Concrete experts: Over-pour?

[yeldogt]

Have decided that I am going to put a wood floor in the oldest part of my studio. This building was originally a 24' wide x 36' deep garage - built about 40 years ago. It has a sloped concrete floor not particularly flat .. lots of minor cracking.

I was originally going to have the concrete floor removed .. a proper base constructed and do a radiant slab with PEX ... but I really want wood ... and a high mass floor is not ideal for this application .. the quote a few years ago for the slab/pex was around 15k.

Currently the concrete floor is about 1" bellow the top of the foundation block at the high end and about 4 inches bellow at the other end .. so it drops about 3" in 36 feet. I was thinking of having a vapor barrier put down over the old concrete and then pouring a new level concrete floor .. ideally to the top of the foundation ... but Im not sure that is think enough?

I would then install another another vapor barrier over the new concrete and 2x4 lumber on the flats, nailed to the slab through the upper vapor barrier with 1.5 inch foam panels between --- as rafters ... I would then place plywood or warm board (depending on $$ available) fastened to the 2x for a subfloor and then a 3/4 wood floor to finish it out.

I'm just not sure how thin the over-pour can be. Is a special product available?

I don't get any water in the building .. and it seems like a waste to go to great expense of ripping it all out and then just cover the new slab?

Any thoughts? I have not priced a new slab without the pex.

 

[ConCretin]

These things can be tricky and I'm no expert but I'll offer up an opinion. Since you are going over it with wood flooring, cracks aren't an issue as long as the overlay stays put.

If the existing floor is structurally stable, just place a concrete overlay using a 3/8 mix. I would use wire mesh to keep the overlay intact across telegraphed or shrinkage cracks. I think I would also want the overlay bonded to the existing floor especially at the thinner end. Maybe tapcon screws at 24" centers.

The other option would be to just frame up a level floor directly off the existing concrete.

 

[rburke65]

Novice in all things here....LLWillysfan......when you say bonded to the original floor you are talking installing the Tapcaons and letting them stand proud as a "post" and then the over lay atop, allowing the overlay to bite the screws? Just learning....

 

[volleyball]

I agree with putting down the vapor barrier and building the wood floor above it. Less work than doing a concrete pour that will get hidden.
Another option is to get roofing foam panels and have them cut to the slope. They do this for flat roofs so it is a common thing to find. Or build your own. Just a big adjustable table and a hot wire.
You could lay sleepers on top of the foam and your flooring. And it would be insulated.

 

[mygarageone]

There is another option ,there is a insulation that is 1/8" thick foil faced both sides and also vapor barrier. You could lay that on the concrete floor , then lay an electric heat Matt system done , then your sleepers and the floor sheeting. It' s done all the time and it works well.
For your application I believe this would be a great solution .
It's also a 120 volt set up.
These days there are a lot of options for your situation. Do an internet search , you'll be surprised.

 

[yeldogt]

Just building a proper floor structure was suggested -- but this ends up raising the floor too much. Even using 2x6 lumber with supports down to the old floor will place the finished floor 7" above the foundation .. the thought was I could spray foam the cavity prior to the subfloor installation.

The reason I wanted to put a vapor barrier on top of the old floor was so it would not have any holes ... the second one on top of the new slab was extra insurance .. but it will have holes from nailing the lumber to the concrete.

I don't want a concrete floor .. heated or not .. I really want to make this space with a wood floor.

The existing floor has a crown to it ... it looks like it was more for utility .. not to work on ... it is not flat enough that I could ever cut foam to fit the angle

 

[mygarageone]

Just building a proper floor structure was suggested -- but this ends up raising the floor too much. Even using 2x6 lumber with supports down to the old floor will place the finished floor 7" above the foundation .. the thought was I could spray foam the cavity prior to the subfloor installation.

The reason I wanted to put a vapor barrier on top of the old floor was so it would not have any holes ... the second one on top of the new slab was extra insurance .. but it will have holes from naming the lumber to the concrete.

I don't want a concrete floor .. heated or not .. I really want to make this space with a wood floor.

The existing floor has a crown to it ... it looks like it was more for utility .. not to work on ... it is not flat enough that I could ever cut foam to fit the angle

The what you can do it is lay 1" x 6" boards on the flat on top of the 1/8" insulation I mentioned and then screw it down . This insulation I am taking about will actually seal it's self around the screw . Depending on the spacing you can use 3/8 or 1/2 ".sheeting and then your wood floor .
Or do a pour over with an 1 1/2 " concrete . Or tear the old stuff out period .
You don't. Have many choices if you are set on not having one floor much higher than the other one.
Check out this site www.insulation4less.com

 

[yeldogt]

I have done a few projects where I built a wood floor over a slab ... two with radiant using warmboard ... so I know that it works. But all of these were with a new properly built and insulated slab.

Surprisingly the old garage floor is not that cold ... so I really think the 1.5 thick foam will be enough.

I just don't know anything about trying to flatten a slab and how thick it need to be.

Mygarageone .. have you ever used that roll product ... I remember years ago it was sold for under slab insulation for radiant ... but it did not provide enough insulation

 

[mygarageone]

I have done a few projects where I built a wood floor over a slab ... two with radiant using warmboard ... so I know that it works. But all of these were with a new properly built and insulated slab.

Surprisingly the old garage floor is not that cold ... so I really think the 1.5 thick foam will be enough.

I just don't know anything about trying to flatten a slab and how thick it need to be.

Mygarageone .. have you ever used that roll product ... I remember years ago it was sold for under slab insulation for radiant ... but it did not provide enough insulation

I have used the stuff from insulation4less , in fact server all hundren sq ft of the stuff and I like it.

 

[Jess]

Have you considered Gypcrete, or a similar self leveling mix? Availability in your area would be the main consideration, but its used to level floors prior to the application of tile and other finishes. Mixed very wet, pumped in and it flows out to level. I did a large crawl space floor that was rough and out of level, tiled and its now used as a meeting room and complex party space.
Jess

 

[ConCretin]

Novice in all things here....LLWillysfan......when you say bonded to the original floor you are talking installing the Tapcaons and letting them stand proud as a "post" and then the over lay atop, allowing the overlay to bite the screws? Just learning....

That's exactly what I was thinking. Even if the overlay 'came loose', I don't think it would go anywhere but thought some mechanical connection would be a good idea.

Drilled and epoxied bars would be better but there's not enough depth and the cost would be more.

Thinking more about this, I'm wondering if shrinkage in the slab could possibly generate enough tension to shear off the tapcon screws and if cutting some control joints would relieve the tension enough to prevent this. Probably over-thinking it.

Lots of other suggestions to consider also. Be sure to let us know what you decided. Good luck