Questions about building a hearth

[Brian103]

I am having a Malm Zircon 34 (woodburning) installed, and had a few questions about the hearth construction. I know minimum dimensions and have purchased 8x8x.5 terracotta tile to build the hearth.

I don't know the exact location of the stove install, as it may move an inch or two in any direction based on clearances for chimney. Is it possible to build the tile hearth on 1/4 inch backerboard in place without securing it to the hardwood floor, then slide it an inch or two, if needed to center under the stove? I was thinking I could mortar and grout tiles, then finish the edge post install. I would like to have a plumb line for the chimney install, but the house is remote and I don't think I will get them to take two trips.

The other question I have is about finishing the edge of the terracotta tile. I would like to leave the edge exposed to show off the thick tile. Does it make sense to cut the backerboard 1/4 inch short on all sides, then grout along the bottom, as well as grout the exposed corners (horizontal to vertical grout lines)?

Thanks,

Brian

 

[begreen]

That won't work, it will flex easily and crack between the tiles. If you want to have it movable then the backerboard should be attached to something that is not going to flex. I would use at least 3/4" plywood for that together with 1/2" cement board to make it more rigid.

PS: What does the manual list for hearth insulation requirements for this fireplace?

 

[Brian103]

Thanks for the quick reply. The hearth requirements are, "A floor protector is required to protect the floor in front of the fireplace opening from sparks. The floor protector must be a minimum of 3/8 inch thick non-combustible material such as brick, concrete, slate, ceramic tile, or a listed floor protection board such as Wonderboard or Homosote".

Based on that spec, I'm not concerned about the half inch terracotta protecting, but I am concerned about the issue you brought up on flexing. Maybe I do put it on plywood and run some molding around the plywood after the install.

 

[begreen]

With 1/2" terra cotta tiles the hearth is going to be quite heavy. Even 3/4" plywood may flex if it is lifted. You may be better off getting a crew together to slide it into position if needed. Or just build the hearth slightly oversized to give yourself more wiggle-room without moving the hearth at all.

 

[Brian103]

Oh- I don't intend to lift it. I am going to construct it exactly where I think it should be. I just want to be able to slide it over a bit if needed.

 

[CincyBurner]

You could attach a layer of wool carpet padding/ underlayment to the bottom side of the 3/4" plywood. It'll slide easily on bare, finished floor, even with a heavy hearth; however, it will raise the hearth above surrounding flooring.

Don't skimp on the backer board, or fasteners to the plywood (it's more than I had initially thought), but it is the foundation for the mortar and tile. Follow good guidelines and you'll be OK. There are lots of pics, youtube videos, and past posts on this site.