Part 5. Backers and Adhesives.
Choosing a backer and the appropriate adhesive is very crucial to the success of your mosaic project. Being familiar with your choices in backers and adhesives will help you achieve the desired result you want with your mosaic piece.
Backers, bases, substrates, all refer to the same thing – what you will mosaic on. Normally, backers should be nonflexible surfaces, but there are some exceptions such as mesh. Always start with a clean surface and make sure your base will be able to support the weight of your tiles, adhesives and grout.
Porous bases like terra cotta pots, wood, MDF, etc., should be sealed. You can use a mix of white craft glue and water to seal them before you mosaic. If not sealed, you run a risk of your tiles popping off since the base will absorb the moisture from your adhesive and weaken the hold. Plywood is best for indoor projects as it can expand and contract in cold climates. Keep in mind that wood eventually will decay if exposed to moisture.
Tile backer boards (wedi board), ceramic, stone and cement bases need no sealing. They are great for outdoor or wet areas as well. Cement backer board is another choice for outdoor projects, although it is very heavy and harder to cut.
Fiberglass Mesh is a great way to work on a project in your studio, off-site. You place it over your pattern, which is protected by clear plastic wrap, and glue your tiles to the fiberglass mesh. It is ideal for large mosaics that may need to be cut into sections. Be careful of the fiberglass as it can irritate your skin.
Styrofoam is another fun material to use as a base. You can sculpt it, or buy it in shapes like a ball. I like to apply a thin layer of thinset and then while it's wet, cover it with fiberglass mesh to give the Styrofoam extra strength and durability. Then I use thinset to adhere my tesserae to it.
There are a myriad of adhesives that are used in mosaics. Everyone has their favorite and there are differing opinions on what works. So, here is a general overview for you.
White craft glue (I use Weldbond), is great for indoor projects. You can use it for gluing glass, vitreous tiles, and many more materials. It is also used in sealing backers, as mentioned above. It dries clear, is easy to work with and clean up.
Mirror adds great shine and reflectivity to mosaics and is fun to have in your art. You should use a silicone sealant to glue mirror down. Do not use white craft glue as in time it will eat away the silver backing leaving a black spot.
Thinset (mortar) is what I use for my outdoor projects or for mosaics exposed to wet areas. You can use thinset on just about any tile, glass, found objects, smalti, marble, dishes, etc. It is a little more challenging to work with as you need to control the amount you use so it doesn't interfer with your grout lines. It comes in powder or pre-mixed. You can add colorant to it and use it for both your adhesive and your grout.
For metal surfaces, epoxy can be used. It is a 2-part adhesive and has strong fumes, so work in a ventilated area.
Silicone adhesive works well for glass on glass. It is clear and waterproof.
These descriptions of bases and adhesives will help get you started. There are many others that mosaic artists are using, so I encourage you to continue to research and share your own experiences with our mosaic community.
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