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Unread 06-25-2021, 09:46 AM   #1
victorhall
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Question on thinset for large format tile on fireplace

Hello,
We're about to install two large format tiles on a fireplace and would appreciate a recommendation on what thinset to use. These are 1/2" thick porcelain pieces that are marble-look alike. Each piece is about 7' tall and 3' wide, with a cutout for the fireplace insert in the middle. The looks is "bookmatching" the marble, like it's been split open.

Our stone/tile guy suggested using a silicone adhesive ("black mamba" or "X350,") but I'm convinced that we should use a thinset vs. a silicone. Just seems like a construction adhesive is a massive shortcut. He's being patient with me, and says we can use an LFT thinset.

Your advice would be greatly appreciated! I'm also trying to get ahold of Mapei and will gladly report back for posterity

Thanks in advance!
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Unread 06-25-2021, 11:27 AM   #2
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Welcome back, Vic.

It would help a lot to know what substrate you're bonding these panels to.

This is a wood-burning fireplace?
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Unread 06-25-2021, 11:37 AM   #3
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Thanks CX!
Bonding to 1/2" durock on steel studs (16ga).

The fireplace is a mendota gas insert in a former wood-burning chimney. They can put out some heat, but are enclosed and vent through stainless liners, so they stay "clean" around the fireplace opening.
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Unread 06-25-2021, 11:43 AM   #4
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Here are pics of the project, with the tile "dry-fitted" for now.
Mapei offered initial advice on the phone to use a rapid set mortar due to the heat (possibly Granirapid?), but are going to follow up with an e-mail.
Attached Images
  
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Unread 06-25-2021, 12:42 PM   #5
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Manufacturer of those panels doesn't give any guidance on their installation?

Not sure just why a rapid setting thinset mortar would have anything to do with the heat consideration, but perhaps I'll learn something new when you post what they tell you in writing.

I would caution that using a rapid-set mortar with pieces that size could be very, very tricky.

My opinion; worth price charged.
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Unread 06-25-2021, 01:04 PM   #6
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Thanks again CX!

Mapei was GREAT about getting back to me. There's some good stuff in their literature about tiling near heat below. I am concerned about the short pot life...

Here's Mapei's response:
Attached is a Document for Tiling Near Heat: https://cdnmedia.mapei.com/docs/libr...rsn=2dc7d40c_4

All the Tile Mortars recommended are Rapid Setting Mortars.

I recommend using any of the top 4 Mortars listed for installing large Tile or Slabs.
- Granirapid System
- Ultraflex Rapid
- Mapei Ultralite S 1 Quick
- Ultraflex LFT Rapid

I checked on the pot life, the time it will last in the bucket and its 30 minutes.

Open time is the amount of time that you must install the tile onto the mortar, and it is 10 to 20 minutes.

This is for Rapid Setting Mortars.

I recommend following the Industry Standard per the TCNA (Tile Council of North America) for the installation of the tile or slab.

First Key in or Burn in the Mortar to the substrate using a flat trowel or the flat side of a trowel.

Spread the Mortar in one direction only using the recommend minimum ½” square Notched Trowel.

Back butter tile back side of the tile or slab with Mortar.

Also, there may be another recommendation for large slabs.
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Unread 06-25-2021, 04:04 PM   #7
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Vic....as CX pointed out, no idea why a rapid set morter is any advantage here. You aren't running a race, eh? Frankly, I would entertain a morter like Versabond LFT or the Mapai Ultraflex 1 or 2. Pot life is better. 4XLT is also good.
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Unread 06-25-2021, 05:52 PM   #8
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I wouldn’t use a rapid set mortar and I do a fair amount of panels. We use Customs Pro-Lite or Mega-Lite depending on what is available. If you haven’t yet you need to prime the back of the panels.
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Unread 06-25-2021, 08:12 PM   #9
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Why would he need to prime the back of the porcelain panels, Jeff? Not familiar with that requirement.

Vic, I'm still confused about MAPEI's recommendations. While I understand the difference between the use of calcium aluminate in lieu of some or all the Portland cement in their rapid set mortars and how that could affect hot material installations, I don't still don't see the advantage in your application. And I see some very significant disadvantage in using a rapid-set mortar for setting those large panels.

Perhaps I'm still missing something.

My opinion; worth price charged.
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Unread 06-26-2021, 06:40 AM   #10
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Thanks all. I am really appreciating the discussion on this.

Is there a calcium aluminate option that doesn't have such a short pot life, or does that go hand in hand with rapid set?

These panels will see temps potentially up to 350.
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Unread 06-26-2021, 07:11 AM   #11
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Question

Just about all the panel manufacturers have this in there tech guides. The back of the panels are quite smooth so using eco-prime grip or similar give it something to bite to.

If your expectation is the panels will get that hot I would have reservations about that. Some panel manufacturers have Rapid set mortars in their tech guides and I suspect that’s why the Mapei rep suggested it, not so much because of the heat.

If for some reason the thinset kicks quicker or it takes you longer then you anticipate to spread the piece and the wall and get it installed you will be in a bad spot. Once you get it up you need time to adjust and beat in.
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Unread 06-26-2021, 09:15 AM   #12
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Jeff, I don't have a copy of the new ANSI A137.3/A108.19, Standard Specifications for Gauged Porcelain Tile and Gauged Porcelain Tile Panels/Slabs, because I'm never gonna install any myself and we don't get a lot of questions here on the forums for such installation. And because last time I looked it was available only in digital format and cost 75 bucks. I'm hoping some benevolent manufacturer will send me a paper copy if ever such is printed.

That said, as described by the OP, these would not fit into that category anyway at 1/2" thick and I've no real idea what the back of the panels might look like. But even at that, when we (TYW) attended a training session for installation of such Gauged Porcelain Panels (still referred to as thin porcelain panels then), at the facility of a manufacturer of such products, no mention was made of the use of any sort of bonding agent painted on the panels prior to applying thinset mortar.

We were using MAPEI mortars at that training session, under the watchful eye of their head technical services guy (and a member here). The subject of hot area installation never came up, nor did the use of any rapid-set mortars. My concern about the rapid-set mortars comes from that very training where it would take an absolute minimum of three, and preferably four trained/experienced tile mechanics to get those big panels and the wall covered in mortar and successfully installed with anything close to the commonly required 80 percent coverage.

Perhaps all that's changed? Perhaps a bonding agent is now called for in A108.19? I dunno, but these panels the OP has, at a half-inch thick, don't sound like they'd fall into that gauged category in any case. Hell, gonna take four guys just to lift those things.

You have a copy of A137.3/A108.19 at hand?

My opinion; worth price charged.
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Unread 06-26-2021, 05:34 PM   #13
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Hey cx, my ANSI book is several years old, I get them for free normally from a distributor but Covid monkeyed that up. That said there isn't anything from ANSI that I know stating that it is required. Manufacturer's however do suggest the step.

The classes I have been to never said a peep about using it either but that was 5+ years ago. I've personally never seen a bond failure but have friend who has redone more than a few because of it. It certainly could have been installer malpractice, they weren't all the same installer so that gives pause to me anyway.

After talking to several manufacturers at Coverings that was enough for me to start adding it into practice. It is on all of the materials I have used up to this point.

Page 7 below

https://cdn1.neolith.com/wp-content/...mentado-EN.pdf

Page 29
https://www.inalco.es/en/archivos/gu...06-2021-en.pdf

and so on.


You'll start seeing posts like this become more prevalent as time goes on, it's slowly creeping into mainstream. It's become more popular for countertops so bathrooms, fireplaces etc will follow suit.
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Unread 06-27-2021, 08:45 AM   #14
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I had a gas fireplace installed recently, and i planned to install a surround of 3/4" marble slabs onto Hardibacker. The fireplace manufacturer recommended an unmodified thinset. I explained it to a Latacrete rep and he recommended Latacrete 317, so that's what I used.
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Unread 09-20-2021, 01:52 PM   #15
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Sorry for the delay, but wanted to close the loop on this post for possible future reference. After a ton of research, I ended up using Mapei Ultralite S1 Quick for this project.

Install went Ok, but was stressful, since I used the granite guys that bought the stones. Nothing against countertop guys, but they were not tile experts and it showed in my discussions with them. They did have a slick vacuum tool to bring the stones together. But I can see why this type of project calls for skilled tile installers. It could have gone very sideways. Unfortunately, finding true craftsmen, especially in my area, is very challenging. I did a test run with the thinset to get a feel for how long I really would have to work. I mixed enough for one stone at a time, and we got each one up in about 10 minutes after mixing, using three guys to trowel thinset onto the wall and stone.

Attached are pics of my "test" rig and of the final result.
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