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Do I need a subfloor over concrete?


Integraoligist's Avatar
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06-05-11, 09:45 AM   #1  
Do I need a subfloor over concrete?

Hey all,
Here is my situation. I am on a Slab of concrete in my kitchen and dining room. It's pretty much a 400 sq. ft. square with a bar coming out of center about 8 ft.

Well, it's not perfectly level... there was laminate in the kitchen area (1/2 of the area) and carpet in the dining room (the other 1/2). And to seperate the two there is a 1" concrete step. The kitchen area actually slopes down 1" from the wall to the step. So I was planning on getting some concrete and pretty much leveling out that step over a good portion of the kitchen floor.

There is also a section toward the exterior wall that has a crack in the floor and slopes down maybe 1/2". I was going to add concrete to that to help level as well.

So, a couple of questions.

1. when type of concrete or cement do I use to level this?

2. If I put laminate over the whole thing, do I need wood subfloor? Or can I just put the vapor barrier/foam down and be ok?

3. The laminate floor that was in the kitchen had a lot of mold growth under the laminte, under the vapor barrier, and under the 3/4" subfloor the person before me had down. They had the washer and dryer overflow so I know thats where that water came from.

4. I wanted to just get a grinder and clean the surface of the concrete and pour a wearable concrete over the whole thing then stain it and keep it as is... but there is asbestos glue/tar over the entire area. I dont think it's going to come off the concrete... or will it?

Thanks all for the help!

 
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chandler's Avatar
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06-05-11, 10:59 AM   #2  
You wouldn't use just any concrete, but a specific concrete floating agent to level out the flooring. Not sure about the "step" thing you mentioned, nor how it would affect leveling it all out. Pictures would help. No subflooring would be needed on the concrete slab. Flooring manufacturer's underlayment is required.
It would be great if I could talk you out of installing laminate in the kitchen environment. As you have already seen, water can wreak havoc on the flooring and cause problems. It will happen again, just when. If you must install wood, I would suggest a 5/8" thick engineered click lock flooring, and/or possibly 12x12 tile in the kitchen and engineered flooring in the dining room.
Just offering suggestions for long term use.

 
Integraoligist's Avatar
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06-05-11, 01:01 PM   #3  
Here are a couple photos...
No, i did not want to do laminate anywhere, i already have it in my living room and wanted this kitchen and dining area to be stained concrete. But you can see the black glue/tar and the gray this crap they put on the other section (which also has the tar/glue under it)... it just chips up and i'm afraid the new wearable concrete will do the same thing if I can't get this stuff off.

I labeled the 1" step i was talking about below.

http://img.photobucket.com/albums/v3...ligist/2-3.jpg

http://img.photobucket.com/albums/v3...ligist/1-2.jpg

Thanks!

 
Integraoligist's Avatar
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06-06-11, 07:52 AM   #4  
And if I try to put tile down, do I have to use cement board or is 23/32 x 4 x 8 Plywood Sheathing Sub-floor sufficient?

 
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06-06-11, 02:32 PM   #5  
I would float out that patched area. If you want to lay tile, lay it directly on the concrete, after you have it leveled. You don't install tile on plywood.

 
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06-09-11, 10:38 AM   #6  
Ok, 1. What kind of cement/concrete do I use to float out that area?
2. The asbestos cutback does not want to come up at all! After reading some more info on it, apparently i can not put tile over the cutback? And because there are so many even areas I was told from a friend that I have to put at least a 1/2" subfloor down and just put vinyl sheeting or tile over it because the floor will move because of how uneven it is.

I was thinking of getting 1/4" cement board, screwing it to the concrete and putting ceramic tile down, but then I read somewhere else that you can not put cement boards on top of concrete! AHHHHHHHHHHHH

Is that corrent? Any other ideas? This is driving me nuts!

Thanks all!

 
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06-10-11, 12:29 PM   #7  
I don't think that a self levelling compound is designed to fill a 1" thick requirement, and usually no more than half that. If you are able to apply a bonding agent you can float a cement sand mix to build things up. You have a couple of options after that. You can apply the tile directly onto the concrete with a 1/2 notch trowel and thinset. If there is a need to provide a moisture barrier otherwise to the floor and you do want to install a wood subfloor, consider applying a dimple pad between the plywood and concrete, which provides a moisture barrier but also provides sufficent air flow to avoid moisture buildup under it all. You can install 3/4" construction grade plywood over that product also. If you are installing large tiles such as 18x18 directly over the concrete and want to level things out even more first to provide for a better,smoother result, you can then apply a self levelling compound first over the concrete. Self levelling compound must be covered however and this means anyway that you staining option is out in that case.

 
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06-16-11, 06:39 AM   #8  
equinox,
According to the manufacturers of the couple of self-leveling cement places that i've talked to, i can not use it over this glue that is already on the floor. A cement bonding agent is out of the question because it will not hit the cement, all it will attach to is the glue.

Am I missing something you guys are saying or what?

 
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06-23-11, 02:47 PM   #9  
Are you certain that cutback contains asbestos? Cutback isn't used much anymore, but they stopped using asbestos in it about 25 years ago. Technically, if it contained asbestos you should have had it abated when you demoed the existing flooring.

You should be fine laying over the top of it. As mentioned before, you will need to float out that high area using underlayment (do not use concrete). You will need to float it out at least a couple of feet so you don't feel the slope as you walk across it.

I also agree with Chandler, laminate flooring in kitchens and bathrooms is a bad idea.

 
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