Cutting a new brick ledge into a concrete basement wall

[met33]

I have a 10" thick concrete basement wall holding back 10 feet of round rock backfill, with an estimated top-of-wall reaction of 750 plf. This is new residential construction.

Through a miscommunication, the builder omitted the 3" x 4" brick ledge when pouring some sections of the wall.

I'm considering getting the brick ledge cut into the wall by a concrete sawing company cut. They would use a mounted saw (i.e., it would not be cut by hand). Unfortunately, cutting the new brick ledge will result in saw overcuts approx. 0.25" deep into the notch where the two cuts meet (see attached diagram: Link).

Will these saw overcuts compromise the strength or longevity of the wall? Should they be filled with epoxy, non-shrink grout, or something else?

The brick ledge will be flashed with waterproofing membrane, but there is some concern about freeze thaw cycles if water finds its way into the notch. On the other hand, without the brick ledge, we are looking at a higher risk of water intrusion into the sill plate area. There doesn't seem to be a great solution, but maybe I'm missing something. Any advice would be appreciated.

 

[XR250]

Why use a brick ledge at this point? Can't the brick just be 3" higher?

 

[met33]

That's an option. If it were just brick with continuous flashing, without penetrations through the flashing, it would probably be fine.

Unfortunately, in these locations the brick ledge is for water management where a concrete porch meets the wood framing of the house. There are #4 rebar dowels from the foundation walls into the porch slab, so the brick flashing needs to be cut and sealed around these penetrations, making it more prone to developing leaks (diagram: Link)

The brick ledge would help to prevent standing water from migrating into the wood framing if the flashing membrane or sealant around the rebar penetrations fails in the future.

 

[XR250]

Drop the porch slab a bit lower so the top of the slab equals the bottom of the brick

 

[BAretired]

Below are the two sections shown by the OP.

Cutting a brick ledge should be avoided if possible. For one thing, you may be removing one of the two top bars in the wall, which is not recommended. The #4 bars are not well suited to preventing the porch slab from moving out if there is a force pushing it out, such as frost. If the porch slab is likely to move due to frost heave, brick should not be bearing on the porch slab.

I believe a better solution is available.

 

[met33]

Yes, I have since learned that there are many better ways to approach this detail. I would do it differently if given another chance. But the walls have been poured and framing starts next week.

Big picture, I'm trying to see if anything can be done to improve waterproofing between the porch slabs and the wood framing of the house. The main concern is the #4 rebar dowels that will create penetrations through the flashing membrane, directly adjacent to the sill plate.

There isn't much danger of frost heave. The porch slabs are resting on stem walls that extend at least three feet below frost depth, and the slabs will be structural, rebar reinforced. Backfill under the slabs will be clean rock, again extending well below the frost line. I suppose there is risk of lateral force from frost, if water gets between the slab and the house then freezes. I hadn't considered that before.

I'm considering adding a waterproofing layer on top of the porch slabs, like a split slab roof deck. Basically, covering the structural porch slabs with a waterproofing membrane, drain mat, and a topping layer of some kind like outdoor tile or concrete pavers. This would help keep the slab dry, which in theory would help keep the wood house framing dry.

The photo and cross-section below show the existing porch walls and current framing plan:

 

[BAretired]

Extend the concrete beam down 4" to keep the water out.

 

[met33]

Looks like it might help prevent water entry from below. Is that the idea? I was originally thinking about water intrusion from above the slab, or condensation of moisture from the concrete at the slab edge.

This discussion has made me second guess whether we should even have rebar dowels between the foundation wall, porch stem walls, and concrete porch slab (see yellow arrows in diagram below).

Do these rebar dowels help or hurt the structure? Are they a possible corrosion concern due to exposed rebar at the cold joints between the slab and foundation walls? Any other concerns?

If we cut off the rebar dowels along the basement foundation wall, it would make waterproofing easier where the porch slab meets the wood framing.

 

[BAretired]

I suggest dropping the top of fill below the potential entry point of water. This means using a structural slab or deck instead of slab on grade. If slab is cast-in-place, forms may be left in place. Dimension 'A' is not known.

Base flashing for brick veneer would drain onto the slab or deck. Minimal amount of water is expected. Granular fill assures any water finding its way in will drain to the drainage tile at footing level.

If we cut off the rebar dowels along the basement foundation wall, it would make waterproofing easier where the porch slab meets the wood framing.

Yes, that would be a problem if we drain below the slab, but I suggest draining the brick above the slab. There will be very little water as the porch is covered.

 

[met33]

Yes, the brick will be flashed onto the porch slab as shown in your diagram, and there is footing drain tile.

The porch slab will be cast in place. I've been planning for a structural slab under the assumption that the fill rock will settle over time and leave some voids. Interesting idea to assume a clear span from the start.

The slab dimensions are below. It will be at least 6" thick, but it could be thicker.

 

[BAretired]

Looks good. Keep top of fill a little below joint in wall.

 

[met33]

What about cutting off the vertical #4 rebar dowels, then applying the flashing membrane, and then epoxying in L-shaped rebar dowels into the side of the wall?

The purpose of the L-shaped rebar dowels is to keep the slab locked to the foundation wall horizontally, not to support vertical load.

This would allow continuous horizontal flashing on the top of the wall, without vertical rebar penetrations through the membrane.

 

[BAretired]

and BA[/color]]What about cutting off the vertical #4 rebar dowels, then applying the flashing membrane, and then epoxying in L-shaped rebar dowels into the side of the wall?
That is a lot of work and I don't believe your flashing membrane will function properly if it is cut off by pouring concrete all around it. I don't believe an eleven foot wide slab is going to move away from the foundation wall if it is anchored at both ends, but if that is a concern, provide additional anchors at, say 8' centers, connecting the slab to the floor structure, locking it in.

The purpose of the L-shaped rebar dowels is to keep the slab locked to the foundation wall horizontally, not to support vertical load.
As stated above, there are easier ways to lock it in.

This would allow continuous horizontal flashing on the top of the wall, without vertical rebar penetrations through the membrane.
Yes, the flashing would be difficult to place with the vertical dowels in place. That is why the flashing should be above the slab. The brick will be shielded from rainfall unless there are very strong winds, so the amount of water accumulating behind the brick is minimal.

 

[met33]

Thank you for the feedback. I think you're right, this would be a lot of work, and is likely unnecessary.

Yes, the main flashing will be above the slab, where the brick meets the slab. I forgot to include it in the previous diagram.

It sounds like the key thing is to provide a waterproof membrane between the wood and the porch slabs, to prevent moisture transfer between the two. Whether this membrane extends horizontally over the wall at the sill plate, and past the vertical rebar dowels, might not be of much practical importance.

 

[BAretired]

It sounds like the key thing is to provide a waterproof membrane between the wood and the porch slabs, to prevent moisture transfer between the two.

Agreed, but a 6 mil polythene wrap around exposed wood should be adequate for that.