Seal Composite Trim to Prevent Mold Growth?

LESLIE: Rick in New Jersey wants to know if he should seal composite trim to prevent mold growth. How can we help you today?

RICK: When our house was built, in place of the usual wooden boards that are used to trim around the edges of the roofs and around the bottom of the house, they used a plastic composite-type material.

TOM: OK.

RICK: And it’s used in place of wood and it’s maintenance-free, lasts forever, that kind of stuff. With the exception that any place this wood is – this composite material is cut, it becomes kind of a haven for mold and mildew. And you get green growth there and it’s – you spend a lot of time and effort continually pressure-washing to clean it out. So, what I’m looking for is some means of sealing – is there some way to seal composite trim to prevent mold growth on what is otherwise a maintenance-free material?

TOM: Well, if it’s composite, it may be a product called AZEK – A-Z-E-K. And that’s paintable. And so you could paint those areas and that might tend to seal it in a bit more. Because I think what you’re saying is that the cut areas are probably more absorbent than the surface areas and so you’re getting a little more moisture. Maybe it’s a trap. There’s a little rougher surface there that might be a trap for dirt that feeds mildew or algae and that sort of thing.

So, what comes to mind right away is that you simply could paint it. But of course, you know what comes after paint: repaint.

RICK: Exactly. It takes away the maintenance-free aspect of it.

TOM: Exactly.

RICK: But is there a type of paint that would be more conducive to seal composite trim to prevent mold growth to last longer, like an epoxy-type paint or something like that?

TOM: Not for a surface like that. No, you would just use an exterior paint and you would probably prime it first.

RICK: So it wouldn’t be latex. It would be an enamel?

TOM: No, you would use a 100-percent acrylic latex paint. That’s what AZEK recommends be used. And you also might want to take a look at Sherwin-Williams for the paint manufacturers. I know that they have paints that are specifically made for vinyl or PVC products, which is what that product is. AZEK is simply an extruded cellular PVC.

LESLIE: Not everybody does this but some contractors tend to skip the step of filling holes when it comes to a composite trimming. You know, they’re like, “Eh, you can’t see it. It’s OK.” But this could give you the opportunity – if you’re going to paint the trim, as well – to go ahead and fill any nail holes. And that’ll really give it almost a more natural wood look, the brushstrokes. It could be a good thing.

RICK: OK. Thank you very much. That’s a great idea.

TOM: Thanks so much for calling us at 888-MONEY-PIT.