Exterior glue in Baltic Birch?

[Rick Potter]

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?

[Clint Baxter]

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

[Patrick Morris IV]

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

Pat

[Mel Fulks]

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.

[Brian Tymchak]

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.

[Tom M King]

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

[Mel Fulks]

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.

[russell lusthaus]

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.

[Rick Potter]

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.

[David Utterback]

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.

[Tom Bender]

How about making the picture frame structural?

[Jay Michaels]

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.

[Jim Becker]

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.

[Tony Latham]

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

[Jay Michaels]

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.

[Jim Becker]

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?.

Yea, I do, and I have some damaged PVC sill trim on our 2008 addition that proves it. Over about 20 feet, it moves nearly a half inch in length and with PVC it moves in all directions, not just across the grain like solid wood does. It's less noticeable with the narrower/shorter pieces in other trim areas, however. An exterior rated plywood or other similar will likely be the most stable as a substrate for supporting the mosaic tha the OP asks about, IMHO.

[Ted Calver]

Another thought. At 20"x24" maybe a piece of Corian would work....sink cut out? I know some of it comes in 1/4" thickness, but the regular 1/2" thick pieces might not make the end result too heavy to hang. Don't know about the expansion characteristics. Maybe Keith Outten will chime in.

[Joe Jensen]

I would worry about expansion and contraction. I would look up the data for tile and for the different materials and pick what is closest to the tile. I would also avoid anything that does not like water. Humidity takes longer but it will wreck plywood too.