Silicone Sealant Application for Tiles and Paving

Why not grout the whole wall with one product? Cement grout is hard and rigid, so it suits the joints between tiles on a single flat surface. In a room corner, where the wall meets the floor or along the bath, the materials move differently. A bath flexes a little under the weight of water and a person, and floors and walls expand differently as the temperature changes. Flexible silicone absorbs these small movements and keeps the joint watertight.

Silicone is mainly used:

• in bathrooms around the bath, shower tray, washbasin and WC, and in the internal corners of wall tiling
• in kitchens between the worktop and the splashback tiles, and around the sink
• where floor tiles meet the wall or a tiled skirting
• in movement joints in floor tiling, especially on larger areas, terraces and balconies

The tiler must leave these joints free of grout. If cement grout is pushed into the corner first and silicone is only run over the top, the joint loses its flexibility and cracks.

DIY shops stock many kinds of silicone, and the differences go beyond colour and cost. For tiling you will mostly come across these:

• Sanitary silicone contains a fungicide that slows down mould. It belongs in bathrooms, showers and kitchens, wherever things are often damp.
• Acetoxy silicone smells of vinegar while it cures. It is common and inexpensive, but it can attack some metals and mirror backings and is not suitable for natural stone.
• Neutral cure silicone releases no acid while curing. It suits more sensitive materials and is often also rated for outdoor use.
• Natural stone silicone is made for marble, travertine and similar stone, where ordinary silicone can leave dark, greasy-looking stains along the edges.

Match the colour to the grout so the room looks consistent. Most grout manufacturers sell silicone in matching shades. Keep in mind that standard silicone cannot be painted over, so choose the colour before you start.

A good silicone joint depends less on how much sealant goes into the corner and more on the preparation. In practice, silicone often comes away after just a few months because the surface was not dry or clean.

1. Prepare the joint. All old silicone comes out completely, residue included. New silicone does not stick to old silicone.
2. Clean and degrease. The edges are cleaned of dust, soap and grease, usually with spirit or alcohol, or with a cleaner the sealant manufacturer recommends.
3. Dry. The joint must be dry. Moisture is the most common reason silicone fails to bond.
4. Fill deep joints. A foam backer rod goes into a deep joint first. The silicone then bonds only to the two sides and copes better with movement.
5. Mask the edges. Masking tape runs along both sides of the joint so the edge stays straight and no silicone gets onto the tiles.
6. Apply. The silicone is pushed out of the gun in one steady, continuous run.
7. Tool. The bead is smoothed with a rubber profiling tool or a wet finger into a slightly concave shape.
8. Remove the tape. The tape comes off straight after smoothing, before the silicone skins over.

Silicone cures gradually. It usually skins within a few minutes, but full curing takes much longer and depends on the thickness of the bead. It is sensible to leave the shower or bath unused for at least a day. The exact time is on the cartridge.

The amount of work varies from one bathroom to the next. It is simplest with new tiling, clean open corners and long straight joints. These things take more time:

• removing old, mouldy or firmly stuck silicone
• corners filled with cement grout that has to be raked out first
• many short sections around pipes, taps and the corners of a shower tray
• uneven or wide joints that need a backer rod
• sensitive materials such as natural stone that need a special sealant
• damp conditions where the surface has to dry out before work can start

You can reseal a bath yourself with a little patience and a few simple tools: a knife or silicone scraper, spirit or alcohol, masking tape, a sealant gun, a cartridge of sanitary silicone and a rubber smoothing tool.

1. Cut along the old silicone on both the tile side and the bath side with a knife, then pull it out.
2. Scrape off any residue and remove the rest with a silicone remover, following the instructions.
3. Clean the joint with spirit and leave it to dry completely.
4. Fill the bath with water so it flexes as it does in normal use.
5. Mask the tiles and the bath edge with tape, leaving a gap for the joint.
6. Cut the nozzle at an angle to suit the width of the joint.
7. Apply the silicone in one smooth, continuous run.
8. Smooth the bead with the tool or with a finger dipped in water with a drop of washing-up liquid.
9. Peel the tape away from the joint while the silicone is still soft.
10. Let it cure as the manufacturer states, and only then drain the bath.

Use only a little washing-up liquid and do not spray it directly onto the fresh edge of the joint, otherwise the silicone may not bond well along the edges.

• New silicone over old. It looks quick and tidy, but the joint soon lifts and mould keeps growing underneath.
• Damp or greasy surface. The silicone only looks as if it has bonded.
• Grout in the corners. Silicone laid on top has no room to move and cracks.
• Wrong type of silicone. Acetoxy silicone on stone or near a mirror can leave stains and damage.
• Bead too thin. A thin layer tears easily when the bath moves.
• Using the shower too soon. Water on uncured silicone can spoil its surface.

Silicone is flexible, but it does not last forever. With normal care and good ventilation it lasts for years. Once black spots appear inside the sealant or the edge starts to lift, it is time to replace it, as surface cleaning will no longer help.

When the job is handed over, look at the joints closely and in good light. Check that:

• The silicone is continuous, with no holes, bubbles or gaps
• The edges are straight and the width is even along the whole length
• The surface is smooth and slightly concave, with no finger marks
• No silicone or tape is left on the tiles, the bath or the taps
• The edge does not lift when you press it gently
• The colour matches the grout
• The corners under the silicone were left free of cement grout
• The installer has told you when you can use the shower and bath again