Mosaic Detective – Mosaic Pebble Dish Gone Wrong
This was supposed to be an easy project. A simple terra cotta tray, some pebbles, a few pieces of broken tile and grout. However, the resulting project has a few problems.
Let’s take a look the end product, the actual creation steps taken by the maker of this mosaic and then let’s put our heads together to see if we can diagnose – what went wrong.
Materials: Terra Cotta Tray – 6 inches, Assorted pebbles, glass tile
Step one: - Bottom of Terra Cotta Tray sealed with water/white glue. (Top of tray, where mosaic goes – not sealed.)
Step two: – Pebbles & Glass Tile pieces attached with Silicon Glue along rim, and then inside the tray in a more or less random design.
Step three: – Allowed to dry overnight
Step four: – Grout made and applied, excess wiped off after 30 minutes with soft cloth
That’s all that was done. This object is kept outside in the garden, and only looks good when it’s got water in it.
Here is a list of the Problems with this Mosaic Project Gone Wrong:
- Pebbles on edge are coming off
- Glue showing in some places
- Some pebbles and some tile pieces are barely visible under the grout
- The grout is cracking around the pebbles on the rim
- The grout always looks “powdery”
- The visible glass tile pieces and pebbles always look dull (unless water is in the bowl)
You are invited to be the mosaic detective. What’s your diagnoses? Please make your comments below.
Heidi. this is a just a normal beginners mosaic , it was executed in the way that most mosaics can be, the main thing is attention to detail and knowledge of grouting and sealing is lacking a bit. There are many mosaic books that you would find fun to read and learn from but most of all making mosaics (lots f them) will help with most of your problems. Always think of what colour your grout will be at the outset as this can make a big difference to your choice of tile colour and time spent in design is never wasted. Use a wet look sealer on this and you will be much happier with the end result.
Most people find after doing a mosaic that it is much more than just sticking a few bits onto something….anyone can do that but to make a mosaic that has a wow factor needs time and a little knowledge.
cheers
Jacqui
Hi Heidi, will jot down a few ideas from your list.
I wonder why you did not seal the part you applied the mosaic to. One reason to seal is to stop the terracotta base sucking moisture out of the adhesive and the grout. Personally I prefer to use a proper stone sealer, rather than diluted PVA, as it is made for that very purpose
Pebbles on edge are coming off-
If an object is not well sealed, water can penetrate the substrate (in this case terracotta base) and get underneath an adhesive like silicone, and the tiles pop off. This is even more likely to happen if there is a freeze thaw cycle, the water expands and something has to give!
- Glue showing in some places
Probably too much silicone, tricky stuff to use, enough needed to stick the object, but you don’t want it coming too far up the edges else it shows
- Some pebbles and some tile pieces are barely visible under the grout
When undertaking mosaic with a textured surface you have to be prepared to excavate some of the lower set tesserae when the grout has partially set – I like to use a small nail brush to rub the grout off when it starts going powdery, 30 minutes was probably too too long – about 10 -15 minutes is more like the time needed. However to get clean edges also often need something like a sharp wooden stick to get in the little crevices
- The grout is cracking around the pebbles on the rim
Quite a few possibilities here- one mentioned above- porous base sucking moisture out of grout, therefore grout not setting properly, or old grout ( shelf life is only about 1 year). Grout does not finish edges well, it is a filler not an adhesive, so is likely to chip off edges, need to use a cement based adhesive instead. You can also use an admix product to grout which gives it more flexibility
- The grout always looks “powdery”
Either old grout, or a problem called efflorescence where chemicals from the water leach out an cause powdery deposits
- The visible glass tile pieces and pebbles always look dull (unless water is in the bowl)
I think leaving the grout for 30 minutes may have left a thin layer of cement on the tesserae, and has left them dull. You probably needed a damp sponge to wash the excess grout off, and the following day after grouting should polish this film off with a soft cloth..There are certain acid products that can eat away at this cement film, but need to use caution when using. Diluted vinegar is a good mild acid based cleaner if used soon after grouting, needs to be rinsed off though
Hope this helps. One last point, if I was gong to do an outdoor mosaic, I would use a cement based adhesive (thinset) to adhere tesserae to, in preference to silicone, which is ideal for something like glass on glass. It can be a bit messy , but it does enable you to squish some tesserae down more, or build others up, saving the need to excavate later
Christine (NZ)