repairing subfloor

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  #1  
Old 04-03-11, 12:22 PM
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repairing subfloor

Hi,
The subfloor in my bathroom is rotten. Not horribly rotten, the underside of the subfloor is my garage ceiling and you can't see rot from underneath. But from the top, I can see pits and soft areas and flexibility in the subflooring boards, which are tongue and groove 1x6's.
The rotten areas extend under the cast-iron bathtub and an interior wall. The 2x4 baseplate of the wall has some rot on the bottom. I doubt it's affecting the strength of the baseplate very much.
I don't think there's any way around taking out the cast-iron bathtub. I don't know if it's reasonable to take it out whole and re-use it, or if it really has to be just trashed with a sledgehammer to be taken out. I might buy a new bathtub, which would be lighter.
But, can I avoid taking out the interior wall?
I was thinking that I could remove rotten subflooring boards one at a time, replace them with 1x6 boards, pushed under the interior wall. I would support the ends of the boards by pushing them on top of 2-by-whatever wood, screwed onto the next floor joist (and fastening them there with angle brackets, maybe). If the boards are removed one at a time, I don't think the 2x4 baseboard would sag significantly. I'd use oak 1x6 for strength.
The room on the other side of the interior wall has a hardwood floor, and I hope to avoid having to remove part of the floor for this repair.
I don't know if suitable 1x6 tongue and groove is available to replace the floor boards. If I got standard 1x6 oak boards, maybe I could rip off 1/4" and substitute them in, but it wouldn't be tongue and groove - I don't know if the tongue and groove is necessary for strength? Can one carve tongue and groove into the boards?
Or perhaps it would be easier to take out part of the interior wall, so there's no load on the subflooring in the area that needs to be replaced. In that case I could take out all the rotten subflooring at once and replace it with plywood.
I'm not sure how to rebuild part of the interior wall. But maybe it could be done without too much problem. I don't think this is a load-bearing wall, because it is parallel to the floor joists, and it isn't right on top of a floor joist. So I think it is only supporting its own weight.
I don't think the floor joists are rotten. If they were, I think I would see the wood rotting from below, and the underside of the subfloor looks fine.
So what do people think?
thanks
Laura
 

Last edited by goldym; 04-03-11 at 01:31 PM.
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  #2  
Old 04-04-11, 03:12 AM
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I think you should decide, first, if the tub stays or goes. It would be nearly impossible to change subflooring out from underneath it, so it would, at least have to be moved for that. Cast iron is durable. Does it have any chips on the surface? Just trying to give you justification for removing it and replacing with a lighter weight unit.
Replacing all the bad subflooring is the only way to go. After you check the joisting, you will know better whether or not they will need attention. Use 3/4" Advantech for the subflooring. I would not try to replace the individual boards. Pull what fixtures you can in order to make the install easier.
 
  #3  
Old 04-04-11, 03:28 AM
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I think your trying to do a poor mans (or woman's fix that's never going to work out in the long run. You still will have a floor that lets air come in through the cracks, the nails come loose, there's going to be cupping so the floor will never be truely flat.
That whole floor needs to come out, as well as any other rotted wood, and be replaced with all new subflooring and 2 X 4's.
You cut out the old boards on the outsides of the room with a Toe Kick saw so you can cut right up to the area where it goes under the walls.
1 X6's are what was used 50 years ago before plywood.
I'd remove everything in that room, toilet, vanity and tub (a real pain, but it could be removed and slid over out of the way, fix the floor then slid back in place.
If there's old steel supply lines or drains nows the time to take them all out and replace them, if there not leaking now they will be some day, the shower control valve also needs to go.
The subfloor should be Advantec 3/4" T & G glued to the floor joist with constrution adhesive and screwed down with ceramic coated decking screws, not nails.
Once the whole subfloor is in place the tub goes back in.
The next step which is the underlayment depands on what you plan on doing for a finsihed floor.
 
  #4  
Old 04-04-11, 04:35 PM
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...going beyond the subfloor...

Assuming you've completed the necessary steps of replacing and levelinge bathroom subfloor, would it be outrageous to consider the surface appropriate for tile as is? Or should I consider installing that orange wafffle-like tile underlayment that's all the rage on HGTV?

It seems like overkill?
 
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Old 04-04-11, 04:56 PM
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Tile should not be placed directly on any sort of wood. Some have done it and said it was successful, but it is not an approved method by any tile manufacturer or tile association.

Backerboard or something like Ditra is the way to go.
 
  #6  
Old 04-04-11, 05:32 PM
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Yes, I decided after posting this that taking out the part of the interior wall over the rotten area - removing drywall, wall studs and the 2x4 at the base of the wall - is the way to go. It's only a few feet, and the 2x4 at the top of the wall could stay in place.
Yes, I know the bathtub has to be slid out. Maybe I could pull it out through the gap that I'll have to make in the wall.
The bathtub may be incredibly heavy. It's a cast iron 1950's bathtub, 5' x 32". Anyone know about what those would weigh? A relatively light new Kohler cast iron bathtub somewhat smaller than mine weighs 300+ pounds. Someone told me that 1950's bathtubs were built with thicker cast iron, does anyone know if that's true??? Mine might be 400 pounds or more.
Finding rotten subflooring is actually a hopeful sign. The reason I started tearing down the bathroom is that I've been sick for years and mold in my house is likely the cause. Rotted subflooring could do that to me, it means there's a lot of mold and it takes a lot of mold to make someone really sick.
Laura
 

Last edited by goldym; 04-04-11 at 06:15 PM.
  #7  
Old 04-04-11, 10:04 PM
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Seems like my bathtub is 1/2" thick cast iron. From that it weighs 400-500 pounds

Laura
 
  #8  
Old 04-05-11, 03:39 AM
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Laura, yeah, you have about one option......leave it in place, repairing the flooring as best you can, or breaking it out with a sledge hammer (appropriate safety glasses, gloves and skin covering, of course) and removing it in pieces. It won't be moved from the room as is, I don't believe.
If your control valves aren't a part of the tub, releasing the drain and sliding out (with help) would be an option.
 
  #9  
Old 04-05-11, 05:39 AM
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If you are getting sick from the mold, shouldn't you have a mold abatement company do the work for you?
 
  #10  
Old 04-07-11, 11:15 AM
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In my opinion to do it all right you really need to consider a complete gut with a bathroom that old and check out everything. Also the plumbing may need some relocation to work with the new tub depending on what you buy and whether it will require a surround or not. What type of wiring is in there and does it meet current code in regards to grounding, distance from water sources, and GFI protection. Is there a ceiling fan, and if so does it need replacing, and is it vented properly? Depending on your budget it makes sense to change out all fixtures, and faucets. They don't last forever. Are there any outside walls in the bathroom? What is behind the wall board if there are? Enough insulation? The questions can go on. The Ditra product you may have seen on the Holmes HGTV show is a great product because it not only provides sufficient base strength for tile, but also waterproofs the floor, however even that product requires knowledge to install properly even in regards to the correct thinset to use to install it. Backerboard also should be both screwed and thinset glued down. I would also suggest that you pick up some material and read up on bathroom renovations and modern materials. I know that Holmes has an excellent book out there that incorporates what is known to work best these days based on the most up to date products, and learned failures from the past. In my opinion when it is time to get into subfloors in a bathroom it is time to take a good look at the whole situation and correct it all while everything is pulled out. A complete bathroom reno done by pros would likely start at $5000 and up to twice that depending on what level of fixtures and design elements etc. you choose. Half of that is generally labor so lots can be saved if you can learn first and then do it right as a DIY project.
 
  #11  
Old 04-11-11, 02:24 PM
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equinox,
Yes, gutting the bathroom is essentially what this is turning out to be. The plumbing has been worked on recently and is fine.
Laura
 
  #12  
Old 04-15-11, 08:24 AM
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Hello,
To install subfloors an option used by most people is to build a wooden frame first and then plywood panels lined with insulation and a vapor barrier are placed in between the concrete and the new subfloor.

Thanks
nickjonas Crunch
 
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