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DJNight 09-27-2005 05:30 PM

Subfloor - USG Fiberock help!
Hi, I am in the middle of a bathroom remodel. I am installing vinyl sheet flooring. I removed an old tile floor, to find a 2" thick concrete subfloor that the tiles were set in. To make matters more interesting, the vanity was set before the concrete was poured, so I have a 2" deep depression where the vanity was. I have built up the area where the vanity was with 3 layers of 3/4 osb and leveling compound on the edges. I purchased USG fiberock to put down as the underlayment under the new vinyl. After I got it home, I read on their website not to install it on top of a concrete subfloor. I would like to know the reason and if anyone thinks that I could still use this product for my underlayment. I would be bonding it to the concrete with construction subfloor adhesive and perhaps screws where the wood patches are. Any advise would be helpful. I plan do lay it soon, so please answer back asap if you have any comments. Thanks for the help!


rspainhower 09-27-2005 05:37 PM

why would you not want to put tile back in that space? if not tear out the mud floor.

DJNight 09-27-2005 05:40 PM


Originally Posted by rspainhower
why would you not want to put tile back in that space? if not tear out the mud floor.

Going for less costly/value. Selling the house, doing a "quick" rennovation of the bath for asthetic reasons. Tile would have broke the budget unfortunately.

mighty anvil 10-07-2005 11:02 PM

Fiberock® Brand Underlayment Aqua-Tough is a moisture resistant residential floor underlayment made from recycled gypsum and recycled cellulose. It does not have a paper or a fiberglass mat facing. In fact, it has no facing. It is made up of 80% Gypsum, 15% Cellulose, 2% Parrafin and 1% Crystalline Silica. (Don’t worry, the Respirable Crystalline Silica is listed as only .1% and requires repeated exposure to cause cancer). The gypsum used in Fiberock underlayment is a synthetic by-product of flue-gas desulphurization. Cellulose fibers are recycled from cardboard box manufacturing.

It can be used in both wet and dry areas and is specifically intended as a substrate for ceramic tile, hardwood flooring, laminate flooring and carpeting. It stops telegraphing of bumps and ridges from the structural floor below, and resists swelling, warping and other moisture-related problems that can occur with wood-based products, such as plywood and oriented strand board.

The panels contain no resins, adhesives, solvents or dyes. They are recognized by major resilient-flooring and adhesive manufacturers. Fiberock panels can be cut with a utility knife, but handsaws and low-rpm power saws can also be used. Panels are available in 4 ft. x 4 ft. sizes in 1/4 in., 1/2 in. and 3/8 in. thicknesses, and in 4ft. x 8 ft. sizes in 1/2 in. and 3/8 in. thicknesses.

If it is not to be used on top of concrete it is either because concrete will act as a vapor barrier or it is difficult to get proper leveling or attachment. I don't know which but I don't think it matters for your installation.

This underlayment is made primarily for for ceramic tile in wet areas. There is no reason to use it under sheet vinyl flooring.

But the bigger issue is the downgrading of the bathroom in order to sell the house. The existing mud setting bed is the best substrate possible for ceramic floor tile. It is a major feature that should be taken advantage of. You should fill the depression with patching concrete and install the cheapest ceramic tile you can find. I don't understand how vinyl flooring over Fiberock could be much cheaper. It will easily pay you back in the resale. There is nothing more suspicioius (in addition to looking tacky) than new sheet vinyl flooring in a house for sale unless it is new plastic shower paneling.

beewoolie 11-15-2005 01:35 AM

But I still have concrete subflooring
Like the original poster, I have concrete subflooring. Actually, it's this gypsum-concrete material that was popular seven years ago when this building was built.

I'm putting linoleum in the kitchen, replacing cheap parquet wood tiles. There was no underlayment. The tiles were glued to the gyp-crete. I bought the fiberock because 1) it is cheap, 2) is is very flat, 3) it's easy to work with, 4) it is water resistant.

And, the installation guide is very firm about not installing fiberock over concrete. So far, I've not been able to tell why which is important in understanding how to mitigate that. Is a later of plywood necessary between the fiberock and the gyp-crete? Would a thin layer of foam be sufficient?

Zero Punch 11-15-2005 01:47 PM

DJNight You should be able to pick up some cheap tile at a big box or even a close out at a local tile store which will be less time consuming and cheaper than busting out a mud floor. If vinyl is the only way to go, forget the board and get yourself some floor patch and latex and skim the mud. depending how good you are with a trowel and how rough the mud is it may take three coats.

I reccomend this for the other poster beewollie as well, forget the board over the gypcrete or trying some other "great DIY idea". Skimcoating is the proper method to achieve the results you desire.

beewoolie 11-15-2005 02:13 PM

Skimcoating will be think enough?
The real issue isn't covering the old floor, it's that the original parquet tiles were 3/8" thick and the linoleum is only 2.5mm. A 1/4" layer will even out the floor nicely so that the transition is even between the kitchen and dining room.

I'm guessing, but will soon be investigating, that skimcoating is for smoothing out the old surface. That isn't really a problem. While there is the old adhesive on the gyp-crete, I'm not concerned that it will interfere.

It's clear that the fiberock isn't going to work for me. I'm thinking now that my best bet is to get some 1/4" plywood. It's a bit expensive, but the area is small.

Zero Punch 11-15-2005 04:25 PM

beewoolie, floor patch is still your best friend. You want to feather out from your high spot 1/4 to 0/0 four feet out should do it for a kitchen without notice, tho some may disagree. Just get yourself a nice straight 1x4x4ft screed mix your patch according to directions ya don't want it to wet or dry pour it down and strike it off using your high point as one mark and the present floor level as the other. Get it as smooth as you can, give it a couple hours to dry then knock down any high spots with the back of a finish trowel and hit it again with a thin coat. It will probably take a third coat to finish it smooth.

justdon 11-16-2005 01:43 PM

Another fiberock question?
I posted in general above before I saw this area. Sorry for the double post but need some answers. I have used 1/4 fiberock from menards before under vinyl floor. I need 1/2" now for under doors and walls to replace 1/2" particle board previously tht got wet and___ well you know what that does. I thought it was same stuff and had relative pick it up for me as time was tight. Now he says they told him you cant use Fiberock Aquatough interior panels on floor underlayment under vinyl. You can use floating floors, ceramic tile, or laminates with it okay but NOT vinyl. IF that is a real deal I have to load all this back up and return and exchange for exterior plywood 1/2" . This is a huge job for me and will require alot of expensive floor covering that will be ruined if not right . I like the fiberock undrlayment alot better than plywood, just in case of another flood. And putting down 1/4 plywood then 1/4 fiberock isnt time feasable for me. What to do???

Zero Punch 11-16-2005 03:54 PM

JustDon, USG has two different Aquatough products for interior use as underlayment according to their technical data the FIBER reforced is approved for vinyl here's a link

If you have the fiber reinforced one I believe your good to go.

There is also proper installation instructions available at that site I highly recommend you follow them.


justdon 11-17-2005 09:32 AM

Thanks for the link Zero punch!!!
I read and reread and they didnt specificly say anything regarding my situation. The fiberglass reinforced ones are called underlayment(here anyway) and these I have are called interior panels and they mostly talk about them as wall panels, NOT floor panels alto they make fleeting reference to them there too. I dont see any reinforcing things to them, they look about like small drywall sheets.
Looks like they are going back, but then what else do I use???? I want something good. I dont own this house but very close relatives do and I might someday!! I would rather do it right the first time rather than doing over the second time. This floor is extremely cold in the winter also because it is over an unheated crawl space with zero insulation and the 3-4' block walls radiate the frost very well. Would you insulate the block walls or the floor underneath in the floor joists.. It gets down to minus 10 to 20 degrees, plus a windchill factors down to about minus 80.

Zero Punch 11-17-2005 01:29 PM

JustDon, Sounds like insulation is in order for the block foundation, either foam block or fiberglas batts depending on access glass batts would be the way to go. I take it there are no water pipes in the crawl if unheated or they're away from the foundation walls which would mean that the crawl stays above freezing and between heat loss through the floor and natural heat gain from the crawl floor keeps it above freezing so it would be unwise to insulate the floor you may wind up with another set of problems of frozen pipes. My crawl has the glass batts unfaced they're attached with some type of adhesive, and where the joists set on the plate there is 6" isulation.

Back to your main problem the underlayment. Does Menards rent trucks where you are? If hauling is the problem I'd buy the 1/2 plywood rent their truck then return the Aquaguard on the back haul. They charge like $19.95 an hour around here. Just make sure you get underlayment grade plywood run it parallel to what is down but off set the seams 8" and stagger as well so 4 corners do not meet. If you have acess to a compressor rent a staple gun 1/4 crown 1in. staples about 400 staples per 4x8 sheet of underlayment and a pound of 1in. ring shank nails to tack your underlayment.
If you think it may take you awhile to cut and layout the underlayment just tack it down with the nails, I generally start at one end with me on the sheet place one in each corner and keeping my weight on the underlay spot one in the center about where each joist is located and also one every 16in on the seam while moving backward, then you won't get stuck with addional rental fees on the stapler.
Also most of the staple guns are sequential do not use this feature, place the head firmly on the underlayment and pull the triger. 99% of the problems I see with staples showing through are from cowboys who want to be the fastest gun in the west and this goes for professionals as well. What happens is the staple is in and even sligtly below the surface of the underlay but the underlay is not firnly mated to the subfloor when someone walks across the underlayment it gets forced down and the staples pop up above the surface. Some underlayment has spaceing requirements printed on the down side some do not. I use my 5in1 tool as a spacer, never had a problem.
I ardex all seams and any surface defects in the underlayment mix according to directions use a finish trowel or a taping knife and force the ardex into the seam it will push out slightly behind your trowel, that's ok, when it has dried I take a razor scraper and hold it perpendicular to the floor and draw it toward me with downward pressure. You may need to pull it more than once to remove any high spots but you won't gouge your floor patch or the underlayment as scraping at a low angle will do. You could use a 4in belt sander with 80 grit just don't get agressive.
Sweep her up and your ready for your new vinyl.


justdon 11-18-2005 10:09 AM

Thanks John. I will try to rememer all that. I am a country hick(aka agricultural unengineer, aka redneck farmer) so have own trucks and toys and trailers and staple guns etc. etc. Time is the essential element here!!! Corn comes first, cows close second and energy a distant third. I have a major disability that saps my strength. But will getter done some day... Look out for bug bites, i didnt at the wrong time!!!:mad:

justdon 11-18-2005 10:22 AM

Forgot to add--- The outside block walls have no sill cap on the top of them. Strange but true. The cold radiates, more like wind blows thru the outside of the block into the holes and into the crawl space. As well as radiate thru the inside of the block too. I was down in there one winter(looking for source of problem) and about froze my patoote off. There is a water line across it which does freeze at the outside wall cause somebody who built this was too cheap to buy a frostproof kind. It freezes up but has never broke(yet). Then there is bathroom plumbing around the back part, more wind protected and closer to small crawl hole to get a bit of warmth. Probably 10-15 degrees warmer there. whole crawl space is right about freezing most cold days. Rest of 'old' house part has a full basement, with a 4' water level in spring (go figure). What were they thinking when they put this house 'here'? Moved it in (in late 40's), was old school house and old church, I heard. Addition and crawl space done in the 80's. I objected to the particle board underlayment at the time but was told to keep my mouth shut. Now I pay!!!--don--

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