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Mastic vs. Thinset

Q: To tile the ceiling above my tub, should I use mastic or thinset?

tiling contractor Mark Ferrante spreads thinset with a square-notched trowel
Photo by Reena Bammi

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.


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