I'm a first time patio builder and located your Site by accident. It's very comprehensive with mountains of good info. Good stuff !!
Anyway, onto the construction queries.
Patio size is 6m x 5m: I've decided to install a sub-base just to be on the safe side. I've dug out garden topsoil, etc and reckon I need 4.5 tonnes of DTp1 at 75mm deep for a good sub-base (using your Calculator). Assuming the 75mm depth is "compacted" thickness, what depth of DTp1 should I put in to get a "compacted" depth of 75mm (using a plate compactor hired from local hire shop) ? Would 100mm be enough, or should I fill the base with more ? say 125mm ?
I've also decided to use your 10:1 grit sand/cement mix to bed the paving on, despite the fact that Marshalls recommend the "5 dabs of mortar" method for fixing. (Notice that Stonecraft also recommend this method at the back of their catalogue). Are you sure YOURS really is the BEST method ? :-
1. How thick should this bed be ? 30/40/50mm ?
2. Should it be compacted (with a plate compactor) prior to laying the slabs or should I just lay the bed with a trowel and bed each slab in individually ?
3. I'm a bit worried that as the slabs don't actually "adhere" to this beding mix, the smaller ones (300x300mm and 300x450mm) might actually "move" and the pointing may crack after the job's finished. Ever had this problem before ? Or are the slabs actually held in position by the "buttered" joint and pointing ?
I've spent a quite a bit on the materials and want to be absolutely sure that what I do will last for years and I'm not having to lift the whole thing and re-lay in a year or so.
Thanks
Laying Marshalls Heritage Paving
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84-1093879891
This is a regular request, and I can only give you the regular answer - there is no way of giving definite data for the compaction rate of sub-base materials. The type of material itself, be it granite, limestone, sandstone, crushed concrete etc, obviously has a bearing, as does the moisture content and the type of compaction kit being used, all of which makes it impossible to say, for example, that 105mm of DTp 1 will always consiolidate to 75mm thickness.
However, very, very generally, 105mm of DTp1 will actually compact to around 75mm, but it could be 65mm, or it might even be 90mm. Only trial and error on site will reveal the actual figure.
And yes, you cheeky sod, I AM absolutely certain that my method is the best for laying flags - I ought to know, I've been doing it for long enough! ;)
If you press Marshalls or StoneMarket or any of the others, they will admit that <spit> spot-bedding is a bit of a bodge that's aimed to make flagging easier for unskilled DIYers, and that <spit> spot bedding is not an acceptable bedding method as defined in BS 7533/4 "Code of Practice for the construction of pavements of precast concrete flags or natural stone flags", which requires the bedding to provide, and I quote, "uniform support". <spit> Spot bedding, by definition, does NOT provide uniform support, but supports 5 particular 'spots' beneath the flags.
So, on to your other questions....
1- bed depth depends on the thickness of the flags. As the Heritage flags vary in thickness, so the bed will have to accommodate such variation. but, it should be somewhere between 35-50mm in thickness when compacted.
2 - I find individual bedding works best with this type of flag, for the reasons given above.
3 - Flags do not need to 'bond' to the bedding - this is a common misconception. The only time a bond is desirable is on special applications such as steps. The buttering/pointing does help stabilise the flags, but flags are bed-dependent, not joint dependent, and so it's the bedding that carries the loading and resists lateral movement. The base of the Heritage flags is relatively uneven, and this, combined with the variable thickness and a proper jointing, will resist any creep or slippage.
In situations where slippage or creep (lateral movement) is likely to be an issue, a restraining edge of some description is the preferred 'fix', but as this is a foot pavement only, and you're planning to do it properly, as advised on this site, I can't see that this need unduly worry you. :)
If you did bond the flags to the bedding, and then summat was to go wrong - let's say a drain cracked and caused some of the paving to sink - then salvaging the not inexpensive flags from the damned bedding really would be a nightmare. You'd end up binning most of the lifted flags, as they would get damaged when you attempted to slip a disc while separating them from a monolithic slab of mortar/concrete.
If you follow the advice on this site, you will achieve a first rate patio that gives you years of trouble-free service, or you get your money back! ;)
However, very, very generally, 105mm of DTp1 will actually compact to around 75mm, but it could be 65mm, or it might even be 90mm. Only trial and error on site will reveal the actual figure.
And yes, you cheeky sod, I AM absolutely certain that my method is the best for laying flags - I ought to know, I've been doing it for long enough! ;)
If you press Marshalls or StoneMarket or any of the others, they will admit that <spit> spot-bedding is a bit of a bodge that's aimed to make flagging easier for unskilled DIYers, and that <spit> spot bedding is not an acceptable bedding method as defined in BS 7533/4 "Code of Practice for the construction of pavements of precast concrete flags or natural stone flags", which requires the bedding to provide, and I quote, "uniform support". <spit> Spot bedding, by definition, does NOT provide uniform support, but supports 5 particular 'spots' beneath the flags.
So, on to your other questions....
1- bed depth depends on the thickness of the flags. As the Heritage flags vary in thickness, so the bed will have to accommodate such variation. but, it should be somewhere between 35-50mm in thickness when compacted.
2 - I find individual bedding works best with this type of flag, for the reasons given above.
3 - Flags do not need to 'bond' to the bedding - this is a common misconception. The only time a bond is desirable is on special applications such as steps. The buttering/pointing does help stabilise the flags, but flags are bed-dependent, not joint dependent, and so it's the bedding that carries the loading and resists lateral movement. The base of the Heritage flags is relatively uneven, and this, combined with the variable thickness and a proper jointing, will resist any creep or slippage.
In situations where slippage or creep (lateral movement) is likely to be an issue, a restraining edge of some description is the preferred 'fix', but as this is a foot pavement only, and you're planning to do it properly, as advised on this site, I can't see that this need unduly worry you. :)
If you did bond the flags to the bedding, and then summat was to go wrong - let's say a drain cracked and caused some of the paving to sink - then salvaging the not inexpensive flags from the damned bedding really would be a nightmare. You'd end up binning most of the lifted flags, as they would get damaged when you attempted to slip a disc while separating them from a monolithic slab of mortar/concrete.
If you follow the advice on this site, you will achieve a first rate patio that gives you years of trouble-free service, or you get your money back! ;)
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Paul Robertson
- Posts: 3
- Joined: Thu Feb 26, 2004 10:28 pm
- Location: Dundee
Tony
Thanks for the advice, everythings seems to be going to plan.
Just a question on the "pointing" mortar mix. Joints are around 12mm wide. Should I use a 50:50 mix of coarse sand:building sand in the mortar or should it ALL be building sand. I notice you recommend adding coarse sand to the mix for "wide" joints - not quite sure what "wide" is.
Thanks for the advice, everythings seems to be going to plan.
Just a question on the "pointing" mortar mix. Joints are around 12mm wide. Should I use a 50:50 mix of coarse sand:building sand in the mortar or should it ALL be building sand. I notice you recommend adding coarse sand to the mix for "wide" joints - not quite sure what "wide" is.
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84-1093879891
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Paul Robertson
- Posts: 3
- Joined: Thu Feb 26, 2004 10:28 pm
- Location: Dundee
Hi Tony
I've eventually got all the paving laid and it looks good. Been battling against the British weather and trying to get the job done in evenings and at weekends.
BUT:
I've got a bit of a problem with some of the pointing. I was unable to point the slabs as I went along due to bad weather and got round to pointing them a couple of days later. Some small sections of pointing (100-150mm) are dry/loose and have crumbled - looks as though there's only sand in the joint and NO cement ! Possibly the sand/cement mortar wasn't mixed thoroughly enough or maybe it just dried too quickly. I've removed the loose stuff and am looking for some advice on "fixing" it. Should I wet the "failed" joints and simply re-point the small sections using the same (1:4) semi-dry mix or should I use a stonger (1:3), WETTER mortar to help strength and adhesion ? Would a "plasticiser" make the joint stonger and help the mortar adhere to the sides of the slabs ?
Also, some of my pointing has been affected by rain which has caused mortar spots/stains around the edges of some slabs; is there any way to easily remove these without damaging the finish of the paving ?
Once again, thanks for all the advice.
I don't know if I`d do it again though - it's hard work !
I've eventually got all the paving laid and it looks good. Been battling against the British weather and trying to get the job done in evenings and at weekends.
BUT:
I've got a bit of a problem with some of the pointing. I was unable to point the slabs as I went along due to bad weather and got round to pointing them a couple of days later. Some small sections of pointing (100-150mm) are dry/loose and have crumbled - looks as though there's only sand in the joint and NO cement ! Possibly the sand/cement mortar wasn't mixed thoroughly enough or maybe it just dried too quickly. I've removed the loose stuff and am looking for some advice on "fixing" it. Should I wet the "failed" joints and simply re-point the small sections using the same (1:4) semi-dry mix or should I use a stonger (1:3), WETTER mortar to help strength and adhesion ? Would a "plasticiser" make the joint stonger and help the mortar adhere to the sides of the slabs ?
Also, some of my pointing has been affected by rain which has caused mortar spots/stains around the edges of some slabs; is there any way to easily remove these without damaging the finish of the paving ?
Once again, thanks for all the advice.
I don't know if I`d do it again though - it's hard work !
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84-1093879891
There's a few possible reasons for the failed mortar pointing. It could, as you suggest, have been poorly mixed, or it could have been parched of moisture when placed, or it could be perished cement....however, the fact is that it is knackered and needs replacing.
Increasing the cement content from 4:1 up to 3:1 won't make a massive difference, and I don't believe there's anything to be gained by doing so. Using a slightly damper mix might help; although, if you have a stiff, semi-dry mix, that should have adequate moisture to initiate hydration. Using a plasticiser is more important with wetter mixes, obviously, but it wouldn't do any harm to a semi-dry mix.
I'd cut out any suspect sections of pointing, and cut them back far enough to ensure you're not going to end up with patchy bits of new pointing dotted here and there - cut out full flag widths/lengths of pointing for a better finished effect. Make sure you've a reasonable depth for the new pointing; at least 25mm, and it would be a good idea to dampen the joints before re-filling. Make sure the new mortar is properly tooled and pushed fully into the joint.
Considering the mortar staining, you really shouldn't use any of the acid-based cleaners on wet-cast riven repro flags or on the Indian sandstone, as it can have alarming results with the colouring. Gentle mechanical action is your best option - a wire brush and the edge of a trowel blade to gradually abrade the offending spots and stains. You're never going to get rid of them 100% so don't waste your time aiming for perfection. You have to accept that, in 3 months time, you will hardly even notice these minor spots and stains, unless some eejit points them out to you!
Increasing the cement content from 4:1 up to 3:1 won't make a massive difference, and I don't believe there's anything to be gained by doing so. Using a slightly damper mix might help; although, if you have a stiff, semi-dry mix, that should have adequate moisture to initiate hydration. Using a plasticiser is more important with wetter mixes, obviously, but it wouldn't do any harm to a semi-dry mix.
I'd cut out any suspect sections of pointing, and cut them back far enough to ensure you're not going to end up with patchy bits of new pointing dotted here and there - cut out full flag widths/lengths of pointing for a better finished effect. Make sure you've a reasonable depth for the new pointing; at least 25mm, and it would be a good idea to dampen the joints before re-filling. Make sure the new mortar is properly tooled and pushed fully into the joint.
Considering the mortar staining, you really shouldn't use any of the acid-based cleaners on wet-cast riven repro flags or on the Indian sandstone, as it can have alarming results with the colouring. Gentle mechanical action is your best option - a wire brush and the edge of a trowel blade to gradually abrade the offending spots and stains. You're never going to get rid of them 100% so don't waste your time aiming for perfection. You have to accept that, in 3 months time, you will hardly even notice these minor spots and stains, unless some eejit points them out to you!