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Unread 04-25-2020, 11:37 AM   #16
SWB04
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Yep, this ledger stone is slate, brown, grays, and blacks. I mistakenly used white ("hey it's white; it must be better thinset!!" ... duh) in a similar job. I ended up having to stain all the white mortar that squeezed through, a job which I'm not doing again. This time, it's gonna be gray or bust.

I don't know how much these 24" sections weigh, but they are heavy. (Really crappy stuff, too, 25%+ damage thus far due to poor packing and handing, but ya get what you pay for and I paid about $2.30 a sq ft.) I already have Versabond LFT, but I'd like to fight gravity a bit less. I'll be supporting the stone with a 2x4 over the opening of the fireplace, and all that. However, since you're a pro, you probably know this stuff isn't exactly square. I'll have to tweak each piece in each row, as well as break some of the pre-glued sections apart so that I can add some individual, small stone piece fittings, so the staggered pattern isn't so obvious. Bottom line: I don't want to make an adjustment, only to find out after it's dried that it slipped a half inch, and I have a 3/4 gap in the rock.

I'm just trying to get the right mortar for this job. I "half-a**" enough stuff in my life.
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Unread 04-25-2020, 11:53 AM   #17
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Yes, those won't be exactly square and even if you have no thinset between the stones, you'll still be able to see white thinset. Like I've said, I've never used the Ardex but I wouldn't count on any non sag thinset to hold thick, heavy tiles up without a little sagging. Even 1/8 inch sagging would be bad for you. I would support them somehow. Drive a nail under each end to temporarily hold them across the top of the firebox and under the stones that extend out past the box. To do each leg, I'd measure down from those extended tiles to the floor, figure out the size cut I need at the floor and start there. Work my way up.

I would get a small bag of plastic wedges. I know you're wanting a tight (or no) joint but since they are crooked and out of square, you might need to raise one end of a tile a little to keep them straight. Unless you trim each piece to fit, it's about impossible to butt joints if the tiles aren't cut the same size and square.
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Unread 04-25-2020, 03:33 PM   #18
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Thanks for the tips, Davy.

We're pretty much in sync on this. I may change my mind once I have the substrate set up, but my current intent is just start middle up, i.e. run a 2x4 across the middle just above the fireplace door where I want the stone to start, and use it as a temporary ledger/story board. When I've completed the top half, I'll move the 2x4 down 6" to 12", and work one or two rows at a time, until I reach the hearth, and custom cut the last row. That should keep the rows on both sides of the lower fireplace surround even, and hopefully (!!!), keep me from ending up with a gap between two rows.

No matter what mortar I use, I'm definitely going to cheat on the stiff side. 1/2" horizontal trowel pattern on CBU, burn the back of each section of rock, set and twist. (Hey, the guys on the video's make it look just that easy! ) When I did my last ledgerstone project, I had a smaller, 12" x 6" sections, and I back buttered too much mortar (literally "floated" that rock). The result was well secured rock, and an excessive ... mess. This time, I'm going to just burn enough mortar on the back each stone to fill in any gaps.

The project is simpler than I make it out to be, probably 2-3 days including structure and prep for a trade, and 2 weeks, for me.
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Unread 04-25-2020, 04:49 PM   #19
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I'd use a 1x4 or 1x6 to set the tiles on. Cut a couple legs out of anything to support the 1x6 down to the floor. MDF makes a good ledger board. You want the board to be very straight and 2x4's are rarely that.
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Unread 04-26-2020, 08:04 AM   #20
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I'm not experienced enough to trust any "non-sag" mortar, especially with heavy tile. The little bit of time necessary to build and employ a ledger seems like time well spent given the ramifications. And if you do that any decent mortar will do the job. Gray Versabond, or Versabond LFT is all you'll need.
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Unread 04-26-2020, 09:52 AM   #21
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To me it's well worth the time. Another thing, if you're installing cut tiles that have been thru the wet saw, a non sag thinset may somewhat hold dry tiles and not tiles that are wet. Even if you wipe the water off with a rag, it has absorbed water and may slide a little. It takes time to constantly be checking the installed tiles to make sure they haven't slid a little.
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Unread 05-03-2020, 07:20 PM   #22
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Framing/CBU Preparation

Ignore - questions are a waste of time. I've got it figured out.
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Unread 05-05-2020, 04:38 PM   #23
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Glue for CBU to metal

So, I've done a bunch of things that may not have shown in the last picture, including sealing the back exhaust, adding overhead insulation, adding a 10" high insulation board above the fireplace, and rebuilding that frame so that it's plumb, true, and stronger. Since then I've added some insulation blocking, a 1/2" skin of plywood, and I'm about ready for adding the concrete board.

I've decided to overlap 1/2" CBU (wonderboard lite) 1" on the sides, and 8" to 9" over that top of the fireplace face (which is 10" tall). As Dan suggested earlier, I'll use a single 3' x 5' piece to cover the top of the fireplace face, which will reach over to midway past either one of the vertical 2x8", i.e. plenty of structural support, and will use 2 1/4" screws to go through the CBU and plywood all the way to the studs.

Which brings me back to how to best secure the CBU to the face of the fireplace. Can't pierce it with screws, so it'll have to be some sort of glue. I thought about just using a thin coat of the Ardex x77 (i.e. since it's a sticky polymer mortar), and wrote them to ask about it. They said Ardex has only been tested to 140F, and advised against it.

I also bought a tube of Rutland 500°F RTV High Heat Silicone, which I ended up using to seal the rear exhaust pan/standoff. It's sticky stuff (OMG, working over the top of that fireplace and behind with only 6" clearance, it got all over everything, plus me to. It does seal and it does stick, but it pealed off steel surfaces too easily to give me confidence in that product for this purpose.

I just picked a tube of Locktite PL 3x to use for securing both the plywood to the studs and to reinforce the bond of CBU to the frame. I've used it before, and it's pretty durable stuff. After reading it's specs, I think I'm going to use this to secure the CBU to the metal face.
  • It's listed as non-flammable after cure
  • Short term service temperature is 250F
  • Long term service temperature is 160F
  • Very high compression shear strength

FYI, here's the technical data sheet.
https://dm.henkel-dam.com/is/content...-2015-05-22pdf

While it's not a perfect solution, I don't see the area immediately around this unit face getting higher than 250F ever, nor 160F on a continuous basis (if for no other reason, than it'd be a pretty significant burn risk should someone lean or fall against it). That plus the CBU screws should provide a stable bonding surface.

In reference to Dan's earlier comment: "You'll still need to figure out how to hide the edges of the CBU." Yeah, I do. My fallback position will be to just fill in with a bead of mortar (I've seen many fireplace door openings finished that way). I might be able to create corners for the inside of the door and at the edges of the surround, but that area above the opening would still be a problem. I'll play with it when dry fitting stone and see what looks good.

Finally, the project prep took me about 10 days longer than planned, I've just had eye surgery and can't lift anything for a week, my wife is suddenly having heart surgery tomorrow, and oh-by-the-way, the slate I intended to use for the hearth that has been available everywhere, is today available nowhere. When I found out that even the distributors had to special order it, I just ordered sight-unseen 16" square pieces from Lowes, which will take a couple of weeks to arrive. I planned out everything, except the slate for the hearth.

Aside from the medical issues, I can't start until the slate for the hearth material arrives. I need to build the new hearth to fit the slate hearth exactly, with maybe 1/4" overhang. My hearth target size was looking 18" by 66". I ordered 5 tiles, i.e. 1 extra as a precaution. If all 5 are good looking and unbroken, I'll have an extra and could cut one up four ways to add depth (i.e. finished size anywhere from 16" D x 64" W, to 20" D x 64").

So, there's no hurry, and I appreciate any advice. I was trying to get it all wrapped up by last weekend, but at this point, it's gonna take me a while to complete this project. It'd probably be a 3 days project for a pro.
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Unread 05-06-2020, 07:35 AM   #24
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I'd still be a little leery of any gunned adhesive, Scott.

The slate I installed around my wood burning masonry FP does, eventually, get quite warm, and I'd expect the metal surround of yours to do so also, but much quicker, since there's nothing acting as a heat sink.

You don't need the adhesive for strength or support, you only need it to keep the bottom of the CBU from flexing. If the CBU is hard against the metal then it's a non issue. If it isn't I'd use something non-combustible, with less potential off-gassing (especially when exposed to heat), like thinset mortar.

Not sure I understand where you have the plywood, but I assume it isn't draping over the metal.

For hiding the exposed edges you might consider having some granite or other stone fabricated in perhaps a contrasting color to your tile. Maybe 1X2X the lengths that you need for the two sides and top.

Hope you eye heals quickly. Thoughts, and crossed fingers that Mrs. Scott's surgery goes well with no issues!
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Unread 05-08-2020, 08:36 PM   #25
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For context. This is the target product for installation, i.e. ledgerstone..

MSI Natural Earth Ledger Panel 6 in. x 24 in. Natural Slate Wall Tile

It's a Ledger stone, not a tile. Due to the high breakage rate discovered thus far, and fact that Home Depot is out-of-stock on this product, it's only about a 50%/50% likelihood I'll use this stone. Also, the actual stone shipped came in as about 80% gray slate, i.e. nothing like the pictures. When I can lift again on Monday, I'll sort and grade to figure out if i have enough product. H.D. said that they'd reorder box(es) to replace the broken panels, however, they are "out of stock" probably permanently (since MSI no longer lists this product on their web site). If I don't use this, I'll use a similar color & style (e.g. "California gold", "gold rush", etc.). Trying to contain costs, and this stuff was dirt cheap, so I'm willing to put in a bit of extra installation work to offset the breakage.

I can't think of any sort of conventional pencil trim that would fit with this product. The best I could do would be to heat and break up the slate, and use the slate pieces themselves around the edge as trim. It's something that I'm considering, and may play around with when I'm dry fitting the stone. (Heck, I'll have plenty of broken, scrap pieces to work with.)

Also for context, (re: your comment about the plywood) this is the state of the project thus far (see attached picture).

It's skinned in with plywood and ready for CBU. The plywood on the sides is gaped by the same distance as the stand-off's behind the plywood, so it's in compliance with the manufacturer's requirements.

The piece of CBU that I'm installed in place of the original gypsum insulation board terminates into studs at the top of the board, and into two brackets below. It's not solid in a way that would take on structural weight, as a stud would, but should be strong enough to support a piece of 1/2 Wonderboard spread over the entire plywood substrate (see blue ink), and anchored into the studs.. That area above the top of the fireplace opening, i.e. the metal appliance plus the insulation CBU/board is about 18" high (i.e. 10" steel, 6" original insulation board, and I added a couple of inches so that it would reach the blocking stud above it). That's a lot of that 3'x5' sheet of CBU that is unsupported and unattached to the substrate beneath the CBU. It helps that there are 2"x8"'s on either side of this area that the sheet will be attached to. However, I'm just not comfortable trusting all that weight without some sort of adhesion underneath this approximately 40" x 18" area.

And yeah, I am also leery about gunned adhesive (which is why I've written so much on this thread). There's no mention of gassing after the Loctite adhesive has cured. I think I'll use the Loctite over that top piece of CBU and onto the steel about 5", and then use the Rutland high temp (500F) adhesive on the lower 4" of the top metal fireplace face (leaving at least a 1" margin of black steel at top and sides. The combination should ensure adequate adhesion, yet protect the area nearest the top of the fireplace from heat damage. I don't think the face of this direct vent sealed fireplace gets anywhere near as hot as a masonry wood burning fireplace. The heat is mostly contained inside the appliance, and vented through the top via blowers.

My eye surgery went OK, but it's a nuisance for sure. My wife's heart surgery went well, thank God. Thanks for your kind comments. We're blessed, for sure.

Things are looking up. My slate will be in Tuesday, about 10 days earlier than H.D. originally predicted. So, I'll install the CBU on Monday, and hopefully, we'll be off to the races on Tuesday (i.e. building out the hearth, clean and seal the stone, and then start on the installation).

Pix of the end product to follow.
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Unread 05-10-2020, 04:08 PM   #26
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"I don't think the face of this direct vent sealed fireplace gets anywhere near as hot as a masonry wood burning fireplace. The heat is mostly contained inside the appliance, and vented through the top via blowers." - OP - from last post

After thinking about my statement, I had the brilliant idea, "why not test the theory". I turned on the fireplace, waited until it was good and hot, and then got out my infrared heat gun thermometer, and ....

Temps registered 120F to 180F, as high as 10" over the top of the fireplace. That thing DOES get hot.

I'm still fine with the Locktite PL 3x between the plywood and CBU, as the flashpoint is 250F, and "long term" (service temp) is 160F. As I mentioned in the last post, I'm just going to avoid using it closer than 3-4" to the fireplace opening; I'll use the 500F rated silicone for that.

Still have a question about using polymer modified mortars on the face of this fireplace, to adhere the ledger stone to the CBU. Ardex flat out said that their x77 is rated to 140F max. My (Construction engineer) son mentioned that high heat might "sweat" the polymer out of that mortar over time. He has a good point about that. I sent a question to Custom Building Products asking about what product they recommend for this type of installation.

If I can't get an authoritative answer, I may just use the Ardex for 85% of the fireplace surround, and use plain, unmodified thinset around the last 15%, i.e. the area within 4-5" of the side opening, and 10" of the top opening of the fireplace. It may take time, i.e. allowing each row using the unmodified thinset to fully set and cure, before moving on, but it seems like the surest solution at this point.

It's times like this that I really appreciate the true experts in this business. Any basic trade job looks simple. It's just that 80% of the time, there's no such thing as a basic, or "standard" job, and knowing how to handle the variations separates that amateurs from the pros.
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Unread 05-10-2020, 04:30 PM   #27
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Wonderboard Lite contains EPS, expanded polystyrene. I'm not sure it is really rated for getting that warm. You might want to consider a cbu that is essentially just cement and aggregates. Before using it for this application, I'd contact the manufacturer. https://images.homedepot-static.com/...a503d032f0.pdf
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Unread 05-10-2020, 08:33 PM   #28
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Thanks Jim for your response.

I had differing feedback on that product, so I did run this up the Custom Building Products support "flagpole" to get their input tomorrow. I had been planning on picking up Durock; don't know why I did not (maybe H.D. didn't have it in stock). Didn't want to use Hardie for this purpose, as it's a composite (little or no concrete). The Wonderboard maybe going back.
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Unread 05-11-2020, 02:05 PM   #29
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Tiling near heat sources

That's the title of this Mapei technical note:
Tiling near heat sources

I've discussed my project in depth on the following thread, but just want to focus on mortar for this post:
https://www.johnbridge.com/vbulletin...d.php?t=129100

Ardex says that their x77 product taps out at 140F.
I'm measured 120F to 180F on the face of my direct vent gas fireplace appliance, so Ardex, while good for my purpose (stone on vertical fireplace surround & wall), it's a no go close to the (sealed) fireplace opening.

Talked to Custom Building Products this morning, and they said that Prolite is the preferred solution, but I can't get that anywhere nearby in gray. They said that VersaBond LFT would also be good to 250F, but that it sags on vertical applications (which is why it's labeled "for flooring").

That Mapei reference seems to indicate any of their products with calcium aluminates would work:

- Granirapid® System
- Ultraflex™ RS
- MAPEI Ultralite™ S1 Quick
- Ultraflex™ LFT ™ Rapid
- Ultracolor® Plus FA – only use for grout joints 1/16" to 3/4" (1,5 to 19 mm)
- Mapesil ™ T

(Note: I have no experience with these products.)

My question: What do the experienced pro's here think about using Ardex for the surround, except within 10" of the top, or 2" of the metal sides of the fireplace face (i.e. the hot areas that could exceed 140F), and use just plain unmodified thinset over that fireplace bridge and the 2" sides. I would keep the thinset relatively stiff, and let those areas dry before building stone above them. Subsurface is all CBU (at this point, probably Durock).

I know standard thinset could handle the heat (i.e. it's just portland cement and sand), but will the Ledger-stone panels set vertically on the fireplace near the door with only thinset, pop off in the future?

I'm going to research the Mapei products, but it just seems like keeping this simple is a better route to go, i.e. Ardex for most of the wall, and just standard thinset around the heat source.

Thanks.

Edit: Ok, so I re-read my own post and it answers itself. I can use the Versabond around the hot areas of the fireplace, the Ardex x77 for everything else, and all that extra polymer modified mortar that I'm not really gonna need; I guess I'll use it outside to repair all the spalling that my outdoor concrete picked up last winter.
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Unread 05-12-2020, 05:49 AM   #30
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a little late in the game, but you know you can just add concrete pigment to the white thinset mortar and get the exact color you want. Pigment is pretty cheap. I would use powdered.
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