Do You Put Grout Under Tile? A Practical Guide
Learn whether grout goes under tile, when it should be applied, and best practices for durable tile installations. Grout Maintenance explains proper grout placement and common mistakes to avoid for DIYers.
Do you put grout under tile? In standard tile installations, you do not grout beneath the tiles themselves. Grout fills the joints between tiles after the thinset or mortar has set. Grout underlayment is not intended to support tiles; if you hear about 'grouting under tile,' it’s usually a misunderstanding or a special case such as preassembled tile sheets or edge detailing. For most projects, grout goes on top of the setting bed, not underneath.
Do you put grout under tile? Debunking the myth
When people ask whether grout should go under tile, the answer is usually no. Grout's job is to fill the joints between tiles on the surface. The setting bed, created with thinset mortar, bonds the tile to the substrate. Grout sits above the substrate, filling the gaps between tiles and helping seal the installation from moisture and dirt. Inconsistent or misplaced grout beneath the tile can trap moisture, encourage mold, and create hollow spots that jeopardize the tile's stability as it expands and contracts with temperature and moisture changes.
According to Grout Maintenance, understanding where grout belongs is a key step in a durable tile job. If you ever see someone claiming to grout beneath the tile, ask what problem they're trying to solve. In most cases, the underlying issue isn't grout placement at all but substrate flatness, improper mortar bed, or insufficient curing time. For DIYers, it's tempting to try to solve a wavy substrate by filling underneath; the result is brittle grout, debonded tiles, and a surface that looks uneven. The best practice is to address substrate issues separately: fix the substrate, ensure proper mortar bed, and then grout after tiles are set. Finally, remember that grout around the perimeter is important for expansion joints; you should not fill the space under the tile itself.
Do you put grout under tile? Debunking the myth
Tools & Materials
- Cement backer board or approved underlayment(Solid, dry, and flat with a moisture barrier where needed)
- Thinset mortar(Follow product guidelines for substrate and tile type)
- Notched trowel(Choose notch size appropriate for tile size)
- Tile spacers(Maintain uniform grout lines)
- Grout (cementitious or epoxy)(Select based on area exposure and maintenance goals)
- Grout float(Use at a 45-degree angle to fill joints)
- Sponge and clean water bucket(Wet sponge for cleanup during grouting)
- Sealer (for cementitious grout)(Apply after curing if recommended)
- Mixing bucket and drill with paddle(For consistent grout and thinset mixtures)
Steps
Estimated time: 2-4 hours (installation) plus grout cure time 24-72 hours depending on product
- 1
Prepare substrate and plan layout
Assess the substrate for flatness and damage. Fix any dips or cracks, install moisture barriers if needed, and establish a straight layout line to guide tile placement. This upfront planning prevents uneven grout lines and lippage later on.
Tip: Dry-run the layout with spacers and full tiles before applying adhesive to catch alignment issues early. - 2
Mix and apply thinset
Mix thinset according to the manufacturer's guidelines and spread evenly over a small area. Use a notched trowel to ensure consistent thickness and contact with the substrate, avoiding voids beneath tiles.
Tip: Back-butter large format tiles to improve contact and reduce hollow spots. - 3
Set tiles with consistent joints
Press tiles firmly into the thinset, making a slight twisting motion to seat them and eliminate air pockets. Maintain uniform gaps with spacers and monitor line straightness as you progress.
Tip: Check for lippage after a few tiles are placed and adjust immediately. - 4
Allow setting bed to cure
Let the mortar cure per the product’s guidelines. Avoid traffic or water exposure on the tile surface during this period to prevent shifting.
Tip: In damp or cool spaces, curing may take longer; plan accordingly. - 5
Grout the joints
Mix grout and work it into joints with a grout float at a 45-degree angle. Wipe away excess grout from tile faces with a damp sponge as you go to minimize subsequent cleaning.
Tip: Work in small sections to prevent grout from drying on the surface before you wipe. - 6
Cure, clean, and seal
Allow grout to cure fully, then perform a final cleaning. Seal cementitious grout if recommended by the manufacturer to reduce staining and moisture infiltration.
Tip: Follow humidity and temperature guidelines for sealing to avoid dulling the grout.
Got Questions?
Do you ever grout under tile?
Not in standard tiling; grout goes in the joints between tiles. Some rare edge cases or pre-grouted sheets may look different, but beneath tiles is not the typical practice.
Grout is used between tiles, not under them. Only unusual edge cases or pre-grouted sheets would differ.
Is there ever a case to grout under tile?
In general, no. The substrate and mortar bed support the tile; grout beneath them traps moisture and can cause problems. If you see claims to grout under tiles, treat it as a misunderstanding or a specific edge condition.
Grouting under tiles is not standard practice; usually it signals a misunderstanding or special setup.
Should I use cementitious or epoxy grout?
Cementitious grout is common and easier for DIY projects, but epoxy grout offers superior stain resistance in wet areas. Your choice should depend on exposure, maintenance preference, and budget.
Cementitious grout is common and easier; epoxy is tougher but harder to work with.
How long does grout cure?
Grout cure time varies by product and conditions; plan for a full cure period before sealing or exposing the surface to moisture. Always follow the manufacturer's guidelines.
Cure time depends on the product and conditions; follow the maker’s instructions.
Should I seal cementitious grout?
Sealing is often recommended to protect against stains and moisture, especially in showers and kitchens. Check product guidelines and re-seal as needed.
Sealing helps prevent stains and moisture; follow the product’s instructions.
What causes grout to crack after installation?
Cracking is usually due to substrate movement, improper expansion joints, or improper curing. Regrouting and adding movement joints are common remedies.
Movement in the substrate or lack of expansion joints often causes cracks; regrout and add joints as needed.
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The Essentials
- Grout belongs in joints, not under tiles.
- Fix substrate flatness before grouting.
- Follow cure times and sealing recommendations.
- Choose grout type according to area and maintenance goals.
