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INDIRECT METHOD INDOOR AND OUT DOOR
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It is important to read these instructions fully before you start work. Preparation You must make sure that the surface to which the mosaic is to be fixed is solid. A mosaic should not be fixed to an unsound surface eg. Cracked or crumbling plaster, broken tiles or areas which are likely to be subject to movement or suffer from water penetration. A bad base is one of the most common causes of failure of mosaic fixing. When fixing to a floor make sure that it is solid. If fixing to floorboards all loose boards should be secured and then the whole floor should be covered with ply boarding screwed down at 9" centres. The surface should also be flat because any unevenness will be reflected in the finished mosaic. When fixing outdoors do not fix when it is very cold or wet as the adhesive will take much longer to dry. If your design involves cutting the tesserae you will need tile nippers, goggles and a mask. Design 1 Cut a piece of paper (we use 90 gsm kraft paper) to the exact size of the mosaic you wish to make. Using pencil or charcoal, which allows changes to be made, start to sketch the basic outlines of your design in reverse on the paper. If you use kraft paper it should have one shiny and one matt side. Draw your design on the matt side. If you are doing lettering or copying other complex designs you can trace them in reverse using a light box or daylight through a window. Cutting & laying the mosaic 2. Choose the mosaic tile colours you wish to use. If your design has a border, lay it out on the paper to establish the correct number and spacing of the tesserae. When you begin sticking it is best to start with the border if you have one and then the outline of the main design image. Once these areas are complete you can Fill in the design and then do the background. Mix the Water Soluble PVA glue with an equal amount of water and starting with a small area apply it to the paper with a paintbrush. Do not use too much glue and try not to stick the tesserae too closely together as this will cause problems when fixing the mosaic. A 1‑2mm gap is best. f you need to cut the tesserae hold the tile in one hand and the nippers in the other. Put the very edge of the tile between the jaws of the nippers, then close the jaws, applying gentle pressure. Ideally the tile should snap neatly in half and this can be repeated to make quarter tiles. Angling the nippers will enable you to make diagonal and other shaped cuts. Learning to cut accurately requires a bit of practice but not be put off as the "mistakes" will probably fit somewhere in your design or in your next mosaic. You must remember to stick the front of the tesserae to the paper so that the back of the tesserae is face upwards. If you are doing a large design you can cut it into manageable sections ‑ preferably no larger than 450mm x 450mm. It is advisable to cut it up after you've completed sticking down the tesserae and to cut along natural boundaries within the design. Mark reference points on the paper either side of the cut line so that you can fit it back together properly when fixing the mosaic.
Pre‑grouting 3. When you have stuck the mosaic to the paper put it in a warm place until the glue is dry. You can now pre‑grout. This means putting grout in the gaps between the pieces to prevent the adhesive coming through when you fix it. If your design is large and you have cut it up you should pre‑grout one section and then fix it into place, following no. 4 below. Repeat the process for the other sections one by one. Start by putting your mosaic paper face down onto the backing board. Make sure the backing board is dry. Mix a proportion of the grout powder with water. Add water sparingly as it won't need much to achieve the necessary smooth, thick consistency. Do not use all the grout as you will have to re-grout later. (1kg should be sufficient to grout and re-grout 1/2 sq mt or 5 sq ft. Wearing the rubber gloves apply the grout mixture to the mosaic spreading it evenly between the joints with your hands or with a grout spreader. Make sure all the gaps between the tesserae are filled. Immerse a large tilers sponge in clean water, squeeze it out as firmly as possible and use it to wipe off the excess grout. Use a clean face of the sponge for each wipe so that you don’t spread the grout back over the tiles. Be very careful not to saturate the mosaic as this will dissolve the PVA glue.
Fixing the mosaic in the adhesive 4. Mix the cement based adhesive with water to achieve a smooth, thick consistency. (2.75 parts adhesive to 1 part water). The adhesive will remain workable for about an hour in the pot and has a 30/45 minute working time when on the wall/floor so don't mix more than you need foreach section. These times will vary according to temperature/moisture conditions when fixing. Allow about 1kg of dry adhesive per 0.75m2/5 sq ft. of mosaic. Wearing rubber gloves use the notched trowel to spread the adhesive evenly on to the surface on which you intend to fix the mosaic. Make sure to cover the whole area to be "mosaiced". Keep the trowel's notches in contact with the surface so you can guarantee a uniform thickness of adhesive. The result should be a ribbed effect. If you are fixing a number of sections spread the adhesive over an area slightly larger than the piece of mosaic to be fixed. Pick up the pre‑grouted mosaic, trying not to twist or curve it, then put it, paper‑face up, onto the adhesive and press it firmly into place. Any surplus adhesive can be removed once the section is in position. Then dampen the paper with a wet sponge and wait for the water to soak in. If you have cut up the mosaic you can start fixing the next section whilst the water is soaking into the paper.
After 15/20 mins gently peel the paper off pulling parallel (see sketch) to the face of the mosaic. The mosaic should remain stuck to the adhesive. If tiles come up too, put the sheet of mosaic back into place and dampen down the paper again. This should help to completely dissolve the PVA glue bond to the mosaic. Try again in 10 minutes. Having removed the paper gently clean all the surplus grout & adhesive from the face of the tesserae with a damp, clean sponge working from the outer edges towards the centre of the mosaic. Make sure the mosaic is firmly in contact with the adhesive bed and that you remove any adhesive which has squeezed up between the tiles now, as it will be very hard to shift when dry. It can then be left to dry.
Re-grouting & finishing off 5. The final stage is to re-grout the mosaic when the adhesive is completely dry. The aim is to fill the gaps between the tesserae with grout and give the mosaic an even surface. This can be done by hand wearing rubber gloves or with a grout spreader. When complete wipe off the excess grout with sponge and when dry polish with a clean cloth.
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