HI, Two questions please and I hope I,m not mixing threads.1. is there a hard and fast rule about trowel notch sizes in relation to tile size, and are they different for floors and walls. 2. I was told that modified mortar was for porous to non-porous use and un-modified was for non to non porous. is this true and where does redguard fall into this category.I hope this is'nt to large a post , thanks Ron.

Hi Ron,

Trowel size depends on not only the size of the tiles, but the texture of the backs of the tiles and how flat the substrate is. The type of adhesive also figures in.

Theoretically, if the backs of the tiles were flat, (such as marble tiles), a 1/4x1/4" trowel would be fine regardless of their size IF the substrate was perfectly flat. That rarely happens. So it depends. Also keep in mind that thin set should have a final cured thickness of at least 3/32" for max strength.

We generally suggest a 1/4x3/8x1/4" square notch for standard tiles in the 12-13" range. Maybe 1/4x1/2x1/4" or 1/2x1/2" for tiles larger than that. It also depends on how you mixed it and how you hold the trowel. Set a few, remove them to check for adhesive transfer.

Who ever gave you that advice on which thin set to use is about 20% right. Stop getting tile advice from your barber please.

Jaz

What are you installing?

Jaz

Thanks for the reply Jaz, On the trowel size I think most non pro,s install something between your mesh backed 2x2s to your standard 12x12.Does it make a difference between thinset and mastic? If the 3/32 rule applies to 4x4 wall tile then I'll use that as a rule of thumb. On the mortar advice a friend is tiling a bathroom with a tub but no shower stall. He did not use a vapor barrier behind his durock and I suggested redguard over it because of the poor ventilation in the room. This led to the question about which mortar to use. Any advice about this would be helpful. Thanks Ron

I forgot to mention the bath has a foot tub and shower with no window or vent in a 100 plus year old house.