Most manufacturers recommend using a primer to bond the tile to concrete, wood, plaster, gypsum tile, and plasterboard surfaces. This improves the bonding surface for the adhesive and prevents issues with high porous or non-porous substrates by providing a strong and permanent bond for your tiles. Every surface is different with its own characteristics of porosity, rate of expansion and contraction, and dimensional stability.
The substrates must be level, smooth and free from dust, grease, oil, dirt, curing compounds and sealers that prevent a good adhesion to the tile. All concrete has a fine layer of cement called “laitance” that floats to the surface when concrete is poured. This limits the adhesive bond to the concrete and must be removed using an acid etching of 5% hydrochloric acid, rinsing thoroughly with water and allowing to dry for 24 hours. Other preferred options are: TEC grinding it with an 80-grit sandpaper, shot blasting or scrabbling to form a rough area to apply the primer. Any structural cracks in the concrete not fixed by cement caulking will eventually have the crack carried through to the tile surface. Nonstructural cracks,that do not move, will need a flexible tile adhesive. Low spots in the concrete are not ideal, but they can be filled with fresh concrete and leveled.
All flooring substrates such as tile, vinyl, laminates, rubber flooring, linoleum, particle board, wood and plasterboard must be firmly fixed to the floor. If you think that your wood floor has any varnish, stains or oils, the floor should be sanded and wiped with a damp mop. All finishes must be well bonded to the wood. Any timber flooring exposed to rain may not be suitable for tiles. Sandstone or slate should never be tiled over. Use Thinset removal chisel bit for any loose grout in between tiles.
All surfaces should be cleaned with a damp mop using soapy water and left to dry for the best adhesion of the primer. A temperature of 50-95 degrees Farenheit is the ideal temperature to apply the primer. Various multipurpose primers are available often made of acrylic synthetic resin, aggregates and polymers especially formulated for mechanical adhesion or latex based primers which are water resistant and work well in areas in continuous contact with water, humidity or dampness. Poly Vinyl Acetate Primers are NOT recommended for areas exposed to water or moisture. TEC® Multi-purpose Primer is highly recommended for hard to bond surfaces.
The work area should be ventilated as much as possible since even low VOCs (volatile organic compounds) emit gas into the air. Personal Protective Equipment should include a mask, nitrile chemical resistant gloves, safety goggles, knee pads, a broom, and a large bucket to mix the primer. Instructions on the label will help you to correctly prepare the multipurpose primer. Mechanical mixers work well especially when the instructions indicate that the primer needs diluting for porous material like concrete with a primer to water ratio of 1:3 and wood needs a ratio of 3:1. Gypsum requires either a 1:3 or 1:2 ratio and two coats of primer while all other surfaces require only one. Primer is used full strength for all other non-porous surfaces. First, pour the water into the bucket followed by the primer material and mix it into a slurry for a smooth paint-like consistency. Using a brush or roller, apply the primer in smooth strokes over the surface of the area that will be tiled. Primer dries within 4-6 hours and check if it is dry by touching it with your finger. Once completely dry, avoid walking on the primed surface with dusty shoes. Apply an appropriate polymer-modified Thin Set mortar a maximum 1/4 inch standard thickness with notched trowels. Install porcelain or ceramic tile over the wet Thinset Mortar and grout the tile after 48 hours to end with a nice finish to your project.