This page explains how to mix and use thinset bonding mortar for detailed work with glass mosaic tile and other tesserae.
I. What Is Thinset And When To Use It.
For outdoor and wet mosaics, thinset is recommended instead of adhesives. Thinset is a bonding mortar, which means it is a concrete with polymers added to make it sticky and extra strong. This is particularly important when working with glass mosaic tile, which is non-porous and difficult to bond securely. We use Versabond brand, which we buy at Home Depot, but you should ask at your local building material store what they recommend for your area. (This could be important if you live in a cold climate, and something else is being used by your local contractors, but I suspect it is the same.)
II. Mixing Thinset
The thinset package has mixing instructions, but these are written for mixing the entire package. For detailed mosaic artwork, you will probably want to mix 1 to 3 pounds at most. You can find what amount of water to add per pound by dividing the amount of water recommended for the entire package by the weight of the package.
For Versabond thinset, we add 1/2 cup or 4 oz of water per pound. You can use that same ratio of 1 part water to 4 parts thinset to mix up tiny batches of thinset, such as 1 ounce or water plus 4 ounces of thinset.
We use a plastic measuring cup for measuring the water and a small kitchen scale for weighing out the thinset, which we scoop out with a small gardeners shovel or measuring cup instead of pouring. Dust is an issue, so we wear a dust mask and keep a spray bottle for misting. We also recommend doing the weighing and mixing outside.
For small batches of 1 pound or less, we mix it up in a 32-ounce plastic yogurt container and use a putty knife or old butter knife to stir. For larger batches, we mix in a 5-gallon bucket so that we can mix vigorously without slinging out any material. A smaller bucket (2 gallon) can also be used.
Note that you have to add the water gently and mix slowly at first to avoid stirring up the dust before the powder is wetted. Use a clean paddle or stick to stir. You will notice that it takes some strength to mix up larger batches, and something more sturdy than a paint paddle may be required. We have a mixing attachment that fits into our electric drill for batches of 5 or more pounds.
Mix the mortar until it has the consistency of dough with no lumps. Take care to mix all the way to the bottom of the bucket and scrape the edges to make sure that no powder, lumps or clumps remain. Then the mortar is allowed to sit for 5 to 10 minutes, and then it is mixed some more.
After that, we mix in concrete dye if we want to color the thinset. Typically we use Charcoal colored concrete dye to darken the thinset, and we use it in much larger quantities than recommended. Most recently, we added about 5 ounces to 1 pound of thinset without weakening the strength as far as we could tell, but we make no guarantees about that.
Here is a list of items recommended for mixing thinset:
bucket or plastic container.
small kitchen scale or postal scale
measuring cup or large spoon or small gardeners shovel
paint paddles or a small board for mixing
spray bottle for misting
III. How To Use Thinset For Detailed Mosaic Artwork
Thinset is extremely sticky and meant to be spread with a trowel to mount large tiles or sheets of tile. How do you use it for “one-tile-at-a-time” artistic mosaic work with small tiles without making a mess?
A small trowel or painter’s pallet knife or butter knife can be used to smear the thinset in small patches, and then the tile is pressed into that similar to a normal tiling job. Or you can put a small amount of thinset on the back of each tile, one tile at a time. Either way, you will need a way of keeping your hands clean and a way of cleaning up random drips.
We use the following materials to keep the work clean and efficient:
small plastic lid or tray
putty knife or old butter knife
painter’s pallet knives if available
wet rag floating in a bucket 1/4 full of water
medical examination gloves (optional)
old work surface or shop table.
wadded newspapers in garbage can
The plastic tray or tupperware dish holds a small amount of thinset for dipping the backs of tiles into. Scoop a small amount of thinset into the tray and keep the rest of the thinset in the bucket. Keep the bucket covered and use the putty knife to scrap the sides of the bucket so that all the thinset is in a blob and doesn’t dry out. Mist the thinset sparingly if you see it drying. We can use thinset for up to 4 or 5 hours this way.
As you dip the backside of the tile into the tray of thinset, you will occasionally get some on your fingers. If you are sloppy in how you clean your fingers, you will use up tons of rags. Use this procedure to use only 3 rags:
Scrape fingers off on the wadded newspaper in the garbage can.
Use the DIRTY rag if needed, but try to use as little as possible.
Dip fingers in bucket of water with WET rag.
Use the CLEAN rag to dry fingers.
Whether you spread the thinset in small patches or put a smear of thinset on the backside of each tile will depend on your style and pace of work. If you are improvising your design as you go along, you may find that you use both techniques.
For found object mosaic, we sometimes use a grouting bag fitted with a Wilton brand cake icing nipple. The grouting bag with nipple allows us to dispense the thinset in a very controlled way as if from a bottle of glue. This technique can also be used for flat tile.