Mosaic- Cement adhesives and climate
Another hot week of this summer has passed. It has been hot and humid, which affects materials used in the studio. So there we are – let’s talk mosaic and more specifically glue and how it behaves in different climatic conditions.
The two cement adhesives used by most members of our mosaic group are Optima and Laticrete.
Optima is mixed with a latex milk (no water) to make a flexible glue suitable for most positions and projects, sticking to all sorts of materials except plastic, and will perform well outdoors due to its ability to expand and contract. As it is a white glue it will give you clear results with any pigment you add to colour it. It also sits well under glass giving you high refraction.
Laticrete on the other hand is mixed with water and the flexibility in this product comes from dried latex present in the cement mix. It is also flexible – maybe a little less than optima – and it has a more cementitious feel, showing slightly more crackling when used as a slurry. It performs well in all positions and projects, indoors and outdoors and sticks well to cement and board and can be used over difficult surfaces treated with an optima slurry. Laticrete is light grey and therefore will not give true high chroma colour results when tinted. Also won’t give clear refraction under glass. However, if greyed off colour is what you want to achieve as glue colour – this is the right choice as you are half way there, less black pigment will be needed to darken the colours.
Now to the behaviour of the glue in hot and humid weather. Optima will react by staying quite liquid for a long period – it almost feels as if it liquidises a little more after being mixed. This is good in terms of glue being active for long periods. It also means that you have to be aware that it will not hold as well initially on vertical surfaces as it takes longer to dry and may be more liquid than you thought when mixing it up.
Laticrete will bond to humid air – as it is a glue that will mix with water – watch that it has no opportunity to bind before use – keep the powder in well-sealed containers. Clumping can occur in the bags from storage/compression and can easily be softened with a few hammer blows to the bag. However, if glue has contact with moisture, another type of clumping occurs, as glue gets activated. These clumps need to be sieved out as the glue’s capacity to stick will be reduced.
Mix small amounts- half a cup should do and bag glue in plastic bags to pipe out. This keeps the mixture stable. Never stretch glue by adding more latex/powder/water to it after a batch has been mixed– all you do is interfere with the glue’s capacity to stick. Use up what you have and mix a new batch.
In the studio it is a well kept secret – Optima keeps well in the fridge if you have leftovers – depending on consistency – up to 24 hours – remember though that fresh is best. Do never refrigerate glue for commercial projects – it voids the manufacturers warranty!
Windy weather affects not just us – but also the glue – it hates those conditions and will dry too quickly and be hard to spread and awkward to work with. Cold and dry weather will also quicken the drying process of glue.
Another thing to remember is – try and keep your fingers off glue once it is in place – ready for a mosaic tile – any particles/oils on your fingers will react with the adhesive and spoil its ability to stick.