishful thinking? And finally (no, really!), what do I replace this sloppy clay with? There are two tonnes of sand and three tonnes of aggregate arriving tomorrow, so I'm spoiled for choice. And, you're right about the weather. I just checked the BBC site. Cloudy on Saturday (no rain!). Bring on the cement mixer!! I know that I have written this above, but thanks so much again. If I am the proud owner of 150mm of setting concrete running in a 28 metre strip away from my house on Monday, then you will have made all the difference! |
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Tony McCormack - May 21st 2001 | ||||
It's hard for me to say just what you should do with the sloppy clay, Alan. Excavate and dispose as much as you can, but if you have any problems, you should consult your local Building Control Officer for onsite advice. You don't 'replace' the sloppy clay with anything: you pour more concrete! 
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Mains cable - Scud1365uk - 26 April 2002 | ||||
| On digging out a foundation trench for a 9 inch retaining wall , I have unearthed the mains cable for my house. Unfortunately it runs all the way along the proposed wall. I thought of cutting a peice of drainpipe legnthways so that I can slot it over the cable and then lay the foundation on top. Would this be ok or will i be infringing some rule? The only other alternative involves digging up an existing path to move the cable over and I had hoped not to have to do this.......thanks | |||||
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Tony McCormack - 27 April 2002 | ||||
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Is this the service cable connecting your house to the main under the public footpath? If so, you really need to speak with your local Lecky Board. I know some of the "Utility Cos" would allow you to use a split duct, but others would insist on the cable being re-aligned so that it's not underneath any foundation. They should be able to give you this info over the 'phone on Monday morning.
However, if it's an extension cable from the house to the shed/garage/greenhouse etc, then you could use a split duct, as it's your responsibility, not the Lecky Board. |
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Making up ground - Danny Lee - 9 Aug 2002 | ||||
| I have to make up ground level for a courtyard garden to allow proper cover for drains, etc. I have a great pile of clay muck, could I use that or should I buy crushed stone hardcore. The area is low and can be wet. Intention is to have hard surface, brick or pamments, etc. | |||||
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Tony McCormack - 9 Aug 2002 | ||||
| The trouble with using clay to build up level is that it's a bugger to compact thoroughly, so use sub-base material. Building-up with clay is ok if you're going for soil cover, but for hard paving, I'd recommend sub-base material every time. | |||||
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Prescribed mixes for concrete - Archive - 27 Feb 2002 | ||||
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Hi
I am a student of engineering in Malaysia. I have been given an assignment topic on prescribed mix. Unfortunately, i cant find any information on prescribed mix due to lack of books in the library where i am currently studying. Ive search the web for any kind of information on the subject but to no avail. And then i came across your website,so i hope you can give me information on who, where, what, why and when the prescribed mix is use in concrete work. And if you dont mind can you give me some example to it so that i can fully understand what it is all about. I hope you can give me full information on it as soon as possibe as my dateline is just around the corner. Your cooperation is much appreciated. Thank you. |
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Tony McCormack - 27 Feb 2002 | ||||
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Hi,
Prescribed mixes are simply a 'recipe' to create a concrete of a given strength. We would use a C7.5P mix for bedding kerbs for instance - the concrete is mixed according to the prescribed 'recipe' that gives a cured strength of 28 kN/mm2 after 28 days. A C20P mix might be used to haunch those kerbs. Prescribed mixes is a BIG subject and highly specialised. Try the forum on the Concrete Society website, as there are concrete technologists on there that might be able to help you further. My experience is limited to using Prescribed mixes, rather than specifying or designing them. Good luck! |
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Rendering Walls - Derek | ||||
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Hi all,
I am planning to build some block walls for raised beds and a water feature in the back garden. I am thinking of rendering these walls smooth and then painting them "a la Diarmud Gavin". Has anybody any helpful advice on doing this? I have laid walls before but have never rendered. I am concerned about the best mix, corners, achieving a professional look etc... Thanks for any help, Derek |
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Tony McCormack | ||||
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If there's one job I hate doing, it's rendering. I'd rather unblock sewers with my bare hands than have to render a wall, but here's my tips, for what they're worth....
1 - make sure the mix incorporates a good plasticiser and/or a bonding agent, such as PVA 2 - use a building sand and a mix that's around 6:1 3 - aim to apply approx 12-15mm of render, working with a float and feeding the mortar from a hawk 4 - Angle beading is best for corners - you can get it at most BMs, but make sure it's a plastic type as the steel ones used for internal plasterwork tend to rust. 5 - use a straightedge timber to level off the render once it's applied. 6 - rub-up the work with a damp sponge 12-24 hours after applying. 7 - allow at least 7 days before painting and keep it covered during that period to protect it from the elements Good luck! |
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| Derek |
Hi Tony, Thanks for that. I'm not looking forward to it either. The things we do for love! Derek. |
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How Cold for Concrete? - Cat McDonald | ||||
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What is the lowest outside temperature that a concrete driveway can be layed without compromising its strength? and should this temperature be maintained during the curing process? also how long is the curing proceess? What happens to the concrete (ie. surface cracks etc.) if the concrete is laid below this temperature?
Any advice would be helpful as we have just had a driveway layed a week and a half ago in the mid of January with weather ranging between 30 and 60 degrees and have just discovered a small crack running the width of the driveway. Should we request that our contractor replace that section, the whole driveway, or can it be repaired. We are fearful of more cracks after the contractor has finished up never to be heard from again. Cat McDonald |
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Tony McCormack | ||||
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The temp has to be above 4C and kept that way for the first 24-36 hours.
A lot longer than you think - 28 days is the usual figure quoted, but for most purposes, a concrete slab can be considered 'hard cured' ,ie, hard enough to take foot traffic, after 3-5 days.
It doesn't achieve its design strength, which can mean surface cracking, more susceptibility to structural cracking, an easily-eroded surface and/or or a shorter lifespan.
Have you discussed this with the contractor? Have they offered an explanation? Is the crack significant, ie, does it span the entire width? Did the contractor install crack controls? Was any provision made for movement joints?
You really need to speak to your contractor first and see what they have to say. It's not possible for me to say what the best remedy might be without seeing the slab itself but you're more than welcome to post back here when you have some more info. |
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Cables and Pipes - Paul Mellor | ||||
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Please would you help tell me how deep the service pipes are likely to be, ( before I hire a self-drive mini excavator ).
I need to dig to a depth of 8 inch from the present surface level. Thanks for any info...... Paul Mellor |
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Tony McCormack | ||||
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It's impossible to say, Paul. Although all services are supposed to be at least 300mm down, we've come across lecky cables just underneath flags and gas pipes barely covered by tarmac. If the laying ganng is particularly lazy or it's a Friday afternoon, they seem to ignore the safety regs and just bury it as shallow as they think they can get away with. Cable tv is notoroius for being just beneath the turf or paving of private homes.
Water is nearly always at least 900mm deep, for frost protection, but the rest could be anywhere from 50mm to 1000mm or more. The only way to be sure is to use a CAT (Cable Avoidance Tool) and to have a banksman watching the excavation at all times in case you expose a service. In most cases, though, the services are 300mm or more deep, but, as I've indicated, you CANNOT assume that - assume that they could be anywhere! Good luck - and be careful! |
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| Dexter |
In my experience they can be anything from 6 inches to a few feet i did a driveway and was pretty suprised to find yellow gas pipes just 6 inches below the surface running the length of the front garden so be carefull.
Dexter |
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| Gareth Allwright |
Recommended for gas pipes (according to Transco) is 375mm. I know this as I had my gas pipe repaired after splitting it with a post hole borer! Doh! Worth digging by hand to find them first.
Gareth Allwright |
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Raised ground, paving ,drainage and retaining walls - Tessa - 1 Mar 2002 | ||||
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My neighbour has raised the level of his garden by around 2 to 4 feet (the garden is on a gentle slope and the garden has been levelled so it is higher than the natural level but more so closer to the house than at the end of the garden. Hope that makes sense). They have not used any retaining structure to maintain this difference and it simply leans against my fence which is being pushed over at an angle and also across my garden.
A large part of the garden closest to the house has been paved and there is no system of drainage installed. As these are old terraced houses that already suffer with problems with rising damp i am worried that this is making matters worse.
A- install drainage to ensure that the raised ground level does not affect the houses. The garden is raised about 4ft within 2ft of our houses and there is no drainage so i assume that this affects the water level?
Any help would be appreciated and yes I have spoken to the owner, (he rents it out and is deeply disinterested in my problems). Tessa |
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Tony McCormack | ||||
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Yes, more than likely. If they have undertaken any works that are likely to affect your property, they have a legal obligation to protect your property at all times.
They are NOT allowed to drain their property onto your property, full stop. They *must* provide some method of draining their own property so that it does not impinge upon you or your property. If any damage is caused to your property by their works, they *are* liable.
Impossible to say without being familiar with the site.
Probably, as long as it doesn't affect your property. Levels are a funny thing. There are provisions under local authority planning control to set limits on the levels used for buildings, but this does not always apply to earthworks and/or gardens.
Although the BCO may not be overly keen on getting involved, they will be able to advise on what is and what isn't considered to be acceptable practice in your area. If the BCO say that they cannot get involved, then the next step is to use a solicitor to inform the neighbour that they will be held liable for any and all damage to your property and that they will be liable for any costs incurred by yourself in regard to any remedial works that are required to ensure the safety and well-being of your property, such as retainer walls, drainage etc.
But first, speak to the BCO and let me know how you get on.
Good luck!
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Fence repairs - Richard - 18 Mar 20021 | ||||
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Hi Tony,
Thought I'd try you out with a non-paving question - I have a number of rotten fence panels and wooden posts in the garden that need replacing. The posts were concreted-in but the concrete surface is at least 6 inches below the soil level hence the post-rot (not guilty - previous owner I think!). The last time I repaired a section of fence (I have quite a few panels on 3 sides) I tried to dig out of these concrete lumps but gave up after the first one. It was hard work, it took ages, the hole was huge, and I was concerned about how much concrete I'd need to fill the holes if I continued with this method. So I left the concrete in the ground, staggered the panels by 3 foot, and used metal spikes and wood posts as I didn't want further concrete-hassle as and when this fence failed. The fence I want to repair is more exposed that the previous repair, and I'm on clay soil which I've read can cause problems when using metal spikes, so I think I need to go for concrete to do 'a proper job'. Can you suggest a method to replace the fence rather than staggering it and having 3' sections at either end? Is there a way to use the existing concrete blocks without digging them up? If the posts are concreted in correctly with an exposed sloping top surface, how long should I expect a decent post to last? When they eventually fail, how would you repair them? Lots of basic q's sorry!! Thanks |
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Tony McCormack - 19 Mar 2002 | ||||
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Hi Richard,
I don't know if you've read any of my previous diatribes against met-posts and their ilk - to paraphrase: they are crap. Just ask yourself how many contractors you see using them! I know the concrete haunching can be a bit daunting when it needs ripping out, but it is the best solution in the long run. Get hold of a sledge hammer and a "drift", which is a big chisel as used in a jack-hammer. Use the sledge hammer to drive the drift into the concrete mass and break it into more manageable pieces which can be prised out with a wrecker bar or small crowbar. Hard work, but it's worth it! If you're left with an overly large hole, you don't have to fill it all with fresh concrete once you've got the new posts in position. You can use 'plums' - lumps of the old concrete, old bricks, broken flags, anything hard and inert, to help fill the void. As long as the whole mass is then surrounded with fresh concrete, it will be fine. Put a shovelfull or so of concrete at the base of the hole, then position the post. Use sprags or 'plums' to hold it vertical and in the right place, then add your concrete haunch. I like to use a dry mix, poke it in with a line pin or small crow bar, and then water it in to ensure it fills all the voids. Again, use a bar or a stick to tamp down the concrete so that it's 75mm or so below ground level.
Give it 24 hours to begin the cure before putting in the wooden panels. If you put the panels in while the concrete is still fresh, and the wind picks up overnight, the posts can be blown out of alignment, or even completely uprooted. |
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Richard 19 Mar 2002 |
Thanks for the info Tony, though I have to say I don't really fancy hacking out 16 concrete lumps!!
Final 2 questions (maybe!): why do you suggest tamping the concrete to finish 75mm BELOW ground level? The previous posts were set this way and they all rotted. I thought the concrete top should be just proud of the ground level with a domed top to shed water. With a dry mix, is it a normal 6 ballast:1 cement?
Thanks again |
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Tony McCormack 19 Mar 2002 |
The reason the old posts rotted is nowt to do with the level of the support concrete - it's the nature of the product. If you use un-treated wood for your posts, they will rot, regardless.
Keeping the level of the support concrete down by 75mm or so is done to accommodate the paving or some soil cover. If the concrete comes up to ground level or above, it won't prevent un-treated timber from rotting. Similarly, whether you dome the top of the concrete, or leave it flat, if the timber is untreated it will rot. A 6:1 (1:2:4) is more than adequate for fence posts. You could get away with 10:1 (1:3:7) quite safely. |
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Richard 20 Mar 2002 |
I'm putting in 100mm pressure treated posts so hopefully they will last a number of years...
I knew I had another couple of q's.. what's the advantage of the dry mix in the post hole? when you add water to the mix -what sort of volume would I need for 100mm posts buried approx 550mm? Thanks Tony,
cheers |
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Tony McCormack 20 Mar 2002 |
P-T Posts should give you at least 10 years. the Tanalised stuff is guaranteed for 25 years, which is comparable with concrete posts.
Dry mix finds its way into the voids a bit easier than wetting it up first and then poking it in. There's nowt to stop you using a 25-75mm slump if you prefer, but there's no real gain. Using dry mix saves 10 minutes of turning the mix over to get it thoroughly wetted, that's all!
Volume of concrete per post depends on how big your holes are, but you should get 2 or 3 post per barrowful of concrete. Use 'plums' as I mentioned earlier, if you can - it saves on concrete, it works just as well as using all-concrete, and, if the worst comes to the worst, it makes yanking out the haunching a damned sight easier! |
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Richard 21 Mar 2002 |
I'll see if I can get hold of some tanalised posts - don't want to do this job again before I really need to!
My last Q was...what's the volume of water that's applied on top of the dry mix already in the hole?
thanks |
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Tony McCormack 21 Mar 2002 |
Again, there's no set volume for added water. Just add enough so that all the mix is washed in.
Normally, adding too much water to a concrete will weaken it, but with fence posts, it's not so much the final strength of the concrete that's important; it's the fact that it doesn't allow any room for movement of the post once it's set. |
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Richard 21 Mar 2002 |
End of thread - thanks for all the advice Tony.
ordered all the bits/pieces today - gravel boards and posts are tanalised so it should last!
cheers |
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"Shed" foundation - slimtim - 24 Mar 2002 | ||||
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I wish to build a "shed" out of brick for security purposes. I have planned on a single storey 8ftx8ft structure and need to lay a suitable foundation. I had thought of using just a normal strip foundation, laying several courses and then a dpc and concrete slab floor within that brickwork before starting on the walls proper.
On investigation of the site I notice that drainage from my house runs under the proposed site of the shed. Looking down the inspection chamber (about 5ft away) I deduce that the drains run under the site for the shed. The pipework is 4ft underground. As a neighbours garage sits adjacent to the shed-site I can only presume the drains run under their garage (which is based on slab foundations). The soil is wet clay. The question is - am I okay to use a strip foundation? Do I need to take into account this pipework or can I just concrete over it (albeit 2ft over it)?? |
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Tony McCormack 25 Mar 2002 |
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Hi Tim,
you need to build what is referred to as 'A Bridge' over the sewer pipe. Depending on depth, this can sometimes involve encasing the pipes in concrete and then using "Rocker Pipes" at the start and end to allow some movement. However, if the pipes are deeper than the planned depth of the footing, you literally 'bridge' over them by casting a couple of pads to either side, and then casting the footing as a reinforced span between the padstones.
It's a considerable job, and is not always necessary, but that what the BCOs insist on and, if you want to do it right, that's what's involved. You may of course, completely ignore all this, as some folks do, and never have a problem, or, if you have my kind of luck, you'll find that the pigging drain collapses in 3 months time and it costs 6 times as much to rectify it all! Can you send me a sketch of the site? It may be a simple job, or you may be better off re-routing the drain. |
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slimtim 25 Mar 2002 |
Would I get around all this work if I went for a slab foundation? The shed is about 2metres from the house in the back garden. Any idea whether I need building inspectors approval? I have "plans" in TurboCad - can you read these? If not, I can grab a screenshot. | ||||
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Tony McCormack 25 Mar 2002 |
I'm not sure whether you need Planning Consent or not. It all gets a bit vague when it comes to brick-built sheds, as they aren't actually classed as sheds, Tim. Only wooden sheds are sheds, as that means they're temporary structures and thereby exempt from Planning Control, but Bricks is permanent!
It can't do any harm to give your local BCO a call, just to ask what the position is. You'll probably get a lot of handy advice, often free, and it really is better to be safe than sorry, as, if you ever come to sell the property, it prevents the buyer's surveyor asking awkward questions that drive down the selling price. Send me a TurboCad dwg file and I'll take a look. at the usual address. |
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Stepped Boundaries - Richard Malin - 29 Mar 2002 | ||||
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Hi Tony,
was on a job today and had a kind of semi - dispute with the neighbour. Property is a 60's detached house, on slight hill with roughly square , about 80m² frontage. ( You've seen millions.) To separate the boundaries, given the hill, there is a row of about 12 edgings, flush to top on the neighbour's side with my customers property being about 5" lower. The neighbour has had his front entirely block paved while I am in the process of pulling out an original and tired old garden and giving it the maintenance free look of little evergreen shrubbery and lots of nice cotswold gravel. The problems began when I took up cast concrete path hard up against next door's edgings - and they moved! Not a lot but definitely push over they did. These edgings are 3' x 2" and 18" deep , and the only thing holding them upright was this heavy cast path. I was haunching them back with lots of concrete, at my own expense, when the moaning started, guy said he'd been watching us all morning. Finally my point! This guy's header course was laid on just sand, relying entirely on strength of the edgings for retention, while I maintained that it should have been done on concrete to prevent this sort of thing happening. The edgings are all on his side, and have been lain in just soil. Who is right legally? |
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Tony McCormack - 30 Mar 2002 | ||||
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Good to see someone else working over Easter, Richard! I've been out supervising a repair job for a mate - it's like being back on the job, apart from the lack of any pay!
Anyway, as I understand it, the neighbour has a block paved driveway and the soldier band courses have no concrete bed or haunch, but have been laid tight against the existing flag-on-edge retainer on the boundary betwen the two properties. It all depends who owns the flag-on-edge. If it belongs to the neighbour, well, there's not a lot you can do. I would [b]still[/b] have laid the edge courses on concrete, but obviously, they can't be haunched. If the flag-on-edge belongs to your client, then the neighbour's edge courses should have been laid on a bed of concrete, and agreement sought from your client to use the f-o-e as a supporting structure. The same applies if it is a shared boundary - agreement should have been obtained before using the f-o-e as a retaining structure for the block driveway.
So, unless the two neighbours want to check their deeds, it's best they agree to the necessary work to both sides, and your client comes to some agreement with the neighbour about covering your extra over costs for unforeseeable accommodation works. 50/50, I'd say. Let me know how you get on. |
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Richard Malin 6 Apr 2002 |
Hi Tony, back at long last!
the debate was really settled on the spot, but neighbour did go around when we had gone for bit of extra moaning- the client had been aware of what was going on and agreed with us so just told the guy basically the same, namely that his block paving should be self supporting. The flags-on-edge are entirely property of neighbour 'cos they line up with side of garage. It was nice to read up on legal side of things, I don't know much of the law and will now have to learn some. I suppose on your previous big or civil contracts the law was half the job? |
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Tony McCormack 6 Apr 2002 |
As a family business, we had a nice little system, Richard. I've three sisters - an accountant, a nurse and a paralegal, so they did the books, the Health&Safety and the threatening letters, plus a brother who's a dab hand on a JCB.
Persoanlly, I hated the paperwork side of the business, especially the contracts and the legal implications. As Bob Cray sings, when you want cheering up...
"You could buy me a house,
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Mix for fence posts - Richard - 24 Apr 2002 | ||||
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Hi Tony,
Just about finished my fencing but I've run out of ballast with 4 posts to go. I have some grit sand and soft sand left from my patio - would any of this be OK to use? I also have some surplus house bricks I could break-up to add a bit of meat if required!
cheers |
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Tony McCormack - 25 Apr 2002 | ||||
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You could use the bricks as 'plums' - these are big lumps used to reduce the volume of concrete required for non-critical pours, such as fence posts.
If you can't get hold of an extra bag of chippings/gravel, make a reasonably stiff mortar mix at around 6:1 and pour some of this into the hole around the base of the post, just enough to come up the side of the post by 50mm or so. Next, drop in the 'plums' trying to wedge them between the post and the sides of the hole as you proceed. Make sure the top of any plum is at least 50mm below what will be the top of the fastening mix.
Once the plums are in place, add more of the mortar and use a hose to wash it in to all the voids. Use as little water as possible, as extra water makes for a weaker mix. You can top off the last 100mm or so with a dry mix of sand and cement, as this will draw up sufficient moisture from below to initiate curing. Good luck! |
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Hoggin alternatives - novicejohn - 29 Apr 2002 | ||||
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Hi Tony, what an excellent site. wish i had found it before starting my diy project but hope you can help now anyway.
i have started a large garden path project on a waterlogged clay garden with a slope/drop of about 3'.
would this action further weaken the drive? if i don't go down to subsoil would the channel trap water, freeze in winter and give further problems? as a novice (but gaining blisters daily) i am extremely careful with my newly acquired angle grinder but am i being too adventurous with this idea? would the method i describe work anyway? alternatively as i am limited on funds and at this time could not consider a totally new drive would it be feasible to put a tarmac layer over the lot and find another source of hardcore for the path.? sorry for the lengthy list of questions but they are interrelated and at the moment i am hold until i sort out the issues raised. |
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Tony McCormack | ||||
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Hi John,
as far as I know, Hoggin doesn't get as far north as Derbyshire, but you might just find some in the south of the county at Travis Bloody Perkins, as they do sell it darn sarff. The usual alternative in and around Derbyshire is limestone chippings with limestone fines, the 'fines-to-dist' you mention. Most of it comes from Dowlow up near Buxton. It gives a similar finish to hoggin but, in my opinion, is far superior as it doesn't get as claggy as hoggin. As for your driveway, you've hell of a job sawing through all that concrete, and, with a nangle grinder the blade will wear and what starts out as a 100mm cutting depth very soon becomes less than 25mm and is pretty useless. If you're intent on doing this, then hire a cut-off saw with a diamond blade, or better still, a floor saw, as these give a constant depth of cut. Make sure you have a hose running or the neighbours will be suing you for dust contamination! How feasible all this is, and what effect it would have on the rest on the concrete isn't easy to say without seeing the job, but it's not's something I would undertake lightly. What width would the two remaining concrete strips be? They need to be at least 750mm wide and at least 100mm thick to stand any chance, and even then, I'd be worried that they could crack transversely (across-wise). You could counter this by sawing crack control joints while you have the saw available. This means sawing 25-50mm deep transverse cuts into the remaining strips at, say, 3m intervals, so that if (or when) the strips crack, they do so at these sawn joints rather than at some inconvenient point. Once you've broken out the central strip, you can fill that with tyyour chippings and it shouldn't give any serious problems, as long as it is properly drained and water isn't allowed to pond within the channel. As I said, it's a lot of hard work and, depending on the layout and available funds, I'd give serious consideration to jack-hammering the lot and starting with a new surfacing. The idea of putting bitmac over a cracked concrete base is a bad idea because of the phenomenon known as reflective cracking which is discussed on the Resin Bonded Aggs page, IIRC. Does that help or are you just more confused? |
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| novicejohn - 30 Apr 2002 |
Tony,
many thanks for your speedy and informed reply. you confirmed some of the doubts i was having over the cutting of the concrete and i have decided to leave the job until i can replace the whole drive. it would be pointless to try and tackle this job with the inherent risks you mention and i feel i have been given a genuine unbiased opinion regarding laying a tarmac surface over the existing concrete and the potential for reflective cracking. i will also now seek out a local supplier of the tough 'fines to dust' limestone and leave the 'softer' hoggin to our friends in the south. many thanks for your assistance. no doubt i'll be back! |
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Sleeper terraces - Richard Malin -18 May 2002 | ||||
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Hi Tony,
am just starting a new job on a rear garden, one that has a slope upwards away from the house. The client wants 3 flattish levels held up with railway sleepers, each in a slight arc to make it a bit more difficult. Quoted it weeks ago and got the sleepers delivered,the steel, concrete etc without too much bother and today now I really look at it I'm thinking what do I use as a starting height for the sleepers? It was all long grass before but now it's strimmed and rotavated the garden has a definite steeper rise toward top right and a slight rise left to right overall. If we set the sleepers too low we will have too much soil over; too high and parts of neighbours' fences will be undermined. I'm sitting here scratching my head Tony. Please help me out. I'll buy you a beer. Honest! |
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Tony McCormack - 20 May 2002 | ||||
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You can only set the sleepers low enough to have their bases covered or hidden by the earth or paving, but not stuck up in the air. Find the lowest point, set the base of the first sleeper at that level, and use that as a reference for all the other, subsequent sleepers.
It might be easier to add a bit of extra topsoil or whathaveyou in certain spots to help you hde the bottom of the timbers. Is that possible? |
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| Richard Malin -30 May 2002 |
Hi Tony,
thanks for that. Only finished job on Tuesday, took longer than I thought. The starting point seems obvious now- the bottom of first tier level with slabs across back of house. In fact we sloped the terraces upwards slightly, about 3" over ten feet, and eventually put in a single height lower tier and double height upper. The height difference over entire garden was around 40" so taking three sleeper heights ( 10" apiece ) and adding 10" of slope sorted it all out. Just to make it more awkward the bloody bays went uphill right to left as well as having staggered starting points ( as well as being curved ). Have taken some start to finish pics, they can accompany that crate of Boddingtons that's headed back up the M6! |
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Tony McCormack |
I look forward to receiving them, Richard.
Are you finished for the Bank Holiday, now, or are you going back out to work? |
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Richard Malin 30 May 2002 |
Hi Tony,
I don't have holidays, just rainy days! Sitting here doing quotes etc. getting fed up and listening to some music to forget about the awful weather. Have just listened to The Doors' Riders On The Storm and that old song by The Cascades - now what was it called? Seriously though I'll go in tomorrow if poss. and then knock off till Tuesday. Feel like I've earned it. Can't wait for the footie! Cheers! |
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Tony McCormack 30 May 2002 |
What about "Why does it always rain on me?" by Travis (Perkins)?
"I can't stand the rain" by Ann Peebles? Anything by Wet Wet Wet?
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