One of the commonest problems associated with baths, shower trays and wash basins is the difficulty of sealing the gap between the edges and the walls. It is extremely important that this is done effectively as, apart from being an unsightly dirt trap, water continually splashing through the gap can lead to attacks of rot in floor timbers, as well as damaging decorations in the room below.
An ordinary cellulose filler will be adequate, but you’ll probably find that it won’t last for very long. After all, repeated soakings are bound to start it crumbling. And even if this can be avoided, the chances are that the movement of the bath relative to the wall — as it fills with hot water or as someone climbs in or out — will have the same result.
The answer is to use a special kind of filler, one that is both waterproof and flexible. called silicone mastic. This is frequently sold as bathroom sealant in small tubes, or, for larger jobs, in cartridges that fit into a special mastic gun. In addition to white. it is available in a selection of colors to match the variety of colored bathroom suites now on the market.
If you are faced by a crack up to 3mm (‘/sin) wide, then filling it is a straightforward job. All you do is squeeze a bead of mastic along the gap, holding the nozzle at an angle of about 45′. If you are using a cartridge gun: you can cut the nozzle to produce a bead of the correct size. If the mastic ends up on surfaces where it’s not required, wipe it off with a damp cloth before it sets. With the bead in place you’ll have to finish it off with a piece of dowel or narrow piping. Dip it in water to prevent the mastic from sticking and don’t be tempted to use your fingers — you won’t get as neat a finish and you could run the risk of inadvertently getting mastic in your eyes.
However, if the gap is wider than 3mm (1/sin) or so, you’ll find it increasingly difficult to apply the bead smoothly and neatly, and to prevent it sagging once in place. The solution is to caulk the gap before applying the mastic. This involves filling the crack with soft rope or twists of soaked newspaper to provide a base that will help the mastic to bridge the gap until it sets. Provided you finish off with a good covering of mastic, there’s no reason why this shouldn’t last. However, it is a fiddly job and you might prefer to use an alternative method.