How to properly caulk a plastic shower?

Question

I have installed a 3 piece plastic shower wall liner and the two vertical seams require caulk. I've caulked them with GE Silicon II bath and shower caulk multiple times but it always pulls away from the plastic after a short time (1-3 months) leaving a crack between the plastic and the caulk.

I have a theory that it's either a change in temperature causing the walls to expand (the walls get really cold in the winter, but heat up when a shower is taken), or that the plastic is really smooth and doesn't get a good 'stick' to to caulk, ..or obviously something else.

How can I caulk these seams so that it doesn't pull away from the plastic?

Answer 1

The most likely reason is that this specific caulk doesn't have good adhesion to the specific plastic. The problem is solved by using some other caulk - the best bet is to figure out which plastic you have and look for caulk that claims "adhesion to X" where X is your plastic.

I had a similar problem once - otherwise very useful Henkel sealant that adhered to tile so good I had to cut if off with a knife wouldn't hold on PVC window frames. I changed the sealant to the one that claimed adhesion to PVC and it still holds perfectly.

Btw maybe elastic silicone sealant is a better fit for the application you describe.