I’m to build a limestone retaining wall for a customer. It’s to be approx. 2′ high and backfilled. I’m debating whether to face a poured wall, or just lay up the blocks. I’m thinking that draining the backside of the wall with 1″ rock and seep tile would inhibit lateral pressure. Specifically, I have a run up the side approx 24′ long, make a 90 degree turn, and a run across the front of the yard approx 34′. That run is interrupted midway by a set of steps to the upper level. If I use blocks only (no poured wall), they would be relatively thick. I’d have to check with the local quarries, but I’d guess 14″ or so.
What do you think?
Replies
If you use just the limestone it's not realy retaining is it?
It's just that I've seen so many of these walls move.
limestone and water do not play well together, be careful
Thanks you two for your cautions. Without checking my original message, I'd guess that I didn't say I would lay up the limestone with mortar. However, I'm well aware of a mortared wall's ability to withstand lateral pressure (or not). So does anyone think it would be overkill to pour the footing and wall (6"?)with continuous rebar, face and cap it with limestone, and use drained gravel backfill?
Yeah, that's overkill for a 2' wall. Gravity is more than enough at that height. Anything under 4' can be made out of concrete blocks on a compacted base, unless there are some really crazy conditions. Gravel backfill and filter fabric is a good idea....that's not a mistake, it's rustic
I think it depends on what the grade does behind the wall. Does it go back flat, gentle slope up or steep slope like 2:1 or 1:1? The steeper the slope, the more the wall will need to hold. If the wall is only 24" high and you use 14" blocks, you'll only be two blocks high with one partially buried. Doesn't sound like much of a wall, more like a border. Forget the mortar, just stack the top block 1" back from the face of the bottom block, throw some washed stone behind it and lay your filter fabric and topsoil up to meet grade.
Eric
Eric,
Thanks for thinking about this. I am at fault for underestimating readers' interest in this. I should have provided more explicit spect.
I've speculated about the size of the limestone blocks that may be available (not having had the time yet to go to the quarry). If I can find some to match the existing foundation, they will be of variable w (8-16")and h (6-12"). Thickness I'm guessing to be 14". The finished grade will be level. He wants a mortared stone wall look. In sum, I'm leaning towards a 2' high mortared stone wall on a steel-reinforced concrete footing with drained, gravel backfill, unless I read something here that cautions strongly otherwise.
Sorry to sound like a cheapskate, but would it not be cheaper to use thin Limestone to veneer a concrete block wall. I don't doubt that limestone would hold, but why spend the money. Or, is limestone cheap where you are? Good luck either way, sounds like fun work to me, well sorta.
Dan
It sounds like you've got it mostly right. Make sure to include weepholes at 3 to4 foot intervals along the base of the wall, 1"pvc works well.Create a level bed for the footer, stepping down if necessary to accomodate for sloping terrain. If building on unstable ground use a vibrating plate compactor on footer bed. Use twin re bar in the footers with some upright pieces to tie into the blocks. 8" block is plenty big. You might consider installing big o pipe in the gravel drainage. Landscape cloth is probably unnecessary. Make sure you have the stone on-site, so that you can design the footer to accomodate your material. Think about the cap! On a low wall, the cap is often the most visable feature. All of this said, I find that traditional dry-stacked stone retaining walls are more permanent, beautiful, and fun to build. Good luck.
Stoner,
Thanks for your reply. I apologize for taking so long to respond -- been real busy.
If you've the time and energy, I'll offer some more questions:
Does the traditional dry-laid method lend itself well to dimensioned stone? Or better to natural field stone? If dimensioned stone is best mortared, would you recommend laying them in front of a poured concrete wall?
Why do dry-laid walls last longer?
I can understand dry-laid for walls (such as between plots of land or as boundaries), but for retaining with unequal, lateral pressure? You do use the term "retaining", and I wanted to clarify.
I don't like to turn my back on a challenge, but can you come to Alton, IL to do this job? :^) I've got too much to do and not enough time.
Cut (diminsioned) stone is easier to stack - especially for a beginner. Costs much more. Sometimes, much much more. An experienced guy is able to get the job done much faster with cut stone.
Random or fieldstone can take exponentially more time for the beginner. This type of material results in more waste, or discarded stones unable to find a home. The stone is cheeper, but you'll need much more of it and a lot more time.
Dry stacked walls CAN last longer than some mudded walls because of the degree of built-in structual support and balance the mason includes. Some poorly built mudded walls fall apart because that same structual support (in some fashion or another) isn't there.
Built correctly, drystacked walls make nice retaining walls. Choose the right materials, prepare the site properly, and factor in for proper drainage. Want the process to go faster? Use bigger stones. Find some nice flat, 1 foot thick muthas and go to it. Two over one and one over two. Every coupla of feet, a stone has to go all the way through the stack and cover as much flat area as possible.
Beginners are best to learn using drystack methods. The material can be recycled in the event of error.
And when people need a two foot high retaining wall built in their hind yard, I believe they have to do it themselves so they really appreciate what's involved. The future maintenance issue becomes major then.
Thanks for your reply. I appreciate your efforts.
I like doing that kind of work, but would rather consider it a hobby. I've contacted a couple of experienced stoneworkers for bids. It will be interesting to hear their discussions about the pros and cons of dry-laid vs mortared.
hey Tim, The reason that a properly built dry-stack wall will outperform any masonry wall over eons lies in the innate flexibility, and drainage characteristics of dry laid walls. The earth is in a constant state of flux , especially in cold climates, where freeze/thaw forces cannot be indefinitely resisted using rigid engineering approaches. A dry stack wall Is flexible along its entire length. If properly constructed, the stones will lock more tightly together,as they continue to accomodate seasonal,generational, seismic, and hydrostatic forces.All of the oldest surviving structures in the world are constructed of dry laid stone. A properly built dry stone wall is harder to quantify than an engineered wall. You can't build a dry wall from a set of plans. The craft of dry walling is more akin to poetry, than mathematics. Only the waller knows if the heart of the wall has been carefully filled. Almost any stone can be used, but flat stones are easier to stack than round ones. Dry stone walling is more labor intensive, and derives its permenance from the wallers experience, and understanding of the manifold forces which will affect a wall over its lifetime. All retaining walls should have a batter, or slant toward the bank, undulations also serve to strengthen long walls.Think about your cap, put your capstones aside before laying the base course. Good luck with your project,sorry I can't come to help, but I'm pretty busy here in Whistler,B.C.
Hi Stoner. Thanks for your long message. I can appreciate the benefits of dry laid stone walls. Unfortunately, this particular customer just told me that he spent money for that on another project. So the wall work is indefinitely delayed. Hopefully, I'll have that opportunity soon. I do quite a bit of landscaping as an avocation and really enjoy working with stone. I've picked up quite a few ton of boulders in the Ozarks and have left them scattered across Illinois. Some future geologist might be baffled. What kind of stone do you have to work with in Whistler?
Doesn't the nature of the soil have a lot to do with the engineering for a retaining wall?
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Yes, Bob. Thanks for the reminder. My experience in this neighborhood has been that there is various fill. I would be backfilling with the tailings from the footing excavation. A trial dig might be in order.
I'll probably find some bricks, bones, and grubs. (There's treasure everywhere!:)
the problem with limestone itself is: limestone is a very soft stone, its more like lime/ sand that dried into a stone like product. water will erode the stone. So after many rainfalls there will not be a wall left. But its a great contruction material because it will hydrade like an cement product. But limestone as a stone is very weak
It's not rain water per se that it the problem with limestone, it's acid rain. And if you live outside South Florida you may have acid rain bad enough to affect your stone. The acid in the water leeches the lime out of the limestone, and then it corrodes away. Serious problem with all our architectural monuments, pyramids, etc. Same thing happens to unprotected concrete. Needs waterproofing.
Acid rain... ah yes. A legacy from W. R. Hearst, Dupont, and our Secretary of the Interior, getting rich by outlawing hemp.
SamT