Anti-mould coating for plywood?

[Mark A]

Hi chaps,

Not sure if this is the right department...

I've made 18 window boards for my house out of birch plywood with a softwood lipping on the front to simulate solid timber. The house is old and stone-built, and the internal sills are lime-rendered (as are the walls).

For a couple of weeks the window boards were placed in their corresponding positions unpainted, though I've since painted them with waterbased undercoat and satin. I noticed one particular board in an unused room had a postage stamp sized patch of mould growing on the edge nearest the window. I've re-sealed the window, so moisture shouldn't be coming in any more, though I'm a bit concerned about mould growing on the underside unseen after they're fixed in place.

Looking in my shed I found D4 external PVA, half a tin of black Evercryl and yacht varnish.

Are any of the above a permanent barrier against moisture and mould growth?

Or is there something else worth trying?

Cheers,
Mark


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[Woody2Shoes]

...one particular board in an unused room had a postage stamp sized patch of mould growing on the edge nearest the window. I've re-sealed the window, so moisture shouldn't be coming in any more, though I'm a bit concerned about mould growing on the underside unseen after they're fixed in place.

Hi,

I think that in the first couple of bits I've quoted from your post I detect a possible misunderstanding about the source of the moisture causing the mold. What you're probably seeing is warmer and moister air, from elsewhere in the house, finding its way into the cooler un-heated/used room, cooling and giving up some of its moisture - I wonder if the unused room is near a kitchen/bathroom (or maybe at the top of the stairs?) i.e. the source of the moisture is probably internal to the house.

I'd varnish all hidden surfaces (esp. edges) in this kind of situation with polyurethane floor varnish or similar (and paint/varnish the visible ones) - as an alternative, another favourite of mine is alumium primer. The finish won't stop condensation, or even mould growth necessarily, but it should stop staining/rot for years on untreated timber like yours. Another option might be paint designed for kitchens/bathrooms which explicitly include a fungicide (I suspect most paints have something in them to stop mould).

Cheers, W2S

PS another part of the mould reduction strategy is to improve extraction/de-hehumidification of the warm air at source (esp. kitchen/bathroom)