Variation on tiling fireplace surround. [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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06-05-2019, 04:44 PM
Starting research for installing tile on the face of the front wall of a newly installed wood-burning zero-clearance fireplace. The manufacturer identifies a perimeter "hot zone" and specifies wire lath and non- combustible material set with Type S mortar. Looking at layered ledge stone or a ledge-stone look porcelain. I'm most comfortable setting with a modified thin set, so would like to transition away from the mortar. The tile will cover the face on the wall 65" wide from floor to ceiling. Th inset products seem to share a threshold of 250 degrees F until there is a breakdown. Hard to know surface temperatures as distance from the heating unit increase, but it is undoubtedly somewhere beyond the designated zone. Long way to ask if Type S mortar is suitable for interior vertical installation of tile.

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06-05-2019, 04:59 PM
Lath it, skim coat a mortar bed with type s nice and flat, then tile it using a thinset bondcoat as usual.

06-05-2019, 05:18 PM
Thanks for the prompt reply. Very logical and practical advice. The glitch, unless I'm just overthinking this, is that tech support for Mapei, for one, advises to not use any of their products where surface temperatures exceed 250 degrees. So I'd likely have to use the Type S to set the tiles closest to the fireplace. As I move out, I thought I'd install CBU and use a modified thin set. Thanks, again, CaliGrown. At the Quikcrete site, product info lists use for brick and veneer stone, but does not mention porcelain tile.

06-05-2019, 05:31 PM
I’d lath everything that will have tile and skim coat it with type s mortar then just use your standard thinset to set your tile. Type s doesn’t have the same grab as thinset does. You’ll want your tiles to stick with full coverage between the bondcoat and substrate, especially with the temperature swings. I’ve installed tile and stone around fireplaces and fireboxes without trouble from the heat output.

06-05-2019, 06:38 PM
I'm with Chris. Use the mud bed as the substrate. Let it set and stick the tiles to it with the thinset.

06-05-2019, 06:40 PM
Here's a fireplace we tiled a few weeks ago.

06-05-2019, 07:38 PM
Thanks to you both. The specs from the fireplace manufacturer are a bit perplexing. They call for CBU on the wall surface up to ceiling height or eight feet. They caution about high temps because the wood-burning unit throws out significantly more heat than does a traditional fireplace or gas-fueled device; and they specify no polymers due to the potential for breakdown and possible odors. I was confused by using a CBU as the substrate without using the customary modified thin set. I'm thinking, now, that I could use the existing and solidly secured 5/8" Sheetrock, apply lath and scratch coat of mortar, and set the tiles with an unmodified thin set at least closet to the unit. The wire and mortar would provide the requisite non-combustible surface saving me from tearing out and replacing the sheetrock. We're installing a non-combustible mantle at 45" above the floor, so I could switch over to a modified thin set once I get to that height if that would be better for bonding strength and reliability. The forum is always an appreciated resource. Next puzzle is why the picture posts rotated.

06-05-2019, 10:08 PM
Davey, do you put that mud-bed on from the top down? Is it a standard four or five to one mixture?

David , can you post a link to that engines installation PDF? usually they have a diagram with an angle outward from the wall and height above the fireplace so you can know how high your mantle can be above a fireplace. I can't imagine you can have a mantle above the fireplace if it's requesting CBU all the way to the ceiling. I've only installed a couple gas fireplaces. I use the metal studs up 8 or 10 in an out to the sides like they say in the instructions. usually the CBU is free-floating about 8 or 10 in above the fireplace to the metal stud.. But I have tiled mine with thinset but I use natural stone strip tile on the last one I used LFT thinset. I've never heard about not using thinset and I know I used thinset with natural natural stone before and no stones fell off in 15 years
Buts it's gas 40,000 btu

06-06-2019, 05:53 AM
Dry pack is 5 to 1 but this is wall mud. Wall mud is roughly 4 sand to 1 Portland and 1 lime, mixed with more water than deck mud. I nailed 1/2 inch thick sticks up the sides and lined up the center screed stick with the side sticks. The center ended up being about 3/4 thick because of the crooked wall.

06-06-2019, 07:30 AM
Teddy - Specs posted. I interpret as Durock with unmodified thinset suitable for high temperature use. So, is Durock + unmodified thinset appropriate setting material for porcelain tile.

MAPEI - Technical Service
06-06-2019, 08:13 AM
Hey David, hopefully this helps a bit:

Unmodified mortar wouldn't be my first choice in an area that sees large temperature fluctuations. The lack of flexibility in an unmodified mortar could come back to haunt you once that fireplace goes into service.

Instead, I would go for a rapid-setting mortar for this project. Ultraflex LFT Rapid, or Granirapid would be my two suggestions. LFT Rapid is a bit easier to get your hands on, and much less expensive, but Granirapid is the top of the line option.

If you go with a ledger-look porcelain, there will likely be grout joints, and Ultracolor Plus FA is our best grout option near a heat source.

06-06-2019, 01:47 PM
Hello Holden:

Thank you. I was not keen on use of non-modified with porcelain tile, heat issues notwithstanding. The curious part of all this is that Durock specs a temperature limit of 250 degrees F so it would seem that it would be the limiting factor rather than the setting material. Fortunately, the porcelain creates a dry-layered ledge-stone look and no grout is needed. Much appreciated.