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Mastic vs Thinset – Which should I use? - TileTools

Mastic vs Thinset – Which should I use?

There’s a newer tile adhesive introduced to the market that falls into the mastic family, some make claims that might end up causing you damage down the road. This article doesn’t want to discourage you from using mastic, we only want to encourage you to use them when it’s appropriate. First let’s go over the differences between mastic and thinset mortar.

What is Mastic?

Mastic is an organic glue made from the sticky resin of the mastic tree. It’s available as a thin-liquid, thick glue, or a sticky paste. Liquid Nails® would be a notable example of the thin-liquid form where it comes in a caulking tube and squeezed out along a wall or joists to hold load-bearing walls and ceilings in place. It’s also used as a temporary hold for fixtures so they can easily be screwed into place by one person.

Mastic as a tile adhesive has a number of drawbacks, since it’s organic, it can harbor mold in high-moisture areas, it also will re-liquefy when submerged in water and lose it’s adhesive strength. Some manufacturers are promoting their tile adhesive as water-resistant and safe when subjected to limited moisture exposure, they further claim that it can be safely used to tile the walls of tub surrounds. This is where we personally have questions. It’s not that we take issue with the specific language used by the manufacturers, we just have an issue with what we perceive as a disregard for reality when making their claim.

We feel that mastic tile adhesives are a great time-saver when laying tile, but knowing the laws of physics and nature, we feel that mastic adhesive is not appropriate for use anywhere where moisture is present. Although the manufacturer is correct in stating that tile will hold up to limited water exposure, who’d want to choose mastic over thinset when using it in area where limited water exposure could possibly end up being “more than limited”.

Let’s say you tiled your shower using mastic and you shower in it daily. Everything will work out fine if your tiles remain properly sealed and no cracks form in the grout, and your shower-head performs perfectly. But what will happen if you’ve formed a tiny little crack in a tiny little area of your properly sealed tile where moisture not only penetrates, but has a tendency to wick and spread? Will your mastic adhesive hold up? What if the mastic does hold up when a little bit of moisture penetrates? What about the organic property of mastic? All that’s needed for mold growth is moisture and an organic food source. Mastic is food for mold! Another drawback is that mastic doesn’t provide much structural support and cannot be used to build up minor “off of level” imperfections in a floor. You’ll end up with more “tile lippage”, in the end this tile lippage will have an impact on the overall aesthetics of your tile project.

Although there are drawbacks with mastic, there are advantages. Mastic has superior holding strength, easier to apply, and sets quickly. When used to tile walls it’s strength allows you to set tile, and if you’re good with eyeballing, you can set tile without the use of spacers. If you attempt to set wall tiles using thinset without spacers, you’ll end up with a bunch of tiles that have slid into each other before the thinset has had time to set, resulting in a giant mess.

With that said, ALWAY read the manufacturer's instructions and follow specifications and guidelines!

What is Thin-Set?

Thin-set mortar is like Portland Cement, only thinner. It’s a mixture of cement, finely graded sand, and a water-retention compound that allows the cement to properly hydrate. You’ll find thin-set sold with the words “thin set cement”, “thin-set mortar”, “dryset mortar”, and “drybond mortar”. Whatever name you find it as, we’re talking about the same thing. Thinset is designed to adhere well in a thin layer that’s typically not greater than 3/16″ thick. Thinset also provides structural support so that very minor adjustments in height can be made.

There’s also a medium bed (also known as LFT or LHT) thin set mortar which is a variation that’s used for slightly larger applications. This is used with large, heavy or thick tiles. Then there’s yet another variation of thin set for thick-bed installations. Thick bed installations generally are based on the traditional method of packing a mortar bed of a surface before installing the tile. The tile can be adhered to the mortar bed either while the mortar bed is beginning to dry or after the mortar bed has cured.

The advantages of thin-set is that it can be used in areas where there are high amounts of moisture present. Although thin-set is not waterproof, it is isn’t water soluble. When moisture is present, it will not return to a liquefied state as mastic would. Another advantage is that it’s inorganic and thus is not a food source for mold growth.

Now on with the battle of Mastic vs. Thinset!

  1. Shower floors – Thinset
  2. Shower walls – Thinset
  3. Bathroom floors – Thinset
  4. Bathroom walls – Thinset
  5. Kitchen floors – Thinset
  6. Kitchen walls – Mastic
  7. Kitchen countertops – Thinset
  8. Kitchen backsplashes – Mastic
  9. Other floors – Thinset
  10. Other walls – Mastic (where moisture is not present)

Keeping in mind of course, the material being installed. Mastic can only be used for ceramic and porcelain tiles usually not larger than 13"x13".

What size trowel do I use?

For Mastic

Follow the manufacturer’s directions on the packaging.

For Thinset

Visit our popular blog: What Size Trowel Do I Use? for an explanation of which size trowel to use

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Tim - May 22, 2024

Can I use Thin-set for 12" X 24" wall tiles in my bathroom. There is a free standing tub in the area.

Henry Allen - December 6, 2023

Trying to decide between mastic and thinset is like choosing between a hamster and a race car for your morning commute. One’s sticky, the other’s cementitious, and neither will make your breakfast. Just pick one, and let the tiles do the talking. Because, let’s face it, they’re the real divas here. 🚗🐹

Jan - May 17, 2023

That ole gal at Lowe’s in Campbellsville Ky knew what she was talking about.

Peter - February 27, 2023

Great job simplifying this!!! Thank you!!

John Bougthon - May 17, 2023

Questions: What is the primary water proofing for ceramic tile installation ?
It seems to me that the entire installation of any tile on any surface is dependent on the grout and sealer. Do you have to seal the edges of ceramic tile where thereis no glaze ? This newer style super grout is aledgedly water proof. Is it true ? It says it can be used on swimming pools . anyone please respond if you know the facts rather than just an opinion. Thanks, John

Mike Kelly - May 17, 2023

I know it says “Other walls – Mastic (where moisture is not present)”, but what about when installing tile on a fireplace? I will be installing 13″ × 39″ tile on an electric fireplace wall. It wont give out as much heat as a wood burn or natural gas, so can I use mastic or should I go with mortar? Surface is 6′ × 12′. Thanks in advance.

tony Maloni - May 17, 2023

what is the best thin set to put down on top of Terrazzo flooring in a wet commercial kitchen

Roxstech News - May 17, 2023

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ADAM HEVNER - May 17, 2023

Very good article. Using mastic on kitchen backsplash or walls that are not exposed to a lot of moisture is great. As long as you are using no more than a 1/4" V notch or square trowel. Bonds better to painted finished sheetrock than thinset. Longer work time before it flashes over. Holds more weight. But pretty much all flooring, shower, tub, walls require the right grade of mortar/ thinset. The only time I use mastic in showers is with vct on decorative bands/feature strips to bring them out level with the walls. I cut the vct into the right size strips. Adhere the mosaics or glass or whatever to the vct. Then use thinset on the back of the vct to bring the decorative bands flush with the wall tile. Been using this method for 10+ years and never had a call back. Great way to give your custom showers the perfectly flat finish without that extra time and mess

Lou - May 17, 2023

Use thinset always for porcelain tile
Use mastics for a bisque tile. Subway. Wet or dry

unless it’s a steam shower. Then thinset always always always ! 😃

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