Quick answer: Use thinset mortarfor floors, wet areas, and large or heavy tile — it’s the default for almost every job. Mastic (ready-mixed) is fine only for dry walls and small tile. Epoxyis the strongest and most water-resistant but is costly and tricky, so it’s reserved for demanding commercial and wet settings.
“Tile glue” isn’t one product — there are three families, and using the wrong one is a common cause of tiles that pop loose. This guide explains thinset, mastic, and epoxy, and which to reach for by project. Once you’ve chosen, work out how much to buy with how much thinset do I need and the right trowel notch.
The three adhesive families
| Adhesive | Form | Use it for | Avoid for |
|---|---|---|---|
| Thinset mortar | Powder, mix with water/latex | Floors, showers, wet areas, large-format, stone | Nothing major — the all-rounder |
| Mastic | Ready-mixed in a tub | Dry wall tile, backsplashes, small ceramic | Floors, showers, large or heavy tile |
| Epoxy | Two-part resin + hardener | Commercial, industrial, chemical/wet exposure | Most DIY — expensive, short working time |
Thinset mortar (the default)
Thinset is a cement-based powder you mix to a peanut-butter consistency. It cures hard, resists water, and bonds under load — which is why it’s required for floors and wet areas. It comes in two forms:
- Unmodified thinset — cement, sand, and water-retention additives. Used where a membrane or substrate requires it (many uncoupling and waterproofing systems specify unmodified over their membrane).
- Modified thinset — unmodified plus polymers/latex for a stronger bond and a little flexibility. The common choice for most floors and walls over cement board.
Thinset also comes in gray and white — use whiteunder glass, marble, and other translucent or light tile so the adhesive doesn’t show through. Large and heavy tiles often call for a medium-bed / LHT (large-and-heavy-tile) mortar, which holds a thicker bed without slumping.
Mastic (dry walls only)
Mastic is a pre-mixed organic adhesive that’s ready to spread straight from the tub — convenient and grabby, which helps hold wall tile in place while it sets. But it is not waterproofand doesn’t cure properly in constant moisture, so it belongs only on dry walls: a kitchen backsplash, a dry accent wall, small ceramic. Never use mastic on floors, in showers, in steam areas, or with large-format tile.
Epoxy (specialist strength)
Epoxy adhesive is a two-part system that cures to an extremely strong, water- and chemical-resistant bond. It’s the choice for commercial kitchens, industrial floors, and aggressive wet or chemical exposure. The downsides are real: it’s expensive, has a short pot life (you must work fast), and is less forgiving to clean up. For nearly all home projects a quality modified thinset does the job for far less money.
Which adhesive for which project
| Project | Recommended adhesive |
|---|---|
| Floor (any room) | Modified thinset (medium-bed for large-format) |
| Shower walls & floor | Thinset per your waterproofing system — never mastic |
| Kitchen backsplash (dry) | Mastic or thinset; thinset for glass/stone |
| Large-format / heavy tile | Medium-bed (LHT) thinset mortar |
| Glass or translucent tile | White thinset |
| Commercial / chemical exposure | Epoxy |
How much adhesive will you need?
Coverage depends mostly on your trowel notch and tile size — bigger tiles need a deeper notch and use more mortar. Work out bags with how much thinset do I need, and don’t forget the rest of the material list: grout and, where needed, backer board. To get your tile quantity first, use the tile calculator.
Frequently asked questions
- What is the difference between thinset and mastic?
- Thinset is a cement-based mortar you mix with water (or with a latex additive); it's strong, water-resistant, and required for floors, wet areas, and large or heavy tile. Mastic is a ready-mixed organic adhesive that's easy to use on dry walls but is not waterproof and shouldn't be used in showers, on floors, or with large-format tile.
- What tile adhesive should I use in a shower?
- Use a modified or unmodified thinset mortar appropriate to your waterproofing system — never mastic. Mastic doesn't cure properly in constant moisture and can harbor mold. For glass and some stone, use a white thinset to avoid showing through translucent tile.
- Can I use mastic on floor tile?
- No. Mastic isn't rated for the loads a floor sees and stays somewhat flexible, so it's a wall-only adhesive. Floors need a cement-based thinset mortar, which cures hard and bonds under foot traffic.
- What is the strongest tile adhesive?
- Epoxy tile adhesive is the strongest and most chemical- and water-resistant, which is why it's used in commercial, industrial, and demanding wet settings. It's expensive and has a short working time, so for most home projects a quality modified thinset is the practical best choice.
Getting your surface ready first? See what you can tile over and whether you can tile over existing tile, both of which affect which thinset you should use.
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