STEP THREE – Adhesive for Exterior Mosaic Projects
In Step 3 of your easy garden mosaic you select and apply an appropriate exterior adhesive, lay the tesserae, and affix with heat (for heat-activated adhesive,) or allow to dry for 24 hours with most other adhesives. The following is a list of adhesives that I recommend for exterior use. This is not a list of all adhesives that can be used outdoors, just those that I find work well.
Suggested Adhesives for Exterior Projects:
- No Days Mosaic Adhesive
- Silicone Caulks and Adhesives: GE Silicone II Window & Door Sealant, Dap Clear Silicone Sealant, Lexel Clear Adhesive Caulk
- Thin-set Mortar – *see information below
No Days Mosaic Adhesive
“No Days Mosaic Adhesive” is a quick acting adhesive that is activated by heat from a Heat Gun or your home oven. “No Days Mosaic Adhesive” becomes liquid at 160 to 165 degrees Fahrenheit, and then solidifies and adheres the two materials together as it cools. It will not re-liquify unless it is heated to the same high temperature again. I find that it is much easier to use “No Days Mosaic Adhesive” on a flat surface such as a flagstone, flat stone. or tile, rather than a curved surface, such as a flower pot or rounded stone. It is more expensive than some other exterior adhesives and not as easily available, but it is great for completing projects in a hurry – same day from beginning through grouting. You can find No Days Mosaic Adhesive online at Delphi Glass or at Hobby Lobby, (though my local Hobby Lobby keeps a very limited supply on hand.)
Silicone sealant, as described by one of the manufacturers, GE, is: “permanently flexible, and adheres to most woods, ceramics, glass, aluminum, and steel. This caulk creates a weatherproof/watertight seal around your windows, doors, air conditioners and duct work.” I like to use the Windows and Doors type for exterior projects. I usually use the clear stuff, but the white caulk may be a good choice if you are using cathedral glass and you want to bring up the color a bit.
Some silicone caulks indicate that it is ready for water in 3 hours after application, but, if you read the fine print, the manufacturer recommends 24 hours for complete curing. I always give it at least 24 hours. Silicone caulks can get messy. Be careful not to apply it too thickly; it can squish up into the space between the tiles so there is no room for the grout. Some people object to the smell, but it’s not too bad, especially if you use it in a well-ventilated area (outdoors is a good idea,) and I recommend leaving it to cure in a well-ventilated area away from people and pets. The cost is reasonable and you can buy it in large or small containers. (The large ones require those metal caulking guns to use.) You can buy small squeezable tubes of GE-II for about $5 at Home Depot.
(Note: Use silicone caulk with care and wear gloves. Silicone caulks can be harmful if swallowed, inhaled or absorbed through the skin. Read the MSDS (Material Data Safety Sheet) for the product you choose for complete information. The MSDS is available on the Home Depot website for products they carry; for other products contact the manufacturer.)
If the mosaic is in an item that will hold water, such as a birdbath or fountain, your best bet is to use thin-set bonding mortar instead of glues or caulks. Thin-set is a strong polymer-modified dry powder mortar to which you add water. You can buy quick setting mortars that cure in 6 hours; others may take 24 hours to dry.
You have to be careful when working with mortar; it contains Portland cement. It is caustic and considered a “hazardous chemical” by OSHA. It is harmful if swallowed, irritating to eyes and the respiratory tract, and can cause burns in the presence of moisture if it gets into your eyes or onto your skin, (and eyes do tend to be moist.) So, WEAR RUBBER GLOVES, A MASK, AND EYE PROTECTION while mixing the mortar powder with water, so that you do not inhale dust particles or get them in your eyes, and KEEP YOUR GLOVES ON while working with mixed mortar. (These are the same precautions you should take with grout. Read the MSDS (Material Data Safety Sheet) for the product of your choice for full information on warnings and precautions. The MSDS is available on the Home Depot website for products they carry; for other products contact the manufacturer.)
This post is part of a series on Mosaics on the Rocks: