Not sure how I got roped into doing this thankless task on knees. One of my oldest friends in the world has a rental in B-town. Cute little 3 bedroom. She's moved to Vermont to hang out with her aged parents. Comes home every 6 months to fix things and take stock. She runs it as though she still lived in the front office annex where she crashes and they all her housemates.

The floor next to the main shower suffered some persistent leakage damage over some years, discovered about 2 years ago, after which another guy found and patched the leak around the door.

The floor has been cobbled together ever since, a flap of vinyl (linoleum) over some bits of plywood covering the void where rot was removed. The shower is 2 inches lower than the bathroom floor - it has an custom easy walk in feature and is large - good for handicapped.

I cut away an area of floor about 60" x 36" - the top layer of particle board had blistered up, swollen up - the sponge effect. A bit strange, the subfloor is 3/4 ply, with half inch and then quarter inch particle board on top. I thought I'd go with two layers of 3/4 ply to replace. Now I'm wondering if I haven't screwed up. The first piece of ply is glued and screwed down. The top piece has been cut and fitted but not glued or fastened. The original subfloor measured 1 7/16 and the two widths of ply likewise - 23/32 times 2. Now that the ply is in place, it's noticeably thicker, at least a 32nd and I'm thinking it would show big time under the vinyl. I tried planing the ply down with my power hand planer but it's tough going to take off 1/128 on a piece that size. The extra thickness might be due in part to moisture from my efforts to get up the old vinyl - moisten it to dissolve the glue, this after slicing the vinyl lengthwise in one inch strips. Maybe shoulda kept the ply away from the wet action. You have to let the old vinyl soak awhile before you can pull it up and I had to keep moving. The particle board is not smooth either from the rigors of scraping off stubborn vinyl residue.

And there's the matter of the seam between old and new. At first I thought PatchAll and then I decided on Bondo. But then I remembered that Bondo can bulge out of wood sometimes. Not sure if that's from being out in the weather. Under vinyl, it will likely stay dry. But I just don't know.

My best guess is that either a thin layer of thinset or hot mud - the gyp-board type plaster that catalyzes - would be best to fill gaps and just skim coat the whole thing and then sand it later. One web DIY recommended a Portland cement product for final gap filling, and thinset is. Probably the best odds on no shrinkage or swelling. But then I lose another day while it dries. I want to put the vinyl on tomorrow. Have done vinyl twice before but neither job was all that great, OK but with flaws.

I might have to get some $43 a sheet plywood - very smooth face and replace the piece I have now. I wanted to stay away from particle board. It's flat but swells up like a sponge. You only get one shot at it.

Sorry to run on. This stuff is harder than it looks.

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1986 300SDL, 362K
1984 300D, 138K

YOu can level it with latex concrete. I did it in my old house on ancient t and g boards and installed vinyl tile. It is amazing that the latex concrete will stick effectively to wood but it does.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Sounds good but I never heard of the stuff. I imagine it needs at least 24 hours to cure.

__________________
1986 300SDL, 362K
1984 300D, 138K

Sounds likely.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Every time I needed to level between two sections of plywood, I use Flashpatch

http://www.umaco.com/pdf/data/flooring/Flash-Patch2005.pdf


Sets up almost too quick........and you can easily smooth it with a hand grinder.


Any of the flooring stores will have this or a similar product. I wouldn't bother with anything else.

Talk to a company called Silpro. they make one of the best self leveling tile underlayment and a range of repair materials that work with their system.
Ardex also makes similar products but I don't recommend them as their after use product support is crap.

If you want a truly water proof system you need to look into Ditra and Kirdy. Ditra is a waterproof membrane that goes down in top of the wood subfloor and the thinset goes on top and then the tile and Kirdy is a membrane system that goes on the concrete wall board behind the tile under the tile thinset. Installed as per manufacturer specs thay will render a totally waterproof bathroom. think about this-I installed Ditra/Kirdy when I redid my MOTHER IN LAW'S bathroom! If that ain't proof, then I'm crazy!

I also strongly recommend using the dense foam shower pan and curb system as it will not absorb water and is easy to install and comes pre beveled so no field adjustment is needed.

It sounds like you need to rip out all the particle board and install marine grade tounge and groove plywood using stainless or rhodium screws and Silpro system as a underlayment then flashpatch to do final leveling. Any flake board, particle board or luan will always absorb water as they are all just sawdust and glue pressed together under high heat. They have NO structural rigidity. Plywood is designed with contrasting grain to act as a self supporting material and marine grade is treated to resist absorpition.

The choice of fastener is also important as rust/corrosion is a path for leakage. The 3x expansion of rust will force open/up anything and become the conduit for water intrusion.

IMHO the entire subfloor should be done as a patch is the weakest part of the system.

I've used a lot of the white powder floor leveler over the years in old houses. Mix some with water. put it down with a trowel. It sets up fast.
Around toilets and showers, if at all possible, I coat everything with epoxy before putting the floor down. I'd never use particle board anywhere near water. That just is a curse.
In a rental property, I wouldn't be worrying about 1/32nd. I'd have a hard time getting exercised over 1/8th.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

ardex worked for me, and it dries fairly quickly, depending (obviously) on thickness. you can apply linoonce it's dry - maybe 5,6, hours.

remember, it's a rental (no?) so don't get too crazy.

__________________
"The law, in its majestic equality, forbids the rich as well as the poor to sleep under bridges, to beg in the streets, and to steal bread."

It sounds like the latex concrete has been eclipsed by better products in the twenty years since I used it.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Excellent advice all. I was under serious time constraints and didn't get to see much of it before I had to proceed but I'm likely to do this again. My third time with vinyl flooring and I'm getting better but on some of these jobs I appreciate the value of the good ol' apprenticeship concept.

I use to think the ol' "jack of all trades, master of none" was cute but it's looking more and more like a curse. I mean I sorta have much of carpentry, door installation, and woodworking in general down but when the only available work or at least the work of a regular client who needs it is something else, oh well, soldier on.

When I finally got the old flooring off, I realized the subfloor in question was 3/4 ply with half and then quarter inch CHIPBOARD on top. Almost worse than particle board, which can at least be scraped and reused, more or less. Damn chipboard was coming up in big pieces rendering it junk. Luckily, the top 1/4 inch had been put down in a previous remodel, and not glued so it was easily removed.

My favorite lumber yard in Berkeley, Truitt and White, recommended an "engineered sub floor material" Matrixx brand - it's high quality plywood, exactly a quarter inch thick, 5 x 4 sheet, impervious to water swelling, supposedly. Around $26 a sheet. Only needed three sheets. I took out my second layer of 3/4 ply I was going to use and replaced it with half inch ply. It was still a 16th too thick, so I had to grind off that much, this on a piece about 5 x 3. Luckily, the glue under the first ply was a good guide, as soon as it was gone, I'd gone far enough. W/o that guide, would have been a ***** to take off a uniform 16th.

Put it in, put down the Matrixx with those high quality screws used for holding down hardy board, I forget what they're called, but they're good. Slightly broader head and double depth thread, they stay down nicely, and rarely strip out the wood. I used Fix-It-All, a sort of plaster of paris product for the seams and screw holes. Probably a lot like the product BC mentioned - it dries enough to sand in about an hour. Recommended by an old contractor guy at the lumber yard, guy has been around, said it doesn't shrink. You don't find that kind of help at Home Depot.

I had been in a hurry and bought the wrong trowel, the one they recommend for the same glue on carpet. The one for vinyl has smaller teeth and openings. It was late, I used the one I had and held it low, with many pulls this way and that. Came out OK but oh man, get the right trowel for the job. Too much glue leads to persistent pockets of wet glue under the vinyl which can distort and finally dry all weird. I had a 100 lb. roller so it came out all right, I had just slightly too much here and there.

I landed on my feet but this is harder than it looks.

__________________
1986 300SDL, 362K
1984 300D, 138K

On a job where I have more time and freedom, I'd like to do it more deluxe. This lady had three tenants/housemates living there and 4 days to get it done. This was't actual tile, just the big sheet vinyl stuff. We did a bathroom once with Kurdi under the thinset and tile and so far, praise God, no leaks.

I came around to the POV of your last line. I had a hard time sleeping one night wondering in what ways my patched in subfloor would screw up down the road. Could have ruined the whole job, and redoing it would be starting over, essentially. I got the foundation for the 1/4 inch Matrixx stuff pretty level so I think it's OK.

__________________
1986 300SDL, 362K
1984 300D, 138K

My firm has the Engineering and Design contract to rebuild the floors of schools that age from 110 years to less than 30 years so i have seen the entire range of designs that just didn't work.

In the teens to 20's they used Asphaltic Concrete (65/35 mix) which lays easy but the asphalt shrinks due to gassing off of the petrochemical base. I see floors that are sinking, rippling, etc. Abate the ACM tile and shotblast the asphat to the concrete base which is frequently Cindercrete (aggregate was clinkers and coal chips) not bad but not really stable. Scarify and lay down MASCO with a nylon mesh embed and then Silflo with appropriate sized aggregate (depending on depth can be up to 3/4") in 2" lifts then top with Silpro.

The contractors work nights/weekends and over Winter/Spring/Summer breaks-last week I had guys going 24/7.

What is funny is the most trouble is the 60's to 70's floor slabs where the Architect decided that WWM #9 mesh would replace rebar. I spent a week figuring out how to fix 10 floor slabs in a school because the original builder didn't install rebar at the beams and all the slabs have cracks over the beams-lots of retro install work-new rebar, epoxy, etc.

On a multi family building with a wood floor system, NEVER use chipboard, flake board, OSB or Luan-they can shrink, will absorb twice their weight in water and heave. I've seen many ceramic tile jobs that were well laid but failed due to heaving of the subfloor. A $20,000 job resting on a $1.98 base!

If you have to redo a bathroom-use DITRA and KIRDY system for a total waterproof membrane. I trust it so much I used it in my Mother in Law's bathroom.

If I can be of help just PM me.