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Old 08-02-2019, 12:39 PM   #1
rkymtn_consultant
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Mastic? Is it really that bad?

Hi everyone, I've been lurking around these forums for years but this is the first time I've posted. I'm a home inspector and construction consultant from Lakewood, CO (just outside of Denver). I've formally worked as a remodel contractor and project manager.

First I'll start off with a little background to my question, feel free to skip down a few paragraphs for the TLDR version.

Recently, one of my clients who is building a new home in a remote location had one of their bathrooms tiled with Custom Building Products Omnigrip because they wanted the bathroom finished by the time the well/septic was in as to have a functional bathroom on site. There was no source of water except for a small portable cistern, hence the use of Omnigrip (and disposable tools).

Anyhow, the tile setter, who is actually also the plumber, wasn't excited about using mastic until he was using mastic and then said it was "great". Apparently, he had never used it before. The tile went in really fast and the finished product looks amazing. He finished before the well was in, but wanted the well in before grouting, so it ended up being almost 2 weeks before the bathroom was grouted with Kerapoxy, which was partially chosen because this bathroom will be used by the construction crew for the remainder of the build and we wanted to keep the chance of staining low. A second consideration was preventing moisture from getting to the mastic after the grout was in. When it was finished I asked him how he felt about the longevity of the work and he said he didn't "see how it was going anywhere".

I'm currently remodeling our master bath. I will use Custom Building Products Prolite on the shower walls (no shower floor, there is a tub). The floor is already in and set in thinset. For the remainder of the walls, which is about 250 square feet of 3x10 ceramic tile going from floor to ceiling, is a "high quality" mastic really that bad?

If I set in a high-quality mastic (is that an oxymoron?) and epoxy grout is the longevity of the tile job really going to be less than if traditional thinset were used? People make it sound like tiles are going to fall off the walls in a year. I've never used the stuff and always been on the "it's crap for noob DIYers" bandwagon, but since I've never used it I don't know if that is substantiated.

The only reason I'm even considering this is because I have a pregnant wife who has zero energy (meaning I'm picking up the slack on a bunch of domestic chores), a 5-year-old with more energy than the Energizer bunny (meaning I'm chasing her around constantly and constantly having to stop what I'm doing to "come'n'see", or whatever) and I'm about to start trying to squeeze in tiling my bath on weekends and evenings. I'm not too lazy to mix thinset, but the mixing time and cleanup time eat into the time I have to set tile.

If mastic is really that bad, does anyone have any time-saving suggestions? Is epoxy mortar any quicker?

Sorry for the wordy post and thanks in advance for your help with this!
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Old 08-02-2019, 01:25 PM   #2
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how big were the tiles? the product literature states it is specifically for small format tile:
Ideal for small format for ceramic, mosaic, quarry, pavers,
gauged slate, porcelain and gauged stone tile installations on walls,
floors or countertops. Recommended for tile up to 12" (30.5 cm) on
any side. Can be used with tile up to 15" (38.1 cm) on any side but dry
time significantly increases. For tile with any side greater than 15"
(38.1 cm) CUSTOM recommends using a polymer modified cement
mortar specifically for large format tile.

It also states the following:
Recommended for interior use only. Do not use for steam rooms,
shower floors or underwater. For those installations, use CUSTOM®
Polymer-Modified Mortar Systems.

I think mastic is garbage for anything other than a backsplash in a non-wet room. BUT, there are some manufacturer reps that claim SOME of the products can be used for much more.
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Old 08-02-2019, 02:24 PM   #3
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Hi Mike, thanks for the reply. I did take a look at the product literature and it should work based on what they state since the tiles are 3"x10". I've always said mastic is garbage as well, but my only experience is tearing it out, so, what do I actually know?

This application is interior use, not in a steam room, and not on a shower floor nor underwater. Is there a chance this stuff has become much better over the years due to all of the dismissals from the pros but still gets a bad rap based on its prior bad acts. I mean, they actually claim that you can use it on shower walls! I wouldn't, however, that seems INSANE!

Another thing that had me thinking about using mastic was a visit to my parents' house which has an original 1951 bathroom with plastic tiles (yuck) set in mastic that are mostly still intact with the exception of the ones that my dad peeled off the wall recently to see how stuck they are. The few he tried to peel off broke into pieces, so It's holding pretty well. Somehow they held up for 68 years, which is a shame because they look AWFUL!.
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Old 08-02-2019, 02:27 PM   #4
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Just realized you said were, so you probably meant my client's bathroom. They were 3 x 6 laid in a running bond pattern. They did the tub surround, the wall behind the toilet and above/beside the vanity to about 4'.
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Old 08-02-2019, 03:04 PM   #5
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What will you be setting the tiles over? Is it just cement board, or is there waterproofing involved?
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Old 08-02-2019, 03:25 PM   #6
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The substrate is Custom Building Products Wonderboard. All seams already have the sandwich of thinset/tape/thinset in place. After mudding the seams I went around the room with a straightedge and floated out the walls where needed to make sure everything is dead flat and plumb. If I use tile adhesive I'll probably double-check that since it can't be corrected with mastic the same way you could with thinset. There is no waterproofing in place in the areas I am considering using mastic on. As I mentioned, I'll still use thinset on the tub surround, which does have RedGard on it.
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Old 08-02-2019, 06:52 PM   #7
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I've carried water to the job from home several times in the past. A couple clean trash cans half full with lids will carry plenty water. Just depends on how bad a guy wants to work.

The mastic from the 50's and 60's was not water soluble (the stuff I remember wasn't) and would stick to about anything it touched. I remember dad bringing gasoline for scrubbing his tools.

Most of the mastic showers I've replaced had mold behind the tiles. But, many of those were on greenboard. I would use thinset, it does breathe better.
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Old 08-02-2019, 08:05 PM   #8
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I was going to say "absolutely do not use mastic over waterproofing". But it is acceptable over bare concrete board on shower walls, although not the shower floor.

But thinset mortar is so much better than mastic. I'd never use it in a shower, even though the manufacturer of some of them claim it will work.

I've also hauled water to the job site many times. Most days I could do just fine with 20-25 gallons of water, and that includes water for a wet saw.
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Old 08-02-2019, 08:28 PM   #9
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Davy, thanks for your reply. Btw, I checked out your site; nice work!

Since my post was wordy I thought I'd clarify in case I made it difficult to tell I was talking about 2 different jobs. One is already done. The current project is in my home and the only reason I'm considering mastic on the walls (and only the walls, not the tub surround) is for time savings.

Again, the reason I'm thinking mastic is that I can squeeze in 20-minute increments of tiling here and there and get a lot more done than if I had to wait for 1 hour+ periods of time when I know I won't be disturbed. I know it isn't as good.

I did call CBP today and the tech there said the application I have suits the product but he'd wait several days if not longer to grout citing that the mastic needs to dry. He stated the adhesive is strong enough to outlast the project and also said the shear strength once set would exceed 1500 lbs per tile. Seems good enough, and if I use epoxy grout it seems like it'd stay dry. I've got a few other projects going, I'm ok waiting a couple of weeks after setting the tile to grout.

Given that most don't like mastic, my only other alternative is throwing out thinset that I don't have time to finish with. What's the consensus on using cheap unmodified thinset and cheap trowels? Home Depot near me has CBP CustomBlend for ~$6/bag and 1/4 x 3/8 square notch trowels for ~$4. I've never personally used it, but it's cheap enough that if I get distracted and have to leave 1/2 a bag to harden with the trowel in the bucket it's no big loss. Would this be a preferable alternative to the OmniGrip? It looks like the shear strength is 3x that of the mastic (150 psi vs 50 psi).
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Old 08-02-2019, 08:31 PM   #10
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Matthew, the bonding requirement for a Type I (important distinction) organic adhesive (ANSI A136.1) after a 7-day water immersion is the same as the the bond requirement of your thinset mortar bond to your RedGard or similar A118.10 waterproofing membrane after a similar 7-day immersion. Your tile is not likely to fall off the walls of a tub/shower surround.

That said, I still wouldn't use the stuff in that application. Actually, I wouldn't use it for setting tiles at all, partly because of my earliest experience, which was similar to Davy's in that the stuff is like a tar baby; it sticks to anything it touches and is sometimes neigh onto impossible to clean off. And I swear it would sometimes get stuck on things it didn't touch.

[Edit] Now that I see your last post I gotta say, "Please don't use that Custom Blend for anything other than bedding CBU on a wood subfloor." Spend enough to get a useful product from Custom, which would be their VersaBond, and just mix smaller batches if you find you're throwing away a lot of extra.

My opinion; worth price charged.
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Old 08-02-2019, 08:32 PM   #11
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Thanks, Kevin. I won't be using it on any shower walls, just the walls outside the shower/tub area. The specs make me think it's sufficient but I've heard so many people call it junk throughout the years that I'm just afraid that if I use it I'll be regretting it.
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Old 08-02-2019, 08:36 PM   #12
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Matthew, unless you're buying really high-dollar mortar, you're not going to lose a whole lot. That's provided you don't mix up large amounts at a time.

I would try about 1/4 of a bag at a time, maybe 15 pounds, and keep a water bucket close by with a stiff-bristled brush in it. If you get called away, quickly scrub the mortar off the trowel and you're good.

Most thinset mortar is good for about two hours after you mix it up, so you can come back and keep going without having lost anything, provided you don't grossly exceed that time frame.
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Old 08-02-2019, 08:39 PM   #13
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Thanks, CX. I have a good friend who is a retired homebuilder who said something similar about its consistency/stickiness.

He also said, "just tile the whole room with mastic and hurry up and get the house for sale, it should last that long". We have no plans to move any time soon, maybe this means I should have no plans to use mastic anytime soon?

Thanks for cautioning me about CustomBlend, sounds like there's a reason I've been avoiding it. At this point, I'm really liking ProLite, maybe I should just stick with that.
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Old 08-02-2019, 09:06 PM   #14
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Like Kevin said, you don't have to mix up much at a time so you won't be throwing much away. If you don't have time to wash your trowel, set it in your bucket of water and you can wash it when you get back.

I feel like we aren't saying what you want to hear. I would ditch the mastic in a wet area. In my opinion, if it's not good enough for a shower floor, it's not good enough for shower walls.
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Old 08-02-2019, 09:47 PM   #15
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Thanks, Davy. Just to reiterate, I have no intention of using mastic on any shower walls. The shower walls do have RedGard on them and will be tiled using thinset.

I wanted to use mastic on the wall behind the toilet, the wall behind the vanity and the walls near the entrance to the bathroom (the one around the corner from the vanity and the wall with the window). I've exported some images from SketchUp so you can see what walls I'm referring to. The wall with the towels hanging on it has been RedGarded so it's getting thinset. The tub alcove walls have Redgard on them already and will be tiled with ProLite thinset.

While I'll admit it'd be nice to hear some mastic success stories, I don't necessarily want to hear anything other than the truth. I'm open to any tips, methods, or products that can speed up this project without compromising quality in a way that will be noticeable either now or in the foreseeable future. We do plan to be in this house for a long time.
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