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Luark
04-12-2011, 10:34 AM
I'm planning to replace the subflooring in my bathroom with 3/4" plywood, both because some of it is rotten and because I may put in ceramic tile or stone. I think the joists are ok because the subfloor doesn't look damaged from below.
The old subflooring is 1x6 tongue and groove diagonal boards - house built in the 50's.
I figured I'll reinforce the subfloor with 3/4"plywood between the floor joists, supported by 2x boards screwed onto the sides of the floor joists. Before cutting out the old subfloor.
I think this would stiffen and strengthen the floor a lot? The joists already have cross-bracing by 1x boards here and there, but perhaps plywood between the floor joists would also help?
What size 2x's should be attached to the sides of the floor joists to support the plywood? What size screws to use? Would toe-nailing the 2x's first help to snug them up against the plywood from beneath?
Also, it would probably be better to cut the subflooring flush with the wall. Somebody told me, rent a toe-kick saw for this? Would my reciprocating saw do? There is a flush cut attachment for a reciprocating saw.
The bathroom is about 5' x 8' and the area I'd be tiling is 5' x 5'.
I live in New York State.
I want to make the finished floor waterproof.

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bbcamp
04-12-2011, 11:06 AM
If you are going to cut out the subfloor anyway, why bother working under the floor to install some plywood between the joists? You can do all that from above a lot easier.

Use 2x2 as your cleats (for supporting the plywood pieces) and deck screws long enough to penetrate mostly through the joists, say, 1-1/4" to 1-1/2". Apply some construction adhesive, then screw the cleats to the joists. Use a strip of your plywood to gage how low to set the cleats. It's better to be a hair high than low.

For cutting the subfloor flush with the walls, either a toe-kick saw or a recpricating saw will work. Toe-kick saws are somewhat more dangerous due to the lack of guard and their habit of kicking back when you hit a nail or get it bound in the cut. Re-cip saws can cut wires and other things you can't see, so best you get under the floor to verify the path is clear first.

As far as stiffening this floor, your plywood and cleats will certainly make the subfloor stiffer. The joists need to be checked to see if they are stiff enough for stone. Use our Deflecto tool in the dark blue tool bar. You will a tile underlayment, too.

As for waterproofing, it's my opinion that waterproofing a floor is a waste of time and money unless you also provide a safe path for the water to escape. Tile and underlayments are sufficient for the every-day spills a bathroom might see, but for the big floods, such as a broken pipe or overflowing toilet, the water will find a way out, even if it flows under a wall, out the door or down through a pipe or HVAC penetration in the floor. You must seal them all, and put in a drain to be completely effective.

Luark
04-12-2011, 01:59 PM
If you are going to cut out the subfloor anyway, why bother working under the floor to install some plywood between the joists? You can do all that from above a lot easier.
Various complicated reasons :) I can work under the floor easily, it's my garage ceiling and it's exposed right now.
For cutting the subfloor flush with the walls, either a toe-kick saw or a recpricating saw will work.
Would the toe-kick saw make a cleaner cut and to an exact depth? I would rent it I guess. Yes, I'm a bit nervous about using one, because of the kick. But I do know where the nails are, I wouldn't run into one unexpectedly. A recip saw is a rather rough tool, for gorilla like demolition :)
Use 2x2 as your cleats Only 2x2? I would have thought at least 2x4's and maybe 2x6. There's a cast iron alcove bathtub on the floor, and full it would weigh about 800 pounds, which is half supported on an exterior wall, but that's still a lot of weight.
I hope to drag - or cause to be dragged :) the bathtub out into the next room. Empty, it weighs about 350 pounds. The plywood and cleats under the subfloor will help with that since there is some rotten subflooring under the bathtub and dragging a cast iron bathtub over a rotten subfloor without support under it, gives me the willies.
As for waterproofing, it's my opinion that waterproofing a floor is a waste of time and money unless you also provide a safe path for the water to escape. Tile and underlayments are sufficient for the every-day spills a bathroom might see, but for the big floods, such as a broken pipe or overflowing toilet, the water will find a way out, even if it flows under a wall, out the door or down through a pipe or HVAC penetration in the floor.
Yes, I'm not talking about catastrophic spills, only about things like water seeping through failed caulk. I'm replacing the toilet which should help with that since a cracked toilet tank is one kind of catastrophic leak. Catastrophic spills had better just not happen.
thanks
Laura

bbcamp
04-12-2011, 05:08 PM
You can use any 2x material that makes sense to you. Going one nominal size smaller will more than double your joist stiffness, so that is worth doing if you need to do it.

I'd say the toe-kick will give you a cleaner cut. You don't need perfection, though.

Moving the tub out does not mean doing it over unsupported and rotted floor planks. You can lay down some temporary plywood. I assume you intend to re-use the tub, or else I would recommend breaking it apart with a sledge hammer. Good work out, and you can release a lot of inner demons, should that be an issue for you.

One of the hardest places to waterproof is the toilet flange penetration. Between the necessary gap between the pipe and subfloor, and the holes for the flange bolts, there are plenty of ways water can get by. Only wall-mount toilets are free from this particular demon.

Luark
04-13-2011, 04:35 PM
You can use any 2x material that makes sense to you. Going one nominal size smaller will more than double your joist stiffness
You mean having 2x4's on either side of the joists will more than double the stiffness?
There's an interior wall resting on the subfloor, parallel to a floor joist but not on top of it. I think the plywood under the subfloor which supports the interior wall should at least be supported by 2x4's. The baseplate of that wall is rotted by the way so I'm planning to bolt the wall header to the ceiling joists, and take the base plate and wall studs out to replace the base plate.
I got about L/440 out of the deflecto program, although it's probably better than that because my bathroom sits on the end of the joists, not the middle, and there's all this cross bracing. The joist ends under my bathroom sit on a cement block wall.
Moving the tub out does not mean doing it over unsupported and rotted floor planks. You can lay down some temporary plywood.
That sounds like a really good idea because it would be level with the hardwood floor in the next room over.
Yes, if it's not too hard to slide the bathtub out, I plan to get it refinished while it's out then slide it back in.
Thanks much. I've been sick for years and this rot and mold is likely why. So right now I'm concentrating on doing what's necessary to get the rotted areas out.
Laura

bbcamp
04-13-2011, 05:22 PM
I meant to say using cleats that are one nominal size smaller than your joists will more than double the stiffness of your joists. I didn't see what your joists were, but if you ran the Deflecto right and got L/400~ish, then you shouldn't have any problems whatsoever with your plans.

Luark
04-17-2011, 08:19 PM
So two of the bathroom walls are parallel to the floor joists and resting on subfloor between the floor joists. In order to cut the subfloor flush to those walls, I would have to support it with plywood between the floor joists, so the wall isn't resting just on pieces of subfloor sticking out from the joist.
However it would be difficult to put plywood between the floor joists, under one of those walls, because there are pipes in the space between the floor joists, and a lot of nails. So I can't cut the subfloor flush to that wall, I'll have to leave about a 4-inch strip of the original 1x6 tongue and groove subfloor.
Is that an issue with tiles or stone? Even if it did cause a tile to crack, it would be in an area behind the toilet and under the vanity that isn't very visible.
thanks

bbcamp
04-18-2011, 04:31 AM
I'd agree that that location would not see any traffic, so double layer subfloor won't be necessary. That pre-supposes that the floor around the toilet is beefed up enough to handle the day to day usage. You won't be able to use a membrane as your tile underlayment unless you first cover the planks with some plywood. That leads us to a chicken or egg question: you are trying to get a double wood subfloor by first installing plywood under the planks then replacing the planks with plywood. However, you can't do that under the wall, so you will be leaving the planks as a single wood subfloor. You can't install tile or any tile underlayment over planks, so you need a layer of 1/2" plywood over the planks. If you do that, you might as well skip the plywood under the planks. Rip out the planks that you can get to, replace with equal thickness of plywood, then cover the entire area with 1/2" plywood (I think you can get by with 3/8" since the planks will be behind the toilet and vanity), and a tile underlayment.

Luark
05-01-2011, 01:25 PM
You can't install tile or any tile underlayment over planks

If I leave the 1x6 T&G to cover the first floor joist from the wall, it will stick out 2 3/16" from the wall (not 4" as I thought earlier). Does this much matter, if I'm using some kind of waterproofing membrane?
If so, I could probably add a 2x4 under the subfloor, screwed into the wall side of that joist, and screw the T&G subflooring into that, so the T&G could be cut almost flush to the wall. I don't think that would run into protruding nails etc.
I was thinking that I would be using 1/4" cement backing board over the subflooring, no?
I have been putting plywood between the floor joists, supported by 2x4's.
thanks
Laura

Houston Remodeler
05-02-2011, 08:25 AM
I like your idea of adding the blocking to the one remaining piece of strip wood.

Luark
05-05-2011, 07:21 AM
I like your idea of adding the blocking to the one remaining piece of strip wood.
Yes, if I screw 2x4 into the joist, and then screw the tongue and groove slats into the 2x4, and the ends of the slats are also nailed into the joists - that ought to stabilize the 2+1/4" strip of tongue & groove that sticks out from under the wall, pretty well.
I wonder if that would be stable enough so that I can use tile backing board over it with some kind of waterproofing membrane?

Luark
05-08-2011, 03:43 PM
Well, I rented a toe-kick saw for cutting the subflooring, from Home Depot. It didn't seem all that dangerous to the body, if you're out of the path of the kick. The one I rented had a guard. But if it kicks it might destroy objects in its path. Luckily nothing got seriously harmed, even though I tried pushing it backwards and it kicked. It does have a very powerful kick, not something you could easily brace against.
There's a flush cut attachment for a dremel or similar, which several people recommended to me as a reasonable thing to use, slower than a toe-kick saw, less violent but can cut closer to corners. I don't have a dremel.
I have a cutout tool, which may be helpful with cutting subflooring. It will help a lot to finish corners and isn't particularly scary.

cx
05-08-2011, 04:25 PM
Welcome, Laura. :)

If you'll visit out FAQ in the dark blue bar near the top of the page you'll find a brief tutorial on properly attributing quotations you post.

In reading back over the thread, seems you still plan to use a dropped layer of subflooring between the joists. Or did you do that prior to removing the old board subflooring?

Luark
05-09-2011, 06:31 AM
seems you still plan to use a dropped layer of subflooring between the joists.
I've done that, and I put in 2x4's underneath to help stabilize the 2" strip of tongue&groove subflooring that sticks out from underneath the wall. Now I'm taking out subflooring.
thanks

Luark
05-10-2011, 05:42 AM
So, I'm having a plumber over soon to replace the toilet and move my cast iron bathtub out into the next room, so I can replace the subfloor under it.
I don't know yet exactly what I'm going to do for a finished floor, but having the toilet flange raised 1/2" over the height of the subfloor seems about right.
So how about using a flange extender as a spacer under the flange, to support it? I want to use something that can't grow mold as a spacer, and a 1/2" hard plastic flange extender might work well. I would temporarily support the toilet on 1/2" durock.
Any suggestions&ideas?
thanks

bbcamp
05-10-2011, 06:07 AM
Better plan is to remove the flange, do all your subfloor prep and tile work, then install the flange on top of the finished floor.

cx
05-10-2011, 10:59 AM
Laura, if you're not gonna do your own plumbing, have the plumber remove the existing toilet flange and leave it out until you decide upon and install your flooring. A new flange can then be properly set on top of that flooring.

My opinion; worth price charged.

Luark
05-21-2011, 07:01 AM
Laura, if you're not gonna do your own plumbing, have the plumber remove the existing toilet flange and leave it out until you decide upon and install your flooring. A new flange can then be properly set on top of that flooring.

The plumber told me he has a flange that's somewhat adjustable. I told him the finished floor would be between 1/2" and 3/4" over the subfloor, and he said that's fine.
The problem with trying to do it all at once - replace subfloor, install underlayment and finished floor - is that I have a whole lot of stuff to do before the finished floor goes in. And, I'm chronically sick. The reason for this whole project is because mold in the bathroom is likely what's making me sick. So I can't put off getting out the mold under the toilet and bathtub, in order to do all of that stuff.
Yes, I leave plumbing (except for very minor things) to the plumber :) He told me they might have to take out the old cast iron drain pipe for the toilet, because it would have a lip formed over the flange, and the bathtub drain pipe will have to be cut.
There's a floor joist under the bathtub that was severely cut into, to accommodate the bathtub drain. There's only 2" of joist left at one point. It isn't as bad as it might be, because this is right next to the wall where the joist is supported. This would have been done when the house was built in the mid-50's, so it's been ok for 60 years or so ... Still, it is quite scary-looking and I might have to do something about it to get the floor stable enough for tiles or stone.
thanks

Houston Remodeler
05-21-2011, 08:25 AM
Laura,

Let the plumber know - if it is at all possible for him to leave the toilet riser pipe loose and not glued / set into place. That way when the tile work is done your life will be much easier. You'll be able to remove and replace the riser as needed since its not attached. When the tiling is complete, the pipe can be cut to the precise size and installed.

If that isn't possible, then extend the riser pipe a bit too far , say an additional 2 or 3 inches more than you think it needs to be. You'll have to work around it, but the pipe can be cut down later to the exact height, perfect every time.