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?)
Drylock is of questionable benefit, IMHO. It's definitely not a solution to a leaky basement...but it sounds like you've done some regrading already which should help with that.
The reason basements are often musty isn't so much from water from the outside but condensation. Basements are humid and cool, so the walls tend to be perpetually wet. The goal, then is to insulate the walls so help prevent that moist air from hitting the cool wall.
When using fiberglass, that's permeable to the air, so the solution is traditionally to put up a plastic vapor barrier. However, if water does leak in from outside, you've now trapped it.
As such, I strongly recommend going with the Building Sciences corporations recommendation of using XPS foam board against the wall and no additional vapor barrier. The XPS acts as a moisture retarder, yet will let moisture eventually dry through from one side to the other.
I went in to much more detail (including my recommendation to use metal framing rather than wood) with this answer here: https://diy.stackexchange.com/a/8644/1209
When finished, the other objective is to try and reduce the humidity in the basement. If you can bring the basement space into being part of the conditioned space, that's ideal. Alternatively, keep that dehumidifier running.
To answer the specific questions:
Is drylock sufficient to use R-15 batt? Or should I skip it entirely?
In terms of creating an insulated finished space, Drylock is of no use. The purpose of a vapor barrier is to prevent moist air from getting to a surface to condense on. The concrete wall will still be cool regardless of Drylock.
If not then should I put in EPS/XPS? (again Drylock?)
Yes to the EPX/XPS (see my linked answer above).
Would I really need more than that?
Code should dictate what is required. Check your local authorities regarding the amount of insulation you need. EPX/XPS will get you more R-value per inch than fiberglass.
In terms of comfort, the biggest culprits in a basement will be air infiltration, the upper exposed part of the foundation, and the space between the floor joists. Focus on those as well.
Best Answer
As long as the concrete and some time after pouring to set up, water won't hurt anything (they make swimming pools out of concrete). Granted, you'll want it all pumped out and dried out before framing, though.
As for the wood, no real damage should come about after 5 week of being exposed to the weather.
You certainly don't want to leave your framing exposed all winter. And if you are using chip board for subfloors or sheathing, you want to avoid having that exposed at all (unless they are rated for exposure). But for the most part, most houses are exposed to the elements for a few weeks. It's fine as long as things are given a chance to fully dry out before they close it all up.