Replacing bathroom subfloor/flooring

Old 08-14-04, 07:03 PM
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Replacing bathroom subfloor/flooring

I am planning to replace my bathroom flooring -- it was vinyl tile, and I want to replace with laminate. In taking up some of the tile, I saw that the particleboard subfloor is badly damaged from water, so that has to go. This is above a crawl space -- I don't know what the joists look like yet. It's an interior bathroom (no windows), but has a ceiling fan venting directly to roof. About 6' by 8' area, not counting tub and rectangular cut-out.

I've checked the related threads here and found some useful information, but have these questions:

Is laminate a good choice for flooring in a bathroom? Yes, the floor has had too much water on it in the past, but the kids are mostly gone now, and the one remaining is now responsible enough not to leave wet towels or sweaty socks on the floor (knock on laminate, and yes, he has to help with the project).

I know I need to remove the vanity and extend the subflooring under that, and of course remove the toilet. Is it really necessary to remove the tub? That would be pretty involved, and I don't know of any problem with the tub support directly.

Is CDX plywood (that's exterior grade, right?) good for the new subfloor? Is that available TIG or does it matter? Would Adventec be better than plywood? I know that I need to plan the thickness along with the flooring to get the right level.

Is there any appreciable advantage to putting insulation under the subfloor, when there is no other floor insulation in the house? This is in a moderate coastal California climate.

Is some kind of underlayment advisable, either for squeak prevention or moisture barrier?

Should some sort of sealant or caulking be used under the laminate along the edges, or along the seams in the laminate? What about recommended baseboard along the wall and tub? I don't think I want to keep the vinyl baseboard that's along the wall now.

Lots of questions. Thanks in advance for any advice on this project.
Old 08-17-04, 02:05 AM
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Well you've done some prior thinking before diving into this without a plan, this is good!

On the removing the tub issue, you're really going to need to get under the area & take a look at the joists & subflooring below to determine if it need to go as well. The particle board subfloor, doesn't bode well IMO that the flooring beneath the tub is still in satisifactory condition. Once water soaks into that stuff, it starts to swell, which is why it shouldn't be used, but still is by alot of tract home builders as a means of cutting costs. Once you remove all of the vinyl tile you maybe able to determine how bad it is under the tub, but I'm afraid at least one trip crawling under the area in the crawl space is going to be called for.

My personal answer pertaining to the laminate in the bathroom, is no it's not a good choice, but I am not a big fan of the laminate floors, that doesn't mean I won't install them if that's what the customer wants, but I will inform them as to other options & many times they change their plans. Others would give you a response that's exactly opposite of mine on this issue. Personally I like ceramic or porcelin tile on a bathroom floor, but many times this isn't feasible due to framing & deflection issues due to inadequate framing of the subfloor.

CDX or exterior grade plywood is definitely the best possible choice for your new subflooring, that is something I always insist on when remodeling.

In your particular climate, I can't see an advantage in adding insulation into the floor.

Depending on what type of finish floor covering you choose it may be advisable to put down a layer 30# roofing felt over the subflooring as a moisture barrier, check with your flooring manufacturer for specific recommendations & follow thru with their advice.

When I do tile floors & here again I'm speaking about real tile not the vinyl junk, you would caulk with a waterproof caulk next to the tub & along the edges where the floor meets the wall. The laminate floors I've installed weren't in wet areas, so we always installed traditional wooden baseboard. However you can also buy baseboard which is made from MDF (medium density fiber) while this isn't real wood it is very durable, paintable and works just like wood when it comes to sawing, drilling or nailing. That would be a better choice for a bathroom IMO.

Hope that helps, but do post back if you still have questions. Good luck!
Old 08-17-04, 08:11 AM
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Thanks very much for the thorough reply. I'll examine the tub support more and reconsider the flooring choice.
Old 08-17-04, 11:31 AM
Dave McG
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I change out about 4-5 bathroom floors per year. Vinyl tile and bathrooms don’t get along and pressboard should be outlawed in damp locations. It is a common problem we face here in Calif. Replacing bath floors and resetting new tubs adds a lot of business for us. First, the tub does not always have to be pulled or replaced. Often a leaky toilet and not the tub are the problem. If the flooring is “softer” around the toilet more so than in front of the tub (step next to and behind the toilet), the problem may be the toilet and or the wax ring. Look for the presswood sub-flooring to be worse under and around the toilet than elsewhere. You can check under the tub to see the condition of the sub-flooring. If the job doesn’t call for replacing the tub, and the sub flooring under the tub is good, I don’t pull it. I cut the sub-floor at the tub and add stringers to support the new sub-floor joint.

CDX plywood usually doesn’t have many ply, so I use “sturdy floor”, a plywood with a lot of ply and rated for damp locations. It is available at most lumberyards and Home Depot. My cut starts in the doorjamb and takes the whole floor. Be sure to glue the plywood down to the joists and I like screws over my nail gun in a wet location. Although sturdy floor is TIG, it doesn’t matter in a bathroom. You should only have one joint and it will only be 4-5’ long. Just place the joint over a joist.

Although we have put lots of laminate in kitchens and baths, I don’t recommend it. Laminates are nothing more than a glorified presswood. Of the 25+ bath floors I’ve done in the last five years, only one or two were the result of the bath water. Toilets or vanities caused the rest. Putting laminate in is just the same as replacing the sub-flooring with presswood. To make matters worse, it will have all those seams to let the water penetrate into the presswood. The guarantee is that the photo surface will last 15 years. There is no guarantee about it not soaking up water like a sponge. I have seen laminate floors that have become cupped and warped after time; but the photo surface is still good.

Vinyl sheet goods are the best protection. If we are going to put down vinyl, I put down a final layer of ACX plywood over the sturdy floor. ACX is very smooth and will give the vinyl a very smooth look and being “X” rated, it will stand up to the moisture. I only put down ¼ ACX, nailed well and no glue. That way in 25 years when you want to change the floor, the ACX will come up and the sub-floor will not need replaced. Also, if you change the entire floor, the level of this floor does NOT have to be exactly the same as the rest of the house. If the transition is in the doorjamb, up to ¼” will disappear where the carpet meets the bath flooring.

Please take a good look to see where the problem is. Chances are, it is not the wet towels. If the toilet itself is the problem (maybe a tank leak), all of your work could be for nothing. Good luck with your project! Dave.
Old 08-17-04, 05:14 PM
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and thanks to you!

More good ideas, thank you. I think that perhaps the most damage IS near the toilet, but I will have to investigate that more, and check out the joists and tub support in the crawl space.

When you say "stringers" at the (potential) subfloor joint, do you mean wood strips crossing the joint that are nailed in from below on to the joists? Plywood strips? 2x4's?

I'm now convinced that laminate isn't a good choice for us -- vinyl sheeting sounds good. I know that cutting that exactly right is an art, so perhaps I should get a contractor for that part. But a contractor wants to be certain that the subfloor is built properly, so I'm not sure how that will work.
Old 08-18-04, 04:17 PM
Dave McG
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While under your bathroom, look for white water stains (calcium) on the sewer pipe directly below the toilet. A leaking wax ring will “usually” show on the drainpipe. Leaking vanities sometimes will leak out the side near the toilet. If you have a joist that is not the best, you can sister in one next to it. Try not to cut out a joist if you don’t need to. They are a real pain to get back in. In the last 5 years or so, I can only remember having to remove “1” joist (80+ year old home).

Pressboard does not always show damage from underneath. If you have two bathrooms, then go for it. Once the rotten floor is out, you can see what you have. Even in homes with only one bath, I can’t tell until I get the rotten floor out. I always tell the homeowners that even after the inspection, I’m not sure until I take it apart. I can get it apart and reset the new sub-floor in a day, sometimes a really long day.

“Stringers” are just what you thought. 2x4s or 2x6s nailed to the joists below the new joint. A good floor guy can fill quite a bit. Your new sub-floor doesn’t have to be perfectly against the tub or at the “exact” same level as the old sub floor, a little higher than the old is OK. Get out the old phone book and look for a “wholesale carpet store”. They are usually a warehouse with no storefront. The kind I’m talking about won’t even like selling to the public. These warehouses only like selling to carpet and vinyl guys. Ask the warehouse to recommend someone. Often these are the same guys that work for the big contractors and work on weekends for a fraction of the price. $60-70 is about the normal price for labor, ($100-120 for a kitchen). Offering to pull and set the tiolet for him can save money. At those prices, I don’t brother doing vinyl.

A good vinyl guy is just that. He will come in looking for a semi smooth level floor. What’s under the floor is of no concern to him. YOU DON’T NEED A CONTRACTOR TO LAY A VINYL FLOOR. In Calif you don’t need a contractor if the job is under $500 and a contractor won't do the job, he will just send out a guy who works for him. Save the money and take your family out to dinner.

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