For verticle surfaces, installing over plywood or drywall is fine if it is an aesthetic installation and not a wet area. Use ceramic tile mastic. DO NOT USE THINSET MORTAR.

Flexible plastic or other material, thin composition paneling that has 'give', etc, should not be used as the grout will quickly crack and the tiles will pop off. Surfaces must be solid, free of loose paint, wallpaper, dirt and grease, etc., and must be able to support the weight of the tile and grout It may be necessary to 'key' the surface by scoring or sanding it so the your adhesive will stick to it. Particle board is NOT a suitable surface. Backerboards Backerboards are waterproof and come from your local Do It Yourself home improvement store. They come in sheets which can be cut to size. It is commonly used to cover the wall under your shower tile and over wood floors to be tiled. Most are made of a concrete composition. 'Hardibacker' is the brand name for a backerboard that is easier to cut and lighter weight than cement boards like "Wonder board". Both are water resistant and secure well with thin-set. Backerboard cannot support itself and must be attached to something else. It can be screwed into wall studs, cement block walls, just about anything. For more information on Hardibacker go to James Hardie's website, (manufacturer of Hardibacker). I want to make a tile mosaic to put on my house above the entryway outside. My house is made of stucco. This is also my first large-ish scale mosaic project, going to be approx 3' square. The problem is this: The area where this will be going is about 15 feet up in the air, so I wanted to be able to put the mosaic onto a backer board and then attatch that to the house. But, my design is very rounded, and from what I have read on the web, it is extremely difficult to cut something like hardibacker into rounded shapes. I don't want to use wood because that will rot in no time with the Florida weather. ----------------------------------------------------------- Follow-Up Postings: KimmyStar Mon, Jan 3, 05 at 13:04 perrisquirrel, I did a half round backerboard piece. It's down the page a bit 'Grouted Sign'. While it isn't 3', it is rather large. Draw your circle out. Score it all the way around. Then score from the circle to the outside of the backerboard and break off in sections. If you have uneven edges, take a screwdriver and a hammer and gently tap. Worked like a charm for me. Kimmy ----------------------------------------------------------- bondo4 Thu, Jan 6, 05 at 15:11 I cut a circle out of concrete backer board for my table using a saber saw and about 1/2 a dozen blades. It took a bit and next time I'll wear a mask (lots of dust) but it worked quite well. You do have to go slowly though and be prepared for some horrible noises as the blade dulls. Buckster Sat, Jan 8, 05 at 23:41 Are you talking about wonderboard. This is a concrete type board. Also what do you use to put the tile onto the board, also did you use tile? ---------------------------------------------------------- KimmyStar Sun, Jan 9, 05 at 7:29 Bucky, Wonderboard...hmmm...I think so. The brand that I buy is Hardibacker, I think. It comes in sheets and is impregnated with concrete. Basically used in kitchns and baths where tile and grout are exposed to water. Found mine at Lowe's. Comes in 1/4" and 1/2". There is also a product called Wedi board, which is styrofoam covered in concrete. It's supposed to be wonderful, too. Another variant on the styrofoam/concrete material is called easyboard. Any or all of these are what is recommended for outside use. Wood May warp or crack in extreme humidity or dryness or if exposed to the elements. Where temperature changes may cause wood to expand and contract and cause grout to crack you may want to choose a backerboard to go over the wood. Painted or stained wood should be sanded and free from peeling paint. Wood for larger projects should be at least 5/8" thick to guard against warping. Even treated or exterior grade wood will warp! (the treatment is so that it will not rot) If it is to go outdoors it must be exterior grade AND either attached to a frame (such as a table base) or have a backerboard glued and screwed over it (see backerboard). Then tile over the backerboard. Wood elements from craft stores (frames, shelves, birdhouses, boxes, etc.) are ready for mosaics but are NOT suitable for outdoor use. Wood can be sealed with a 50-50 mixture of WeldBond and water. Do not seal wood with water sealers such as Thompson's water seal. They leave a waxy finish on the wood that prevents the glue from sticking. Formica Must be very clean. Consider using TSP soap (Trisodium Phosphate). Should be keyed first with very coarse sandpaper or a utility knife. Remove any peeling pieces. Nice flat surface to work on. Metal Must be free from paint. Rust must be treated with rust remover and rust blocker first. Test adhesives first (see Test First at the top of this page). Concrete Remove any algae or mildew with a bleach wash. Can be sealed with a grout sealer first. Note: for birdbaths use caution and make sure sealers will not cause water to be toxic to birds. Call the manufacturer's toll-free number that will be listed on the sealer package. Terra Cotta Remove any algae or mildew with a bleach wash. Remove all dirt and dust. Can be sealed first with a 50-50 mix of WeldBond and water (paint on with an old paintbrush and it will suck it right up). Grout sealer or Saltillo Tile Sealer can also be used. Drywall Must be free from peeling paint, dirt, etc. If your mosaic is a large one I suggest screwing a backerboard over the drywall (screw to vertical supports ("studs") behind the drywall) as the drywall may not be strong enough to support the finished product. (From Wits End Mosaics) azglasslady Wed, Aug 18, 04 at 7:51 Has any one tried putting mosaic on Formica? I have a low 26 x 46 counter next to the Garden Tub (the listing said) in the master bath which is almost useless. I have a plant and a candle sitting on it now. There is a shower in the bathroom also, so don't use the tub. I would like to put mosaic on it to jazz the room up, and can use my scrap glass or get tile for design. Thanks for your help. Pat CEDobson Wed, Aug 18, 04 at 8:02 I have done mosaic on formica. I used stuff from Home Depot in the tile section called AcrylPro, comes in a big tub, and it sticks on everything, dries hard as a rock, and clean up is easy. I have, however, only used ceramic tile, so if you are using glass, i'm not sure. As a testament to its sturdiness, I did an entire living room wall in mosaic, and not one tile has budged yet, or during the grouting stage. Chris

Thanks all! I know Ditra doesn't stop flex, just thought it might help reduce cracking from the flex that I fail to eliminate if that makes sense. :) There is a space about 8" tall above the cabinet doors under the counter which should allow for placement of a sturdy corbel or something at the end. Couldn't hurt, right? (Especially since I have no plans to ever sit there. ha!) Anyway, do I want a decoupling membrane over my second piece of plywood? Or can I skip it if I get everything nice and firm? It's supposed to be a dry area but it is a kitchen...

You are asking about "deflection rating". The answer is: we don't know. The deflection rating of a wood joist floor requires TWO pieces of information: The distance between joists (the "on centre" measurement between one joist and another) TOTAL subfloor thickness. The thickness of BOTH layers of subfloor added together. So....you need to find out several more things before you can continue: 1. You need to find out the allowable deflection rating for your product, The thickness of subfloor required (using the "on centre" measurements of the joists you have) to achieve that deflection rating Cement backer board does NOT add structure. That means you could drop down 3 INCHES of cement board and it won't add a darn thing - other than costs and height. Tiles are SOOOO much fun!!!! Go ahead and look up deflection ratings. Then measure your joists (on centre measurements) and find out what you already have. Now compare that to what is NEEDED to get a tile into place. And don't forget the crack suppression membrane.