A guide to using silicone
General information and guidelines
The point of siliconing is threefold:
- To mask poor cutting in corners.
- To waterproof holes made after tanking.
- To neutralize movements in the surrounding structure.
If you use regular grout in corners where there might be structural movement, and then use silicone over it, you defeat the purpose of the silicone, and you risk cracking. Over here, we refer to silicone as "movement grouting", for just that reason. Use silicone where it is due, and regular grout where it is due.
Do use silicone:
- Where the substrate is concrete which is less than one year old (it shrinks).
- Where the substrate is board material, eg drywall, mounted on a wooden or metallic frame (moves with temperature and humidity).
- In new buildings, regardless of substrate, as there will be movement.
- Where one substrate material meets another (eg concrete floor meets plasterboard).
- Where sanitary wares, counter tops, etc, connects with tiled surfaces
You don't need to use silicone for structural reasons:
- Where all surfaces are made from concrete which is more than one year old. Prefereably, they should be more than two years old.
There are a few other circumstances where it might, or might not be appropriate, but I can't be arsed. Tell you this though: It's safer to use silicone, than to not use it. If you think it's needed, from structural reasons or otherwise, then by all means use it. Bear in mind that silicone joints and harder to keep clean than regular grout joints, and that there are many different types of silicone. Chose one suitable for you intended application.
If you want to do movement joints outdoors, you might want to use polymer reinforced silicone.
As for drying: Drying times are almost always listed on the tube.
Guide to siliconing
Grout the surrounding tiles, but make sure there is no grout or otherwise where you intend to use silicone.
If you feel unsure about your technique, and feel you might make a mess, use masking tape of some sort.
Apply the silicone in nice even strings. There are two general types of silicone tools you use for smoothing: One which removes excess, and one which doesn't.
If you tool removes excess, it's good if the string is a little thicker than you want the finished result to be. If your tool doesn't (your index finger is in this category), you'll need to be careful to not apply too much, especially if you aren't using masking tape.
Use some sort of liquid which stops the silicone from sticking. Some silicone manufacturers sell special anti-sticking liquids, which you apply to the tool, and to the silicone string. Most however, use regular detergent (soap) mixed with water. Make sure it's colourant free first though. Strong detergent will ruin the silicone.
Apply the anti-sticking liquid using a water spray, to your tool, and the surrounding tiles, as well as the silicone. If you use masking tape, you only need to spray the tool.
Smooth the silicone with the tool, using a long, even motion.
If the tool removes excess, dump the waste in a waste bag before it starts making a mess.
If needed, spray the tool and the silicone again. When the silicone has a suitable thickness, you might want to go over it using your finger, in one light, long motion. If you've used masking tape, remove it when you're finished.