A Comprehensive Guide to Choosing the Right Adhesive and Grout

How to Choose the Right Tile Adhesive and Grout: A Complete Guide

The Bottom Line:

Choosing the right adhesive and grout depends on matching the material to your tile type, substrate, joint size, and exposure conditions, with thin-set mortars classified by ANSI A118 standards for bonding strength and grouts ranging from sanded and unsanded cementitious options for standard jobs to epoxy and urethane grouts for demanding wet or high-traffic environments.

The Short Version (For People Who Want to Get It Right the First Time)

Here is the honest truth. The tile is the star of the show. But the adhesive and grout are what keep the show running. Choose wrong, and your beautiful tile floor becomes a callback nightmare. Tiles pop loose. Grout crumbles. Water gets underneath. Mold grows. The customer calls you.

An adhesive is what bonds the tile to the substrate. Grout fills the gaps between the tiles. They serve completely different purposes, but they work together as a system. Thin-set is not grout. Grout is not thin-set. Choose the wrong one for the job, and the whole installation fails.

The Tile Council of North America (TCNA) Handbook and the NTCA Reference Manual both contain detailed selection guides that detail the different products and considerations based on the type of tile selected and the exposure in which it will exist. This guide is going to walk you through everything you need to know to make the right choice every single time.

Let us get to work.

Part 1: Choosing the Right Adhesive

Adhesives are what hold your tile to the substrate. There are three main categories: thin-set mortar, mastic, and epoxy adhesive. Each has its place. Each has its limits. Here is how to choose.

Thin-Set Mortar: The Industry Workhorse

Thin-set mortar is the most common adhesive for tile installations. It is a cement-based product that comes as a dry powder and is mixed with water or a liquid additive on site. Thin-set is designed to be applied in a layer typically between 3/32 inch and 1/4 inch thick.

The key to choosing the right thin-set is understanding the ANSI standards printed on the bag. The American National Standards Institute (ANSI) has clear classifications for tile adhesives. Look for these on the bag before you buy.

ANSI A118.1: Unmodified Thin-Set (Dry-Set Mortar)

This is the simplest type of thin-set. It contains Portland cement, finely graded sand, and a water-retention agent. There is no added latex or polymers. It relies on moisture to cure and bond properly.

When to use it. Unmodified thin-set is required for installations over certain waterproofing membranes and uncoupling membranes. Schluter KERDI and DITRA, for example, specifically require unmodified thin-set meeting ANSI A118.1. It also works well over concrete, cement backer board, and drywall in dry areas.

When NOT to use it. Do not use unmodified thin-set over plywood. It does not adhere to wood when dry. The plywood absorbs the moisture the mortar needs to cure, and the bond fails. Also avoid it for porcelain tile in demanding conditions without checking manufacturer specs.

ANSI A118.4: Modified Thin-Set (Polymer-Modified)

This is the industry workhorse. Modified thin-set contains latex polymers that improve adhesion, flexibility, and bond strength. You can buy it with the polymers already in the powder, or you can buy unmodified mortar and mix in a liquid latex additive in place of water.

When to use it. Modified thin-set is ideal for porcelain tile, ceramic tile, and stone over plywood and cement board. The latex allows a small degree of movement in the substrate, making it suitable for exterior locations, wet areas, high-traffic areas, and over vinyl flooring. This is the standard choice for most residential and light commercial jobs.

When NOT to use it. Do not use modified thin-set over impervious membranes like Schluter KERDI and DITRA unless the manufacturer specifically approves it. The mortar cannot dry properly when sandwiched between two impervious layers, and the cure time can extend from 14 days to over 60 days.

ANSI A118.11: High-Performance Modified Thin-Set

This standard requires mortars with the ability to adhere tiles to exterior-grade plywood. Mortars meeting this standard also meet A118.1 and A118.4 requirements.

When to use it. Use A118.11 mortars when tiling directly over plywood subfloors in interior applications. This is the minimum standard for bonding tile to plywood.

ANSI A118.15: Improved High-Performance Modified Thin-Set

This is the premium category. These mortars offer superior bond strength, flexibility, and non-sag properties for demanding applications.

When to use it. Use A118.15 mortars for large and heavy tile (LHT), glass tile, exterior facades, and high-traffic commercial floors. This is what you reach for when the job is demanding and failure is not an option.

A Quick Word on Thin-Set Color

Thin-set mortar comes in gray or white. Choose gray if you are using a dark-colored grout. Choose white if your grout will be a light color. White mortar costs a few dollars more because achieving a white color requires modifications in the manufacturing process. The extra cost is worth it to prevent dark mortar from bleeding through light grout.

Mastic: The Premixed Option

Mastic is a premixed organic adhesive that comes ready to use straight from the bucket. It is made from acrylic and has a stickier texture than thin-set.

The pros. Mastic is easy to use. No mixing. No measuring. It has great tack and nonslip qualities, making it ideal for wall tiles that might slide down before the adhesive cures. It is DIY-friendly and takes longer to cure, giving you more working time.

The cons. Mastic is not water resistant. It should only be used indoors in dry environments. It is never used for floors that will get heavy traffic or for any type of heavy duty commercial use. Using mastic on a floor or in a wet area is a common mistake that leads to tile failure over time. Mastic relies on evaporation or air drying to cure, which means it cannot cure properly in thick applications.

When to use it. Mastic is best for wall tile in dry areas. Backsplashes, wainscoting, and bathroom walls above the splash zone. Small ceramic tiles that are not exposed to water.

When NOT to use it. Never use mastic on floors. Never use it in wet areas like showers, tub surrounds, or exterior applications. Never use it with large tiles, natural stone, or porcelain.

Epoxy Adhesive

Epoxy adhesive is a two-part system that cures through a chemical reaction rather than drying. It is the strongest and most chemically resistant option available.

When to use it. Epoxy adhesive is used in commercial kitchens, industrial facilities, laboratories, and other demanding environments where chemical resistance and ultimate bond strength are non-negotiable. It is also used for glass tile and other materials that require a tenacious bond.

The downside. Epoxy adhesive is expensive, difficult to apply, and requires special skills. It is overkill for most residential installations.

Part 2: Choosing the Right Grout

Grout fills the joints between tiles. It contributes to the integrity of the installation and affects the overall look. Choose wrong, and your grout will crack, crumble, stain, or scratch your tile.

The TCNA Grout Selection Guide

The TCNA Handbook includes a detailed Grout Selection Guide that details the different products and considerations based on the type of tile selected and the exposure in which it will exist. The guide covers sand-Portland cement grout, standard cement grout (unsanded and sanded), high-performance tile grout (unsanded and sanded), epoxy grout (100% solids), epoxy emulsion grout, furan resin grout, and premixed polymer resin grout.

The TCNA Handbook explains that Portland cement is the base for most grouts and is modified to provide specific qualities such as whiteness, mildew resistance, uniformity, hardness, flexibility, and water retentivity. Non-cement-based grouts such as epoxies, furans, and premixed polymer resin grouts offer properties not possible with cement grout.

Cement-Based Grout

Cement-based grout is the most common type of grout and can be used for just about any tiling project in your home. It is easy to work with and comes in a variety of colors. To keep it looking its best, cement-based grout should be sealed periodically.

Cement-based grout comes in sanded and unsanded varieties. The type you choose depends on your grout joint size and your tile material.

Sanded Grout

Sanded grout contains fine sand particles that prevent shrinkage and cracking in grout joints.

The pros. Sanded grout is stronger, denser, and generally more durable than unsanded grout. The sand gives it a grittiness that can help improve traction when used on floors and gives extra stability when installing heavier tiles on walls. Sanded grout performs better under pressure and is less prone to cracking and shrinking. It is the preferred grout for tile floors and any tile surfaces subject to weight and pressure.

The cons. The sand particles can scratch delicate tiles. Keep sanded grout away from glass, polished stone, glazed ceramic tile, and metal.

When to use it. Sanded grout is best for joints of 1/8 inch or larger. It works great with porcelain, ceramic, and rough stone tiles such as slate and travertine. It is the standard choice for floor tile installations.

Unsanded Grout

Unsanded grout lacks the sand aggregate that reinforces sanded grout.

The pros. Unsanded grout is non-abrasive, making it ideal for use with tile materials that scratch easily. It finishes smoothly, giving a clean, polished look. It is also easier to push into narrow joints because the smooth formula flows easily without leaving voids.

The cons. The lack of sand to reinforce its hold means unsanded grout is less durable than sanded grout. It is not suitable for wide joints or floor applications.

When to use it. Unsanded grout is best for joints that are under 1/8 inch. It is ideal for glass tile, metal tile, marble, and other polished stone surfaces. It is commonly used on walls and backsplashes where tight joints are the norm.

Epoxy Grout

Epoxy grout is a waterless, two-part system that cures through a chemical reaction rather than drying. It creates a dense, non-porous joint that resists moisture, stains, and chemicals.

The pros. Epoxy grout is stain proof, waterproof, and does not require sealing. It resists stains, won't crack under pressure, and is ideal for high-traffic areas due to its durability and resistance to cracking. It is more durable and resistant to chemicals, stains, and water than cement-based grout.

The cons. Epoxy grout is costly and the method of application is slightly more difficult compared to cement-based grouts. Some homeowners may think the finished product looks plasticky compared to cement grout. It has a few more mixing and application steps. Special skills and precautions may be required.

When to use it. Epoxy grout is the best choice for tiling projects that will be exposed to high amounts of water, such as swimming pools, showers, and outdoor installations. It is also ideal for commercial kitchens, restaurants, and any area where stain resistance is critical. While most professionals will use cement-based grout for a shower, that grout will require frequent resealing, which may make epoxy grout a better choice for ease of maintenance.

Urethane Grout

Urethane grout is a newer option that combines some of the benefits of cement and epoxy grouts. It is pre-mixed, requires no sealing, and offers good stain resistance and flexibility. It is easier to apply than epoxy but more expensive than cement grout. Use it in areas where you want the durability of epoxy without the difficult application.

Furan Grout

Furan grout is a specialty product used in industrial and commercial applications requiring extreme chemical resistance. It is difficult to find and harder to install than other grouts. It is overkill for residential installations.

Part 3: Putting It All Together - Selection Matrices

Adhesive Selection Matrix

Grout Selection Matrix

Common Adhesive and Grout Mistakes That Cost Contractors Money

I see these mistakes on job sites constantly. Each one leads to callbacks.

Mistake 1: Using mastic on a floor. Mastic is not strong enough for floors. It fails under foot traffic. The tiles pop loose. Use thin-set on floors.

Mistake 2: Using mastic in a shower or wet area. Mastic is not water resistant. It re-emulsifies when wet. The tiles fall off. Use thin-set or epoxy in wet areas.

Mistake 3: Using unmodified thin-set over plywood. Unmodified thin-set does not adhere to wood. The bond fails. Use modified thin-set meeting A118.11 over plywood.

Mistake 4: Using modified thin-set over Schluter KERDI or DITRA. Modified thin-set cannot dry properly when sandwiched between two impervious layers. The mortar stays soft. Use unmodified thin-set (A118.1) over Schluter membranes.

Mistake 5: Using sanded grout on polished marble or glass tile. The sand scratches the surface. The tile is ruined. Use unsanded grout on delicate tiles.

Mistake 6: Using unsanded grout on a floor with 1/4 inch joints. Unsanded grout shrinks and cracks in wide joints. Use sanded grout for joints 1/8 inch and larger.

Mistake 7: Not sealing cement-based grout in wet areas. Cement grout is porous. Water soaks in. Mold grows. The grout deteriorates. Seal cement grout in showers and wet areas.

Mistake 8: Using the wrong color mortar under light grout. Dark gray mortar shows through light grout. The grout looks discolored. Use white mortar under white or light colored grout.

Quick Reference: ANSI Adhesive Standards

Frequently Asked Questions

What is the difference between thin-set and grout?

Thin-set bonds the tile to the substrate. Grout fills the joints between tiles. They serve completely different purposes. Do not use one in place of the other.

Can I use the same adhesive for walls and floors?

Not always. Walls can use mastic in dry areas. Floors need thin-set for strength. Always match the adhesive to the substrate and the application.

Do I need to seal epoxy grout?

No. Epoxy grout is non-porous and does not require sealing. Cement-based grout should be sealed periodically.

Can I use sanded grout on glass tile?

No. The sand particles will scratch the glass surface. Use unsanded grout on glass tile.

How do I know if my thin-set is modified or unmodified?

Check the bag for the ANSI standard. A118.1 is unmodified. A118.4, A118.11, and A118.15 are modified. You can also look for terms like "polymer-modified," "latex-modified," or "fortified."

What grout should I use in a shower?

For showers, you have two options. Cement-based grout is common but requires frequent resealing. Epoxy grout is more expensive but is stain proof, waterproof, and does not require sealing.

Can I use mastic on large format tile?

No. Mastic is not strong enough for large format tiles. Use thin-set mortar.

A Final Word From The Tile Shoppe

Here is the honest truth. The tile is the star of the show. But the adhesive and grout are what keep the show running. Choose wrong, and you will be back to fix it. Choose right, and the installation lasts for decades.

At The Tile Shoppe, we carry a full range of adhesives and grouts for every application. Thin-set mortars in every ANSI classification. Mastic for dry wall applications. Epoxy grout for the most demanding environments. Sanded and unsanded grout in every color you can imagine.

Come talk to us before your next job. Bring your tile type, your substrate, your joint size, and your location. We will help you choose the right products for a successful installation.

Because a floor that stays bonded and a grout that stays intact is a floor that makes you look like a pro.

Now go install some tile. And choose the right adhesive and grout.