I am frustrated and need advice fast. I am preparing to build a wooden subfloor on a cured concrete slab that sits at ground level. I did not pour the slab, but I do know that it was poured over a dirt garage floor, and that there was NO plastic sheeting laid down first. The concrete appears to be approximately 4-5 inches thick all around. The slab is sound and dry for the most part at this time, but I have concerns about moisture leaching up in the spring, as there are cracks appearing in the concrete already (it’s a year old).
I want to lay pressure treated 2X4 sleepers on their side before sheeting the area with Advantech 4X8 material, which seems to be the product of choice today. My dilema is this: The finish floor will be a very expensive maple hardwood floor used in dance studios. The subfloor must be as level as possible, so I wanted to trowel down cut-back asphalt mastic, cover that with 6 mil plastic sheeting, then fasten the sleepers to the concrete with powder catuated fasteners or maybe concrete screws like Tapcon.
The rub is, that I have looked and looked and called and called, and I CANNOT find this famous cut-back asphalt mastic anywhere. Any flooring book I have read suggests using it the way I planned to, or laying the sleepers themselves in “rivers of mastic” if no fasteners or plastic sheeting are used. Does anyone have any idea where I might find this stuff, or even what company makes it? I need to get this thing done and I want to seal it all up correctly. If you have any suggestions, please let me know. I will be forever greatful. Thanks.
Replies
Greetings Fuzzy,
This post, in response to your question, will bump the thread through the 'recent discussion' listing again which will increase it's viewing.
Perhaps it will catch someone's attention that can help you with advice.
Cheers
Peach full,
easy feelin'.
The last project I did over a slab I used a product called Delta FL a dimpled plastic membrane. It keeps the subfloor suspended 3/8" above the slab and allows any moisture wicking through the concrete to dissipate because of the continuous air gap formed by the dimples. On top of the membrane I used 3/4" T&G ply screwed to through the membrane and into the slab every 12" O.C. Our finish floor was Marmoleum but after the plywood subfloor you could use just about any finish flooring you wanted to. Nice thing about this product is its low profile which keeps the floor build up to a minimum.
I'm pretty sure regular wet/dry stick ashpalt roof repair/patch (which for the life of me I can't think of the name brand but is a white and black with orange metel can) commonly called "bear chet" would serve the same.
Bostik makes a urethane based membrane designed for use on top of slabs prior to placement of wood strip flooring. I believe it is called MVP. The product is troweled on and is super tough when dry. Potential sources include wood flooring stores, Lumber liquidators, maybe Home Depot or Lowes.
The bucket says you can get 200 sf of coverage per gallon of product. I have never been able to get more than 150 sf.
Bruce
Thanks to all for the responses. Hiker, I actually stumbled across the Bostik MVP at a Lumber Liquidators. I was a little shocked at it's price ($170 for 5 gallons), but decided to try it anyway. As I poured some out on the floor, I noticed small raisin-sized lumps in it, which I then attempted to trowel out. I was alarmed to see that these lumps were small bits of partially cured material, which promtly rolled up into even larger balls of goo when the trowel was dragged over them.
I returned the can to LL, and was told that they had seen the problem before, and they immediately offered to replace it with a can that I first opened to inspect before leaving. The new can was fine, and the product is absolutely amazing. It troweled out easily into a pattern of shallow ridges, which then settled out into an almost glass smoothe surface. It took about 48 hours to get nice and firm, with minimal smell. When completely cured, this stuff is unbelievably tough. I let a small puddle of it in a plastic cup cure, and I couldn't poke a hole through it without pushing hard with a screwdriver.
When the floor had cured, I screwed down pressure treated 2X4 sleepers with 4 Tapcons on each board. In the future, I might be tempted to screw down the sleepers while the product is still wet or maybe just tacky. I am certain this would help insure the sleepers would never pull up from the concrete. This approach would make for a tricky installation while crawling around on my hands and knees among the sleepers and wet goo.
Anyway, I am more than satisfied with the product, and wouldn't hesitate to use it again. The price is steep, but it sure seems to produce a durable and moisture proof membrane on bare concrete. I finished off the subfloor by laying 6 MIL poly sheeting over the sleepers, taping the seams, and then laying 4X8 sheets of Advantech T&G onto the sleepers. It looks good and should keep the Canadian maple hardwood floor that is still to come, free of moisture related problems. Thanks again for the help.
Glad it worked out
Bruce
What did you need the second vapor barrier for? Bob's next test date: 12/10/07
Two reasons for the second vapor barrier Jim.
#1. The friend I am doing this for is a hopeless toxin-phobic, and is worried about the "fumes" from the Bostik MVP leaching up from below and sending all of her students to an early grave. When the finish floor is all done, I may tell her that a new report indicates that "the vapors from 6MIL plastic sheeting have been determined to be deadly to women".
#2. I am and have been all my life, a hopeless anal retentive. I have tried to get over it many times, but I just can't help myself. I don't pick up my dirty socks for days at a time or fold my laundry, yet if I had my way, I would have an inspection port allowing continuous electronic monitoring of sub-floor moisture content, so I could sleep at night...lol I'm just kidding to some extent, but in my youth I was a student pilot as well as a deep-water scuba diver. Either of those two pursuits demand equipment redundancy if you have any desire to live beyond the age of 25, so if one of anything is good, then three will calm your nerves.
I promise that if this floor ever buckles, I will post photos of the ugly results, including any bruising I might sustain from the owner. Thanks again for the help everyone.