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  1. #1
    Join Date
    Feb 2015
    Posts
    2

    Smile Repair or Replace Old Plank Subfloor?

    Hi, Everyone!

    I'm doing a complete gut of a very tiny 3/4 bath (<35 sf). The original (1950s) subfloor consists of 1 x 8 planks placed diagonally to the joists. These were, in turn, covered by 1/2" plywood and, finally, a piece of 1/4" masonite. This combination nicely transitions height-wise to the hardwood floor on the other side of the door. Water has damaged all three layers, de-laminating and rotting the plywood and turning portions of about three of the boards into balsa wood. Only one floor joist shows evidence of (very minor) damage. One wall is an outside wall; it meets a 2 x 6 interior service wall.

    My original thought was to remove and replace the damaged portions of the affected planks with new lumber, making sure that my cuts were on a joist and/or supported with new blocking as necessary between the floor joists below. But then I thought, "They don't build floors like this anymore, so maybe I should just cut out the old subfloor planks all the way to the wall plates, put down a new piece of 3/4" plywood and build the floor (backer board & tile) up from there." As an alternative, instead of going wall-to-wall I suppose I could cut the planks just enough to get rid of the damaged sections and put a smaller square of plywood in the space I created.

    My concern here is making sure that I pick the option that will maintain structural integrity. In addition, this is a new kind of project for me and I'd like to find out how the pro's would do it.

    Can anyone point me in the right direction?

    Thanks!

    Gary Hansen
    Denver, CO

  2. #2
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    6,598

    Default Re: Repair or Replace Old Plank Subfloor?

    Replacing the entire subfloor is an option which is commonly used by floor guys. Just match the plywood thickness to meet your height needs. You will have to address the damaged joist before you do that.

    Replacing only the damaged portions is also a choice, but not as good as the first choice.

  3. #3
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,969

    Default Re: Repair or Replace Old Plank Subfloor?

    First you'll need to determine if your joists are capable of handling a tiled floor. To do that head on over to the John Bridge Tile Forum and click on the handy dandy deflecto-meter. There you will enter the joist size, span, species, spacing and related information. Once you have the deflection stiff enough for ceramic or natural stone, then we can talk about subflooring.

    You can start a thread on the JB tile forum, post pics and get speedy answers for your project. Tell them we sent you.

  4. #4
    Join Date
    Feb 2015
    Posts
    2

    Default Re: Repair or Replace Old Plank Subfloor?

    Good Morning:

    Many thanks to dj1 and HoustonRemodeler for your input. Sorry it took so long for me to respond.

    To dj1, the damage to the single joist I mentioned consists of an area on top of the 2 x 8 joist that measures about 3 in. long by about 1 in. deep and is not near as ugly as the dry rot I found on the floor planks. I would have no problem sistering that joist if you think I should.

    To HoustonRemodeler, I took your advice and visited the John Bridge forum. I used the longest joist span (6.5 ft) I had in the "Deflectolator" and was told that my floor would be rated for both Ceramic tile and Natural stone. I registered on John Bridge and, as you suggested, will try to start a new thread there today. Now that we know the floor is rated for tile, let me know if you have any suggestions for the subfloor. As I mentioned, I was going to go with wall-to-wall replacement of the planks with 3/4 plywood and backer board...

    Thanks again to you both.

    Gary

  5. #5

    Default Re: Repair or Replace Old Plank Subfloor?

    Why don't you think about the hardwood flooring.?

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