Thinset Overview - Thinset is a cement-based adhesive you mix with water OR a liquid polymer additive for added flexibility and durability. It is the same product used in construction by tile installers. There are many different manufacturers of thinset, and each manufacturer may even have several types. It is essential to familiarize yourself with the product you're purchasing, selecting the appropriate one for your project application. Read the bag! There is a wealth of information included, and product specifications vary. You can also visit the manufactures website to learn more.

Please note that the setting or "drying" process of the thinset is not a drying process at all. It is a curing process that happens through a chemical reaction between the thinset powder and water. Too much or too little water can affect the quality of the cure of the product. Thinset is better and stronger if given an extended period to cure. Hot days and sunlight are not your friend, nor are porous backers that wick the moisture out too quickly. It is a good practice to cover your work at the end of each session with a slightly damp towel and plastic to keep the curing process going. (This applies to grout as well). Not all thinsets listed below are chemical cures. Each is noted below.

Thinset comes in three main types.

Non-Modified Thinset– This means that no polymers are integrated into the mix. Most manufacturers will recommend using an admix to replace all or part of the water for higher bonding strength and flexibility. (Chemical cure) Polymer Fortified/Modified – These are the most widely used among both artists and the tile industry. These products already have the polymer and are meant to be mixed with water. (Chemical cure)

Epoxy Based Thinset – Epoxy Thinset is quite different from cementitious thinset. They are formulated with epoxy resins and a filler powder. Epoxy thinsets offer greater bond strength and chemical resistance than polymer-modified cementitious thinset. This performance comes at a price, and epoxy thinset is much more expensive than regular thinset. Typically, they are only used to bond to difficult substrates or where extraordinary chemical resistance is needed, and there are drawbacks. They are mixed from two parts and must be combined in precisely correct proportions to set correctly, and they are more challenging to work with and have a shorter pot life. Epoxy thinsets are a chemical cure, but the rules above do not apply. It is a reaction between the chemicals in the two parts of epoxy.

Premixed Thinset – This is ready to use with no mixing required. Premixed thinset is an alternative to traditional thinset mortars and an excellent choice for interior artwork where no water is present. It is easy to use and ready when you are. If the container is kept sealed, it has an extremely long shelf life. Unlike traditional thinset, premixed thinset is air-cured. Using it to adhere tile Larger than 8" x 8" will significantly lengthen its dry time, as will installations where the tile is face-mounted with plastic tape. Within all the above types of thinset, there is also a subset of rapid setting vs. standard set time. Rapid set thinset is rarely a good choice in the artist's world unless you are installing on a vertical wall and are VERY well prepared to apply your pre-mounted mosaics quickly. The work time is substantially shorter.

Within all the above types of thinset, there is also a subset of rapid setting vs. standard set time. The work time is substantially shorter. Rapid set thinset is rarely a good choice in the artist's world unless you are installing on a vertical wall and are VERY well prepared to apply your pre-mounted mosaics quickly.  

Important Safety Considerations: ALWAYS wear a dust mask or respirator while exposed to thinset in its powdered state. The moisture (water) is the last ingredient that the thinset needs to start getting hard, and you don't want lungs full of hard cement! Here's why once inhaled, the thinset comes in contact with your respiratory system full of moisture. Once mixed with water, it is safe to remove your dust mask.

 

Mixing Tips:

  • Only mix as much thinset as you can use in one two-hour work session. Once mixed, it will not keep until the next day. 
  • Mix a new batch if your thinset is getting too hard to work with. DO NOT add water once the mixture has set for more than 5 minutes. Adding more water will make it weak. Remember the curing process. Adding water interrupts it. A tip: Working it by moving it around, kneading or stirring will help to soften it a bit and give you more work time. 
  • You might be wondering why you would ever use thinset? I have to tell you that thinset is always my adhesive choice for exterior applications and most interior installations unless I am working on a backing that requires a clear or flexible adhesive. It works, it's permanent, and if they can tile your kitchen floor and the sides of buildings with it, it will undoubtedly work for anything you will make!
  • My best thinset tip - I mix my thinset in an old sour cream container. That way, I don't have to clean it up. I can simply toss it. Once mixed, I place the thinset in a sandwich-size Ziploc bag. You can then nip off the corner and apply it to your surface, similar to using a cake decorating bag, and spread with a palette knife.  Always opt for the heavier freezer/storage bags over plain sandwich bags. They are heavier plastic and hold up better.
  • Thinset is your best choice if your base is concrete, terra cotta, cement backer boards, WediBoard, and most permanent installations.
  • It is the only adhesive you can use to really 'float' tiles. Floating means you can build up the adhesive under a thinner piece of tile so that it is flush with the thick tile next to it.
  • It is best to seal cement, brick, terra cotta, and other porous surfaces before applying thinset. These materials will wick (draw) the moisture out of the thinset to weaken it quickly. I recommend Kilz, but it is always best to consult specifications for your product.
  • Unused thinset in its powdered form must be stored in an airtight sealed container. If left in the open bag, it will absorb moisture from the air and begin to cure. You will notice somewhat hard clumps of varying sizes. The lumps will be easily broken down with your fingers; however, It is a sign that it has absorbed moisture, and the chemical cure has already taken place. It is no longer useable and will never be as strong as it needs to be. Check it for clumps, even if you have just purchased a new bag. It still has a shelf life in the bag, and/or it may not have been appropriately handled before your purchase. 

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