Hearth extension construction: How to provide tile underpayment with the lowest profile

[Bend]

Hello, Thank you for reading. I appreciate your advice. I will upload images & apologize for not doing it earlier. I am working on an IPad & can't seem to figure out how to do it, so I am going to upload images at the library on a computer. I have a question about protecting the plywood in the hearth extension. Please see The attached drawing. Currently the fireplace floor & hearth extension are at the same level (except for the small, 4-in area between them, which is deeper). The drawing shows the sandwich that will be constructed to create the hearth extension. My insert requires an R-value of 1, so the layers of 1/2-inch Micore and Durock will be more than adequate. My concern is with the edge of the plywood toward the fireplace. It seems that 3/4-inch edge of the plywood needs protection. Or am I obsessing too much about this. I am wondering if it would be necessary or beneficial to glue some Micore to that edge using Fiberfrax LDS Moldable (high temperature bonding putty with a melting point of 3200 degrees F).

 

[Bend]

here is a drawing that will add information to the question I have. Thank You for your input.

 

[Bend]

I am trying to upload a photo of the general area, but I am not able to do it. I am working on my lunch hour from work & so I will try again tomorrow. I appreciate any help you can offer. Thank You

 

[Intheswamp]

here is a drawing that will add information to the question I have. Thank You for your input.

Can you make that image larger? Thanks, Ed

 

[begreen]

The sketch is great, it will help us visualize that you are trying to accomplish. It's a bit small to see details. If you are having problems posting a larger size, PM me and I will help you get a bigger one posted.

 

[Intheswamp]

BG, in regards to Bend's question about the edge of the plywood needing protection, I think what it's talking about is something that has concerned me, also. If we only build a hearth pad that extends from the face of the fireplace out into the room then there will be the back side of the hearth pad that will be a couple of inches or so taller than the floor surface of the firebox. This will leave the back edge of the hearth pad (that includes a layer of plywood) exposed in what should be a heat/fire protected zone. This back edge can't be trimmed with the same wood trim as the rest of the pad is trimmed with, thus either a non-combustible/insulation trim has to be devised or either the pad extended completely to the back and sides of the fireplace and sealed well against the walls. It seems like a double layer of micore (since there's already a solid surface to build on) topped with durock and tile would work and would make the floor of the firebox mostly level with the rest of the hearth making it easier to sweep out. Or a short "trim sandwich" maybe a couple of inches wide could be made to protect the back edge. The trick is to have enough R-value to protect the plywood...here's a couple of feeble thoughts....the bottom image comes closer to doing that than the first....the bottom piece of durock could be replaced with micore and the R-factor would definitely be attained. Just some thoughts...

 

[Bend]

Thank You Be Green & In the Swamp,
My brain has been in such a knot over this. I like your idea Swamp. It also solves the problem of leveling the stove. I could use a 1/2-in & a 1/4-in layer of Durock in the firebox & then it would be level all the way in. Thank You!
I made another image. the previous one was a camera image. This new one is a computer image with DPI 72. Hope it is better.
Thank You Again SOOOO much!

 

[Bend]

I am not able to upload the image (photo) of the hearth area. I think there is a restriction on sending that type of file on this library computer. THANKYOU again for your help!

 

[begreen]

So far the planning looks ok. I would like a visual to make sure there aren't any snags. I don't think you need to glue the small micore strip in place. If it is held captive by the sandwich, that should be fine. It can't go anywhere.

Check your PM.