Partial replacement of concrete slab**homeowner question

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    We own a home built in the late 1800s, a large attached garage was added likely in the 30s or 40s. The garage has a nice stem wall and a continuous slab. There are 3 rooms in the garage. The laundry room is about 12×11 and had a floor drain. The slab developed a large crack and had some sinking in the SE corner.

    Concerned that there might be leakage from the floor drain, we had a large section of the laundry room slab (about 80%) cut out and replaced. We ran a new drain line straight out to the main and decided to have the new pour level, without adding another floor drain. The contractor installed rebar bent into an L shape horizontally into the existing slab. Not being at home during the pour, I can’t be certain he added rebar under the new pour. We’ve had some unusual experiences with the contractor.

    There was old mortar left on our slab from a previous chimney removal, as well as some old paint in places. Our son in law used his cement grinding tool to remove the rebar and got a bit carried away. While he was removing old paint he also removed the feathering where new slab meets old. This left a small seam exposed.

    We plan to paint the floor with Rustoleum garage rocksolid epoxy system. Question: Do we need to add some sort of bonding or sealer to this crack prior to painting? I will try to upload a photo. Thanks for any advice.


    Good grief! He used his grinder to remove mortar, not rebar!

    Mesa, Az

    If not going to fancy with the coating but do want to address the crack you could

    A) Fill it using anything designed specifically for that application. Easiest and cheapest would be a caulk/cement based product that comes in a caulking tube.Most don’t require a prime make sure that it will dry semi-rigid, as my suggestion would be to grind it flat/smooth after it dries.

    B) Cut a straight line with a 1/8″ blade, coat the floor, then fill it with a joint caulking, grout, crack repair material, etc. And leave it uncoated.(easy to repair if you know it will bug you.

    General idea is that it could always come back, you dont know how it was adjoined to the existing, and nobody can stop the earth from moving.

    Grinder to motar isnt really to be concerned over, as for one it helped open the crack up and with the adhesion for the epoxy…..I grind most all my floors that receive coatings. It appears the existing slab is hard finished and the re-pour wasn’t in which the re-pour shouldnt much prep for the epoxy install but be sure to on the existing….I don’t know what you plans are for prep or what the “kit” suggests just make sure it increases the porosity and theres no chemical residue after.(depending on method)

    Fort Lauderdale, Florida

    Whatever you fill the crack with, it is now an expansion joint, it will probably come back.

    I say use some polyurethane sealant in the crack once you clean out all the dust in it. This stuff is designed for exterior applications so there is an odor while it cures so make sure you have good ventilation.

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