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Hello, I live in an old house circa 1910. We eventually would like to finish the basement. While the foundation is in great shape, the walls are crumbling. We could just brush our hands on it, and the walls turn to sand. Is there a product out there that we can put on the walls to prevent the crumbling? Something that would let the walls breath, so as not to lock moisture inside the walls? Ive tried to search ebrandon, but Im having trouble finding anything useful. Thanks!

If your concrete walls are crumbing, then I would suggest the damage is already done. The best, and only real protection you can offer a basement wall is to dig around your house from the outside and protect the exterior of the foundation walls with a water proof membrane, and install weeping tile.  
 
Moisture in concrete isn't necessarily a bad thing. As long as concrete is wet, it's getting stronger. What concrete does not like however, is sulphate. Your basement may have been poured before the advent of type-2 (sulphate resistant) cement. Concrete mixtures, specifically cement, have really improved over the years, and damp concrete usually won't degrade over time, just look at how well Hoover Dam is doing. The only downfall to damp concrete is a damp and mouldy basement.

If it is 1910 the foundation is likely a stone and rubble foundation wall. If the walls are crumbling it may be the backfill that is supporting the walls. Digging out could cause catastrophic failure. You need to have a registered structural engineer come and assess and give recommendations on how to remediate any possible issues. Even if you feel it is in good shape. Crumbling could be a symptom of larger issues.

I had the same situation and conversation with a local contractor who told me to get it Spray Foamed.  
He said they should apply it thick , like 6 inches or so .  
This will act as a water seal and stop the mould smell.  
Then I guess you can build from there. Although if you don’t have weeping tile to get rid of water gathering around the outside of the walls where would the water go ?  
I never did this procedure but think it’s worth looking into.

Spray foam will cover the problem, but not cure it. The spray foam will not adhere to the wall, nor will it stabilize the deteriorating concrete. Better to get a professional (ie. not the contractor who suggests spray foaming it). Depending on the circumstances, could use a product called "Xypex", which should be available from Wheat City Concrete, which is sprayed on the inside of the wall, or the wall could be cleaned and parged from the inside. Xypex will soak into the concrete and cures to a hard coating that stabilizes the interior finish. Root cause is the lack of dampproofing on the outside of the foundation, allowing water to permeate through the wall.

Yes Xypex works great. I have used it on my house back in mid 90's. Home building center has it on the shelf too.  
Brush your walls so loose stuff is gone, Follow instructions on package and you will be fine. If your foundation is that bad i would recommend doing a few coats. Xypex is a great product but it isn't cheap..  
 
Edited by Jim.50.005, 2019-02-19 17:10:00