Many architects and builders, especially here in Mexico, are having a love affair with silicone caulk. They use it in many applications where it is not the best option. So why is it so commonly misused?

Try to buy something else and you find out why. Superior caulks like polyurethane and rubber butyl can be hard to find and you may have to order it and wait.

Just a few Pros and Cons

We could talk about caulk for months but let’s just remember a few things about a few types of caulk and that will suffice for the average homeowner.

Silicone (100%). It is clear or white and most are not paintable. It’s main advantages are its stretch and strength coefficients and it remains flexible for a very long time. If applied cleanly (see my “how to caulk neatly” blog) it has a low visual impact although it is shiny on flat surfaces like stucco or painted plaster.  It is a remarkable product in this regard. It’s weaknesses include low adhesion compared to polyurethane and rubber butyl and because of this water can get through it over time. If it has a biocide or is mildew resistant, it can be used in tub shower areas.

Polyurethane. Pros include strong adhesion, durable over time, comes in colors (mostly in the U.S.). Can be found sanded to match grouts in bathrooms (see also “siliconized acrylic”). I am a fan of this caulk and have used it in tough applications for many years. It does dry out just a little over 20 years and gets stiff in the tube if not used within a year or so.  But it adheres like construction adhesive which is a very good thing unless you have to remodel and tear something out that is held together with polyurethane.

Rubber Butyl. This is an awful product to use, very sticky, messy, black or brown….but oh my does it last….and stick….and flex (careful, some types shrink). This is the best performing product and that is why window manufacturers and automobile manufacturers use it. If you are worried about water infiltration (around pools, fountains, windows and doors) then rubber butyl may be the way to go. But can you find it? I will let you know where in another blog.

Acrylic/Latex. Mostly garbage. Sorry but it is a marginal product that has a few indoor uses to fill cracks before painting (“painter caulk”). Don’t use it in the bathroom  or outside no matter what DAP says. Mold resistant …..not in my opinion. It may be “siliconized” and this improves performance considerably and may make it a paintable caulk. But why ruin a good product like 100% silicone by adding a crap ingredient like latex?

That’s the basics of the four types of caulks.