What Type of Mortar for Backsplash? A Complete Guide

Choosing the right type of mortar for your backsplash is crucial to achieve a long-lasting, beautiful result. The mortar acts as the adhesive between the backsplash tiles and the wall, so using the proper type matters greatly. There are several factors to consider when selecting mortar, including the backsplash material, the wall type, and exposure to water. This comprehensive guide will examine the most common backsplash and wall materials, the different types of tile mortar available, and provide recommendations to ensure success with your project.

Backsplash Materials

The most popular backsplash tiles and materials include:

Ceramic and Porcelain Tile

Ceramic and porcelain tiles are classics for backsplashes. They come in a huge range of styles, colors, shapes, and textures. Ceramic tiles are made from clay that is fired at high temperatures. Porcelain tiles are denser and less porous than ceramic. Both offer durability and water-resistance.

Mortar Recommendation: Polymer-modified thinset or mastic.

Glass Tile

Glass tile backsplashes provide brilliant color effects and shine. The glass is translucent and available in lots of finishes from shiny to matte. Glass tile needs special consideration due to its weight and susceptibility to damage.

Mortar Recommendation: Epoxy mortar or grout.

Natural Stone Tile

Backsplashes made of granite, marble, travertine, slate, and other natural stones look amazing. However, being porous and vulnerable to staining, sealing is required. Extra care must also be taken during installation.

Mortar Recommendation: Polymer-modified thinset.

Metal Tile

Metal tiles like stainless steel, copper, and aluminum bring contemporary style. Most have protective coatings, but sealing between tiles is still needed. Metal can be prone to scratching and denting if not handled properly.

Mortar Recommendation: Epoxy mortar.

Mosaic Tile

Mosaic tiles are small, usually 1-inch square or smaller. Popular types are ceramic, porcelain, glass, and stone. Intricate mosaic patterns require more grout lines and precision setting compared to large format tile.

Mortar Recommendation: Polymer-modified thinset.

Wall Materials

Common backsplash wall base materials include:


Drywall, also called plasterboard or wallboard, is the most common backsplash substrate. Joint compound is used to smooth seams between drywall sheets before tiling.

Mortar Recommendation: Polymer-modified thinset.

Cement Board

Cement board provides an excellent base for backsplashes. It’s moisture and mold resistant. Joints are taped and mudded. It can be installed over wood or metal studs.

Mortar Recommendation: Polymer-modified thinset.

Existing Tile

Installing a new backsplash over existing tile is possible. The old tile must be well-adhered and properly prepared.

Mortar Recommendation: Epoxy mortar.


Greenboard has a water-resistant coating making it suitable for wet areas. It offers more moisture protection versus regular drywall but less than cement board.

Mortar Recommendation: Polymer-modified thinset.


Plaster walls were common in older homes. New backsplash installations require priming first. Plaster can be prone to cracking and crumbling over time.

Mortar Recommendation: Polymer-modified thinset.

Painted Surfaces

Previously painted walls need proper prep before tiling. Glossy surfaces should be sanded and primed to create tooth and adhesion.

Mortar Recommendation: Polymer-modified thinset.

Tile Mortar Types

With numerous types of backsplash and wall materials, what mortar should you choose? Here are the most common options:


Mastic is a pre-mixed acrylic or latex-based adhesive. It is ideal for indoor use in dry areas only. Mastic offers strong initial grab and is easy to apply. However, it lacks long-term durability and is not waterproof when cured, making mastic a poor choice for backsplashes.

Organic Adhesive

This ready-to-use adhesive is sold under various product names by manufacturers. Organic adhesives contain animal products to make them pliable and tacky. Considered obsolete for tile setting, organic adhesives lack water-resistance and frequently fail over time. Do not use for backsplash installations.

Thinset Mortar

Thinset is a blend of cement, very finely graded sand, and water retention agents. It is mixed on-site adding only water. Thinset provides a strong bond and is naturally water-resistant when cured. Standard thinset may slump or fall out of vertical joints. Polymer-modified versions offer even greater strength and adhesion.

Epoxy Mortar

Epoxy is a two-part adhesive mixed prior to use. Resin and hardener combine in an exothermic chemical reaction that results in an extremely durable, waterproof bond. Epoxy has high early strength for immediate grouting. It is often used for glass tile and installing on existing tile.

Hydraulic Cement

Hydraulic cement is used for repairs and flooding issues since it cures when in contact with water. It should not be used for typical backsplash installations. However, Mapei Granirapid System rapid-setting mortar does utilize hydraulic cement technology in a thinset-like product for fast track tile projects.

Mortar Bed

Mortar beds, also called mud beds, provide a thick layer (up to several inches) topped with a cleavage membrane. Tile is adhered to the membrane. Traditionally used in floors, mortar beds see limited use in backsplashes. Thinset is the preferred method.

How to Choose the Right Mortar

Selecting the proper mortar begins with identifying your tile type, wall substrate, and other installation factors.

For natural stone tiles, cement board backer, typical household kitchen backsplashes or tub/shower surrounds with tile areas less than 10 square feet, polymer-modified thinset offers excellent all-around performance. Laticrete 254 Platinum multipurpose thinset is a top choice.

Epoxy mortar provides maximum strength and adhesion for demanding applications like heavy stone tile, green marble that can warp, existing tile substrates, and wet areas. Laticrete Latapoxy 300 stands out among excellent epoxy options.

Standard unmodified thinset works for indoor backsplashes on cement board or drywall where no water exposure exists. However, polymer-modified thinset does these applications too while offering better performance should moisture enter the picture.

Mastics should never be used for backsplashes or wet areas despite being prevalent for decades. Building codes now prohibit mastic for shower and tub surrounds. Improved tile mortars eliminate the need for mastic in backsplashes.

Always consult manufacturer guidelines and local building codes. Some materials like green marble, metal tile, and certain large format tiles have adhesion testing and installation requirements. Framed wall cavities may need reinforcements to support heavy tile or stone.

How to Mix and Apply Mortar

Follow all manufacturer mixing and application instructions precisely. Here is a general overview:

Thinset: Add powder to clean water in a bucket. Mix with a paddle on low speed to a thick, toothpaste consistency. Allow to slake or rest 5-10 minutes. Re-mix before applying with a notched trowel to create ridges that collapse when tiles are pressed in.

Epoxy: Combine resin and hardener in a bucket following exact proportions. Mix thoroughly with a paddle for 3-5 minutes. Mortar will be smooth like pancake batter. Apply with a notched trowel and set tiles immediately before product begins to set.

Mastics: Inside the tube is pre-mixed mastic to apply directly. Spread with a notched applicator that comes with the tube.

Check mortar for proper consistency before starting. Too dry and it won’t adhere properly. Too wet causes slippage and poor bonding. Open time is the window where tiles can be set into wet mortar before skinning over. Mortars stiffen quickly in heat and high humidity.

Apply enough mortar to give tiles full coverage and transfer to the wall. With notched trowel ridges flattened but still visible. Avoid “skinning” where a dry surface forms but mortar beneath remains wet and weak. If skinning occurs, remove and reapply fresh mortar.

Beat tiles into the mortar using a beating block and rubber mallet. Tap firmly to collapse ridges and squeeze out air pockets. Periodically lift a tile and inspect adhesive transfer – minimum 80% for walls and 95% for floors. Do not disturb placed tiles by sliding them through mortar. Adjust only before beating them in.

Grouting and Curing

Always follow manufacturer directions on wait times before grouting can begin. Here are general guidelines:

  • Thinset: 24 hours
  • Epoxy: 6-8 hours
  • Mastic: 8-12 hours

Use sanded grout for joints wider than 1/8 inch and unsanded for narrower gaps. Grout maintains its plasticity for only about 30 minutes after mixing. Avoid delays after starting to grout. Clean excess grout off tile surfaces as you work before it dries and hardens.

Curing takes place as excess moisture leaves the mortar. Tile installations become stronger over the first 3-4 weeks. Avoid heavy cleaning during this period. Extended high humidity inhibits proper curing and gaining strength.

Troubleshooting Mortar Issues

Tile installation problems can still occur with the right mortar if other factors are incorrect:

Tiles fall off walls

  • Unclean or unsuitable substrate
  • Inadequate curing time before grouting
  • Too large of notched trowel teeth leaving thin layer

Tiles crack or break

  • Mortar too thick, causing stress on tile
  • Tiles slid through mortar instead of beaten in
  • Tile below minimum thickness for application

Discolored grout joints

  • Unsealed natural stone allowing staining
  • Grout not cleaned immediately while wet

Efflorescence whitish haze forms

  • Excess moisture in mortar escaping through grout
  • Slow evaporation of water due to humidity

Hollow or loose tiles

  • Contaminated bonding surfaces
  • Insufficient mortar for total coverage
  • Tiles not beaten in firmly

Careful surface preparation, using quality mortars, and properly installing tiles minimizes problems. When difficulties do arise, consult manufacturer troubleshooting guides for the quickest remedy.

Frequently Asked Questions

Here are answers to some common questions about mortar and backsplashes:

What mortar should I use for a shower backsplash?

Polymer-modified thinset or epoxy mortar are excellent choices for a shower surround where direct water contact occurs. Avoid mastic in wet areas.

Can I use thinset on painted drywall for a backsplash?

Yes, thinset adheres well to properly prepared painted drywall. The key is sanding glossy surfaces and applying a coat of primer first.

What is the best mortar for glass tile backsplash?

Epoxy provides the strongest bond for heavy glass tile. It resists moisture and withstands temperature shifts better than thinset.

Do I need special mortar for penny tile backsplash?

Penny rounds are a type of mosaic tile with a small format. Standard polymer-modified thinset works well for penny tile installations. Just apply it with a small notched trowel.

Can mastic be used on backsplashes?

Technically yes, but mastic is not recommended. It lacks long-term bonding strength for prolonged water exposure. Stick with more reliable thinset or epoxy mortars.

What thinset is best for large format subway tile?

Polymer-modified thinset allows extended working time needed for large tiles like 12×24” subway style. It also resists sagging on vertical applications.

How long does mortar take to dry before grouting a backsplash?

Check manufacturer guidelines, but typically 24 hours for thinset and 6-8 hours for epoxy mortar until tiles are firmly set and ready for grouting.


Choosing the proper tile mortar results in strong, lasting backsplash installations resistant to water damage. Consider tile material, wall substrate, and exposure to determine if polymer-modified thinset, epoxy, or other mortars are best for your project. Follow all preparation, mixing, application, grouting, and curing steps carefully. Patience allows adequate drying times so tiles properly adhere before finishing. With the right mortar and proper installation techniques, you will enjoy a beautifully tiled backsplash for years to come.