Making a mosaic trivet, Part IV: Grouting mosaics
- Part I of this four-part series was about preparing the board: https://helenmilesmosaics.org/making-mosaics-2/how-to-make-mosaics/preparing-the-board.
- Part II covered choosing materials and a design: https://helenmilesmosaics.org/making-mosaics-2/how-to-make-mosaics/mosaic-designs-and-materials/.
- Part III dealt with cutting, laying and fixing the mosaic: http://helenmilesmosaics.org/making-mosaics-2/how-to-make-mosaics/making-a-mosaic-trivet/
Now it’s time to get down and get dirty. Roll those sleeves up, tie on your pinny and get out the rubber gloves – the moment has come for grouting mosaics.
NB: If you use porous stone as your mosaic material, then you need to apply a layer of varnish on the finished work BEFORE grouting to protect the stone and stop it ending up with a horrid grey film.
You’d be surprised how many people are not sure what grouting mosaics means. Just in case one of those people is you, grouting is when you fill in the gaps between the mosaic tiles to strengthen and protect the work. It also has the effect of bringing the piece together as a co-ordinated whole. It’s the most common method of finishing off a mosaic – but not the only one.
to grout or not to grout
1. Grouting the mosaic using tile grout – the same sort of grout as you’d buy to grout your bathroom or kitchen tiles. This lovely little thing from Scarab Glass Works shows very clearly what I mean – the grout is the grey bits.
2. ‘Self -grouting’ : many mosaics are made by pressing the tesserae down into a soft tile adhesive thin set which squishes up around the sides of the pieces and holds them down. The famous Byzantine mosaics are made in this way:
3. Not grouting at all. The mosaic pieces will be firmly bonded to their substrate and if they are also placed close together, grouting is superfluous. This piece below from Jacqueline Iskander non-grouted: 
Getting ready
Before you start, you will need to make sure you have a way of getting rid of your excess grout. It’s nasty stuff, blocks drains and is generally yucky so you can either:
- Find a corner at the back of the garden to swill out the used containers and rinse off your tools.
- Or, be ready to use lots of scrunched up newspaper and paper towels to give your tools and containers a thoroughly good clean after use.
I have a friend who once proudly told me she deals with the problem by taking her grouting bowls out into the street and sluicing them off into the public drains. Errr, no, that doesn’t work either. Any drain is a drain and the whole thing about grout – even watered down grout – is that it hardens and becomes as solid as concrete.
Right, we’ve got that clear, so the next thing you will need to do is to:
prepare your tools and supplies
For this you will need:
1. Rubber gloves.
2. Plastic sheets to protect your surfaces/the floor under where you are working.
3. Two deep plastic bowls or buckets. Old ice cream containers will work just fine.
4. A spreading tool. An old plastic loyalty card is ideal for a mosaic this size or you can buy spreading tools at any hardware shop.
5. Two good, thick sponges.
6. Grout. I use Isomat Multifill Smalto 1-8mm, which means that it will fill joints up to 8mm wide. I also tend to use grey – sometimes called cement grey. I could write a whole separate post about grout colours but, for now, let’s keep it simple.
7. A spoon or implement of some sort to mix the grout.
8. A bottle/jug of water. I also find it handy to have one of those water spritz things which are used for spraying plants so that you can fine tune the amount of water you add.
9. Stiff plastic, scrubbing brush for cleaning.
Method – mix and cover
1. Put your gloves on and make the grout according to the packet instructions in one of your plastic tubs. Add the water in dips and daps and keep mixing until you get the right consistency – you are aiming for a paste: not runny, not with water sitting on the top, and not too firm. I read once that the best consistency is that of a cow pat and I regret to say that that is the analogy I always use.
2. With a sinking heart (it’s never easy), put a big dollop of this horrid, dark, goopy stuff on the front of your beautiful mosaic. Use the spreading tool to push the grout into the gaps.
3. Next, cover the whole mosaic with the grout and don’t forget the edges:
4. Use your fingers to push the grout into all the gaps. You will find little air bubbles appearing as you apply the grout, so keep going until all the holes are filled.
remove and clean
5. Now use the spreader to remove the excess grout.
6. Fill your second plastic tub with clean water. Soak both of the sponges and squeeze out every last drop so the sponge is damp but not wet.
7. Wipe the front of the mosaic with the sponge – once. Then turn the sponge and using a clean side, wipe the mosaic again. It’s vital to always use a clean side of the sponge. Otherwise, you are just smearing grout residue over the cleaned parts of your work.
8. Keep going with both sponges, frequently rinsing them out and using fresh water until the front of the mosaic is clean. It will still look slightly on the grungy side, but don’t worry, it will come off in the final clean.
9. Leave to dry for a good, long while. There is no rush so better to leave it for more time rather than less. Once it’s thoroughly dry, get a stiff plastic brush, clean water, and give it an energetic wash.
10. Put four, little, felt self-adhesive patches* on the back of the mosaic so it can be put on a polished wood surface without scratching it. *The ones hardware shops sell to put on chair legs.
Drum roll….Der, der! You’re done. Congratulations.
Keep tuned for the next mosaic project: making a mosaic on mesh.