What is Pre-Grouting?

This process is an essential part of the indirect method. Grout is applied with any of the grouting tools to the back of the paper faced mosaic. The backs of the tile are sponged clean, leaving the grout to fill in the joints. This stops the adhesive from coming up between the joints and improves the adhesion of the mosaic to the backing material. It also begins to dampen the water-soluble glue which makes the paper easier to remove, but also makes the paper easer to remove, but be careful, it also makes the mosaic more vulnerable at this stage. It will hold together for at least 10-15 minutes but it is important not to leave it to long or the tiles will start to drop off when you turn the piece over into the adhesive bed. When the paper has been peeled away the excess grout on the face of the mosaic must be sponged off while it is still wet or it will harden into an uneven surface.

What materials should I use for an outdoor table top?

Mosaic Materials. Both vitreous glass and unglazed ceramic tiles are frost proof and can be used out doors. Polished marble will loose its sheen over time and aquire a duller, 'honed' finish. Glazed ceramics that have been fired at a very high temperature, such as floor tiles, will be frostproof but most bathroom tiles are porous and their glaze may spall off when exposed to the elements.

Backing Materials. The ideal backing for external mosaics is concrete or sand and cement, but this makes for a very heavy table top! Tile backer board is beautifully light and can be used outside but it is not very strong and should be supported underneath with a hardwood or metal framework. Also the edges are unsightly but difficult to attach a frame to so the ideal solution is to drop the finished panel into a 'tray' that will both protect and hide the edges. The easier solution is to use an exterior grade plywood or MDF board, to which a metal angle frame or timber beading can be attached. It is important to paint the back and sides of the board to prevent water penetration as this would cause the board to bend. Any exterior varnish or paint can be used but it is a good idea to apply plenty of coats to be certain of a good seal.

Adhesives. If you are sticking to concrete or tile backer board use Arduflex 5000, available in grey or white. If you are sticking to timber you must use Bal-flex, which is a highly flexible two part adhesive that will allow for the inevitable expansion and contraction of the timber base. You should try to avoid any cavities behind the mosaic by pressing the mosaic into the adhesive bed with some force to flatten out the ridges formedby the notched trowel.

Grout. All the grouts we sell are waterproof and they should help to prevent the ingress of water. It is important to apply the grout carefully so that there are not any tiny holes that will allow water in.

How can I calculate the quantity of tiles I will need for a particular piece?

It is simple enough to work out the overall quantity you will need by calculating the area of the piece. For squares and rectangles just multiply the height by the width, and for circles use the formula 'pi*r2 (3.142 x radius x radius). If you express the dimensions in metres, i.e. 0.3m rather than 30cm or 300mm, your answer willÊ be expressed in m2. This is helpful because 0.1m2 is the area of one sheet of vitreous glass tiles, so it is easy to translate your area into numbers of sheets. For instance 0.25m2 would be 2 and a half sheets, and 0.03m2 would be a third of a sheet. If you want to by your tiles loose you can work out the weight you need because one sheet weighs 700g.

You should also allow 10-15% extra for wastage in cut-piece work. Assessing the proportions of different colours in the design is a less precise science, and there is no substitute for guesswork based on a visual judgement of relative quantities. it is wise to overestimate as there is nothing so frustrating as running out half way through. There is also the danger that the shade of the batch will have changed slightly if you have to come back for more. Building up a small stock of spare tiles can also be useful because it will help you plan out future mosaics and sometimes provide inspiration for colour combinations you would not otherwise have thought of.

How can I work out the quantity of grout I will need?

As a guide the 1.5kg bags of grout will cover about 0.75m2 of cut-piece mosaic. This however can only be an approximation as the amount will vary from piece to piece. Work made up of very small pieces will have a higher proportion of joints and thus generally use a bit more grout. Some work is also much more widely jointed than others and this will also increase the quantity of grout. Using the indirect method and pre-grouting also tends to use rather more because it has to be sponged off twice, once from the back and then again after the final re-grout.

How can I work out the amount of adhesive I will need?

The 1kg. tubs of Arduflex will cover about 0.5m2 if the adhesive is applied in an even bed with a notched trowel, as you would using the indirect method. Working direct will tend to use more adhesive, partly because the bed will not be combed own and also because there is often more wastage with some adhesive drying before it can be used. Using the direct method with materials of different thicknesses will also use more adhesive if you are building up behind thin pieces to flatten out the surface. If you can remember it is a good idea to measure out the adhesive with the same container so that as you work you can get a feel for how much area a particular quantity of powder will cover.