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Community and Q&A

Waterproofing Limestone Basement Walls

cody_fischer | Posted in General Questions on

I am finishing a limestone foundation wall + concrete slab basement with moisture issues. This is a 100+ year old house with no vapor barrier, waterproofing, or exterior insulation. Exterior grading is in good shape.

Before posting this question, I’ve tried to glean all I can from these great articles and comment threads linked at the bottom of this post.

Proposed Approach:
1) Install exterior gutters
2) Install interior French Drain system and sump pump per Hammer & Hand details…only variation being the dimple matt only extends 4″ up foundation wall. Sprayfoam is applied directly to wall (per Martin Holiday) rather than on top of a full-wall dimple matt.
3) Finish floor with the following: 10 mill poly taped to foundation wall poly/dimple matt, 1″ depth self-leveling subfloor, 2″ EPS, plywood, LVP

Clarifying Questions::
Q1) Poly v. Dimple Board vs. Only Spray Foam on walls: With a limestone foundation wall, my waterproofing contractor is telling me it would be better to apply the closed cell spray foam over the top of a dimple drainage mat or poly. The thought being that the dimple matt/poly will provide a surface /path for the water to drain down and over to the drain tile system.

@Martin Holiday – in several places, you’ve said that poly is fine, but unecessary and that its fine to apply closed cell sprayfoam directly to the foundation wall.  Wouldn’t that prevent the water in the limestone from draining down to the drain tile?  If the water is trapped in the limestone / not finding its way to the drain system, won’t that degrade the limestone/structural integrity of the foundation over time?

Q2) PVC vs. Corrugated Perforated:  It seems like most images of drain tile systems on GBA and the Hammer & Hand spec all use perforated PVC pipe. Corrugated Perforated seems to be the standard industry go-to and a lot less expensive. Internet abounds with claims and counter claims about which drains better, clogs less, etc. Any community opinions?

Q3) River Rock vs. Crushed Stone: Smooth, washed river rock appears in most GBA pictures and is recommended elsewhere on the internet. But H&H specifies clean crushed stone. Any community opinions on what drains best and is least likely to result in clogging?

Dealing With Basement Water from the Inside

Vapor Barriers for Basements and Crawlspaces

Using a Dimple Mat to Keep a Basement Wall Dry

Fixing a Wet Basement

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  1. Expert Member
    BILL WICHERS | | #1

    Yes, spray foam directly against the inside of a cut stone foundation wall will prevent water that leaches through from draining down to the interior perimeter drain. That shouldn't really be a problem though, because you should be taking steps on the EXTERIOR to prevent the water from getting inside in the first place. Interior side drains are just a bandaid, the real problem is on the exterior of the wall and is a lack of proper water proofing and/or drainage. It will be hard to install dimplemat tight to an irregular wall too, and you'd risk the spray foam pulling away from the wall. At the very least, if you go this route (which I don't recommend), I would put a bunch of tap cons on maybe a 1 or 2 foot grid on that wall, with maybe two inches and the head sticking out from the surface to give the spray foam layer to grab on to so that it can stay in place.

    You generally use rigid foam against flat wall surfaces (block or poured concrete), and spray foam against irregular surfaces like a cut stone foundation. What you want to avoid are lots of voids/pockets between the insulation layer and the surface of the wall, and spray foam is an easy way to make sure that everything is filled.

    I don't think there is much difference in practice between perforated PVC and perforated corrugated drain tile, provided that you use some kind of sock over the entire perforated section. A typical sock is a geotextile material with a granular fill between the geotextile layer and the surface of the drain pipe. The purpose of the geotextile layer is to keep out fines that would otherwise fill the spaces between the aggregate, and the aggregate is there to beef up the surface area of the outer layer to make sure water can get in even with some fill dirt slightly clogging the geotextile layer.

    For gravity drains, I prefer smooth PVC pipe, since it allows for higher flow rates. I wouldn't, for example, use the corrugated stuff for an underground drain for the gutters for that reason.


  2. cody_fischer | | #2

    Thanks Bill -

    I understand exterior approach is best but it isn’t an option because of cost and it’s an urban lot with extremely limited access. All I can do from the outside is gutters.

    It sounds like you don’t recommend dimple mat on such an uneven surface, and therefore would opt for spray foam.

    If I am spray foaming and it prevents water from draining down to the tile….should I just not do the tile at all?

    Alternatively, if finishing the space isn’t 100% necessary, would the more durable foundation friendly solution be interior drain tail, no foam, and just install a heat pump hot water heater to dehumidify (doing the last one anyway)?


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