mastic or thinset? face of fireplace mantle

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Old 08-13-12, 09:30 AM
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mastic or thinset? face of fireplace mantle

I built a custom fireplace mantle. It is made of two layers of red oak. the first, or bottom layer is the structural layer. it is screwed down into a 2x6 that runs horizontally. it is about 1" thick and in the two "wings" on the sides I drilled holes in the edge and put 6" long screws horizontally through mantle into the framing behind. then the second layer sits on top. it is secured with short screws that go into holes in the edge of first layer and up into second layer. I may put some 23 gauge nails with my pin nailer in the back. the front and side edge I intend to put a decorative tile. I tiled the front of fireplace and used thinset. but I was thinking that mastic would be better in this application. since the two layers are only about 2" total thickness, there isn't much space for the tile to bite and if there is any shifting between the layers, such as expansion from heat of fireplace, I was worried that the tile would loosen up. since this is completely dry, would mastic be better? isn't it more flexible?



 
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Old 08-13-12, 12:08 PM
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Can I ask why you want tile facing this pretty oak? Would not an oak 1x band a little wider than the mantel with the excess sticking below the mantel be appropriate. I know it is all in taste, but you know how I like wood. How do you plan on attaching the tile? Directly to the wood? Don't think it will make for a happy day.
 
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Old 08-13-12, 12:49 PM
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We kinda like the look with the tile in front:





yes, I was putting it right on wood. the bag of thinset that I used to put the tile on face of fireplace with says wood can be used, although I used hardibacker there. whoever put my old tile on kitchen floor laid it right on the plywood and it was good for the 10 years I was here till I did renovations. and the mastic I'm told is similar to construction adhesive, so that surely would stick to the wood.
 
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Old 08-13-12, 03:04 PM
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Then I would go with the mastic. Others may like the thinset, but I believe in this situation the mastic would work better. You'll have to tape each piece to keep it from slipping while it dries.
 
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Old 08-13-12, 03:10 PM
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I was leaning toward mastic as well. good point with the taping. thanks.
 
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Old 08-14-12, 12:07 PM
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There is no mastic or thin set that tells you it's good to bond ceramic tiles or stone trim pieces to sawn lumber. Plywood yes, (although a poor method), but not lumber.

Thin set for sure will not work. Ceramic tile mastic isn't much better. Construction adhesive or silicone might work best. Still the wrong thing to do, but perhaps the best choice.

Jaz
 
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Old 08-14-12, 12:54 PM
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OOh, good point Jaz. Hammerash, look into PL Advanced. It will offer a long term bond, and I believe much better than mastic. Like Jaz said, it ain't right, but it's better than the alternative.
 
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Old 08-14-12, 12:59 PM
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I have read several places that mastic is essentially construction adhesive, just that construction adhesive has consistency to use through tube, while mastic is to be spread with trowel. even the following from this site seems to support that:

Correctly Apply Mastic Adhesive | DoItYourself.com

so why is this the "wrong thing to do"? and what would be your opinion on the right way to do it?
 
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Old 08-14-12, 01:49 PM
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It's not "wrong", it is just the mastic is too thin, as you noted. The PL Advanced has more body to it and a superb holding power. Remember you are not putting tile up on a wall. You are putting single pieces along a horizontal surface hung out in infinity. Different ball game.
 
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Old 08-15-12, 01:27 PM
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do you think I can get the tile to have small gap between it and mantle that I can put grout caulk in so it matches rest of fireplace? or when using construction adhesive do you have to push the tile against the wood completely so it is almost touching? didn't know if I could put on thick, support it while dries, and leave a small gap that I can caulk? maybe take old tile and test trying to mount it with gap.
 
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Old 08-15-12, 04:22 PM
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Hammerash - I would probably rough up the wood a bit to give the mastic a better grip. I would not hesitate to use mastic in this application. It ain't rocket science and for the life of me I can't figure out what's "wrong" about it.

Bottom line - what's the worse that can happen?
 
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Old 08-15-12, 04:49 PM
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I think the mastic probably would work. but the mastic at home depot did say not for hardwood. not sure why? I can see that hardwood not as dimensionally stable as plywood, but in my application I am sure it would be fine. I didn't bother to buy any. got loctite PL supreme advanced construction adhesive and got piece of tile attached to some oak scrap with it right now. seems solid after about 3 hours. will let sit overnight and then see how strong bond is.
 
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Old 08-15-12, 04:50 PM
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Mastic shouldn't be used on dimentional lumber, its too unstable. it might last a week or two before it loses its grip or movement weakens the bond. Use the construction adhesive as mentioned, you can use round toothpicks as spacers, then caulk the joints with matching colored caulking. If i'm not mistaken, that type of tile trim has a solid back, so you could either bury the toothpicks in the adhesive, or put them on the edge, pull them out later
 
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Old 08-16-12, 06:38 PM
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I would go with a liquid nails. Every thing else requires a trowel of some sort.
 
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Old 08-17-12, 03:28 AM
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I can't figure out what's "wrong" about it.
Wayne, as with my disclaimer, it is not "wrong". There's just a better solution. As he indicated the instructions state not to use it on hardwood. I too, feel the mastic will fail once the two layers of dimensional wood destabilize against each other. Then the worst that can happen....will happen, it will fall.
 
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Old 08-17-12, 03:27 PM
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I read the instructions on a can of OmniPro mastic that I have in the garage. Hardwood is not a recommended substrate - BUT - that makes me wonder why. The only reasons I can think of doesn't have anything to do with adhesion - trust me it will stick - I think it has more to do with concerns about movement of the hardwood substrate as stated earlier in the thread. Then I started to think that maybe they were concerned about laying tile directly atop a hardwood subfloor.


Being bored and looking for an excuse not to mow the lawn I took a piece of 1X red oak out of the scrap bin and measured it. At a shop temperature of 80* F the wood measured 5.390" wide. I popped the board into the freezer at 0* F for a couple of hours, took it out and remeasured immediately. The board was 5.382". I allowed it to return to room temp and measured again. The board was 5.388". That's not a lot of movement for a delta T of >80*.

I'm not suggesting that temperature coefficient of wood is something that can be ignored. I have a house full of paneled wood doors and there is noticable movement. What I'm suggesting is that in this application I would not worry about it. Mastic is a resin based adhesive with holding power as great or better than thinset. I just don't see a mastic bedded tile popping of because ofminiscule substrate movement.

I've attached a pic of last year's tile experiment. It's two pieces of tile stuck directly to a piece of 3/4" plywood with OmniPro mastic. The chipped corners are from my failed attempts to pry the tiles off the board with a Wonder Bar. The only way that I could get the tile to budge was by driving a wedge between the tile and the board. I posted the pic today because I found the board behind my garage this spring. It had spent most of the year, including lots of rain and at least 4-5 days buried in snow, out in the elements. The bond seems to be as strong as it was when I tested it a week or so after set the tiles.

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Old 08-21-12, 10:34 AM
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I'm sure that the tile has been stuck by now or that the OP opted for a different material but just in case.

On Saturday I stuck some scrap tile to two pieces of 1X oak similar to the set up the OP has with his mantle . I didn't have any chair rail tile so I stacked three pieces of field tile to approximate the weight of chair rail. I back buttered the tiles with mastic. I held the tiles in place for 24 hours with painter's tape with the 1X oak suspended.

After 24 hours I removed the tape and left the tiles suspended until today. 72 hours later the mastic is still in a plastic state (stale bubble gum) but I could not lift the tiles from hte wood with moderate force. I then tested the adhesion with a spring scale. I applied 20# of force both centered and again at a single point on a couple of corners. There was no measurable separation of the tile from the hardwood substrate.

I am 100% confident that tile set using the method proposed by the OP would be successful.
Again, I'm not looking to pick a fight or start an argument, but I think that a negative response to a poster's plans should be substantiated by something quantifiable.
 
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Old 08-21-12, 02:28 PM
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Wayne, Not sure which post you were referring to regarding a negative response, so to clear the air, did you place two pieces of oak together in sandwich form, and then put the mastic on the edge and then attach the tile? I have seen two pieces of wood shrink/expand at different rates, causing a failure in hardened adhesive. Adhesive that doesn't harden may not be an issue. Another concern I had was the surface area being mated. It just seemed too small for mastic alone, thus the recommendation for PL.
 
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Old 08-21-12, 04:51 PM
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Larry,

I honestly didn't intend to ruffle any feathers and if I did I apologise. That was not my intent.

Everyone in the tile business thinks of mastic as having inferior adhesion qualities when in fact it compares very favorably with thinset. I read stuff here every now and then and all I can conclude is that the poster has never used the stuff.

As for the "not recommended on hardwood" caution from the mastic manufacturer consider that they simply had not bothered testing that application because they saw little need for it. More likely though they probably expected somebody to try to use it over a strip hardwood floor where it would probably fail.

In this case the OP simply wanted to stick some tile weighing probably 6-8 oz on the edge of a mantle. I would imagine that there are a dozen adhesives that would work, only one of them being mastic. You could probably get away with a quality double sided tape.

I tested a 1X6 oak board for temperature stability. It moved less than .010" in width for a delta T of 80*. I don't see why a similar piece of wood alongside would be any different. In any case I sandwiched two pieces of oak in hte same plane as the OP's mantle. I did not fasten them together in an effort to maximize the possibility of differential movement. I would imagine the OP's mantle is nailed/glued/screwed together.

The total bond surface for the tile was only 1 1/2" X 6" yet I could not pull it off by hand. When I used the fish scale to measure force I applied 20# (got nervous to pull harder). The tile did not move and yet the mastic is still soft enough that I can cut it with a utility knife. In another week I'll guarantee that the only way to get the tile off is destructively. I know that because I've tested it.

If I set tile for a living I would use thinset. Mastic has it's limitations (set up time, tile size and moisture issues (IMO over rated but I would not submerge it - I tested that too)) and it costs more. Get a small bucket of mastic and play around with it. I think it will surprise you.
 
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Old 08-21-12, 09:15 PM
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Usually these threads get locked by now. Ok, as a professional, I would never set over dimentional wood, seen too many failures. They're the first pieces to fail. theres basically 2 types of mastic..type 1 and 2. basic mastic is just for drywall certain other substrates, type 1 can be used over plywood, CBU's, cement etc, but not in wet or damp areas. Mastic can reimulsify even after it has set, then dry out, but still it is weakened. Mastic may grip better than thinset, but only on certain substrates, and it takes longer to dry, and shrinks and pulls as it is drying, thats why its never used on stone..among other resons suh as staining and "bleed thru". If the mastic says "don't install over hardwood"...then there's a reason for it ( manufacturers warranty) should be a top concern, and as a tile setter, I wouldn't want to eat a job because of it, the factory rep wouldn't rule in my favor. I've also tore up DIY projects where tile was set over hardwood, sometimes it was there for months, sometimes years. I wouldn't take the chance. I have seen some grades of mastics crystalize over the years, but the new modern mastics are always evolving their formulas. The older mastics were more akin to modern day construction adhesives..flamable, solvent based. Mastics now vary in quality more so than ever..but..some are real garbage. So why take the chance?
 
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Old 08-22-12, 12:22 AM
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Wow, I didn't know about all these other responses. I didn't get an email notice of them. anyhow,after my last post I set my tile using loctite PL fast grap premium construction adhesive. I put a small board under the mantle and using clamps to hold it in place, then used 1/8" spacers I had and embedded them in four corners of each tile, then laid tile and supported it on the white wood and taped in place:





I let them dry 2 days and then removed everything and used grout caulk. here are some photos of finished product:













I think it looks real good and more importantly so does wife! Thanks for all the help. Wayne, I like your style. I don't always believe manufacturer either. sometimes they do things just to cover their own A**. I think they are just tryin to keep people from laying over hardwood floor as you suggested. In my setup with the bottom board layed flat on 2x6 and then screwed horizontally through the "ears" into wall and two boards attached to each other by screw about every 8" apart, I doubt any significant movement and the mastic likely would have been fine. But I had already tested and bought the construction adhesive and went that route. Everyone, thanks all for the help.
 
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