Some instructions for applying mortar said to use a trowel with square notches for a floor, and v-shaped notches for a wall. I wanted to ask why, but I can’t find the same webpage again.
Why use different notches for floors and walls? For that matter, why is the trowel notched at all? To let air escape?
Janet
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Replies
The notches are a way of measuring the depth of th emud or mastic applied.
it also ensures good contact between the tiles and the mud. As you mash the tile into place, the high spots spread out in contact, so there is more surface area touching than otherwise and also making a sort of suction fit beyond the chemical adhesion.
If you were to try and spread a smooth coat to stick the tiles to you might get only 60% contact and adhesion, but with notching, you get 80% or more.
I can't explain the square vs V notch style advice you read. In my experience, I do more V-notch with mastic and square with thinset. The size of the notch also varies with type of tile and viscosity of mud. Most tile boxes and thinset bags have recommendations for their product.
What exactly are you installing?
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Those instructions you are quoting are, shall we say, 'imprecise'.
The type of tile (wall/floor/whatever) has little if anything to do with what kind or size of notch you want on your trowel; it is the size and thickness of the tile itself and the size of the grout line which determine what trowel to use.
Briefly, if you use a trowel with too small a notch for the size of tile and the width of grout line you're setting, you won't get enough adhesive laid down and the tile won't stick properly. If you use one with too deep a notch, the excess thinset (or mastic) will squish up into the grout lines and drive you outta yer mind raking it outta there. (The thinner the tile, the more you have to watch out for grout-line squeeze out.)
The trowel controls how much goo is laid on the wall/floor/whereever by how deep and wide the notches are. Think of each notch as a little flow gate which dispenses a metered volume of thinset or mastic. The tilesetter controls how well the trowel does that by keeping the trowel pretty close to perpendicular (about 70-80º) to the surface and using enough muscle to ensure that the teeth are actually screeding the excess adhesive off properly.
Big (12x12 and up) tiles are usually set with fairly wide (¼" or 5/16") grout lines; tile manufacturers will specify biggish (3/16" or ¼") square notches for laying these because they are big and heavy and need a lot of goo to hold them solidly. But, they are usually back-buttered, with the tilesetter holding back or beveling off the thinset at the tile edges to make damn sure there will be no squeeze-out into the grout line.
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