What backing to use for making mosaic numbers for outside?

Leanne: I am wondering if you can set them into concrete

Any piece of scrap wood or metal will work. You need something sturdy and rigid.

Wedi board is probably the most commonly used lightweight substrates among mosaic artists. It's a German product normally used in the construction industry as an underlayment for bathrooms, showers, floors, anywhere that needs waterproof material. What is it exactly? Wedi board is a foam board covered with a thin layer of fiberglass mesh and a cement coating. It is entirely waterproof and weatherproof, very rigid so it won't warp, and super lightweight. It can be used indoors and out in all climate conditions. Available in 1/4" and 1/2" thicknesses each sheet comes 3' x 5" (36" x 60") so you can often get many projects from one piece. Its easy to cut with utility knife and leaves a smooth edge that will need to be framed or covered. It is important to note you need to plan ahead when it comes to hanging. If you are not framing, installation of hanging hardware and edge treatment should be done before you begin your project.You can use most any adhesive with Wedi Board but is was created for use with cement based adhesives such as thinset. Please make sure you are using the correct adhesive for your project final display location..

One of the drawbacks to WediBoard is availability. It is not carried at your local home improvement store. Contact you local tile and flooring store to check for availability. GoBoard, Durock Ultra Light, Kerdi Board and other foam core products - Similar to WediBoard all of these products are lightweight, rigid, water and weather proof, and tempertaure stable. All were developed for the building trades for showers and flooring underlayment and all of the above cutting, hanging, and adhesive instructions above for WediBoard apply. The upside here is that one or more of the these products can be found at most local home improvement stores. The same hanging and edging practices used for Wedi Board apply here.Wood - Although wood is readily available one must proceed with caution when selecting this as a base material. Wood is vulnerable to changes in humidity or temperature and can warp or crack, thus popping tiles and cracking grout. needs sanded to aid in bonding, free of loose or peeling paint,and sealed. Wood elements from craft stores (frames, shelves, birdhouses, boxes, etc.) are ready for mosaics but are NOT suitable for outdoor use. We recommend Kilz. It not only seals but acts as a bonding agent for your adhesive. Do not use sealer's like Thompson's water seal, as they leave a waxy finish that prevents adhesives from sticking.

Treated and exterior grade lumber also is not a choice. The treatment that it receives is to prevent rot and does not prevent warping.

* Best advice - If you are using wood. Keep it indoors where the humidity is more stable and your piece will not get wet. SEAL IT! Use a high quality bonding primer such as Kilz.

Plywood - Although wood is readily available one must proceed with caution when selecting this as a base material. Even plywood is vulnerable to changes in humidity or temperature and can warp or crack, thus popping tiles and cracking. It may be used successfully indoors in smaller sizes and should be sealed with Kilz or similar primer. Multi-layer birch cabinet plywood is a good choice for interior art work.