Caulking a bath tub or shower is really simple if you know a few tricks. From caulk choice to the smoothing process, this post describes all the tricks you need to pull a professional looking job.
Choosing the caulk
There are many different types of caulk out there. Suffice it to say that in practice, you have the choice between silicone caulk or vinyl latex caulk. There are also "siliconized latex caulk" which have a little bit of silicone in them. I am considering caulks for shower surrounds / bath tubs so I’ll talk about interior bath caulk only. Vinyl latex caulk is waterproof and recomended for bathroom usage so in this article, "latex caulk" will be used as a synonym for "latex caulk".
Latex based caulk usually becomes hard after setting while silicone caulk remains soft. Before it sets, latex caulk can be cleaned up with warm water while silicone caulk is difficult to clean (there are products which claims they can and I have tried many, none of them did a good job on my hands ;-) ).
The choice of caulk depends on the surfaces it will have to stick to and how much they will move to the respect of each other. Usually, fixture manufacturers recommend what kind of caulk (latex or silicone) should be used. If you have lost the installation instructions for your fixtures, you can guess what kind of caulk you need by observing the caulk currently installed (this assumes whoever caulked previously respected the manufacturer’s instructions). If it is soft (kind of like jello), this is most likely silicone caulk. If it is hard to the touch, it is most likely latex caulk.
In general, one can summerize the properties of caulk as follow:
100% Silicone Caulk: Can adhere to most surfaces, great elongation (ideal for surfaces which can move like shower surrounds), can be immersed in water and are long lasting. Paint will not stick on 100% silicone caulk. It gives its best results on non porous surfaces. It is naturally mildew resitant.
Siliconized Latex Caulk: The preferred caulk for painters: Adheres to most surfaces and can be paint with latex paint. They have a number associated with it: the number of years they can last so choose the highest possible.
(Vinyl) Latex Caulk: An inexpensive alternative to siliconed latex caulk. Poor quality latex caulk will set hard and will not last very long if the surfaces are moving. This caulk won’t fill large cracks.
You can find mildew resitant caulks. Essentially, chemicals were added to slow down mildew growth. Use these in showers / bath tubs if you can.
Remove the old caulk if any. This is critical to get the new job to properyl bind and seal the join. Adding caulk over existing dried caulk will not cut it. There are chemicals sold at homes centers which facilitate caulk removal. Just put the chemical on the caulk and wait until the caulk reaches the consistency of butter. Scrap of use a plastic putty knife and / or a clean cloth. You can also use the good old technique: a utility knife and a plastic putty knife. Be careful not to damage the surfaces you are removing caulk from.
Wash surfaces where caulk will be applied so they are clean and free of dust. Let surfaces dry completely before attempting any caulking. You can use an air blower for this.
Applying and smoothing the caulk
Before applying caulk, use painter’s blue tape to delimit where the caulk will be applied. This little trick will help you get clean caulk edges (see picture below).
Using a caulk gun, apply the caulk so it just fills the seam betwen surfaces. Resist the urge of putting too much caulk.
Take a small receptable and fill it with water. Dip your finger in the bucket and as it is wet, smooth the caulk from top to bottom, in one complete movement. Remove the extract caulk from your finger, dip in water again and perform a second pass as necessray.
Immediately after you are done, carefully pull the blue tape. This will remove all the caulk on the sides and leave perfectly straight edges (see right picture below).