moisture getting into foundation after spray foam and exterior seal

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moisture getting into foundation after spray foam and exterior seal

Post by raebug »

I have a 1916 house with field stone, pebble, concrete mixed foundation. We recently had the interior of the foundation spray foamed and the exterior walls skim coated with a concrete type mix. We also had interior drain tile installed. Now, about one year later the spray foam around the windows is pushing inward (away from foundation wall) and the exterior skim coat is pushing outward(away from foundation wall). The skim coat guy came to 're-do' the exterior skim coat and found that the foundation has turned to sand.. and is damp. How did this happen and why? I've had numerous guys out in different professions and they are all stumped (contract, concrete, structural engineers, etc). please help, thanks!

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Re: moisture getting into foundation after spray foam and exterior seal

Post by V-Man »

I'm stating the obvious I guess but you have water still coming into your foundation from some source. I take it nobody really tried to pinpoint the problem before offering solutions such as the drain tile and interior/exterior seal, which is always a bad idea when it comes to old, lime based mortar foundations (you have lime based mortar since its turning to sand and based on the age of construction). The sealing traps the water, eventually the interior seal (in your case, the spray foam) fails because the water is trying to get out from the hydrostatic pressure, while the exterior seal does a double-whammy in trapping the water, particularly because they used a portland cement based skim coat (portland doesn't breathe like lime and allow the water to naturally come to the surface). When you trap water in lime-based mortar foundations, eventually the mortar fails and turns to sand. The moisture is the trapped water. I had similar issues to contend with but fortunately dodged the wrong solutions. Sorry you were steered the wrong way, but I'm finding most contractors and "experts" nowadays no nothing about old foundations.

Basically you need to find the source of the water and hope its something you can address (like gutters, roofing, exterior ground sloping, chimney cracks). You fix these first. It might take a season or two and sitting down in the basement pondering this over a beer or two. You have to get rid of the skim coating, as putting a concrete (portland cement based) coating is the worst thing you can do to a lime based mortar foundation. The only other worse thing they could have done was painted the interior with Drylock. if you have a high water table or other natural source causing water to wick up into your foundation, it may be that your basement was always naturally wet to a certain degree or during certain times of the year and the only reason why the foundation wasn't compromised over the last 100 years is because the lime mortar allowed the water to exit and evaporate.
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