hello all, im in the process of getting the materials for building a 60"x60" hearth pad. this is the size for my stove (jotal 600cb firelight) as recommended by the retailer.  im planing to use 3/4” or 1/2” plywood followed by 2 layers of “fiberrock” (with tile on top) witch will have a R value well over that required by the stove, something like 1.5.  my problum is that the sheet’s of plywood and fiberrock are only 48“‘x96’. Im not sure how to connect the two pieces of board to form the total size of 60"x60"

Just a suggestion, but use two layers of plywood. Be sure to run the joint perpendicular to each the other one. Do same for the fiberrock. I would recommend glue (wood glue) the plywood together just to add strength. For the cement board (fiberrock) the home centers have a mess tape to use at the joint, the joint is to be filled with some type of mortar mix (or something similiar). Your may try to mortar the two layers of cement board together for strength. I recently built a “pedestal” for our new stove PE T6. It is constructed out of bottom 3/4” Plywoood, 2X6 frame, top 3/4” plywood, two layers or cement board, all topped off with a tile top and sides. Looks really nice and raised the stove about 8” total.

Just some things to think about.

aussieblake

What are you setting this on?  If you’re building this from the floor or sub-floor up, then all your pieces simply get screwed down to the floor/joists.  Construction adhesive between the layers would be fine, but maybe not necessary.  I’m not familiar with “fiberrock” (as you described it), but have built a number of tiled floors, showers, & countertops.  Most often I’ve used Durock (comes either 1/4” or 1/2” thick) for the tile base, and that means mixing up and spreading a thin layer of thinset to lay the Durock on (after the substrate plywood, or whatever, is securely in place), screwing the Durock down to the substrate with special screws, then fiberglass tape and more thinset to seal the joints between the panels of Durock, then thinset and the final tile, then grout and finish.  Since you screw down the individual pieces of plywood, then thinset and screw down the Durock, then seal the joints, there’s no need to fasten them to one another along any of the edges...unless you think you’re building something that could be moved one day, but that’s not what it sounds like to me, nor is it what I’m trying to describe (nor is it anything I’d ever want to try to move).  That would be an entirely different story.  Since you’re just looking to build something structurally sound and not waterproof, you could probably do all this even more simply.  Rick

I was planing on building it as a free standing unit, not attached to anything just laying on the floor. and didn’t want the weight of the stove to break it at the seam where the two pieces join

will be on top of soft wood floor in finished house.

thatnkx for all your input.

You could find a real lumberyard in your area.(not the BORG or Lowes) They will carry Baltic Birch plywood in 5x5’ sheets.
Al

Not sure if it can be done any more but at one time you could special order a sheet of plywood that is correct size for table tennis or ping pong. If my memory is correct, it is something like 5’ x 8’.

"im planing to use 3/4” or 1/2” plywood followed by 2 layers of “fiberrock” (with tile on top) witch will have a R value well over that required by the stove, something like 1.5.”

If your “fiberrock” is not micor and is really a cement board like durock or wonderboard, then you will not be getting to R of 1.5 with your hearth as described. I believe the 1/2” wonderboard only gets you 0.2 per sheet. I used two layers of sheet material for my hearth and had to use butt joints in the sheets. I was sure to spread the butt joints out so that they would not be on top of each other.