My tile sheets are a mixture of linear slate and glass and I would like to know to grout when there's a combination. The concern is that the grout (unsanded) will stick to the natural stone and ruin its appearance. I have researched the problem and found a number of possibilities, however there is no clear winner.

Cool Earth Linear Slate Glass Tile

Cool Earth Tile


  1. Bulk apply sealer to all tiles before applying grout but risk is that it will discolour the glass.
  2. Apply sealer individually to only stone tiles before applying grout. Tedious!
  3. Mask natural stone with tape but risk having it come off during grouting. Risky.
  4. Coat all tiles with soapy water before grouting. Apparently this prevents grout from sticking to natural stone?
  5. Use a piping bag instead of a float in order to grout only the gaps between tiles.
  6. Bulk apply grout without sealing and try to get as much off the stone before it dries.
  7. Bulk apply grout without sealing and deal with consequences.
  8. ...?

If my main concern is appearance, and I am willing to put in a reasonable amount of extra work (compared to grouting just 100% glass tiles), how should I proceed?

  • You should do a test grout on a left-over section first. What does the manufacturer suggest?
    – ojait
    Commented Jan 13, 2016 at 0:34
  • I have looked into it and the manufacturer recommends sealing the entire mosaic before grouting. Looks like option #1 is a go!
    – Dave
    Commented Jan 18, 2016 at 22:07

2 Answers 2


Clarification from the manufacturer:

"Natural stone should be sealed prior to grouting. A premium penetrating sealer is recommended for a natural look. A stone enhancing sealer can be applied to darken or highlight the features of the stone. The sealer is safe to apply over the entire mosaic with the glass."

  • If you don't want all the pores to show specks of grout (sometimes it's a desired look) you WILL be sorry if you don't seal natural stone or un-glazed tile before you grout. I can't see how sealer would damage glass, if it does you're screwed anyway; you'll have to "liberally apply" sealant at least twice afterwards. Glass tile has never seemed to be bothered by it in any of my installs.
    – Mazura
    Commented Jan 23, 2016 at 22:52

You do not state how large the area is, but assuming it is an entire back-splash Option #6 is your best bet.

If applied with proper technique the grout is unlikely to discolor the natural stone, or at worst it will change very slightly but uniformly. You need to have several buckets of clean water along with several grout sponges and perform a "dirty", "clean", then "finish" sponging. Never wipe the grout with a sponge that has not been rinsed and wrung, and change your water frequently (especially the "finish" bucket).

Once the grout has set, use a diluted mixture of muriatic acid and water and carefully do a "haze" sponging to remove all traces of grout.

An additional "haze" sponging the next day will remove all powdery traces of dried grout and haze from the tile.

  • The area is about 20 sq. ft. I will trial your technique on a spare section of the tile to see how it ends up looking. I am glad to hear that I may not need to put in a lot of extra time and effort for this job.
    – Dave
    Commented Jan 13, 2016 at 15:53

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