Is mastic out of favor?

A few years ago some of the plumbing had to be replaced in the bathroom of the house I grew up in, and part of this was to remove some mosaic tiles that were put down about 1974 using a mastic. Man, getting those babies up was a great deal of hard work, and now that ceramic tile has entered a project of my own, I find everyone pushing thinset. Is it really better? If there were a bit of floor flex, wouldn't a plastic mastic tend not to crack as much as a thinset cement? And with a bit of mastic coming up between the tiles, wouldn't it keep water from the plywood (yes, right on the plwood!), rather than continuing to suck it down as a cement would after going through the grout? Now the floor was 3/4" diagonal T&G with 5/8" plywood, so perhaps flexing wasn't all that much a problem (I've forgotten the exact joist spacing & depth, but 2x10 16" OC seems to stick). Still, with all the effort needed to remove these tiles, why's everybody now down on plastic mastic?
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snipped-for-privacy@hotmail.com ( snipped-for-privacy@hotmail.com) said...

I prefer thinset on a concrete-like surface. That includes concrete floors, wood floors with a mortar base preparation, and concrete tile backer board.
For applying tiles on a drywall surface, I prefer mastic. The only exception to this is when applying a tile "base board", I will usually use thinset since I am already using it for the floor.
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snipped-for-privacy@remove.daxack.ca.invalid (Calvin Henry-Cotnam) writes: | snipped-for-privacy@hotmail.com ( snipped-for-privacy@hotmail.com) said... | > | >A few years ago some of the plumbing had to be replaced in the bathroom | >of the house I grew up in, and part of this was to remove some mosaic | >tiles that were put down about 1974 using a mastic. Man, getting those | >babies up was a great deal of hard work, and now that ceramic tile has | >entered a project of my own, I find everyone pushing thinset. Is it | >really better? | | I prefer thinset on a concrete-like surface. That includes concrete floors, | wood floors with a mortar base preparation, and concrete tile backer board. | | For applying tiles on a drywall surface, I prefer mastic. The only exception | to this is when applying a tile "base board", I will usually use thinset | since I am already using it for the floor.
How does the thickness of the layer of thinset compare to that of mastic?
I'm doing some repair work where eventually the edges of the repair have to line up with the existing tiles. The existing tiles are attached to a plaster wall with mastic. I can set my backerboard at whatever depth I want, but obviously it would be nice if the surface could line up with the plaster.
It's been suggested that I use thinset rather than mastic because this is a tub surround/shower, but if the thickness of a layer of thinset is different from that of mastic I think I'll be making my life much more difficult by using thinset.
A related question: assuming I have a choice, is it better to make the transition from old work to new in the middle of a tile or at a joint?
                Dan Lanciani                 ddl@danlan.*com
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I have read that mastic is not to be used where there is significant water presense.
Bob
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With a sufficiently flexible floor, it doesn't matter what adhesive you use, you'll be cracking the grout and even the tiles.
With 5/8" ply over 3/4" T&G, flex isn't going to be much of a problem.
However, modern tile installation uses a special plastic underlayment that permits the _entire_ sheet of tile to float - much like centuries ago where they floated the mosaic tile on an adhesive, over a layer of sand. So not even expansion/ contraction of the subfloor will bother it.
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Chris Lewis, Una confibula non set est
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Thinset in water areas are the way to go. Mastic works nice when you work from the middle and go down. I found that with a thinset applied the tiles will start sliding down the wall.
There ARE certain mastics that are waterproof, but a nice thinset (if using the home depot stuff use the flexbond) worked great for me.
Use the regular mastic on walls that arent going to get water on it.
snipped-for-privacy@hotmail.com wrote:

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I don't know what the deal is on mastic. I used mastic (a good $$ grade from a real tile supply house) directly on plywood, and not a thing has budged in 23 years. This is a rental unit that's had over a dozen tenants. Also used in in the bath area, but a black seal coat was put down first. Also, no defects. Same groat, no maintenance at all.
I wonder sometime if the cement board thing is mostly marketing.
Bill

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Your experience is more like mine with this bathroom floor. Perhaps mastic formulations have changed since 1970 or so. This stuff holding those mosaics on the floor was quite hard, and appervious to any water treatment.
Oh well.
bill allemann wrote:

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