Grout vs Thinset: Differences and Which to Use

Grout is a cement-based filling material used to fill up the spaces between tiles after they’ve been installed. Thinset- meanwhile- is a cement-based material used to facilitate structural bonding of tiles to the subfloor. To make grout and thinset, polymers are usually added to cement to improve their bonding/adhesive strength.

However, that’s as far as the similarities go. In this blog, we go through the differences between grout and thinset, complete with a comparison of their structural strength.

Grout vs Thinset: Differences

Purpose

While grout serves both an aesthetic and functional purpose, thinset only serves a single functional purpose. Grout not only fills up the spaces between the tiles to prevent water and dirt from penetrating into the foundation surface; but also forms beautiful grout line patterns, especially if colored grout is used.

Thinset- on the other hand- is an adhesive that facilitates bonding between floor tiles and the subfloor. Since thinset is used beneath the tiling and can’t be seen like grout, it doesn’t serve any aesthetic purpose.

Materials

Grout is usually made by mixing cement with sand or silica, and various bonding elements. However, depending on the type, the grout may or may not contain sand. Thinset- meanwhile- is made by mixing cement, fine sand, and a water-absorbent element.

Versatility of Use

While it’s possible to use thinset in place of grout, it’s not advisable to use grout in place of thinset. This is because thinset boasts greater structural strength and can be used to fill in the gaps between tiles if grout isn’t available. Grout- however- cannot be used as an adhesive to stick the tiles to the concrete subfloor, as it’s structurally weaker compared to thinset.

Consistency

Remember, grout is made by mixing cement lightly so that it forms a light paste that pours easily between the tile spaces and sets fast, but isn’t strong. Thinset- meanwhile- contains more cement in the mix, forming a heavier paste that cures slowly, but is strong.

See also: Caulk vs Grout, Is It Necessary to Seal Grout?, Sanded vs Unsanded Grout

Which is stronger: grout or thinset?

Thinset is made to be structurally stronger than grout, as strong bonding is needed between the floor tiles and the subfloor. Grout- while also containing polymers for added structural strength- isn’t as strong as thinset; as the narrow spaces between tiles can be sufficiently filled up by a material with moderate structural strength.

How soon can you grout after thinset?

Before grouting the spaces between your recently installed tiles, you should at least allow enough time for the thinset adhesive beneath the tiles to dry. Typically, it takes about 48 hours for thinset to completely dry up. If you apply grout before the thinset underneath has cured, you run the risk of tiles cracking as you step on them.

This is because the grout cuts off the air supply to the thinset below, further delaying the completion of the curing process. And since wet thinset cannot effectively facilitate adhesion, your tiles will either get misaligned or crack under pressure.

Can you use grout as Thinset?

No- it’s not advisable to use grout in place of thinset- as these two don’t boast the same structural strength. As such, grout isn’t able to effectively stick tiles to the concrete subfloor as well as thinset does. On the contrary, though, it’s possible to successfully use thinset in place of grout.

While you shouldn’t use grout in place of thinset, it’s totally possible to use a mix of these two substances as a reinforced material for filling in the spaces between floor tiles. This is especially helpful as an alternative to using grout by itself if the gaps are significantly large. By adding thinset to sanded grout, you’ll get a mix that’s structurally strong enough to effectively fill up tile gaps as large as 10-millimeters.

Do you need to remove thinset before grouting?

Yes- it’s important to remove excess thinset from between your grout lines before applying grout. This is because if you grout over thinset, it’ll bulge higher than the actual grout level once dry; causing small, unsightly bumps on your grout joints.

You also need to ensure that you remove the extra thinset from the grout lines while it’s still wet, as dry thinset is difficult to remove.

The procedure detailed below will guide you on how to properly remove thinset prior to grouting:

1. As you’re pressing each tile down on the surface during installation, wipe off any excess thinset that smudges over to the grout joints using a damp piece of clothing. You can also use a narrow object like a margin trowel to reach in between the tile gaps and dig out residual thinset sitting at the base of the grout lines.
2. If there’s any dried thinset still left in the grout joints after some time, dig it out using a razor knife and then wipe the edges of the tiles using a sponge. This step is- however- labor-intensive; which is why you’d want to remove as much excess thinset as possible while it’s still wet.  
3. If you can still see exposed thinset bulging above the grout lines after you’ve poured your grout and it has cured, you’ll have to dig through the grout and dig out the thinset using a margin trowel. Then, finish off the process by using a vacuum cleaner to suck up any thinset debris that’s still lying on the edges of the tiles and in the grout lines.