How to Grout Porous Stone Tile Backsplash

Grouting a porous stone tile backsplash can seem daunting, but with the right techniques and materials, it can be a straightforward process. Proper grouting is essential for sealing the pores of natural stone tiles and preventing stains, cracks and damage. This guide will walk you through each step of grouting porous stone tile backsplash, from preparation to clean up.

Choosing the Right Grout

Choosing the proper grout for porous natural stone tiles is critical. Traditional sanded grouts are too abrasive and can scratch softer stones like marble or limestone. Instead, use an unsanded grout specifically formulated for natural stone.

Key factors to consider when selecting grout:

  • Texture – Use unsanded grout for polished or honed stones. Sanded grout is only for rough tile surfaces.
  • Color – Pick a grout color that matches or contrasts nicely with your tile. Light grout suits lighter stone.
  • Performance – Seek grouts made for natural stone that resist staining and offer maximum adhesion.
  • Epoxy – Epoxy grout provides an ultra-durable, waterproof seal for higher traffic areas.

Some top-rated unsanded grouts for porous stone tiles include:

  • Mapei UltraColor Plus FA
  • Laticrete PermaColor Grout
  • Custom Building Products Polyblend Sanded Grout

Be sure to use the grout specified for natural stone. Portland cement-based grouts can scratch and stain. When in doubt, consult your tile supplier.

Grout Joint Size

The width of the grout lines, or joints, between your tiles will depend on the type and size of your stone tile:

  • Small mosaic tiles: 1/16 to 1/8 inch joints
  • Medium-sized tiles: 1/8 inch joints
  • Large format tiles: 3/16 to 1/4 inch joints

Wider grout lines are better for porous stone because they allow for maximum grout coverage to seal tiles and prevent moisture penetration.

Follow your tile manufacturer’s recommendations for proper grout joint size. Wider grout lines may require a sanded grout. Adjust your grout lines to balance aesthetics and performance.

Gather Your Materials

Grouting stone tile requires a few special tools and materials. Gather these supplies before starting:


  • Unsanded grout for natural stone in the right amount for your project


  • Grout float for spreading grout
  • Grout bucket for mixing
  • Grout spatula for packing joints
  • Sponge and bucket for cleaning
  • Tape for borders
  • Tremoller tool to remove haze

Other Supplies

  • Grout sealer
  • Cotton rags
  • Paper towels
  • Gloves and eye protection

Prepare the Tile Surface

Proper prep before grouting is vital for good adhesion and sealing:

  • Let mortar fully cure – Allow tile mortar to cure for at least 24 hours before grouting.
  • Clean thoroughly – Use a pH-neutral cleaner and rinse thoroughly. Remove all dirt, dust and debris.
  • Seal prior to grouting – Apply a natural stone sealer 1-2 days before grouting.
  • Cover borders – Protect borders with painter’s tape to keep grout off.

Check for any cracked or loose tiles and repair prior to grouting. The tile surface must be clean and dry before applying grout.

Mixing and Applying the Grout

Now it’s time to mix and spread the grout. Carefully follow the product directions:

  • Pour cool clean water into a bucket for mixing grout.
  • Slowly add grout powder while stirring constantly to avoid lumps.
  • Allow to slake for 5-10 minutes then remix before using.

The grout should be thick but still spreadable. Adjust consistency as needed with a bit more water or grout powder.

Use a grout float or squeegee to spread grout diagonally across a small section of your stone tile:

  • Hold the float at a 45° angle and work the grout thoroughly into the joints.
  • Take care not to smear grout onto the tile surface. Keep grout inside the grout lines.
  • Completely pack joints full to seal properly.

Continue in small sections until all tile is grouted. Take frequent breaks to give your arm a rest!

Cleaning and Polishing Grout Lines

As grout begins to firm up or haze on the tile surface, start cleaning:

  • Use a damp sponge to gently wipe grout haze off tile faces, rinsing the sponge frequently.
  • Wipe diagonally across tiles to avoid pulling grout from joints.
  • Change water buckets often to keep the slurry from re-depositing on tile.

Repeat the rinse and sponge process until tiles are completely haze-free. Allow grout to cure 24 hours before polishing.

Once cured, use a soft cloth to gently polish grout lines and finish smoothing the joints. Avoid excessive rubbing or you may pull grout out.

Remove any remaining haze with a tremoller sponge and grout haze remover. Thoroughly rinse tiles and allow them to fully dry.

Curing and Sealing Grout

Freshly grouted porous tiles need proper curing and sealing:

  • Allow grout to cure 24-48 hours before getting wet.
  • Keep the room ventilated and humidity low during curing.
  • After curing, apply a natural stone grout sealer following product directions.
  • Sealant adds waterproofing and stain resistance. Reapply yearly.
  • Avoid heavy cleaning for 7-10 days while grout continues to cure.

With proper curing, your grout lines will be uniformly smooth, tight, and sealed. Enjoy your stunning new stone tile backsplash!

Frequently Asked Questions About Grouting Stone Tiles

What’s the easiest way to apply grout?

Use a rubber grout float in a swirling motion across the tile to pack joints thoroughly while avoiding smears on the tile face. Holding the float at a 45° angle gives you the best control.

Should I grout stone tile before or after sealing?

Seal natural stone 1-2 days prior to grouting. Sealing first prevents grout from staining the porous tile. After grouting, seal the grout lines again for maximum stain protection.

How long does grout take to dry and cure?

Grout dries in 24 hours but continues curing and strengthening for 5-7 days. Avoid heavy cleaning while grout cures. After a week, grout should be fully set.

Why is my grout cracking or crumbling?

Cracks often occur due to inadequate curing or too-narrow grout lines. Harsh cleaners can also degrade grout over time. Re-grouting may be required in severe cases.

How do I get a smooth grout line on stone?

After grouting, polish gently with a soft cloth once grout has firmed up. Avoid excessive rubbing or you may pull out grout. Use a grout haze remover once cured.

Can I use sanded grout on porous natural stone?

No, sanded grout can scratch softer stones. Use only unsanded grout formulated for natural stone. Wider grout lines may allow sanded grout on very dense stones like granite.

What’s the best way to remove dried grout haze?

Use a tremoller sponge and pH balanced haze remover after grout has cured 24 hours. Harsh acid cleaners can damage stone. Rinse thoroughly.

Do I need to seal my grout?

Yes, apply a natural stone grout sealer 1-2 weeks after grouting to protect from stains. Reapply yearly or as needed. Cured grout is still porous.

How do I fix cracks or holes in existing grout?

Carefully dig out old grout with a spline tool or dental pick. Re-grout the joints with fresh grout, matching color as close as possible. Let cure completely before sealing.


Grouting natural stone backsplash tiles reinforces adhesion, seals pores, and prevents staining. With the proper unsanded grout, tools, and techniques, you can achieve durable, long-lasting grout lines that enhance the beauty of your stone mosaic. Pay special care to prep, mixing, application, cleaning, curing, and sealing when grouting porous tiles. Following the steps in this guide will help you gain confidence in grouting your stone backsplash project. Be sure to allow adequate drying and curing time for strongest results. Your gorgeous new backsplash will provide years of hassle-free enjoyment with proper grouting and care.