Mastic vs. Thinset
Q: To tile the ceiling above my tub, should I use mastic or thinset?
I'd like to tile the ceiling above my tub. Should I support them while the adhesive sets?
—Aileen Toce, Jacksonville, Fla.
Mark Ferrante of Ferrante Tile replies: You don't need supports if you use a no-sag thinset, a cement-based tile adhesive with a latex fortifier. I've stuck heavy 12x12 marble tiles on a ceiling with it and they stayed without any help. This is definitely not a job for a mastic, a premixed organic adhesive that's convenient to use but doesn't have thinset's grip. Here are some other differences to consider:
Offers formulations for glass tiles and heavy tiles, among other kinds.
Does not support mold growth.
Has no VOC emissions.
Pro-friendly: sets up in 15 minutes; apply grout in as little as 6 hours.
Unaffected by heat or water.
Shelf life of one year.
Sold as a powder in bags; has to be mixed.
More goes to waste; everything that's mixed turns hard.
Takes practice to get right consistency.
Only tiling supply stores offer variety of thinset choices.
Sold in small buckets; no mixing required.
Scrape unused material back into bucket; keeps up to one year.
Widely available in home centers and hardware stores.
DIY-friendly: sets up in 30 minutes.
Unaffected by heat.
Not suitable for wet areas.
Emits some VOCs.
May support mold growth.
Not suitable for tiles made of glass, those larger than 10x10, or those of irregular thickness.
Wait at least 24 hours before applying grout.