I’m finishing construction on a new house on the San Francisco Bay peninsula. The plumbing subcontractor made a mistake on the waste layout and we had to abandon the initial 6″ hole in the foundation and cut a new one higher up in the stem wall. After we’d dried in but before the drainage had been installed and the patio was poured we had a large rain storm and quite a bit of water came into the crawl space through the abandoned hole. The house and landscaping are done now but we haven’t had a rain storm since in order to see if there is a problem. The mud in the hole is still a little damp despite very dry conditions.
My question is whether there is a way to plug the hole from the inside of the foundation that will make it reasonably water resistant. Because of the patio slab, there’s no easy way to access it from the exterior.
I’ve attached a drawing of the condition I’m describing.
Replies
Grout
Dig out the mud, clean the concrete, and fill from the inside with non-shrinking grout. Honestly though, spray foam might work just fine, too.
Cast a concrete plug about 1-1/2" smaller (assuming the hole is round) then secure that well-centered in the hole using something like GreatStuff expanding urethane foam.
Be careful to use just enough foam to hold the plug in place at the outside of the foundation, maybe wood wedges on the inside.
Once the foam's cured, remove the wedges & fill the remaining circular ring with hydraulic cement, using a dowel & mallet or other tamping means to make sure it's well packed against the foam.
Add new layers of cement as the initial layers harden. It sets up quick so you ought to be done in a few hours.
Oh and document your T&M to back-charge the plumbing contractor who should have fixed the problem he created before it rained.
Yeah, it's unclear why the plumber didn't fix his goof, but it should be feasible to fix it now.
Basically clear the hole as best you can (it looks like the rat slab may be blocking it to a degree), dig out beyond the wall an inch or three (so your patch can "key" beyond the wall, try to get the cut surfaces fairly clean (for better adhesion), then use whatever you can think of in the way of mortar to close it up. Basically you want a non-shrinking mortar, so hydraulic patching cement is probably the best choice, but you'll need a lot, and maybe some sort of form. (You might consider first fitting several pieces of concrete in there and filling in around with the hydraulic cement.)
I gather the thing is a minor SOB to access, so that will no doubt color your decisions to a degree. And be assured that anything you do will be better than the open hole.
While you're in there, make sure that the space around the sewer pipe is well-sealed.
thanks
Thanks for the ideas. I'm going to try the hydraulic cement route. Access will be a bummer so I hope I'm not under there too long.