I had a structural engineer come out today who said I'm borderline needing to stabilize my foundation. He said, if I can manage the water outside my house better, I would be very much likely to need foundation repair in the future. Since I have rocks along the foundation wall, he said it would make sense to put a plastic water barrier under that landscaping to divert water from seeping into the ground close to my foundation (on top of proper grading).

I went looking and finding plastic comes in different thicknesses which ranges drastically in price. Does anyone know what mil plastic I should use for a task of keeping water from seeping into the ground under my rock landscaping?


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Since you must have moving water I would want to go with a 10 or 12 mil polyethylene. 12 mil is a bit more expensive but it holds up to soil movement better than thinner poly sheeting products. I use 10 mil on my French drains to prevent dirt from migrating as easily it should work similarly to prevent erosion at your foundation.

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