Trowels and Thinset

Trowel sizes:
Trowels come in several shapes and sizes generally from 3/16" v-notch to half-inch square notch. The proper trowel size is basically matched to the tile size; the smaller the tile – the smaller the trowel; the larger the tile – the larger the trowel.

Also, floor tile needs a heavier mortar bed to stand up to foot traffic. The following chart will give you specific uses for a variety of popular trowel sizes.

The size of the trowel is intended to give a substantial mortar bed underneath the tiles for good attachment and durability. You want a mortar bed that will stick to a significant percentage of the tile without voids or hollow spots, which are vulnerable to breakage. Most non-professionals will pick an undersized trowel for the job. If you’re not sure, don’t be afraid to go with the larger sized trowel.

Be familiar with the various trowel sizes before you begin your job.

Mixing thinset:
Most tile bedding mortars or thinset mortars are high quality and contain dry latex additives for flexibility and durability. For a lasting job, a good quality thinset is well worth it.

You'll need some 5 gallon buckets, a decent power drill and a mixing or beater bar.

Start by adding a little clean cold water to a clean mixing bucket. An inch or two should do. Don’t use warm or hot water. The heat in the water will accelerate the hardening of the mortar.

Now pour in a half bag or less of dry thinset mix. Mix it a little with the beater bar attached to the drill. The mixer speed shouldn’t be more than 300 revolutions per minute, or medium to low on a variable speed drill. High speed mixing adds too much air. Gradually add more cool water until the mix is sticky wet, but does not slump or fall down when you stop mixing. Mix very thoroughly up and down, round and round, side to side until the mix is creamy smooth with no lumps. When you have it mixed to the right consistency, it’s time to stop and slake. Letting the mortar slake or rest is a very important step in a good thinset mix. Let the thinset rest for about 10 minutes. This allows time for the dry activators and additives to chemically do their work. The thinset will start to stiffen-up and get thick.

Now re-mix the batch and the mix will loosen-up and return to its smoother and looser original consistency. Proper slaking will insure that the additives are activated and will extend the working time or pot life of the mortar. If the batch starts to thicken as the job progresses, just remix it and it will loosen up. Never add more water to a mixed and slaked batch.

Spreading thinset:
With the proper trowel size, properly mixed thinset and a properly prepared setting surface ou’re ready to spread the thinset and attach tiles. For additional information read our article on surface preparation here.

Hold the trowel at a little less than a 45 degree angle to spread the thinset.

Only apply as much thinset as you can work in 10 or 15 minutes. Use the trowel to dip into the batch bucket and scoop out some thinset. If the thinset is mixed properly, it should stick and mound on the trowel without dripping off like thick soup.

You might dip only a few or several times to get enough thinset on the setting surface depending on the trowel size. Spread the thinset over the area you intend to set, with the emphasis on sticking it to the setting surface. Some say this is best accomplished by using the flat side of the trowel first, but it seems to be an extra step.

Once the thinset is generally spread over the setting area, start combing it into every square inch of the surface. Hold the trowel at a little less than a 45-degree angle. The more vertical you hold the trowel, the more thinset you apply—the flatter you hold the trowel the thinner the mortar bed will be.

The important thing is that you hold the trowel at the same angle throughout the job, making the mortar bed the same thickness every time. Comb the thinset to every corner and edge and then re-comb. As you move the trowel through, it will screed off excess mortar. Conversely, areas with too little thinset will show up as voids in the shape of the trowel notch.

Add more mortar to thin areas and comb through it again. The idea is to make the mortar bed as even as possible and to be consistent throughout the whole job.

You can now start bedding tiles. As you go, the thinset should remain sticky. If the thinset starts to crust over, you will loose attachment. You can re-comb through crusted over thinset or just remove it and start over.

After you have set the first few tiles, pull one up to make sure you are getting good attachment and coverage. If not, you may need to change to a larger trowel or remix the thinset.

We hope these tips help you on your tile project. Good Luck!

How-To-Tile Articles

Grout: Problems and Solutions
Trowels & Thinset
Surface Preparation
Transitions
Cutting Tools
Tile Design Guidelines
Caring for stone
Applying Grout
Porcelain or Ceramic?
Granite Tiles
What is Tile Bullnosing?
Bullnosing Ceramic Tile