Extending a hearth for ember protection, have some questions

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New Member
Jan 9, 2024
I'm installing a VC Encore in front of an open fireplace, and need 18" of ember protection in front of the existing slate hearth. Rather than putting down an expensive piece of metal to cover the wood floors, I opted to cut out the wood flooring in that area and will replace it with slate. My local stone yard sells 3/4" thick (same thickness as the wood flooring) slabs of 12" x 18" slate for $7 each, which means 5 of them will perfectly fit the 18" x 60" extension area, at about 10% of the cost of the metal plate, and will look better, in my opinion.

I'll use Quikrete mortar mix to set the slates, with a dark tint to roughly match the slate, unless someone has a a better idea for how to cement the slate in place.

Lastly I'm wondering if I need any barrier between the wood sub-floor and the slate slabs. There's insufficient depth for cement board, so I could use tarpaper, which was between the oak flooring and subfloor as installed. Or I'm also considering aluminum flashing, since it's not combustible like tarpaper. But the slate ember extension will probably not get hot enough to worry about it, so maybe I'm overthinking it!

Any thoughts appreciated.
- Steve
I believe, ember protection is any fire proof material. No "R" value material needed between combustible material, the wood sub floor, under the stove.

Mine was the same requirement. I built the hearth and wall stone before the 3/4 oak floors were put in. I used stucco wire mesh on the walls and the floor with a scratch coat. It's a good way to tie all the stone work together on a wood base. The stone is 2". I under cut the blue stone edge so the floor fits under the front edge of the stone.
A thin (1/8") layer of self-leveling compound would help protect the wood sub-floor from embers, even the slate or grout cracks. A paint-on isolation membrane would add very little thickness, but would reduce the likelihood of cracking due to horizontal movement of the wood.

Watch out for cracking due to vertical deflection. An isolation membrane won't help with that. How sturdy is the subfloor? The usual 3/4" plywood / OSB over 8" joists on 16" centers may not be enough.
I did something similar to what you are suggesting. I used with 16" square 1/2" soapstone tiles. I cut out the floorboards and subfloor, then added new joist sleepers below to stiffen the floor and get the height to come out right so the tiles would be flush (the layers are: new 3/4" subfloor, high strength grout, 1/4" Hardie backer board, more grout, tiles). Straightforward to do, but it took some work to get right.