You can install an interior weeping system similar to what you would normally do on the outside, but without the waterproofing.
Start by jackhammering out about two feet of floor around the edges of your garage, as close to the walls as you can get. Dig down until you reach dirt, and if that's not at least two feet down, keep going. Now, put down a couple inches of 3/4" crushed gravel, and then install weeping tile (it's not tile anymore; it's 4-6" corrugated plastic drain pipe with a nylon mesh sock over it). Make sure the sock is continuous across any joins you make in the weeping tile for corners etc. This is a good time to direct those drain holes down into this trench, where the water they drain will flow into the weeping tile. You'll also need a sump, or a connection to a downhill storm sewer; direct the weeping tile to this sump pit or the storm drain. While you're doing all this a center drain can't hurt too much; you can tie it into the weeper wherever it's convenient, just make sure the garage floor and the drain flange are level, or that the garage floor slopes slightly to the drain.
Now, you can install waterproof sheathing on the interior walls contacting the concrete. Normally this product is designed to go outside the foundation walls, but in cases where that's infeasible it can work this way too. The idea is to trap moisture that weeps through the wall behind the sheathing, where it will then be directed down the wall and under the slab to the weeper. So, you'll install the sheathing, which should have an air space between wall and most of the layer, and make sure the end is down in the trench by the weeper.
Backfill the rest of the trench with 3/4" crushed gravel up to the slab footing, then patch the slab with new concrete. Your garage should stay much drier.
Well this is a pretty big deal because we don't know the cause.
First let's go over common reasons we get cracks on new floors.
- Soil wasn't properly compacted. Soil should be compacted with a rock bed on top.
- Bad mixing at site. Especially in the summer contractors pump too much water in the mix. The water makes the concrete weaker and it does crack easier.
- Bad mix at plant. Just a poor mix of materials coming in.
- Bad environment for mix. Too hot, rain, too long to site, whatever.
- They didn't cut the concrete or didn't cut it quick enough. The concrete needs to be cut (I suggest every 10x10 foot area) to allow for expansion. It really needs to be cut the first day.
- Didn't use rebar. This is a common cost cutter and I have seen rebar pulled before pour.
- House was built on unstable land. Could have been a landfill, could have springs underneath, whatever.
- Soil type wasn't conducive to their install method. Really too many things to list here but basically different types of soil expand and contract more due to moisture levels. Also it is possible that it was pushed even further by either a lot of rain or a drought.
Those are what I got off the top of my head. I am positive there are more reasons for cracks in your basement. If I were to totally guess I would say they didn't prep right in that corner - It seems like the corner is dropping on you already and maybe it wasn't floor wasn't compacted correctly. The crack starts on the outward "L corner" which is normal but heads right across the corner - most insignificant cracks in concrete tend to be straight. This crack has its shape for a reason.
What do I think you should do? First ask questions. See if the contractor knows why it cracked. "It happens" is not an answer. My reply would be "Me not paying you happens too." If the contractor/builder doesn't want to take blame (it is their fault) then you need to get a psi reading on the floor, measure its thickness, and also prove that the floor is rebarred/reinforced correctly. You will almost certainly need an engineer. Even if the problem is obvious your builder is less likely to move until it is proved from a creditable source.
You cannot sit on this. If the mix was bad - well did they use the same mix for the walls too? If it was bad prep, what happens when you have issues in a couple years? I have seen basements that have had to be repoured and it is a mess. Also will set you back 10K in the states.
Again, no matter what anyone tells you - cracks in a fresh floor are not acceptable. This is a sizable crack. Even if an engineer checks everything out I would demand a longer warranty on the basement floor and to have them seal it. Either that or they start over.
Note (based on additional pictures: I am not there so it is a bit of conjecture. But it is not a good sign when an area is relatively dry and you have a corner that is not only wet but it seems dropped too. It is a guessing game for me too at this point, not seeing what you have going on. My top 2 guess (and they are guesses) -
#1 - They dug and compacted. While digging they left over dug out that corner and then filled it. Then they never compacted it correctly. After it rained a few times, the corner started dropping. Also when I have a slab compacted the rock is part of the equation. I don't see any rock in your pictures.
#2 - You have some sort of natural underground current or spring. I have a stream that is 3 feet under, about a foot from my house - and I can't imagine if it where a foot over and 2 more feet down.
(Do you have any pictures right before they poured?)
Best Answer
You may have to adjust your ideas of what's needed to get this done.
You make sawcuts and drill holes as close as you can to the place you need to open, but it may well not be practical or possible to limit that to the particular room you want to work in, especially since you appear to be planning to run the pipe inside framing with drywall you don't want to disturb on the other side. Welcome to "drywall repair is comparatively easy, and breaking concrete requires a degree of access."
Or you make your hole on the side you plan to access, watch Shawshank Redemption 12 times for inspiration, and delicately hammer and chisel your way under the framing, but no further. By which time you could have ripped the wall apart, bashed the hole open, and repaired the wall 3 times over, but it's your choice.
One approach, depending on exactly what you need to do and what you are willing to rent, is to use a holesaw (for the lumber) followed by a diamond core drill (for the concrete) to make the hole for the pipe, and just cut a hole in the floor on this side of the wall for access, that does not directly connect to the hole for the pipe.