Premixed thinset vs. mix-it-yourself [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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09-06-2006, 02:59 PM

I'm getting ready to do an installation. I find that the big box stores now sell tubs of pre-mixed thinset, which I am eyeing.

Benefits seem to be

no mixing
time saving

Drawbacks seem to be
seems more expensive
unknown whether there is a quality issue (a new product)

Any opinions or pointers to previous posts on this subject?


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09-06-2006, 03:05 PM
Beware premixed thinset. It is not the same as bagged thinset mortar that you mix yourself.

Real thinset mortar contains portland cement, which chemically reacts with water to harden. Sealing it in an airtight buckek will not stop the chemical reaction from proceeding. So it's impossible to make a real premixed thinset.

What is labelled "premixed thinset" is really sanded mastic. Ideally, such labelling would not be permitted. Mastic is suitable for use on walls, in dry areas, for ceramic tiles (not natural stone) that are no larger than 8" x 8". Anywhere else, use real thinset. And anywhere that you can use mastic, thinset will work, too.

09-06-2006, 03:43 PM
Read my post from this morning entitled "Tell me,how bad is it? I think it will give you a good idea of the forum's opinion about premixed thinset. After I log off here, I'm going downstair to start popping tiles.
These guys know far more than I do, but I do know that the 35 lb tub of thinset you buy at Lowes does not work well on concrete slabs with 12 inch tiles, no matter what the container says

Dr. Olds

09-06-2006, 04:06 PM
The stuff will never cure and will re-emulsify, e.g., turn into mush.

09-06-2006, 04:56 PM
Thanks to those who replied. It was not clear from the labeling on the tubs that the stuff is mastic. Actually, mastic might work in my installation, but I do not want to deal with it.

I plan to complain at the customer service desks at Lowes and Home Depot regarding this product. HD now stocks two (2) types, one for porcelain/marble/granite (if memory serves) and one "regular" version.

This is really a travesty. I would enjoy hearing from others who have something to add on this pre-mixed "thinset."


09-06-2006, 04:57 PM
I heard it put really well somewhere on this forum. The mastic stays wet in the pail when the lid is closed so likewise, it is going to stay wet (at least for a long time) when sandwiched between a backerboard/substrate and the grouted tile. The tile acts as the lid, essentially.

09-06-2006, 05:07 PM
That's it Joe. Use it for ceramic tile on a backsplash or wainscot on a wall. That's it period. Don't use it with a trowel larger than a 1/4" v-notch.
We hare are real happy that they continue to sell it a HD and Lowes it is a continued source of work correcting installations with these materials.

09-10-2006, 09:32 PM
I used mastic on my shower that has 12 x 12 tiles, about a year ago and have had no problems to date. I did let it dry a couple weeks before I grouted though, so maybe that made a difference. This shower gets used 5 times daily.

09-10-2006, 09:43 PM
Giving it extra time to dry will help but most mastics on the market will turn to mush like Scooter said. Problems will normally show up along the bottom rows of wall tiles. I hope thinset was used on the shower floor, that's the worst place to use mastic.

09-11-2006, 09:48 PM

I took the advice of everyone here and another board.. buy the powered stuff and mix it your own. Get the mixing paddle/eggbeater for ~$12.00 and you'll thank yourself later.


09-12-2006, 01:22 PM
mastic even on drywall in a shower can last a long time - many years sometimes. Or so it would seem. As the guys have pointed out - it's what you DON'T see that matters. Mold is the most obvious. And even with the towel method it's going to get wet back there - eventually becoming a permanent condition in a daily use shower. somewhere along the line the bottom 3 or 4 rows will fail completely and the repair guy will probably rip out enough to put up a strip of CBU and new tiles with thinset. Tile that doesn't match of course. The rest of the tile is pretty much held together by the grout becuase the mastic bond has loosened long ago. When you finally rip it out you'll be glad the health department guy isn't watching lest he condemn the whole site.

yep, that pretty much describes my old shower. :cry: