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Unread 07-11-2008, 07:49 AM   #1
handymanbb
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Subfloor advice

Hello all,
I am new to this site, but after reading other replies I am confident that you all can help. I just completed gutting my bathroom (everything original from 1952). There was a tile floor on a floated cement base. After romoving the tile and cement base, I am left with 1"x4" boards. Most of the boards are in good shape.There are 1/4" gaps between many of the boards, and by the toilet and tub a few are soft. I was going to originally cut out this subfloor and replace it with 3/4" plywood, but I can't really sister up the joists below because of lots of electrical and plumbing in the way. My plumber told me to just go over the existing subfloor with the 3/4" plywood. Problem being that would make my finished floor too high. My question is can I go over the boards with 5/8" or even 1/2" plwood? I am planning on using Ditra over the plywood (tiles are 12" porcelain). Also, when attaching the plywood over the subfloor, I thought that it would be better to put some three inch screws through the plywood and existing subfloor into the joists. I will use smaller screws throughout the rest of the field (every 6 inches). Am I way off here? Thanks in advance for your help.
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Unread 07-11-2008, 08:10 AM   #2
cx
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Welcome, handymanbb. Please give us a first name to use, preferably in a permanent signature line.

Isn't it interesting that plumbers, who rarely know the requirements for a pre-slope under a shower pan liner (covered in the plumbing code) always somehow know how to properly complete all other aspects of a remodel?

I'm confused about your problem. If you had a mud bed (I'm guessing that from your description of the "cement base") under your tiles, why would you not have room to add plywood to the existing board floor?

Also don't understand about the sistering unless you've calculated your joist deflection and found the structure wanting for a tile installation. That the case?

Adding plywood over rotted or damaged board subflooring isn't a good idea. If that board subfloor is not sound, you really should remove and replace it, despite all assurances by your plumber.

Perhaps some photos of what you have there would be helpful. We like pichers.

My opinion; worth price charged.
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Unread 07-11-2008, 08:14 AM   #3
Dave Taylor
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Howdy bb and..........

thanks fer' joining our forum.

Please give us a first name you may be known by..... bb sounds so round :---)

bb asked:
Quote:
My question is can I go over the boards with 5/8" or even 1/2" plwood?
sure can, bb.... if your sawn 1" x 4" planks are in decent shape, flat and... well affixed to the joists.

However, bb, you should ask another question of yourself first.
'Will my (bb's) floor substructure (joists) support a new 2008 type ceramic covering?"

Use our whirl' famus' Deflecto tool at the top of this page to determine the answer.... than tell us the deflection reading ol' Deflecto gives you and.....the floor stats you entered to get that deflection reading.

Thanks bb..... we can proceed from there.

PS: What CX says.... he da man.
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Unread 07-11-2008, 08:57 AM   #4
handymanbb
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Thanks guys. Dave, I used that deflecto tool and got 377. Seems like that is O.K. for the tile. CX, since the mud bed is gone, I have a difference in height of about 7/8" between the current subfloor and the hallway outside the bathroom. If I put down the 3/4" plywood + the Ditra + the thinset and tile (1/4") I will be at least 3/8" to 1/2" higher than the hallway floor. This is why I was wondering if I could go over the existing subfloor with maybe 1/2" or 5/8" plywood to get the finished floor closer.
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Unread 07-11-2008, 09:17 AM   #5
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Brad, I've read your original post, CX's questions, and your replies, and I'm still confused. Normally '50's era mud beds were very thick, like 1.5 to 3 inches, so removal of a mud bed and tile should give you lots of room. If the plank subfloor was installed on top of the joists, removing the planks would not require sistering the joists, unless you were trying to correct a slope issue. Sometimes, the planks were recessed into the joist bays to permit a thicker mud bed. The joists were often shaved to a "V" on top to prevent the mud from cracking. If this were the case, you couldn't simply install plywood on the planks and the joists, unless you filled the space with more plywood. See our confusion?

Pictures would be nice.


P.S. A slight height difference between the bathroom and hallway is common and usually un-noticable if handled properly. Don't let that dictate your tile setting methods.
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Unread 07-11-2008, 10:04 AM   #6
handymanbb
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Thanks for your reply Bob. Sorry about the confusion about the sistering of the joists. The reason why I mentioned that was because if I removed the existing plank subfloor and put plywood, the joists run parallel to the bottom plate of the wall and I would not have anything to screw the side of the plywood to for support. Again, blocking is not possible for support because of electrical and plumbing that is in the way. Anyways, I don't know how to shrink the size of the photos to get them to upload. I'm kinda new at all of this posting stuff. If I can remove the very small damaged sections of plank (maybe one or two boards), can I go over top of it? If so, do I need the 3/4" plywood or can I go smaller?
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Unread 07-11-2008, 10:35 AM   #7
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Hi Brad,

I think you need to figure out how to post the pictures, because you're not coming through clear.

Download Irfanview http://www.irfanview.com It's free. Then when you open a picture file in that program, go into the Image menu and find resize/resample. That will allow you to reduce the size of the pic.

Whatever you do, the subfloor needs to end up being very solid.
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Unread 07-12-2008, 08:32 AM   #8
bbcamp
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OK, replace the bad planks, screw the good planks to the joists real good, and install 1/2" minimum plywood, screwing it to the planks. Then install an underlayment, either backerboard or membrane, then your tile. Again, if you have a height transition at the doorway, we can deal with that later.

Your old mud and tile should allow you room to do this, though. How thick was the stuff you removed?
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Unread 07-16-2008, 11:44 AM   #9
handymanbb
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Thanks Bob! I just finished laying down the new subfloor. I decided to replaced some of the damaged sections of board with plywood. Next I attached 3/4" plywood to the boards and joists using 3" exterior screws on the joists and 5/8" exterior screws on the boards. I also left a 1/8" gaps around all edges of the plywood. I can't believe how stiff the floor is now! It is rock solid and ready for the Ditra.
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Unread 07-16-2008, 01:57 PM   #10
bbcamp
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Tile on, Handydude!
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