Basement Sub-Floor Using Sleepers - Need Some Pointers

[CHDinCT]

So I'm soon to start on putting a sub-floor over my poured basement concrete slab. The house is 25 years old and we've never had leaks or standing water in our basement, but we have a LOT of dampness and get a lot of efflorescence, and the slab get a mottled look (blotchy dark areas), so I want to cut down on the dampness and avoid tracking that white power all over our upstairs hardwood floors.

I've gone back and forth on how to do it, using either PT sleepers over 6 mil plastic, then 3/4" T&G subflooring glued and screwed, or those dricore 2'x2' squares. I've done a search here and saw some other products mentioned, but none of them seem to be sold anywhere near me, only the dricore product. My problem with using dricore is that the concrete floor is very uneaven and I would need 6-10 bags of floor leveler first. Dricore can be shimed, but only up to 1/2" per the spec's I've seen, and I have some places that are over that. Plus, using cedar shims to level the sleepers would be a whole lot cheaper and faster than floor leveler I think. Also, about 20 years ago, I tried to cut down on the dampness by putting down a product called Thoroseal (normally used to seal concrete walls), then putting epoxy paint over it - didn't work and most of the Thoroseal flaked off over time, but not everywhere). So I'm not sure I can get a good bond using floor leveler.

So assuming I go with sleepers my questions are:

- Is 2' on center, with Styrofoam in between enough, or do I need to ge 16" OC like normal wall/floor framing?
- Planning on using a Ramset to nail the PT sleepers down, but I read somewhere that they tend to deflect if there's any space between the board and floor. Will I have any issues shooting them through 1" PT and say up to 3/4" of shims? Never used a Ramset so I'm not sure what to expect.

Any other rec's are welcome as well. Thanks

 

[Cord]

Honestly, it sounds like you have moisture wicking through the slab. I'd be afraid of creating a mold issue by over framing the floor. Would you be willing to use a ceramic or porcelain tile?

 

[CurlyDave]

I would be more concerned with the nails the Ramset shoots being properly galvanized for the pt sleepers. Today's pt is a lot more corrosive than many people realize.

 

[ace10]

I put down 2X4 PT sleepers under my basement floor. I don't have any moisture issues whatsoever, but wanted a softer floor under foot and also the option of using real wood flooring.

I didn't use any plastic.

Shot all the sleepers into my 12 year old slab. It was no easy task. Expect to use hot loads in the .25 cal gun. Driving the ringed 3" nails coated for PT direct contact.

I did not shim the sleepers, instead I actually planed each one down according to the pitch of the slab. Which was an absolute time suck. Crazy, crazy, crazy amount of effort. Around the sump, I had to shim the joists up a bit, and yes, the nails did want to deflect a bit. Maybe 25% of them gave me trouble.

I used Polyiso ridgid insulation between the joists. 3/4". Used scrap strip of the insulation to pad the sheet out to flush with the top of joists.

Glued and ring shank nailed the 3/4" decking to the joists.

Joists were 16" on center. Probably could stretch them out to 24" OC given the 2" extra width of the joists. Maybe compromise and go 20"?

 

[merlynr]

Check into cork tiles. I think they can be snapped locked onto a concrete floor with the recommemded vapor barrier. If something would happen and you have a moisture problem in the future you can remove them and dry things out and you're good to go again. I put them in a basement room in place of an old carpet and they are nice to walk on and they are organic from a cork tree.

 

[CHDinCT]

Honestly, it sounds like you have moisture wicking through the slab. I'd be afraid of creating a mold issue by over framing the floor. Would you be willing to use a ceramic or porcelain tile?

Yes, definitely have moisture coming through but no standing water. I put in an industrial dehumidifier that pumps itself out last year to see if that would solve it but as expected, it only takes the moisture out once it evaporates into the air. I was thinking the plastic would stop 98% of the moisture migrating through the slab. Going to talk to a neighbor who did the same as I'm planning years ago, but I don't know how much moisture he had in his basement.

Tiles would definately require a lot of floor leveling. I think the concrete guys must have been drunk the day they poured my basement slab. Plus the Thoroseal I applied was left rough in a lot of spots (wasn't thinking about finishing the basement back then).

 

[CHDinCT]

I would be more concerned with the nails the Ramset shoots being properly galvanized for the pt sleepers. Today's pt is a lot more corrosive than many people realize.

Good thought. I will check to see if the nails are rated for today's PT (ACQ?)

 

[CHDinCT]

I put down 2X4 PT sleepers under my basement floor. I don't have any moisture issues whatsoever, but wanted a softer floor under foot and also the option of using real wood flooring.

I didn't use any plastic.

Shot all the sleepers into my 12 year old slab. It was no easy task. Expect to use hot loads in the .25 cal gun. Driving the ringed 3" nails coated for PT direct contact.

I did not shim the sleepers, instead I actually planed each one down according to the pitch of the slab. Which was an absolute time suck. Crazy, crazy, crazy amount of effort. Around the sump, I had to shim the joists up a bit, and yes, the nails did want to deflect a bit. Maybe 25% of them gave me trouble.

I used Polyiso ridgid insulation between the joists. 3/4". Used scrap strip of the insulation to pad the sheet out to flush with the top of joists.

Glued and ring shank nailed the 3/4" decking to the joists.

Joists were 16" on center. Probably could stretch them out to 24" OC given the 2" extra width of the joists. Maybe compromise and go 20"?

Thanks for relaying your experience. I'm looking at a 27 cal. semi-automatic gun and thinking of using 1x4 sleepers so I was hoping to only need 2.5"
nails. It looked so easy watching Youtubes of people shooting nails into concrete, but as usual, it's just never that easy. Like you, I may need to shave a few boards down if I hit a few unexpected high spots. Spent some time with a few levels and a string line to try to find the highest spot, so I could work out from there - don't have one of those fancy rotating laser levels. If I use rigid foam insulation (Owens Corning Foamular) I was thinking 2' OC would work since the floor won't actually span any voids (well theoretically anyway).

 

[CHDinCT]

Check into cork tiles. I think they can be snapped locked onto a concrete floor with the recommemded vapor barrier. If something would happen and you have a moisture problem in the future you can remove them and dry things out and you're good to go again. I put them in a basement room in place of an old carpet and they are nice to walk on and they are organic from a cork tree.

Hmm, didn't think of that. I will check it out, but I may still need to level the whole area first, but maybe not if they're flexible enough. Thanks

 

[JimRB]

The pourable floor leveler is some pretty neat stuff. I have used it and have watched "pros" use it. Personally I would rather pour than shim, and do tile afterwards. That moisture coming up concerns me for any floor covering that supports mildew.

 

[dave1949]

I usually find I have not done enough research on these types of projects. I would hate to see you do that work and buy the materials if it fails later. Not to offend, but I think you may be covering up an issue and hoping for the best.

One problem is the sleeper nails will all be penetrations of the vapor barrier. Another is you will probably have quite a bit of humidity fluctuation that isn't friendly to wood flooring. You could see cupping of the boards.

There is a lot of info out there, other people have confronted the same problems. It's just a matter of getting the right advice. You might try help boards operated by someone like Quikcrete or similar where you can post your situation and ask for recommendations. You never know what gems may be be uncovered. These folks are well regarded: Products You might ask about membranes that a floor "floats" on too rather than the nailing sleepers approach.

I would +1 the tile idea. But you still need to clean, bond, level, and maybe seal, the existing floor. Ceramic tile itself will take saturating conditions. The thin-set mortar used to bed the tile could be outdoor/exterior rated which ought to be moisture tolerant after curing like concrete. I think tile done right is your best chance of avoiding problems later.

 

[CHDinCT]

The pourable floor leveler is some pretty neat stuff. I have used it and have watched "pros" use it. Personally I would rather pour than shim, and do tile afterwards. That moisture coming up concerns me for any floor covering that supports mildew.

I think I'm going to contact a few of the floor leveling makers to discuss my situation. Having tried to seal it and paint it years ago, I'm not sure I can use one or not. All of them require a latex sealer as a bonding agent before using the leveler. All of them I've researched say the floor must be clear of efflorescence. I don't know if that just means vacuuming up the loose powder or that the concrete shouldn't produce efflorescence. If I can level the floor, I'd go with the dricore product since it leaves a space between the sub-floor and concrete so it can breathe. You also leave a 1/4" space along all walls. The de-humidifier will remove any moisture that comes out of the slab. That was my plan until I discovered how out of level the whole thing is.

 

[CHDinCT]

I usually find I have not done enough research on these types of projects. I would hate to see you do that work and buy the materials if it fails later. Not to offend, but I think you may be covering up an issue and hoping for the best.

One problem is the sleeper nails will all be penetrations of the vapor barrier. Another is you will probably have quite a bit of humidity fluctuation that isn't friendly to wood flooring. You could see cupping of the boards.

There is a lot of info out there, other people have confronted the same problems. It's just a matter of getting the right advice. You might try help boards operated by someone like Quikcrete or similar where you can post your situation and ask for recommendations. You never know what gems may be be uncovered. These folks are well regarded: Products You might ask about membranes that a floor "floats" on too rather than the nailing sleepers approach.

I would +1 the tile idea. But you still need to clean, bond, level, and maybe seal, the existing floor. Ceramic tile itself will take saturating conditions. The thin-set mortar used to bed the tile could be outdoor/exterior rated which ought to be moisture tolerant after curing like concrete. I think tile done right is your best chance of avoiding problems later.

No offense taken. I'm partly trying to find some great solution I haven't thought of or come across doing research. Since I run a industrial de-humidifier all year, I don't expect a lot of humidity variation. The unit is set at 53% humidity and I've never seen it vary more than a few percentage points. I know sleepers over a plastic vapor barrier has been done for years when finishing basements, so it works, but it's a bit old school. Just don't know if in my situation there's too much moisture to take a chance even with a vapor barrier. Nothing I can do about the nail penetrations, except maybe use an ice and water type roof sealer under the sleepers - just thought of that now actually.

 

[oldpilgrim]

20 years ago, I ramset the PT sleepers at 16" on center, then laid plastic over them. I pressed the plastic to the floor between the sleepers and inserted styrofoam between the sleepers over the plastic. Then came the 5/8 plywood and a carpet.

I had only a bit of dampness on the concrete before this job and this method has worked well all this time. The floor is dry and warm.

 

[dave1949]

No offense taken. I'm partly trying to find some great solution I haven't thought of or come across doing research. Since I run a industrial de-humidifier all year, I don't expect a lot of humidity variation. The unit is set at 53% humidity and I've never seen it vary more than a few percentage points. I know sleepers over a plastic vapor barrier has been done for years when finishing basements, so it works, but it's a bit old school. Just don't know if in my situation there's too much moisture to take a chance even with a vapor barrier. Nothing I can do about the nail penetrations, except maybe use an ice and water type roof sealer under the sleepers - just thought of that now actually.

Glad you weren't offended. Anything you could do to lower the ground moisture would make all flooring choices better and easier.

Any suspicions about the source of the moisture or any good way to get more drainage? If the concrete is really ugly it would be a lot easier (mentally at least ) to saw out some drain pipe channels if there is any gravel bed depth below the slab to work with.

I think it would drain a floor area somewhat if you cut the floor, dig a trench maybe 18" deep and put washed stone and a pvc drain pipe in--if you have somewhere to drain to or make a sump pit. The stone leaves a void that's easy for the water to seep into, the pipe takes it away. I guess the hardest part is deciding if anything that involved is really necessary.

Do you have radon gas to think about? Holes in basement floors, like sump pits or the joint between the slab and wall, are supposed to be a big source of radon.

 

[CHDinCT]

Glad you weren't offended. Anything you could do to lower the ground moisture would make all flooring choices better and easier.

Any suspicions about the source of the moisture or any good way to get more drainage? If the concrete is really ugly it would be a lot easier (mentally at least ) to saw out some drain pipe channels if there is any gravel bed depth below the slab to work with.

I think it would drain a floor area somewhat if you cut the floor, dig a trench maybe 18" deep and put washed stone and a pvc drain pipe in--if you have somewhere to drain to or make a sump pit. The stone leaves a void that's easy for the water to seep into, the pipe takes it away. I guess the hardest part is deciding if anything that involved is really necessary.

Do you have radon gas to think about? Holes in basement floors, like sump pits or the joint between the slab and wall, are supposed to be a big source of radon.

Not totally sure of the water source. I think there are some underground streams since I get sinking in my front yard that I've filled 3-4 times and the low spots just come back. I do have curtain drains that work. I can see water streaming out of the pipe after heavy rains. The builder left a 16"x16" cutout in the basement floor for a sump pump in case one was needed, but after 3-4 years without standing water I closed it up due to Radon fears, which I did test for many years ago. Showed very little back then - below the danger point. Suppose it could have changed. It is something I've thought of retesting for.

I did have a basement waterproofing company look at it last year. They said no need for an interior weeping system since I don't have leaks/standing water. Just said the best I could do was run a good dehumidifier to pull out what moisture comes through the slab.

 

[CHDinCT]

20 years ago, I ramset the PT sleepers at 16" on center, then laid plastic over them. I pressed the plastic to the floor between the sleepers and inserted styrofoam between the sleepers over the plastic. Then came the 5/8 plywood and a carpet.

I had only a bit of dampness on the concrete before this job and this method has worked well all this time. The floor is dry and warm.

Thanks. Interesting you put the plastic over the PT sleepers. That would avoid penetrations, just not sure what the long term result would be for the PT in my case given the high evaporation rate now.

 

[dave1949]

Not totally sure of the water source. I think there are some underground streams since I get sinking in my front yard that I've filled 3-4 times and the low spots just come back. I do have curtain drains that work. I can see water streaming out of the pipe after heavy rains. The builder left a 16"x16" cutout in the basement floor for a sump pump in case one was needed, but after 3-4 years without standing water I closed it up due to Radon fears, which I did test for many years ago. Showed very little back then - below the danger point. Suppose it could have changed. It is something I've thought of retesting for.

I did have a basement waterproofing company look at it last year. They said no need for an interior weeping system since I don't have leaks/standing water. Just said the best I could do was run a good dehumidifier to pull out what moisture comes through the slab.

I guess the waterproofing company decided the amount of moisture didn't warrant a lot of expense, that's good.

You are changing the situation with the dehumidifier if you cover the floor with a vapor barrier and flooring compared to bare concrete. With flooring and a barrier any humidity reaching the air would have to pass through the barrier and flooring before the dehumidifier could remove it. In effect, that may mean you are removing humidity from damp wood flooring versus damp concrete. That would be worst-case.

Best-case would be you put down the barrier and there isn't enough hydraulic pressure to penetrate any openings (from nails) and you live happily ever after. Your idea of using a membrane that would tend to seal the nail holes sounds good although I would check-out floating floor techniques too that would avoid those holes.

 

[bucktaker]

Not to Hijack but what Dehumidifer are you using? I have a cabin that we are fighting the humidity in the basement. Going to pull the subfloor and install new 6 mil plastic and run a good dehumidifer, its over a dirt floor

 

[CHDinCT]

Not to Hijack but what Dehumidifer are you using? I have a cabin that we are fighting the humidity in the basement. Going to pull the subfloor and install new 6 mil plastic and run a good dehumidifer, its over a dirt floor

This one:

https://www.youtube.com/watch?v=0TA6ANZELX8

Not cheap partly because you have to get it from a "Basement Systems" distributor, which I think are in every state. It's a franchise. Had them out to evaluate my situation. $1,700 was the price, but my basement stays at whatever level you set it at and never have to empty it, etc. I think they say that levels below 55% prevent mold/mildew from forming, so mine is set at 53%, but I could lower it.

Here's a better vid https://www.youtube.com/watch?v=6ugOQT8_jQk

By the way, it can be set up outside the area to be dehumidified and the intake and exhaust run via duct work.