Mixing Thin-set Mortar

With the setting bed in place—cleaned, and marked for the layout—it is time to prepare the adhesive. For tiling walls, you will probably use an adhesive that does not have to be mixed. For tiling floors, you can use premixed thin-set or floor tile adhesive, but the thin-set mortar that you mix yourself will be the strongest.

Mixing will be easier if all the ingredients are at room temperature; buy the powder and any additives in advance and store them overnight in a heated part of the house. Mixing can get sloppy, especially if you are using a power mixer. Place the bucket in the middle of the area to be tiled, or on top of a drop cloth. Use a heavy-duty, 1/2-inch drill for power mixing, as a smaller drill may burn out. Keep a second bucket on hand, about half full of water, for cleaning your mixer.

How Much to Mix? Like other cement-based adhesives, thin-set mortar begins to cure almost as quickly as it is mixed. If you mix too much at once, it may be unusable when you reach the bottom of the bucket. On the other hand, it is a waste of time to mix batches that are too small. Professional tile setters mix enough adhesive to last them somewhere between 30 and 60 minutes. However, if you are working in a room with dry air, you may need to mix less mortar. Experiment with progressively larger batches.

Mixing by hand. Mix small batches of thin-set mortar (less than two gallons) by hand. Use a trowel or a stiff piece of wood, and make sure you scrape the bottom of the bucket as you stir.

Using a mortar mixer. Mix larger batches with a mortar mixer mounted on a powerful drill. Clamp the bucket with your feet to keep it from spinning. Set the mixer in and start mixing with short bursts of power to keep the mixture from spilling.

Proper consistency. It takes some practice and experience to know when the mortar has just the right amount of ingredients. The mix is too loose if it runs off the mixing tool. Add more dry ingredients and mix some more. Lift the mixer again. The mortar is ready when it falls off, but no longer runs off, the mixing tool. If the mortar starts drying out before you’ve used it up, discard the batch and mix a new one. Adding more liquid at that point will make the mortar less adherent.

Spreading Thin-Set Mortar

After mixing the mortar, let it direst for 10 minutes before applying. Scoop a small amount onto the setting surface and comb it with a notched trowel. If the ridges hold their shape and do not flatten out, the batch is ready to spread. Begin spreading mortar at the intersection of your reference lines. Take care not to cover up the lines. Work in small areas. If you’ve never tiled before, spread only enough to cover 2 or 3 square feet. As you gain experience, you can expand the size of the working area. Packages of thin-set mortar refer to the open time—the amount of time you have to set tiles on combed adhesive. Use a margin trowel to scoop adhesive onto the bottom of your notched trowel, or drop dollops of mortar onto the floor and then spread them out. Give the thin-set mortar a quick stir from time to time.

1. Apply the thin-set mortar. Hold the smooth edge of the trowel at a 30-degree angle to the surface. Press adhesive firmly onto the surface. Use sweeping strokes to spread to a consistent depth. Don’t cover reference lines.

2. Comb the thinset mortar. Turn the trowel to the notched edge. Hold the trowel at a 45- to 75-degree angle to form the proper depth of ridge. Comb over the entire surface to produce equally sized ridges.

Caution! Working with Epoxy Adhesive - Epoxy-based adhesives are expensive and tricky to use. Fortunately, they are usually not needed for residential tile jobs. But if you have a setting bed that is incompatible with other adhesives, or are installing tile in an area likely to receive extreme heat, epoxies may be necessary. Read all instructions carefully. Wear a charcoal-filter mask, work in a well-ventilated area, and avoid skin contact with the mixed solution. Mix epoxy adhesive by hand and carefully follow the manufacturer's instructions about the proportion of wet and dry ingredients.

3. Check the coverage. After spreading and combing a small amount of the mortar, press a tile in place. Twist it a bit so that it is set in the adhesive, then pry it up and look at the bottom. About 75 percent of the surface should be covered. If too little adhesive has stuck to the tile bottom, the mixture is probably too dry.

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