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Community and Q&A

Does concrete form stay corrosion lead to cracked concrete foundations?

Dry_Humidor | Posted in General Questions on

I was told by someone familiar with Massachusetts building code (I’m in VT) that my 10 inch thick concrete foundation walls with steel form stays not broken off and covered with hydraulic cement) were going to eventually corrode.  That corrosion means to expand, and will crack the foundation.  

Is that inevitable?  I haven’t seen a lot of cracks in my foundation (5 years in), but have seen plenty in similar construction. I also haven’t seen a lot of water coming into my basement, but I am finding the interior basement wall has a lot of moisture at the base which could be from condensation due to convection loop (concrete, ~3/4″ air gap, 2×4 studs with fiberglass / vapor barrier, drywall). 

Is it worth digging up the foundation and treating these stays, along with improvements to damp proofing (tar)?  Is it worthwhile to insulate exterior of foundation?

I’m tearing out the interior wall and was planning to use 2″ iso foam, but am I just going to see water entry in a decade or so from cracks behind the wall?

What’s cost effective and worth doing as a stomp out a mold fiesta in my semi-finished basement?

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  1. Expert Member
    Michael Maines | | #1

    The steel ties will eventually corrode and could spall the concrete but with exterior waterproofing--I like using water-stop hydraulic cement over the tie holes and either a dimple mat or rubberized elastomeric membrane--there shouldn't be enough water or oxygen to allow corrosion on the exterior, and the interior is more likely to be dry.

    If the form ties' rusting actually cracks the concrete in a significant way, your concrete is either not strong enough, not reinforced enough or both.

    Quick anecdote: my mother-in-law's basement toilet had been leaking after rainstorms, but sporadically. It seemed to be when the ground was frozen. After a few visits from the plumber who assured her that the toilet wasn't leaking, I finally solved the mystery--directly behind the toilet is a foundation wall covered with tiles mortared directly to the concrete. I pulled off a tile and there was a rusted-out form tie, letting water in when the soil outside wasn't able to drain freely due to frost. A little hydraulic cement on the inside and it's been leak-free for two years.

    1. Dry_Humidor | | #2

      Thanks for the input. Sounds like it is worth considering digging up the exterior and doing a better job of damp proofing to prevent damage, at least on the areas where I'm considering adding a porch.

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