Rubble Foundation questions

Old 03-24-23, 08:04 PM
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Rubble Foundation questions

Our house (circa 1880) has a rubble foundation, mostly in solid condition though the summer plans were to repoint anything needing attention. Clearing our first corner (inside) we noticed dirt and some water seepage in a couple spots at the base of the foundation where the slab had been poured. We figure this may have been a dirt floor with a slab poured later at the level of the bottom of the foundation, but no matter, our question is what we should do with the gaps were the stones don't dip below slab level to fill these voids where there is nothing but dirt?

In our preliminary research (we're noobs here) we've discovered some discussions about hydraulic cement, mortar, and concrete. Does anyone have experience with this scenario and advice for us?
Old 03-25-23, 07:51 AM
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What is your intent? Are you trying to “waterproof” from the inside? Rubble foundations of that era usually were not mortared. People try to make them solid to try to prevent water intrusion. It cannot be done!

If you are just trying to smooth the surface of a dry wall, you could use a mortar mix. Try some “This Old House” searches for information about types of mortar, etc. I think recent AskTOH segments covered that topic in general and relative to an exterior stone step repair.

Voids near the floor could be allowing water that seeps through the wall to drain under the floor (if you are lucky) rather than flooding above it.

I have created a moat at the base of my rubble wall that directs water to a sump pit.
Old 03-25-23, 05:06 PM
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I'd imagine the foundation must keep going down. The floor shouldn't be below the bottom of the foundation.

But, in the end, it doesn't really matter. I'd treat those voids the same as anywhere else on the rubble foundation. Clean out as much of the dirt as possible, to a max of about 2-3". Dust or blow off the stone and cement floor to clean any remaining dirt. Then fill with a mortar mix and smooth.

As stated, it won't help much with water infiltration, but it should clean everything up and give you a nicer and less dusty basement.

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