Mosaic Adhesives and Grouts
CEMENT BASED ADHESIVES
Tiling adhesive is available in most hardware stores and is relatively inexpensive. The bond to both the tesserae and the backer material is improved by adding a commercial tile bonding agent and priming the backer material with the same product, before applying the paste. Alternatively you can mix your own cement mortar, at one part cement to 3 parts sand – but best add a polymer waterproofing / bonding agent to improve the durability and adhesion of the paste. Cement based adhesives are suited for the indirect method of mosaics for making an adhesive bedding and are best for outdoors work and for floors and heavily trafficked areas.
PVA OR EVA GLUE
Polyvinyl Acetate (PVA) is water soluble, readily available household glue that can be used for non load bearing internal work, such as wall plaques. A waterproof variety is also available called EVA, but it is also not suited for external work. These glues are especially suited for the direct method of mosaics as the mosaic blocks or tiles can be individually buttered with the glue, prior to placing.
WALLPAPER PASTE OR WATER SOLUBLE CRAFT GLUE
Water soluble craft glue or wallpaper paste is used to adhere the mosaic tiles to the paper backing sheet for the indirect method.
There are a number of epoxy resins suitable for both internal and external mosaic work. These two part, very strong technical adhesives are somewhat tricky to deal with as they are extremely sticky, can be quite runny and usually set fairly fast. Not for the beginner to mosaics.
Clear Silicone is useful for working with glass mosaics as it lets through light, it also does not damage the silvering on mirror tiles, but some silicones are not suited for use against cement backing surfaces.
The grouts that we use for mosaics are usually cement based tiling grouts, inexpensive at any tiling or hardware store. A small bag of grout goes a long way. Additives are available to make them more waterproof, wherever this is important. They come in a variety of colours and can also be stained further to suit.
For the purist, plain cement mortar may also be mixed up if preferred – usually at the ratio of one cement to three sand. Pure cement, used without sand, is not usually advised as it shrinks and can crack or pull away from the tesserae while setting. The best bet is to buy your grout ready made.
There are many other more specialised types of grout available, which can be used to enhance the look or improve water proofing and frost resistance. These include epoxy pastes and other hi-tech resins.
A firm favorite is polyester resin ( used in car body filler and glass fibre applications). These 2-part resins are cheap and are readily available from hardware stores and motor parts dealers. There are a large range of coloring tints available to suit these products, including incredibly brilliant metallic tints such as silver and gold – wonderful for experimenting with, if you are looking for special effects. Smearing or spillage is easily cleaned up with a little acetone (nail varnish remover)
It is difficult to tell from the grout powder or wet slurry what the final visual effect of the grouting will be. It always makes sense to experiment with the color of the grout, before commiting yourself finally (and thereby possibly permanently ruining the look of a great project). So always make up a little of the grout as a trial and allow it to dry, so that you can be sure of what the final (dry) color will be.
A common-sense technique, often used, is to photograph the work before grouting, print a few color copies onto plain paper, and then try coloring in the missing grout gaps with a child’s coloring pencils or pastel crayons, until you are satisfied with the overall effect.