Your choice of glue is fundamental to the success and longevity of your mosaic. If you use a water based glue for an outdoor project, your mosaic will fail many years earlier than you would want it to. Creating a mosaic takes time and patience and you’ll be so pleased when you complete a wonderful outdoor piece, so you want it to last for as many years as possible so remember to plan your project effectively and use the correct glue.
The mosaic base (substrate), tesserae (tiles)
, project use, and its location all influence the type of adhesive you will choose. There is a 'glue' for every situation.
Common choices include:
PVA (poly vinyl acetate) Sold under various brand names. Often used for interior mosaics that won't be exposed to the elements. An advantage is that it is very strong and can adhere tesserae to slippery surfaces like ceramic and glass. Diluted, it is useful as a surface sealant prior to applying mosaic or as a strength additive to grout.
Cement Based Mortars: The traditional adhesive made by mixing powdered cement, sand and water. You can get quick setting, pre-coloured, made for glass, tile adhesive (thinset), and traditional mixes. For exterior use, use one that is waterproof and frost proof.
Epoxy Resins: A two part adhesive consisting of a resin and hardener mixed together right before use. They will adhere tesserae permanently to metals. They are often messy, smelly and have different windows of working opportunity before they set.
Other Choices: Silicone, silicone-based glues, ultraviolet curing glues, and construction adhesives. Always check the package and match the adhesive to your tesserae, base material, and the object's final destination.
When I’m creating large outdoor mosaics e.g. for a school I use external tile adhesive (often called thinset online) For smaller outdoor projects I use external Unibond No More Nails.