Sealing crack between Chimney and Foundation (Below Grade)

Ahomeowner

Hi guys,
I posted about this a little while ago concerning the water that leaked into our chimney and then entered the chimney liner and went into the oil-fired boiler. I dug up the chimney and using a hose, we confirmed that the water is entering the gap between the chimney and the foundation (just above where the tree roots enter.)  I’m trying to decide what to use to seal this gap. I thought about hydraulic cement, but I would need to chip away a little bit of the old concrete on either side of the gap in order for the hydraulic cement to stick (according to YouTube) and I don’t want to chip at the foundation right now. So I was thinking some kind of sealant that comes in a tube, like a caulk that can be used below grade?  Or a peel and stick membrane like EPDM?  Or maybe both, for a belt and suspenders approach?  Does anybody have any recommendations?  I didn’t find anything definitive during my internet searching. Thanks!

Jamie Hall

I'd use a polyurethane caulk. And be aware that it will help, but won't be perfect.

Ahomeowner

Update, I dug a little deeper and there is a small piece of concrete approx 30” below grade forming a bathtub at the bottom of this hole. There were two other levels of concrete attached to the chimney, which may have been added to direct water away from the chimney. The top level was no longer attached to the chimney and I was able to remove it by hand, but the middle layer needed to be chipped out. This lower level is directing water towards the chimney because there is a bowl shape to it in the corner. I’m considering the pros and cons of removing it. Thinking of just sealing it from the top, since the problematic crack may continue 8 feet down to the footing. This bowl along with the crack may be the source of the problem.

Jamie Hall

The "crack" probably does go down to the footing. The chimney is almost certainly a separate construction -- not integral with the foundation wall at all, although the footing may be integral with the foundation footing. The real question is what is missing in the seal between the chimney and the foundation and the stove pipe...

MikeAmann

Time to rent the trencher and install a drainage pipe to carry the water away.
You will never successfully seal that area.