If you really want to seal it, then fill the vertical cells in the
blocks with grout up to and above the point where the pipes/conduits go
through. You might want to wrap the pipes with something so the grout
won't bond and prevent you from ever removing the pipes in the future.
There are 2 ways to put in the grout. You can just pump it in from the
top until it fills the cells. Or you can enlarge the hole on the inside
wall, cram some heavy wadded up paper into the cell and push it down a
little bit, then it takes less grout to fill the cell. When the grout
gets up to the point where the hole in the cell is, you can hold a board
or something like that against the hole to keep the grout from spilling out.
Grout is commonly mixed using 1 part cement and 2.5-3 parts sand. You
do put a lot of water in it, to the consistency of a milkshake, but the
extra water isn't a problem because the masonry will suck some of the
water out of the mix.
> Not really shop related but I thought I might tap into the collective
>anyway...
>
> My crawlspace has a concrete block foundation with two gaps where mice can
> enter. One is where the sewer line exits, the other is a largish hole that
> appears to be where the builder planned to run the sewer line but later
> changed his mind.
>
> Now, I know the standard method of patching gaps around a pipe is to pack it
> with expanding hydraulic cement. But for a hollow concrete block foundation,
> that's probably not good enough since each hole thru the block is actually
> two holes (one thru the inner wall and one thru the outer wall). So just
> patching the gap on the inner side still leaves an entry point on the outer
> side. And since the blocks are hollow and unfilled so far as I can tell,
> a rodent/bug/snake can enter through the hole in the outer face and climb up
> thru the inside of the blocks and exit into the crawlspace at the sill plate
> (the sill plate does not appear to completely cover the top of the blocks...if
> it did, I think this whole issue would be moot)
>
> I realize the best solution is to dig down on the outside of the foundation to
> where the pipes exit and patch the gaps in the outer block face. But in my
> case, there are a number of nearby trees and I'm sure that area is one big
>mess
> of roots so this option is a non-starter.
>
> I'm thinking an alternative might be to
> A) patch the inner face with hydraulic cement, and
> B) fill the channels of those concrete blocks within a couple feet of the
> gaps from the bottom up by squirting a thin concrete mix from the
>openings
> at the sill plate down into the channels.
>
> (I figure at least some of the channels in the block must be filled with
>concrete
> so that the sill plate could be anchored to the block but a cursory
> inspection has shown at least some that are empty or are only partially
> filled.)
>
> The idea being that if a rodent found the gap in the exterior block face, it
> wouldn't be able to climb up through the blocks because they'd now be filled
> with something it can't gnaw thru.
>
> Now, there's no vertical room to manipulate a concrete vibrator so the mix
>would
> have to be pretty thin to make sure it flows all the way down...probably
> cake batter consistency. I realize that too much water will result in weak
> concrete and shrinkage but I'm only looking to solidify the blocks...
>
> Has anybody done this sort of thing? Is there a better alternative?
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