Thank you for this amazingly informative site. From the posts, it appears that the time you invest in it is appreciated by its users a hundred-fold. I’ve not seen some of my issues directly addressed elsewhere on the site or I wouldn’t bother you. This confluence of circumstances, materials and concerns may be uniquely peculiar to me, but I would appreciate your input nonetheless. I hope you can help me.
I am a do-it-yourselfer in the US (Pennsylvania where the frost heaves are great and the humidity worse). My standard methodology is to build it so it’ll last 1000 years---guilty of a bit of overkill. I'm also a recycler and frugal. I’d like to use what I have, and, though it may sound like I’m trying to avoid work, I think underkill may be the way to proceed for this particular project.
PROJECT:
I'm building a winding path from my gravel driveway to an out-building where I’m putting my office and from the outbuilding to my deck. The full length of the path will be about 210 feet (64 m). I’ll build a small patio in front of the outbuilding about 150 sq. ft. (13.94 sq. m.), and I’m going to put two wide steps (slate slabs?) up to the building’s doorway from the patio.
SITE DESCRIPTION:
I could build the patio and about one-third of the path in the typical way you describe on your site—the earth is easily removed and I could dump tons of gravel into the void and compact it, etc. However, I have two problems. The first is the paving material (see below). The second is that two-thirds of the path is under some old trees. I’ve double dug big gardens in this area and the roots of the trees show their gratitude by poking through the new surface within two years. The wooded pathway is criss-crossed by huge surface roots I’d rather not remove. I’m wondering if it’s not best to put the path on top of the ground surface rather than fighting nature by digging it in. I can always plant and mound earth up to the sides of the path to disguise its appearance and make it a little safer to use. While the path may be gently undulating in spots, for the most part I should be able to install it so you’d barely notice.
PAVING MATERIAL: SLATE MILL ENDS
I've gotten a great price on what are called "Slate Mill Ends"---basically they’re scrap left after the best pieces are cut to specs. The slates are relatively "square" and they range in size from 6 in. x 1 ft. (15 cm x 30.5 cm) to 2 ft x 2 ft (61 cm square). The bigger problem is they are cleaved and rough and vary in thickness---from each other and within the same piece. The bulk of the larger 2 ft square pieces will be used for the patio and range from 3/4 in to 2 in thick (19 to 51 mm). The smaller slates to be used for the path are predominantly 3/4 to 1 in. thick (19 to 26 mm) so they could be bedded fairly evenly. A few years ago I laid a 50 ft slate mill-end path on finely crushed gravel and spent a lot of time trying to get the surface even---since then it’s become quite uneven because the sand and gravel washed out. Given this material, I can’t use a flat bed and don’t want to take the time make uneven pieces appear flat. Not having tried it, I’m guessing that laying the uneven slate in a bed of mortar is the only way to get the surfaces relatively flat.
MATERIALS FOR BASE - Concrete Panels and Used Sidewalk Slabs
My late dad was a contractor and used to salvage things from various jobs. He salvaged some tongue and groove concrete panels which are about 2 in thick (51mm), 22.5 in. wide (57 cm.) and about 8 ft long (2.4 m). These panels may have been designed as a wall panel but I think they’d be satisfactory for my application. They are also narrow but could be doubled up. Two panels would be 46 in (117 cm) wide. When I bought the slate I anticipated a path about 30 in wide (86 cm.) so I’d be short on slate if I doubled up the panels. 46 in is also a bit wide for my proposed traffic (my personal use and people visiting my office). Doing a curve with these pieces will also be very hard. They will be near impossible to cut because they are reinforced with thick reinforcing wire criss-crossed every 3 in.---I'd need a blowtorch. So my walk would have to be somewhat angular and then I’ll try to fill in with cinderblocks to create softer lines. Being tongue and groove, these panels should be fairly easy to piece together to create a nice patio.
I also have about 50 ft. (15 m) of old sidewalk which are about 10 in thick (25 cm) . These slabs were lifted out in 4-5 ft sections. I could sink these down in the areas easily excavated and it would be easy to match the different levels. These sidewalks are also about 24 in. wide (61cm.). The concrete panels and the old sidewalk are free but super heavy. Once in place and back strains healed, I suppose the weight is a plus when the ground heaves (freezes and thaws repeatedly).
So even though I could use the typical installation method on about one-third of the path and on the patio, I have these (free) concrete panels and slabs which may save us a lot of work. Do you agree?
My son and I will do the work but we only want to do it once. Given the ground conditions and the materials I have, how should I proceed?
Questions:
-Can I use the concrete panels and old sidewalk slabs as a good base?
-Can the concrete panels be placed on top of the ground rather than in-ground in the wooded area, or is this insane as my son suggests?
-Given the panels’ and slabs’ weight, do they need any footers?
-Would the panels have to be laid in a sub-base of crushed stone?
-Assuming the slate will be laid on top of the panels and slabs, and given the slates’ varying thicknesses, should I bed them in concrete and then point with mortar?
-Or should I just bed the slate in mortar even if it does get thick in spots? I’d do my best to pick pieces similar in thickness.
-What kind of concrete and/or mortar mix would you recommend?
I know this was a long explanation but I’ve not seen these issues addressed in any of my research. I have printed your sections on laying brick and block on an inflexible base.
Now that the heat of summer is over, I’d like to get started. Winter comes too early these days.
I look forward to your expert advice. Thanks!
New Slate Path & Patio with a twist
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84-1093879891
Well, that's a fairly comprehensive posting! I'll try and work my way through each of the issues, but I should warn you that UK/Irish practice differs from that in the continental USA, and it might be worth checking my thoughts with someone on your side of the water.
I'm not sure why you want to use these great big concrete slabs and panels as a 'base'. They will be difficult to handle, and, because of their size, will act as bridges or blocks rather than as a base. The idea of a base layer (or a sub-base) is to evenly spread the imposed loads onto the underlying layers. By using monolithic bloacks such as you propose, you are not really spreading the loads, but transferring them directly to the sub-grade. There will be some load transfer, because the paving units are smaller in surface area than the blocks/slabs, but the pavement will behave as a series of unconnected blocks rather than a flexible whole. This, I think, answers your first question.
On your second point, laying these blocks on top of the existing sub-grade rather than excavating to a formation level is possible, but I can't see how it would benefit the final construction. When you've got a flexible sub-base or base layer, then any minor ground movement caused by light frosting or root growth can often be accommodated by the flexible base/sub-base, but, when the base is a monolithic block, any ground movement is directly transmitted to the surface layer.
On to Q3, and the use of footers is wandering further into the realm of major civil engineering work. The idea of using these reclaimed materials is to reduce the amount of labour and materials required, not make even more work! However, if you did decide to use the blocks/slabs, then you probably would need some form of concrete blinding to seat them securely and prevent them rocking or settling over time.
This brings us on to your next point, regarding the need for a sub-base. This project is assuming massive proportions the more you consider it! A sub-base would be ideal, if you were planning to run your 4x4 over the finished pavement, but, as this is supposed to be a pedestrian only footpath, then using a sub-base AND a base layer of reclaimed blocks/slabs is probably going a bit too far.
And so to your final questions, regarding the bedding of the slate. I think they'd be best laid on a full concrete bed. This would vary in thickness from, say, 200mm (8 in.) to (150mm (6 in.) to accommodate the variation in slate thickness, yet provide adequate resistance to frosting. The concrete should be a reasonably strong mix, something around 20-30 Newtons (that's roughly 1 part cement to 2 parts sand to 4 parts gravel), and the pointing should be done wioth a frost-[proofed mortar, mixed at 4 parts sand to 1 part cement.
I'd lay all of this on a base of 150mm of 15-20 Newtons concrete, which would itself lie on top of a 200mm sub-base of granular material laid over a root barrier membrane. This gives us something around the 500-500mm thickness that seems to be the norm for ligt-use footpaths in areas where frost heave is a problem.
The granular sub-base and base layer of concrete could be laid first, and then the paving bedded directly onto the bedding concrete while it's still fresh. As ever, this is much easier when a semi-dry mix is used.
As I said right back at the beginning, you really could do with checking this with one of your compatriots as my experience of frost heave is minimal at best. However, assuming a frost prenetration of 450mm (18 in) this construction should be OK, and should be thick enough to resist interference from roots.
I'd be interested to hear how you get on!
I'm not sure why you want to use these great big concrete slabs and panels as a 'base'. They will be difficult to handle, and, because of their size, will act as bridges or blocks rather than as a base. The idea of a base layer (or a sub-base) is to evenly spread the imposed loads onto the underlying layers. By using monolithic bloacks such as you propose, you are not really spreading the loads, but transferring them directly to the sub-grade. There will be some load transfer, because the paving units are smaller in surface area than the blocks/slabs, but the pavement will behave as a series of unconnected blocks rather than a flexible whole. This, I think, answers your first question.
On your second point, laying these blocks on top of the existing sub-grade rather than excavating to a formation level is possible, but I can't see how it would benefit the final construction. When you've got a flexible sub-base or base layer, then any minor ground movement caused by light frosting or root growth can often be accommodated by the flexible base/sub-base, but, when the base is a monolithic block, any ground movement is directly transmitted to the surface layer.
On to Q3, and the use of footers is wandering further into the realm of major civil engineering work. The idea of using these reclaimed materials is to reduce the amount of labour and materials required, not make even more work! However, if you did decide to use the blocks/slabs, then you probably would need some form of concrete blinding to seat them securely and prevent them rocking or settling over time.
This brings us on to your next point, regarding the need for a sub-base. This project is assuming massive proportions the more you consider it! A sub-base would be ideal, if you were planning to run your 4x4 over the finished pavement, but, as this is supposed to be a pedestrian only footpath, then using a sub-base AND a base layer of reclaimed blocks/slabs is probably going a bit too far.
And so to your final questions, regarding the bedding of the slate. I think they'd be best laid on a full concrete bed. This would vary in thickness from, say, 200mm (8 in.) to (150mm (6 in.) to accommodate the variation in slate thickness, yet provide adequate resistance to frosting. The concrete should be a reasonably strong mix, something around 20-30 Newtons (that's roughly 1 part cement to 2 parts sand to 4 parts gravel), and the pointing should be done wioth a frost-[proofed mortar, mixed at 4 parts sand to 1 part cement.
I'd lay all of this on a base of 150mm of 15-20 Newtons concrete, which would itself lie on top of a 200mm sub-base of granular material laid over a root barrier membrane. This gives us something around the 500-500mm thickness that seems to be the norm for ligt-use footpaths in areas where frost heave is a problem.
The granular sub-base and base layer of concrete could be laid first, and then the paving bedded directly onto the bedding concrete while it's still fresh. As ever, this is much easier when a semi-dry mix is used.
As I said right back at the beginning, you really could do with checking this with one of your compatriots as my experience of frost heave is minimal at best. However, assuming a frost prenetration of 450mm (18 in) this construction should be OK, and should be thick enough to resist interference from roots.
I'd be interested to hear how you get on!
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LVLishious
- Posts: 3
- Joined: Wed Sep 24, 2003 5:21 pm
- Location: Pennsylvania, USA
Didn’t think of all that. Guess that’s why your’re called the “Paving Expert�. Thanks.
I have only one reason I’d use the concrete panels as opposed to pouring a new concrete walk on which to lay the slate: expense. We’ve used the panels elsewhere by just laying them at ground level or just on top of ground and when interlocked with the tongue and groove they don’t really move. Without the interlocking (which can’t really be done end to end), I see your point that they’d be individual floating blocks. I don’t think they weigh as much as nor are they as bound together as sidewalks poured with control joints. I had thought that laying each panel on a couple of inches of crushed stone wouldn’t be much different than pouring a slab over a stone sub-base, but I guess not.
The reason I didn’t want to dig into the root system of the tree is that the old maple and arborvitae are around 85 years old and the surface roots are like tree trunks. There are probably plenty more gigantic roots underground but I didn’t want to damage the trees or make them more likely to fall on my house. So even if I pour a slab I’d form it aboveground and then build up soil on the edges. Am I being too much of a tree-hugger here? Do old trees like a severe root trimming now and then?
The bottom line is that I can’t afford a pour at this time: 65 sq. meters of 6 in concrete? Uh, no. So I may to have to settle for laying the slate directly on top of a shallow gravel base until the spring and then do the job more permanently next summer. I have a pile of gravel. I should be able to shovel the snow off of that path, and as long as it’s flat people should be able to negotiate it safely. I could probably get a season out of it.
There's no comparable site on my side of the pond, and any do-it-yourself site addressing these subjects is skeletal at best. I'll refer to the other resources on your site to do a "proper job".
Thank you kindly for your advice.
I have only one reason I’d use the concrete panels as opposed to pouring a new concrete walk on which to lay the slate: expense. We’ve used the panels elsewhere by just laying them at ground level or just on top of ground and when interlocked with the tongue and groove they don’t really move. Without the interlocking (which can’t really be done end to end), I see your point that they’d be individual floating blocks. I don’t think they weigh as much as nor are they as bound together as sidewalks poured with control joints. I had thought that laying each panel on a couple of inches of crushed stone wouldn’t be much different than pouring a slab over a stone sub-base, but I guess not.
The reason I didn’t want to dig into the root system of the tree is that the old maple and arborvitae are around 85 years old and the surface roots are like tree trunks. There are probably plenty more gigantic roots underground but I didn’t want to damage the trees or make them more likely to fall on my house. So even if I pour a slab I’d form it aboveground and then build up soil on the edges. Am I being too much of a tree-hugger here? Do old trees like a severe root trimming now and then?
The bottom line is that I can’t afford a pour at this time: 65 sq. meters of 6 in concrete? Uh, no. So I may to have to settle for laying the slate directly on top of a shallow gravel base until the spring and then do the job more permanently next summer. I have a pile of gravel. I should be able to shovel the snow off of that path, and as long as it’s flat people should be able to negotiate it safely. I could probably get a season out of it.
There's no comparable site on my side of the pond, and any do-it-yourself site addressing these subjects is skeletal at best. I'll refer to the other resources on your site to do a "proper job".
Thank you kindly for your advice.
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84-1093879891
I hope you manage to get your slate laid. If you take any photo's I'd be chuffed to see them, These 'Slate Mill Ends' sound very interesting.
You may be right that laying a temporary surface on gravel to get you through the winter could be the best option at this stage. I'm supposed to be meeting a US-ian paving contractor sometime later this month, so, if I can, I'll get him to give me a quick briefing on US methods that I could possibly turn into a page of basic hints.
With regard to your trees, if the maple is what we call a Sycamore, then the roots are fairly forgiving, as long as you don't take out too many, but the Arbor Vitae, which is a conifer over here, tend to have shallow, fibrous roots and you have to be more careful, as they rely on the fibrous mat for anchorage. If it's only a small tree, then it shouldn't mind a bit of a trim, but for anything more than 3m high, it's best to consult a tree surgeon.
You may be right that laying a temporary surface on gravel to get you through the winter could be the best option at this stage. I'm supposed to be meeting a US-ian paving contractor sometime later this month, so, if I can, I'll get him to give me a quick briefing on US methods that I could possibly turn into a page of basic hints.
With regard to your trees, if the maple is what we call a Sycamore, then the roots are fairly forgiving, as long as you don't take out too many, but the Arbor Vitae, which is a conifer over here, tend to have shallow, fibrous roots and you have to be more careful, as they rely on the fibrous mat for anchorage. If it's only a small tree, then it shouldn't mind a bit of a trim, but for anything more than 3m high, it's best to consult a tree surgeon.
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LVLishious
- Posts: 3
- Joined: Wed Sep 24, 2003 5:21 pm
- Location: Pennsylvania, USA
My Maple is a Sugar Maple (Acer Saccharum), not a Sycamore (Platanus occidentalis). The Sugar Maple Specimen is so old that it's upper branches look like tree trunks. I'm sure it's not long for this world. The arborists can't really do anything with it, topping is out of the question, and so I'll nurse it along until it split open in some storm. I'll call my local agricutural extension service before I start cutting any roots.
I'll check your site for a North American tips page you put together. I just saw a do-it-yourselfer show where they were laying a path in California with big blocks of granite on a couple of inches of gravel and a few dollops of mortar----they then said basically "don't try this at home kids if you live in the colder latitudes...."
I'll see if I can get a picture of the slate mill ends --- my sister has a digital camera and knows how to download it. I don't think "mill ends" is a term of art but of commerce. When the quarry gets to the end of a run the stone will have a slice left and this is it. Also, when they cleave it and it's too uneven, it ends up in this pile. However, the local quarry sells it for ũ for each piece, no matter the size, so I even picked up the 2 x 2s for ũ each. Can't beat the price.
Thanks again for taking your valuable time to respond to my inquiry and maintain this wonderful site.
I'll check your site for a North American tips page you put together. I just saw a do-it-yourselfer show where they were laying a path in California with big blocks of granite on a couple of inches of gravel and a few dollops of mortar----they then said basically "don't try this at home kids if you live in the colder latitudes...."
I'll see if I can get a picture of the slate mill ends --- my sister has a digital camera and knows how to download it. I don't think "mill ends" is a term of art but of commerce. When the quarry gets to the end of a run the stone will have a slice left and this is it. Also, when they cleave it and it's too uneven, it ends up in this pile. However, the local quarry sells it for ũ for each piece, no matter the size, so I even picked up the 2 x 2s for ũ each. Can't beat the price.
Thanks again for taking your valuable time to respond to my inquiry and maintain this wonderful site.
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84-1093879891
I see that BBC America has inflicted 'GroundForce' on your country, as though you don't already have enough troubles, and they are using the very same paving practices on US-ian projects that we use here in the UK.
I wonder if they'll ever get around to doing the Follow-Ups that we get over here? Basically, 12-18 months after they've made over your garden, the two eejits make an alleged 'surprise' visit to see if you're looking after the plants, or whether you've ripped up the bloody decking and painted the fence any colour other than blue. Given the problem with frost heave, which doesn't seem to be a consideration in their construction works, I doubt we'll ever get to see the twisted and broken paths, and the rumpled pavers that didn't manage to survive even one winter!
Looking forward to your pix! :)
I wonder if they'll ever get around to doing the Follow-Ups that we get over here? Basically, 12-18 months after they've made over your garden, the two eejits make an alleged 'surprise' visit to see if you're looking after the plants, or whether you've ripped up the bloody decking and painted the fence any colour other than blue. Given the problem with frost heave, which doesn't seem to be a consideration in their construction works, I doubt we'll ever get to see the twisted and broken paths, and the rumpled pavers that didn't manage to survive even one winter!
Looking forward to your pix! :)