New paint cracking on caulk bead along exterior trim and j-channel flashing

Question

I recently had new windows installed and replaced an exterior door myself. I have aluminum siding and so there's strips of metal j-channel flashing along the door and window trim, butting up to the siding.

After the trim and jchannel was installed, I ran a bead of caulk between the trim and jchannel, waited a day or so, and then painted with new exterior black paint. After a couple of weeks in the sun, the paint seems to have torn where the caulk hits the steel j-channel. It doesn't appear that the caulk tore. I'm guessing this is because of the change in temperature.

What am I doing wrong? How can I fix this? I'm thinking about putting another light coat of paint over the top but want to make sure I'm not missing something here.

By the way, the caulk is an acrylic exterior caulk that is paintable. I forget the exact type, but it might be DAP alex fast dry or something along those lines.

Thanks!

Answer 1

Maintenance-free siding materials are typically installed with a loose-fastener arrangement because they're floating and move a lot with temperature. It's not common to see caulk against the various components for this reason. What you're seeing is somewhat expected due to stretch in the caulk.

Your siding is a protective and aesthetic covering over a "drain plane", usually a layer of house wrap or similar. This provides the ultimate protection against water infiltration. The drain plane normally includes adhesive or metal flashing to door and window flanges.

By the way, the siding and channel are probably steel. Aluminum isn't often used for siding anymore, as it's fairly soft and more expensive.