Cement Slab sub floor removal and replace

[oto50]

I am new here, thanks ahead of time for any direction.
Cement slab shows several cracks and also has square holes that go straight to the dirt ?
Slab is in Indiana, not sure if slabs are constructed different for different parts of the county?
I am looking to lay down PVC laminate over top of the new sub floor I build.
Questions below..
1. Why the square holes ? Fill and seal them correct ?
2. I have used Bill board material which is poly 20 oz 22 mil for a sun shade off my house. Can I use this same billboard material between the slab and the sleepers as a barrier?
3. Should I use treated wood or will regular 2 x 4s work for the sleepers?
4. 3/4 Ply wood ? Do I need a special kind for the this subfloor ?

Prior owners laid down a moisture barrier overtop hard wood floor that sat on top of wooden subfloor attached to cement slab. They encapsulated the wood in moisture. Mold was growing out of the wood.
House and subfloor was built in the 70s.

Again, Thanks for the assists.

 

[JPfloor]

There are a number of concrete sealers on the market. I would try that. Don’t know what’s available in your area. Mapei makes a good one. Do your research, some are better than others. Try to avoid big box stores. Find a flooring supply store. After the sealer dries an additional moisture barrier under the sleepers couldn’t hurt.

 

[C.J.]

I always wonder why people build up a wooden subfloor over top of concrete.

The square holes in the concrete are most likely from wooden stakes that held the forms n such when the concrete was poured. Fill them in. You’re removing all the old wooden subfloor? What’s the condition of the concrete? How flat and smooth is it? Do you specifically want to put a new wooden subfloor back down? I’m guessing the cost of wood right now has got to be comparable to pouring self leveler and getting a nice flat slab.

 

[DarisMulkin]

I

I always wonder why people build up a wooden subfloor over top of concrete.

That was so they had something to nail into. They didn't have all the fancy glues and moisture barriers back then.

 

[C.J.]

That was so they had something to nail into. They didn't have all the fancy glues and moisture barriers back then.

Yeah but now everything is jacked up 3” higher than it needs to be plus they had mold growing in their living space. That’s a hell of a price to pay for a hardwood floor.

 

[DarisMulkin]

Yeah but now everything is jacked up 3” higher than it needs to be plus they had mold growing in their living space. That’s a hell of a price to pay for a hardwood floor.

Mold back then wasn't a big deal or concern like it is now.

 

[JPfloor]

That was so they had something to nail into. They didn't have all the fancy glues and moisture barriers back then.

Along with other possible reasons... When we refinished our garage and turned it into a bedroom and bathroom we threw down sleepers to raise it up to the height of the rest of the house... Warmer than a concrete slab too.

 

[Jon]

There are a number of concrete sealers on the market. I would try that. Don’t know what’s available in your area. Mapei makes a good one. Do your research, some are better than others. Try to avoid big box stores. Find a flooring supply store. After the sealer dries an additional moisture barrier under the sleepers couldn’t hurt.

May be checking to see if there is air movement between the sleepers as well?