Sealants are typically urethane based or silicon based. Silicone sealants tend to last longer. They also have a really good positive in that they can take a lot of movement. So, if you’re using them in an application where you’re going to experience a lot of movement in the joint then silicone is really, really a good choice.
The downside of them is that you can’t paint them. Paint doesn’t adhere to silicone sealant. The good thing about urethanes is that you can paint them and they skin over very quickly. Skinning over can be important when you’re talking about using them in a job site environment where there could be a lot of dust and things like that.
You don’t want that dust adhering to the surface of the sealant. So, the good thing about urethanes is that they cure quickly and they’re able to resist that kind of contamination. Last but not least is the cost factor. For a long time silicons were considerably more expensive than urethanes.
That is still largely true. However, the prices of silicons have modified over the past five to seven years and the cost differential between silicones and urethanes has been reduced.