If you are not sure which bathroom sealant to use or how to apply it, here are some bathroom compression molding silicone tips that may help you. These tips are from my hands on experience in bathroom remodeling and bathroom silicone specifically.
I was curious about what my competitors and other building trade professionals had to say on the matter of bathroom compression molding silicone, so I read a few pages on different sites to see what advice they are giving. I found a lot of good advice but also some average and plain wrong information, so here are my tips and advice on the subject.
• First of all, do not use any other material but silicone and in particular only use a bathroom grade silicone. Do not use any polyurethane based sealant as it will start to gather mold, soon after application and use, with bacteria and other nasties growing inside and on the surface of it, giving it that ugly dark discoloring as well.
• Make sure that the tiles and grout as well as other surfaces the silicone will be applied to, like bath and sink edge and so on, are cleaned properly and completely dry.
For example, if the tiler has just grouted the tiles then let the grout dry for 2 or 3 days. When the grout has cured and dried, wipe the inch or so strip along where the silicone will be applied, especially in the gaps with a clean cloth moistened with methylated spirits.
If it's an existing bathroom make sure the floor and walls, especially the shower cubicle, is thoroughly cleaned of scum and grease, washed and rinsed and dried before silicone application.
• I always use an "acetic cure" bathroom grade silicone a opposed to a "neutral cure", because it will bond better to surfaces like glazed ceramics, porcelain or glass and I can get a very smooth finish. Acetic cure silicones have acetic acid which etches the surface, thereby providing a better bond. There is about 3% acetic acid found in vinegar, so if you use the acetic cure silicone, it will smell like vinegar during the time it cures and dries.
If you use the acetic cure type bathroom grade silicone, please be aware that once it is squeezed out of the cartridge, it starts to cure and gets a skin on the surface very quickly so there is a need to work fast and smooth out the surface before it gets that skin. It is also the case with neutral cure type silicone but the curing starts even faster with the acetic cure type.
• After preparing the surfaces to be sealed, I use masking tape to tape up along each side of the gap to be sealed, about 3-5 mm to each side of the gap, until all is taped up. This is time consuming plus you need to know what you're doing and work fast once you started to apply the silicone. However the finish that you get is so neat and the surface so smooth that it's worth the trouble, especially when I do high end, expensive bathrooms.