Fighting Mold with the Right Type of Varnish | Southwest Florida Painting

This week’s question involves a subject that is all too common in Southwest Florida: mold.

“We have just stripped Sikkens off of a door and window finish from an exterior oak door. It was black with mold. We are looking for a product that will not mold in our damp climate.”

I am not sure where you live, but if you live in Florida and the door gets any type of sun exposure - especially from the south - a varnished door will not hold up. The door will weather really bad and may even start to separate and crack at the wood joints. Even if you stain the door, then apply the varnish, this can still happen. The reason for this is simple: varnish or stains do not have UV protection. To avoid this, you need a pigmented product for UV protection, preferably an acrylic (latex).  This will not attract mold.

 However if the door is protected from the sun and rain, then you can use a stain and varnish, but will still have a mold issue.  I recommend to  sand the door, wipe off the dust with a tack rag  and apply your desired stain on the door.  Allow it to dry overnight then sand very lightly with 400 sandpaper, wipe off the dust with a tack rag again  and apply your first coat of Spar varnish in a satin or gloss finish.

Allow it to dry between coats then very lightly sand again with 400 sandpaper apply at least one more coat of varnish.

It’s important to understand that varnish is an-oil based product, and because it is an oil-based product you will still get mold growing on the surface, there is no way to stop this.  Oil-based products that are used in Florida attract mold due to the humidity and the oils in the varnish. However, all you have to do is wash down the surface of your door with a bleach and water solution to remove the mold.