Filler for between existing hearth and hearth extension?

[Widow Ralston]

I'm building a removable hearth extension from Durock and Thinbrick with an aluminum frame. Much like what you'd see at the hearth store, but as a DIY it's costing me less than half. Getting a custom to match my existing brick hearth width was more than I wanted to spend.

I removed the existing wood quarter-round trim in front of the brick hearth and there's a gap between the floor and hearth. The gap is approximately 1/4" wide and about 1 1/4" deep (the original floor had been relayerd with 1/4" ply and 3/4" pine). Is there any type of non-flamable filler material that I can place in the seam? Want to prevent the possibility of any embers or ash getting down in there.

Thanks.

 

[fossil]

I s'pose it could be packed & finished with regular old mortar (the pre-mix is commonly called "sand mix"). Would probably match the mortar between hearth bricks. Why do you want to be able to remove the hearth extension? Rick

 

[oconnor]

What about the refractory cement you can buy in the caulking tubes?