QUESTION

In the attached photo thin set 1/16” is on the floor, 1.5” to 2.5” of mortar mix with less than 90% coverage, and thinset 1/16” on the back of the tile.

I though the support material was supposed to be floor mud and/or self leveling then at 1/2” trowel of thinset for the large format tile.

Is mortar mix ok to use that thick? Is this the best installation method.

ANSWER

ANSWER - It is hard to see exactly what they did.  Your message says “photo thin set 1/16” is on the floor, 1.5” to 2.5” of mortar mix with less than 90% coverage, and thin-set 1/16” on the back of the tile.”

That sounds like you are saying that the mortar bed only got 90% contact, which it should be 100% as should the thin-set.

It looks like they are doing a wet set method where they put down the mortar and set the tile as they go rather than pre-floating and setting the tile the next day.   Wet setting is ok, but it doesn’t look like they are doing it correctly.

The mortar looks too wet.  It might not be fat mud (very wet), but it isn’t deck mud or drypack as it should be.  The 4:1 sand to cement mortar should be mixed to a consistency so it looks damp and not wet.  They should be able to take a hand full and squeeze it and it stays in the shape of a ball.

They should be applying the thin-set to the substrate just before applying the mortar.   They can make the thin-set wet enough to apply with a plaster’s brush, which is called a slurry bond coat.  They then apply the dry-pack mortar and compact it thoroughly with a wood float or magnesium float.   Then they apply another slurry bond coat to the mortar bed surface and the back of the tile that is at least 1/16” thick to bond the tile to the mortar bed .   They should achieve 100% mortar surface that is flat and 100% thin-set coverage.  The wet set method makes it easy to get a 100% contact.

The mortar bed method is considered a superior method to the thin-set method if done correctly.    That is because you can compensate for the irregularities in the substrate and be able to achieve a perfectly flat surface that will allow you to avoid other problems.

They could have used self-leveling if done correctly.  Floor mud should be a dry pack mortar that I referenced.  Some installers use fat mud (wet) that isn’t per industry standards because you can’t compact it and it will tend to shrink excessively.

The thin-set application for regular thin-set can’t be thinner than 3/32” thick and can’t be thicker than ¼” thick.  If you have a tile that is irregular in thickness or has warpage you could use a Large and Heavy Thin-set that will allow the installer to go up to a maximum of ½” thick thin-set.  Although when doing a wet set method you can apply a slurry bond coat that is as thin as 1/16” both under the mortar bed and on top of the mortar bed and on the back of the tile.

Mortar bed methods normally require minimum 0.75” thick up to 2” for bonded mortar beds and thicker for heavy duty applications that require other provisions.  Non-bonded mortar beds require a cleavage membrane under the mortar bed and require wire reinforcement suspended in the mortar bed between 1/3 and ½ the thickness.

In all cases the key is whether it is being installed correctly and per industry standards.