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Thread: Exterior glue in Baltic Birch?

  1. #1
    Join Date
    Mar 2003
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    Exterior glue in Baltic Birch?

    My daughter bought a very nice stone mosaic or her trip to Jordan. It has a net back, like mosaic bathroom tile at Home Depot, and should be mounted on a backer board, then hung on a wall.

    She wants to hang it on her front porch, outside, but not where it will get wet, and just a little Sun. It is about 20X24", and reasonably heavy, so I want to glue it to a strong, flat surface to hang. It will also have trim around the edges to encapsulate the small stone pieces, and hide the ply edges.

    Is the glue used in BB going to hold up for dry, but still exterior use? Most exterior plywood I have is not really that flat, and this will be a one shot deal, as I don't think the mosaic could ever be removed intact.

    My other choice is particle board, but that just doesn't seem right.

    I also considered tile backer over the ply, but that will make it even heavier to hang, so leaning against it.

    Any thoughts?
    Last edited by Rick Potter; 12-30-2019 at 12:37 PM.
    Rick Potter

    DIY journeyman,
    FWW wannabe.
    AKA Village Idiot.

  2. #2
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    Not sure about the weathering ability of Baltic Birch, but I definitely wouldn’t use particle board. I be never seen it hold up that well to the elements, and it’s not very light either. My recommendation would be to use MDO. Typically used outdoors for signs and would be both lighter and stronger than particle board.

    Clint

  3. #3
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    What about something like Hardi-backer (tile underlayment) waterproof approx 1/4" thick, wont weigh much different than BB.

    Pat

  4. #4
    MDO is great stuff, repeated wet to dry will not hurt the glue. But the wood plys will split . Mfgs always say the edges
    need to be coated or sealed off in some manner. Cloth glued to any ply wood and then painted makes a product as
    water proof as MDO.

  5. #5
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    Quote Originally Posted by Patrick Morris IV View Post
    What about something like Hardi-backer (tile underlayment) waterproof approx 1/4" thick, wont weigh much different than BB.

    Pat
    That was my first thought as well.

  6. #6
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    There is a Marine Baltic Birch, but I was never quite sure what it is intended for.

  7. #7
    Quote Originally Posted by Tom M King View Post
    There is a Marine Baltic Birch, but I was never quite sure what it is intended for.
    The biggest difference ,maybe only real difference ,is "marine " grade has absolutely no voids. Biggest users could be
    mainly concerned with not having to do any filling on doll houses.
    Last edited by Mel Fulks; 12-30-2019 at 7:59 PM.

  8. #8
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    Katonah, NY
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    marine grade also refers to the glue used. Marine grade ply is what is used to make lap boats, meant for submerged boat planks, so definitely ok for outdoor use. Expensive comparatively to BB ply, for sure.

  9. #9
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    I will check into the Hard-backer, but my main concern is it's thickness. At a quarter inch, and not screwed down in many places like it normally is, I wonder about it potato chipping. That is why I was considering 3/4" BB. With all those plies, I would think it would stay straight. It will be hanging freely on an outdoor, covered front porch wall.

    As I said, it will never get wet, but outdoor humidity changes might warp it??

    I plan to coat the sides and back of whatever I use, and there will be a picture frame type surround to protect edge.

    This is in SoCal...no snow, freeze, or rain will ever reach it, just outdoor humidity in the rainy season.

    Thanks for the thoughts, I only have one try at this, and the Daughter will probably not get to go to Israel, and Jordan again.
    Rick Potter

    DIY journeyman,
    FWW wannabe.
    AKA Village Idiot.

  10. #10
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    I have marine grade mahogany plywood in my stash which might work but you would probably need to buy a larger sheet. I also wonder if you could just paint the backing regardless of the exterior material used. I have also seen some exterior mastic products for tiles.
    Rustic? Well, no. That was not my intention!

  11. #11
    Join Date
    Apr 2017
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    Michigan
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    How about making the picture frame structural?

  12. #12
    I'd consider using a sheet of 1/4" or 1/2" PVC trim material.

    They make PVC 'boards' now in most common dimensions for trim on houses, but they also make sheets of it. It's a spectacularly durable product, won't rot, split, crack, warp, etc . . . and is relatively lightweight. It'd hold the mosaic, while providing a good substrate that would resist any weather thrown at it.

  13. #13
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    The issue with the PVC, Jay, is that it expands and contracts significantly with temperature variation. The OP would need to use extremely flexible adhesive and fillers/grout with PVC as a substrate and even then the bond may not hold up physically.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  14. #14
    You can throw a piece of Baltic in a bucket for a week, pull it out and dry it off and it's fine.

    T

  15. #15
    Jim - do you think PVC sheets expand/contract more within the temperature swings a porch may experience as compared, to say, a piece of wood that will expand/contract with exterior moisture variations?

    I've replaced a host of rotting exterior wood trim with PVC and I haven't detected noticeable contraction since I installed in in 80-90 degree summer days (and it's now in the 20s out there). The longest 'boards' are ~6 feet on the sides of windows.

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