Best way of sealing roof ventilation

Hi y’all!

I’m in the process of mounting some roof ventilation (Maxxair fan) on my van, and I’m struggling to figure out exactly which sealant to go with. Everywhere I look I am getting different advice; there are adhesive strips, sika flex, lap sealants, butyl tape, and various primers to go with everything. It is killing me.

What I have is a plastic frame that needs to be mounted on a metal roof. The opening of the roof is already primed with metal primer (needed anyway after exposing the metal when cutting the hole).

I bought Sika flex-554 as that seemed to be the perfect fit, and I did a little test on the plastic frame just to be sure it would adhere properly. I cleaned the surface properly before applying, and I left it to dry for almost 3 complete days without touching it. In the end I was still able to relatively easily peel it off with my fingers. I don’t feel confident this would hold for very long. Now i’m in the process of figuring out what else to try, and I figured I might as well ask for some advice.


  • Is Sika flex the way to go? If so, what is the most appropriate? I have also been looking at 449, but in the end it seems very similar to 554 (which i already tried) on paper.

  • Do I need a primer for the plastic? Is that perhaps why it didn’t stick good enough?

  • Can/Should I apply some Dicor lap sealant around the edges after the sika flex has dried? Does sika flex and Dicor go well together? Does this make sense?

Greetings & Welcome!

I use a butyl rubber gasket, then dicor if needed. Never skip the butyl rubber.


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