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So there's some long ass backstory - sorry for the wall of text! I figured better too much detail than too little tho.

We recently bought a house in Vancouver, WA (climate zone 8b), a custom job built in 1989, and are remodeling the daylight basement.

We had a structural engineer do an analysis for us and then had a contractor remove most of one load bearing wall plus a second load bearing wall completely and replace them with beams and posts. We removed a staircase and two other walls ourselves.

The staircase stringer ends were embedded in the concrete, as were the bottom sills of all the walls. The tops of the sill plates were only about 1/4" above the concrete.

I wanted to level the floor some before putting down dricore insul armor panels, so I decided I would pull out the 2x4s, grind down the humps around them (nearly 3/4" in some spots), and fill them in with concrete.

When we removed the stringers, they left holes about 3" deep in the concrete. When we removed the sills though, we found that the wall bottom sills were actually three 2x4s nailed together to make a sort of beam ... which actually went all the way below the concrete foundation slab and which rested directly on top of dirt!

The bottom-most 2x4 was pretty rotten, and when I was using the pry bar on it water came out of it like a sponge. The end of this one bottom sill beam-thing also supports a post that holds up a floor joist end that used to be the staircase exit; I cut around this part when removing the embedded 2x4s as I haven't yet sistered the joist it's supporting. The concrete around the wettest part of this bottom sill beam-thing, which is also under that post, was the most rotten and the concrete around the sill up at the top came away like sand with a little gravel in around where the plate was embedded.

So... this so far isn't so terrible and should be fairly simple to fix. However: the basement has two other load bearing walls, which were left because one was the garage wall and the other has a shed load of plumbing in it so it would need to be walled in anyway. These also have this same set up with the embedded 2x4s. I'm worried about the wood is rotting away under supporting walls, but... exactly how worried should I be about this? Will this ultimately impact the structural stability of the house within its expected life span?

Some pics here.

wood under concrete

embedded wood, wet dirt

crumbling wet concrete

more buried wood

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    A few photos may help people to understand your long story better. Who provided the detail for the basement remodelling - the engineer or the contractor?
    – r13
    Dec 27, 2021 at 16:05
  • @r13 there are pics already in the link at the bottom. Not sure what you mean by the detail for the remodel exactly? The structural engineer did the drawings and calculations, the contractor replaced some of the walls with posts and beams as per the architectural specs. His new post showed normal foundation where he dug thru tho.
    – Logos
    Dec 28, 2021 at 19:44
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    I can perfectly visualize what you're describing without looking at the photos... confirmed by looking at the photos. Those of us who can often forget that there are people who can't. Dec 28, 2021 at 21:53
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    I am curious about the answer. And I can add pics! Which I did. Maybe they will prompt someone to weigh in. It seems to me like rot would track along the wood, up into the house.
    – Willk
    Dec 29, 2021 at 16:42
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    It makes sense if this is an unreinforced concrete slab-on-grade. I don't want to guess why there were so many wood pieces left in the concrete, without special treatment/protection, the wood eventually will rot away. If there are no other visible large cracks on the floor, you shall remove all woods, clean, roughen the exposed surfaces, and fill the shallow (not thru the depth of the slab) voids with concrete. For deep void, I'll consider enlarging the void and adding reinforcing steel to avoid future cracks. Also, do not forget to provide a raised pedestal for the wood post.
    – r13
    Dec 30, 2021 at 2:40

1 Answer 1

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No one had mentioned the larger problem at hand. You said the wood was soaking wet and squishy. That is not a good thing and there is another issue that you need to address. There is simply too much water under your house. If you fill the void with concrete the water will make it's way between the new and old concrete and end up in the room. Concrete is not water tight, in fact it actually wicks moisture out of the ground and the moisture will pass through it into the space. Ever seen a basement that has wet walls?...

My house 1/2 of the basement is dirt. There is not one lick of moisture in that dirt. I know this because it is clay and if there was any moisture in it it would be some really mess stuff. You need to address the ground water issue to ensure you will not have an moisture coming up between the new and old concrete.

For a whole of that size I would actually make the whole larger and drill some holes into the existing concrete and epoxy some rebar into it and then pour new into the hole.

You also mentioned leveling the floor. what are your plans for that? With as much moisture as you have under that floor I would be hesitant about adding any additional weight to the floor. If you are going to put more concrete or even a leveling cement across the floor you should grind the floor first to roughen it up and if you mix chopped fiberglass into the cement it will help to keep it from crumbling if there is a thin spot. This is one floor I would not put any kind of carpet or hardwood over because of the moisture in the ground. If that is the game plan you need to epoxy seal the floor first to keep the moisture from coming through and even that is not a gurantee.

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  • Those are all great points and you are right. The moisture is problematic the way. I will find a professional who cash address that for us. Thank you very much indeed!
    – Logos
    Apr 19, 2023 at 13:53

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