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-   -   Stone fireplace and thinset? (https://www.johnbridge.com/vbulletin/showthread.php?t=125592)

jscozz 06-26-2018 08:45 AM

Stone fireplace and thinset?
I am getting conflicting information on this. I am installing Eldorado stone around indoor sealed combustion gas fireplace. It is being installed over 1/2" Durock. The fireplace manufacturer says no latex additives in thinset due to fireplace heat and off gassing. I was going to use Latircrete 272, but they say it needs latex additive to stick to Durock. Catch 22!

Who is right? What is the best product to use for this?

John Bridge 06-26-2018 11:49 AM

Hi Jeff,

I don't think there's a problem with latex "off-gassing," but if you're worried about it just use a very good quality non-modified mortar. :)

jscozz 06-26-2018 12:07 PM

My understanding is that Laticrete 272 is one of the best... but Laticrete customer support says it will not stick to Durock without latex added.

Is the recommendation by the fireplace manufacturer BS? I can't imagine the temperature around a sealed gas fireplace getting too hot at all... otherwise I would have other things to worry about. How are the millions of other surrounds done around gas fireplaces? Are they all done with latex modified mortar? I don't see ANY other installation spec that says UNMODIFIED thinset should be used... ONLY the verbal I was given by manufacturer. It does not even say it in their own installation guide.

cx 06-26-2018 04:04 PM

The Durock manufacturer requires a modified thinset mortar (meeting ANSI A118.4) for use in bonding to their product.

Not all modified thinset mortars are modified using latex. You might wanna check with your mortar manufacturer and be able to satisfy both requirements.

My opinion; worth price charged.

jscozz 11-23-2019 08:56 AM

Stone installation
I am finally getting around to installing stone around my sealed combustion gas fireplace. Dry stack, cultured stone veneer. I have always gotten great tile advice on here and hoping you can point me in the right direction for my first stone install. :)

I have 1/2" durock screwed to studs. I will be adding lath and scratch coat, then stone on top of that. The questions I would appreciate advice on are:

1) Planning on using 1-5/8 lath screws instead of staples, so I get through the Durock into the studs. Any problem here?
2) What is best mix to use for scratch coat?
3) What is best mix to use for stone installation? Can't have any latex modifier in it according to FP manufacturer.
4) The stone has a range of colors (Eldorado Mountain Ledge Charleston). What is best tint color to use for mortar? And should scratch coat be tinted also, or I read trick of using bag to squeeze thin line of mortar against adjoining stones when installing to cover any visible scratch coat (I hate dry stack stone installs you see where all you see is big gaps and scratch coat between).
5) I have to cut Eldorado Chiseled Edge Hearthstone, and a cut edge will be visible. I have the color kit mix for this color... will I be able to hand chisel the cut edge and make it match the factory edges? Or is that very difficult if not impossible to do?
6) The stone looks dull in boxes... may be dust from manufacture? Before installed inside, should it be washed since it is not like outdoor where you can hit it with a hose afterward.
7) Any dry stack tips in general for getting the best final look?

I really appreciate any feedback from those who have learned the lessons already... so I don't screw up my project which I will look at every day for years!

ss3964spd 11-23-2019 09:12 AM

Gotta picture of the stone, Jeff?

Guess I'm not understanding why you're planning to use lath + scratch coat when you've got cement board already installed. Is it because there will be visible gaps between the stacked stones?

jscozz 11-23-2019 09:24 AM

The gap, yes, but also because durock requires modified, FP manufacturer says no modified around FP. Since there is no grout each stone is relying only on its bond to durock.


This shows stone. But I am not using panels. I am using individual stones.

Davy 11-23-2019 11:48 AM

Have you looked at this? https://www.eldoradostone.com/resour...-cement-board/

If you have cement board up, not sure why you need the lath and scratch coat.

jscozz 11-23-2019 03:16 PM

Conflicting info on the net and manufacturer sites. Need modified for cement backer board... don't use modified around a fire place... never install stone without lath/scratch coat... no need for lath/scratch coat on durock... videos of stone installed on durock pulling off easily... etc. etc.

I would prefer NOT to use lath and scratch coat. But i would prefer MORE not to have stones falling out later. :) I was hoping someone would tell me they either install cultured stone all the time direct to durock and what they use... or the opposite... :)

Another reason is that I have an arch top fireplace, and the arch and metal standoff has to support stone also... I think the only way to do that right is with lath spanning from the metal to the durock and scratchcoat. Unless someone has other recommendations?

Davy 11-23-2019 04:36 PM

You said the 272 needs latex added. What about a modified thinset that has additives already in the thinset? Is that the same thing? What about the Laticrete mud that Eldorado Stone recommends? You might want to call the fireplace manufacturer and see what they have to say. I think most installers would go against what the fireplace manufacturer says but we aren't going to tell you to do it.

jscozz 11-28-2019 10:07 PM

I think I am leaning towards using a modified mortar. The fireplace specs say that the area immediately adjacent to the top vent can real temperatures no greater than 250 deg.

1) Any advise on the best modified product to use for stone on durock? Laticrete 255? Laticrete 254 Platinum? Laticrete MVIS Hi Bond? Mapei products? So many choices... what is the best at any cost, best bonding product for veneer stone to durock?

2) Also, any advice for spanning the durock to fireplace top metal arch joint? I can't just mortar to that... for a few accent stones around the arch I will only have half a stone on the durock and half on metal fireplace backer. Since it will be an arch, and grouted between the accent stones, may be this will be ok?


Kman 11-28-2019 10:55 PM

Jeff, you know what happens when you try to please everyone, don't you? :)

Go with the MVIS high bond, and to heck with the nay-sayers.

Davy 11-29-2019 03:09 AM

Jeff, can you post us a picture of the metal arch you're talking about? If you can fasten the Durock to the metal with sheet metal screws, I would. I usually put a mud bed over all the metal fireboxes I've tiled and I use self tapping screws to fasten my lath. If the surface is flush, I don't see why you can't do the same with the Durock.

jscozz 11-29-2019 07:56 AM

1 Attachment(s)
The durock and metal are at same depth (i know it doe snot look like it but the durock is not fully fastened yet). I could push the FP back a bit, but then stone around the perimeter will exceed metal lip and I will see mortar behind it.

Kman 11-29-2019 09:56 AM

Are you trying to cover the entire arch? What size are the stone?

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