Lft thinsets

[Humphreyp]

It's occurred to me, after billions of sqft of tile setting, I do not know the precise answer to: why use lft thinser for tile over 15" on a side, other than that's what the industry calls for.

In so far as I know, the whole surface weighs the same wheather is small or large tile. So in reality, why do I need lft thinset for my next job of 4ftx2ft tile, and not just simple custom versabond?

[smifwal]

Your question is valid, in this I am a sheep and just do what I am told. But I would guess that it has to do with the shrinkage and the limitations of the versabond. I use Ardex X5 white and it covers all the parameters of any job I might face, I use X4 for any 12x12 and subway tile unless it is bigger than 15" one direction (again sheep) but I always have a pallet on hand

[Humphreyp]

Thanks whoever moved the post here.

I've used those mortars.

Ive always used versabond for the most part. Prep was always the key tho. I've gone back to houses for other work and after 15 years the tile jobs look awesome, except for dirty grout. But tile is solid and not cracked.

I've never laid tile greater than 24x12". This should be fun.

[cx]

Pat, there is nothing called LFT mortar recognized by the ceramic tile industry, despite the labeling on product containers from some manufacturers. There are, however, LHT mortars. That's Large and Heavy Tile mortars. Those mortars were previously known as Medium Bed mortars.

The LHT mortars must meet the requirements of one of the existing mortar standards, either ANSI or ISO, and are usually identified by the letter H after the standard number, indicating that they can be applied in thicknesses up to 1/2" after the tile is set (or thicker as stated by a manufacturer). Also frequently by a letter T for thixotrophic, indicating particular non-sag properties.

These characteristics are useful when setting tiles that weight more than 5 pounds per square foot and/or are of ungauged thicknesses.

The reason for the change in terminology was because of a misperception that there was actually a medium bed method of setting tiles as opposed to the thin bed or thinset method and that such method used the thinset mortar to level or flatten the substrate while installing the tiles. At least that's the way I understood the discussion.

The recommendation that such LHT mortars be used for tiles with a side longer than 15 inches is, I believe, based upon the concept that such tiles will be set with larger notched trowels, due at least partly because of the greater warpage of such tiles.

Far as I'm concerned, if your tiles are flat enough and your substrate is flat enough, you can set your 15-inch tile just fine with a non-LHT mortar if you want. And you'll not need the recommended 1/2" square notched trowel to do so. But I've never set floor tiles larger than 20x20 inches.

[Humphreyp]

]Interesting...it basically is for sagging and leaving the irregular warping from becoming unsupported....so for 48"x24" tile......3/4notch and Lht mortar? I'd say they are shy of 5lb a ft. There is nice warping. Not going to stagger them.

[John Bridge]

When I started in the business there were only two types of "thinset," one was white and the other was gray. If you wanted extra strength you mixed it with "milk," originally made by Laticrete.

Only had two types of grout, too. Sanded and unsanded.

We've come many miles since then. I use VersaBond for everything.

[Davy]

I noticed a new Versabond the other day at Home Depot. Maybe it has been out and I didn't see it till now but it's Versabond LFT RS. 39.44 is the cost at HD for gray. I didn't see it in white.

[cx]

At forty bucks a bag, Davy, I'd want that mortar to set the tiles it'sownself, Davy!

The first "leche" I ever saw was Laticrete's 333 "Flexible Additive," which my then tile guy mixed with some Custom thinset mortar. Floor tiles were bonded with that directly to concrete SOG. Worked pretty well, best I can tell. Wazza long time ago.

[jonchicagoland]

Those thixotropic mortars are lifesavers when trying to get coverage on the big tiles. Especially for wet area coverage, 24x48s or 48x48s are....tough.

The idea behind thixotropy is that the mortar becomes more fluid when agitated (or when you move the tile), and then will reset to a "gel" consistency when it stops moving. That allows the mortar to flow somewhat when trying to collapse your ridges. If you've attended any trainings with manufacturers the last couple years, you'll have heard them compare it to ketchup in the bottle.

I'll often use a vibrator on the surface to collapse the ridges high on walls where I don't have quite enough leverage otherwise. With some mortars, you can actually see the mortar around the edges liquefy and set back up.

As far as trowel size, you'll just have to try a few and see. I've had the best luck with the shark tooth trowels on big tiles.

[Dan Marvin]

I think you've covered the basics of these mortars. THinset mortars are designed to be installed as a thin (3/32") layer between a small, flat tile and a flat substrate. As tiles have grown, there is more allowable warpage that can exceed the thickness limit of a typical thinset. At the same time, substrates are frequently irregular and the time allotted to ensuring good coverage has decreased. LHT mortars are designed to fill thicker gaps up to 1/2" when necessary without slumping away once they are in place. They can be an advantage when you're dealing with a large tile on a typical substrate (for severely uneven substrates, use a patch or leveler).

One note about mortar prices - sand and other fillers are the cheap part. Cement, latex, thixotropy agents, and other modifiers add to the cost of the product. Yes, installation products manufacturers sell at a profit but the competition for your dollars is fierce. If a mortar costs more, chances are that it gives you a better potential for success even if you don't do everything perfectly.

[Tile & Stone Guild]

Gray thinset does not exist in my world, for any reason.

[Tiger Mountain Tile Inc]

If you've ever had tile shrink and move on you the next day because you built up the mortar too much then you can appreciate the reason for LFT mortars.

If your floor is nice and flat then you probably don't need the LFT (LHT). But, big tiles with crowns in the center and big trowels to install the mortar are going to put any 'normal' thinset, like Versabond, at it's 1/4 inch limit.

Then if you're floor isn't perfect...

[Humphreyp]

Very very good info. Thank you.

And the whole tile shrinking and moving because the mortar bed shrunk.....that sold me right there.

I read somewhere that these mortars in question have longer pot life. Which is good for large tile. move slow, walk slower, think simple thoughts.

[John Bridge]

If we'd all go back to mud work we wouldn't have to worry about flat . . . unless we screwed it up ourselves.

When my brothers started out in the trade shortly after the Second World War there was no thinset. They used portland cement slurry. I did a shower that way years ago when my helper forgot to load the thinset at the shop. Thank God for thinset.