Concrete floor help !!!!

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Old 05-16-11, 02:44 PM
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Concrete floor help !!!!

I am creating an office in a VERY old [about 60 yrs old] garage. I am also on a very tight budget (I am a student). The garage floor is in somewhat bad shape (pitted, rough, etc). My plan was to use 1/2" Durock ( cement board, backerboard)on top of the concrete slab, with the smooth side up (doesnt really matter ... ). I am most certainly NOT going to tile over the Durock (as even the slightest flex will pop tiles). The purpose was to "quickly and cheaply" get a fairly flat, smooth subfloor. Then I am either going to put tongue-and-groove plywood down, with office-style carpet on top, or a faux wooden floor. My question is, what is the best way to secure the Durock to the concrete slab? I am aware that Durock is NOT meant to be secured to concrete. However, I do not have the budget to fix the existing slab (using self-leveling concrete, etc). I thought PL-400 would be strong enough to secure it, but one test piece has proven otherwise. Then I figured using flat head tapcons (or similar), but that may also not be enough. Again, as I am not putting down tile, a minute amount of flex may be ok, but I want it secured as best as possible. Should I use thinset or mortar to secure the Durock down?

Additional info:
the room is about 110 sq ft. That is about 8 sheets of 3x5 Durock, total cost of $80 and change (just for some perspective).

I didnt want to put plywood directly to the old slab due to possible moisture transfer from the old slab to the new plywood. So I thought the Durock would prevent any moisture transfer.
 
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Old 05-16-11, 03:12 PM
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im sure a real pro will get at you, but im thinking with the materials your already considering forget the durock and just build a small subfloor. as long as there is an air space and your carpeting over the subfloor, worst case is youd need a dehumidfier going in there to keep it smelling proper. carpet is definatly the best choice as it will breathe moisture through it. outdoor carpet, though it feels cheap breathes the best.

--the durock doesnt act as a moisture barrier, and from what i understand its bad to put moisture barriers over concrete. its in their nature to absorb moisture and breathe it out again. if you put a moisture barrier over the concrete that water is bound to condense between the slab and the barrier and go stagnant.

it really sounds like you just want a flat surface.. which the subfloor will provide and if your willing to build it yourself it shouldnt cost much different then the plywood and durrock your already considering.
 

Last edited by keiski; 05-16-11 at 03:42 PM.
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Old 05-16-11, 04:50 PM
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You'll spend more on durock than you will on self leveling compound. Durock is not impervious to moisture, so that reasoning is out the window. Do a moisture test on the concrete. Find an area that isn't boogered up and tape a piece of 3' x 3' square clear plastic to the floor. Wait a day or so and see if there is moisture under the plastic. If so, you have moisture invasion, and anything you put down will be affected by it. Have you considered an inexpensive ceramic tile? You could smooth out the floor and install tile directly on the concrete without worrying about the moisture. Tile will run about $120 (HD Walton brand 12 x 12 at 57 cents a pop), thinset about $30, grout about $30, so it ain't like breaking the bank.
 
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Old 05-16-11, 04:50 PM
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I agree. Lay the studs flat so the 1 1/2 inch rise is all you have, shim them to level and use 3 tapcons to tie them to the floor, one at each end and 1 in the center. Then screw the plywood to the studs with decking screws (coated against rust) and place the carpet.
 
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Old 05-16-11, 05:05 PM
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I didnt want to build a subfloor (floor on top of floor) using 2x4's, as the ceiling height is already locked in at about 82". I "barely" fit a pre-hung door in the exterior rough framing I did. I would have had to do a considerable amount of work to raise the ceiling height in this structure.

How much work is using self leveler? My worry is, as it is a garage, the slope is what, 1/4" per foot? The length along the slope is about 12', that puts me possibly at 3" out of level [I need to check this] from one end to the other. I thought self levelers only work to about 1".
 
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Old 05-16-11, 06:44 PM
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Check it, but I don't think it would be 1/4" per foot. Always good to know.
 
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Old 05-16-11, 09:00 PM
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Yep, it is 3" out of level from one end to the other. I am thinking about using a 2-part concrete epoxy to secure the durock down, also using tapcons [or similar]. I dont particularly mind the unlevel floor, but it cannot flex. Sounds horrible I know, but this is an office in an 80 or so yr old garage. My framing however, was spot on
 
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Old 05-17-11, 05:16 AM
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How is installing durock going to correct a 3" drop? Why are you insisting on durock on concrete? You can repair divots and other aberrations by using concrete patch instead of floor leveler, making a smooth surface to put down floor covering. I don't want you hating yourself in 3 years for installing a product that won't work well.
 
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Old 05-17-11, 10:45 AM
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Chandler [or anyone else], I do not have any concrete experience [should be obvious at this point ]. I want to say if I try to "smooth" out the floor with some kind of compound (mortar mix), it isnt going to adhere very well, and just pop up/flake off. So:
1. How thick must it be applied in order for it to adhere well?
2. Is it possible to really "smooth" the surface with whatever product needs to be applied?
3. What type of product/mix should I use?

For those that have concrete slabs, when putting down carpet or wood flooring as the finished floor, is a vapor barrier needed between the finished flooring and the concrete slab? Would one just apply some sort of sealer to it? I know they have 15lb paper vapor barrier that is used in basements. Would that work?

What about (instead of everything else) using something like DRIcore [or similar]?

I also read this "Floating Engineered Wood Floors were designed for installing over concrete and really work the best. These hardwood floors can simply be installed using their 1/8" thick padding directly on the concrete slab over a 4-6 mil plastic.""

Any thoughts? I really appreciate the help and feedback.
 

Last edited by niehaoma; 05-17-11 at 12:09 PM.
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