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Question DetailsAsked on 12/19/2016

Best Material to use for regrading ground abutting a foundation to prevent water seeping into a basement

basement water leak after snow melt

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AFTER regrading the soil around the house so it slopes at LEAST 2% and hopefully 10% or more away from the house for 1-2 feet bare minimum and usually 3 feet or so in tight (relatively impervious) soils, or more like 6-10' in free-draining soils like broken rock or cleaner sands or gravels where the wter can readily travel back toward the house, then you have several choices for the impervious layer:


1) put down a synthetic barrier (pond liner, typically about 50-60 mil thickness, available at many greenhouses and most building supply yards. Bentonite mat also works but is generally a lot more expensive) on that surface, then cover with whatever you want - shallow root planterbed, lawn, bark, decorative rock, paving, etc. The key is that the impermeable layer needs to have the proper slope away from the house, and of course the surface layer should also slope away unless it is very free draining like bark or stones. If you use pond liner, you can fasten it to the foundation by turning it up against the foundation a few inches and using a liner adhesive (in caulk tubes) or for the most permanent solution using ground-contact treated 2x4 as a batten over it, concrete anchored into the foundation at about 3 foot intervals. Be sure any necessary lap joints (minimize those) are overlapped about 3 feet to reduce infiltration - and if possible raise those up a bit on a ridge of subgrade to water drains away from the joint.


2) put down a layer of relatively impervious soil - a true clay is best of course, or use clayey sand or gravel, or a quite silty sand which is clayey enough to compact well. If clayey soil is not available in your yard or local area, you can use a layer of sand or sandy gravel mixed with bentonite clay - about 5-15% (by volume) bagged bentonite clay mixed in would usually suffice to make a soil that compacts well and is quite watertight - bear in mind this cannot be your final walking surface though because it sticks to shoes and paws and tracks gray clay into the house terribly. You would have to experiment a bit with amount needed for your soil - lesser amounts needed in sandy or silty soil, more in free-draining gravels.


Typically 2 inches thickness is the bare minimum, if not clayey enough that you can ball it up in the hand and roll it out into somewhat of a roll (like a breadstick) at damp moisture, then 3-4 inches (loose placed thickness before compaction) is better. You need to make sure it is thoroughly broken up in placement (not clumpy), dampen to moist but not wet condition, then compact this well enough that after initial spraying water runs off rather than soaking right in. A hand tamper or even a sledge hammer thumped down on the ground with complete coverage can do the compaction for this purpose but a lot of work if doing a largish area. Rolling it in thin layers (1" or so) with a loaded wheelbarrow also works, or of course you can rent a power plate compactor or have a landscaping contractor do it. If you get the moisture right so it makes very tight, compact balls in your fist that stick together enough to throw, even several passes of just walking over it in hard sole shoes with at least doubled coverage is enough. But is DOES have to be compacted, not just put in loose - otherwise it will just become a wet sponge in rains and snowmelt and you might have the same problem again. And of course, if erodable material, will need something erosion-resistant over the top - filter fabric, bark, decorative stones, etc.


3) pave around the foundation - concrete or asphalt, making sure both the compacted subgrade and the paving slope 2% or so away from the house - and that there is an asphaltic waterproof joint sealer placed along the foundation at just below top of paving elevation before the paving is done, so the paving bonds/presses against it and waterproofs the joint at the foundation. Course, this is overkill unless you want a walkway or weed-free zone there anyway.


Note - make sure the final surface is at least 4-6 inches below the siding and also same amount below the top of the foundation to minimize wall rot and insect issues - preferably more like a foot in clear foundation block or concrete in termite country. This may mean some soil removal is necessary before you put the impervious layer on top - but be sure both the subgrade and the finished surface slope away from the house for the 3-10' necessary to drain any water at least that far away from the house - and preferably further if feasible.


Also - make sure the problem was not caused/aggravated by roof runoff due to iced or leaf-blocked gutters dumping rainfall/snowmelt water right at the foundation.


Also - in future - if you get drifting or very heavy snow along the foundation, good idea to shovel it down to below the top of foundation and below bottom of siding to prevent infiltration and also avoid wetting of the wall from the melting snow.

Answered 1 year ago by LCD

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Answered 1 year ago by Member Services




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