Thinset vs mastic for tub and shower

Name: Shayray
Posted: Sun, Apr 11, 2010 at 3:41 pm MST
 
Topic
I have a friend that has tiled for 15 years. He states that thinset is great for counters and floors, but is worthless when stuck to vertical walls and therefore, mastick is superior. Yet, I found a thread on this tile forum that states repeatedly that mastick will not hold up in moisture sensitive applications such as any tub or shower situation. Even the thinset I bought ("versabond" fortified thin set mortar) states that it is a floor thinset and the directions are for thinset on a floor application. Having said all that, I still believe in what I read on the thread I read on this forum which states that thinset is superior to mastick in moisture intense situations. Soooooo.

My question is what is the tip/secret I need to know to use thinset in a vertical application?
Name: Marco
Posted: Sun, Apr 11, 2010 at 3:48 pm MST
 
Reply: 1
Quick point of interest too, mastic is twice as expensive per bucket as thinset is. Use thinset for your shower. Use spacers to keep the tiles from sliding.
Name: Bljack
Posted: Mon, Apr 12, 2010 at 6:29 am MST
 
Reply: 2
I have a friend that has tiled for 15 years. He states that thinset is great for counters and floors, but is worthless when stuck to vertical walls and therefore, mastick is superior.


Let's defeat that statement on several levels. Custom Building Products line of setting materials is sold at tile stores and at Home Depots across the US. With that level of distribution, it's probably safe to say that their Acrylpro mastic is one of the highest selling mastics in the country and their Versabond thinset is one of the highest selling thinsets in the country. Acrylpro is backed with a 1 year warranty, Versabond is backed with up to a lifetime warranty. Mastics are organic, organic = mold food. ("premixed thinset" buckets are mastic too.) Thinset from a bag is portland cement based. Not an organic material. Mastics will reemulsify when exposed to prolonged moisture, thinsets will not. Mastics behind large tile can possibly never fully dry, thinset is mostly a chemical reaction and the limited moisture to shed from the latex polymers will dry out in short order.

Dave Gobis is the Technical Director of the Tile Council of North America and writes articles for several magazines monthly. I'll never forget his last line in an article about thinset selections. "For those of you who still use mastic in wet areas, my wallet thanks you."

My question is what is the tip/secret I need to know to use thinset in a vertical application?


There are nonsag thinsets on the market such as Laticrete 255, Tec 3N1 and Custom Megalite but you won't find them in a big box store. These have the grip and nonsag features that keep lazy hacks using mastic in wet areas. Just as easy, though, you can use any mid range modified thinset such as Laticrete's multipurpose from Lowes or Custom's Versabond from HD with a ledgerboard and starting with your second row of tile.

To set your ledger

-Use a level to find the lowest point of the tub deck or pan.

-From that spot, measure up 1/8" for the caulk joint at the bottom, the actual size of the tile (tile sizes are usually nominal, a 6x6 for example, might only be 5 13/16") and then 1 grout joint. That mark is where the second row of tile aligns.

-Draw a level line around the surround and tack a ledger board at the line to support your second row of tile.

-Set your tile, using spacers above as Marco said in his reply above. When the thinset sets up, remove the ledger and cut in the bottom edge of the first row of tile to maintain a consistent caulk joint at the tub intersection.

FYI, your cement baord will not waterproof the surround. You need to either waterproof behind the cbu by first tacking up 4 mil plastic sheeting or 15 lb roofing felt an letting it overhand the flange of the tub-or-you use a surface applied waterproofing membrane such as Laticrete's "Floor and Wall Watertight" from Lowes, or "Redgard" from HD which are roll on liquid waterproofers or you can use a sheet membrane such as Nobleseal TS or Schluter Kerdi.
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