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Old 01-19-2011, 05:12 PM   #1
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Installing backer board question


I've got a house that was built in the 60s, and under all of my flooring is this thin (1/4" maybe) layer of black disgusting rubbery foam stuff that's glued to the floor boards. In my bathroom, the previous owner put some 1/4" plywood over top of the padding gunk, and laid linoleum. We're remodeling the bathroom now, and I've taken up that 1/4" plywood (rotten!) and linoleum, and would like to put down marble.

My question is this... how do I get the disgusting rubbery foam stuff off of the floor boards, well enough to put the backer board down for the marble?? Scraping is a pain in the booty, and doesn't seem like it's getting the job done well enough for the thinset to bond w/the floor boards. Help!!

PS... any objections to marble in a bathroom?

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Old 01-19-2011, 08:38 PM   #2
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Installing backer board question


It is not reccomended, but you can use 1/2" backer board and go over the foam rubber. Just Put a ton of backer board screws all over the floor. Before you do this make sure there is no movement in the sub-floor. If there is movement, glue and screw 2 bys' between the joists to reinforce the floor. Then the backer.
As I said this is not reccomended but it will make the floor stong enough to put the marble on.

USE PLENTY OF SCREWS!!!!!

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Old 01-19-2011, 08:57 PM   #3
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Installing backer board question


Hi Rooster & Woodman,

I will definitely disagree with your advise Woodman, sorry. Doing what you suggested is not recognized as the right way to go, and will result in cracked tiles or at min. cracked grout.

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use 1/2" backer board and go over the foam rubber.
NO WAY! That foam, or whatever it is has to be removed. Plus there is no advantage in using 1/2" backer as it adds very little strength. 1/4" is made and is recommended for floors unless you need the extra height. Either way, DO NOT forget the thin set mortar under the backer, tape the seams etc.

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As I said this is not reccomended but it will make the floor stong enough to put the marble on.
Wrong. Marble, and all natural stone tiles require a much stiffer subfloor than regular ceramic tiles do. The joists should meet L720 specs for deflection and well as the subfloor deflection. Marble requires a double layer subfloor. I recommend at least 1 1/8" thick if it's 5/8" + 5/8". Otherwise 1 1/4", consisting of 3/4" + 1/2". Over that you need your favorite concrete backer or a membrane such as Ditra.

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Old 01-20-2011, 10:21 AM   #4
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Installing backer board question


JazMan... so you'd recommend scraping as much of the rubber gunk off as possible, and laying Ditra or backerboard over that? Correct? My subfloor is some kind of 5/8 particle board (kind of fuzzes up when you scrape it) over top of some 5/8 plywood... I would say it's more bouncy than most floors, but I'm no expert!
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Old 01-20-2011, 02:06 PM   #5
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Installing backer board question


If your underlayment is particle board, that needs to be taken to the curb, also solving the other problem.

A 5/8" t&g plywood subfloor is the bare minimum allowed in a tile installation. It is highly advisable to install a second sheet of 1/2" plywood underlayment per directions followed by a concrete backer or membrane. How are the joists?

Double check that your underlayment is really particle board and not OSB. OSB is allowed if it's still in good condition. Got pics?

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Old 01-20-2011, 02:39 PM   #6
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Installing backer board question


JazMan, I've been resisting my wife's pleas to get rid of the particle board... you're supposed to be on my side! It's definitely particle board on top, which is completely rotten in spots (I was planning on splicing in a sheet of 5/8 plywood to get rid of the bad stuff). What's the trouble w/particle board (other than obvious water issues)? Are you telling me I'm going to have to tell my wife that she's right?!

Is there any chance that the particle board isn't glued to the layer below it? All I know right now is that there are small nails around the perimeter...
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Old 01-20-2011, 03:28 PM   #7
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Installing backer board question


PS... joists look good (under the bathroom anyways)
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Old 01-20-2011, 04:11 PM   #8
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Installing backer board question


Underlayments should never be glued to the subfloor, but who knows.

PT is not approved anywhere in a subfloor sandwich.

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Are you telling me I'm going to have to tell my wife that she's right?!
Get on your knees rooster.

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Old 01-21-2011, 01:54 PM   #9
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Installing backer board question


Thanks JazMan! I told the wife that she was right, and she didn't even razz me... good woman!

So I've got about half of the particle board up, and will be taking the rest of it up tonight. I'd like to put 3/4" down (there's plenty of room for it)... what kind of board should I buy, and what kind of screws?
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Old 01-21-2011, 02:46 PM   #10
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Installing backer board question


3/4" underlayment grade ply is fine. Do not buy the cheap CDX sheathing stuff. You are not sheathing anything. Then the concrete backer or an approved membrane.

Screws? Buy flooring or deck screws, 1 1/2". No cheapo drywall screws. And remember no glue.

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Old 01-23-2011, 05:02 PM   #11
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Installing backer board question


Thanks Jaz. Got the floor down... just not sure what kind of grid to put the screws in. I've read 4" around the sides and 6" in the field... is that right? Just seems like a ton of screws!
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Old 01-23-2011, 05:32 PM   #12
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Installing backer board question


All depends on the thickness of the plywood. The thinner, the more screws necessary.

When I screw things and people are awed, I always tell them "I've got an uncle in the screw business."

If you used 1/2" or thicker, I think 5-6" in the perimeter and 8" in the field should be good.

Jaz

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