Wood trim maintenance.

I have been using Watco Exterior oil on the gunwhales and wood trim for a few years. Still get mildew stains even if diligent about maintenance. I live in South FL and our summers are hot, humid and storms move through each day. Although the canoe is covered with air circulating, the mildew is hard to control. I keep it on a stand under my patio roof outside.

What other oil application should I be looking at for future end of season maintenance? If switching from Watco to other, how should I prepare the wood?

You could try adding mildewcide,

– Last Updated: Mar-08-10 8:39 AM EST –

available at good paint stores, to the Watco, though if you're using the exterior, it probably contains some already. It is toxic and if you handle your rails a lot, that could be an issue. Unfortunately, the dried oil, wood and any accumulated organic grime are fungus food. Add warmth, humidity and stagnant air, and you've got a nice environment for spores to activate.

If you can't put your wood in the sun to dry out periodically, perhaps you could try and increase air circulation by venting the tops of your cover, leaving the ends open and/or elevating the boat higher off the ground.

A laundry bleach and water solution should work to kill most, if not all, the mildew and remove the staining. If you need to take it further, there are two-part wood bleaches that will work even better but may also lighten the wood more than you'd like.

Try talking to some guys at a boat yard in your area and see what they recommend.

Bleach question
Do peroxide bleaches such as Oxyclean kill mildew on wood as well as chlorine bleaches?


Yes, they would, but mildew is mainly
a surface cosmetic problem. I rub more Watco onto my ash gunwales and thwarts, and some of the mildew comes off in the process. But I’ve never seen an indication that the mildew is going deep into the wood.

I deliberately neglected my western red cedar deck for 15 years, refusing to put in the time and money necessary to peroxide and treat it annually. There was a lot of mildew, lichen, and even moss on the surface when I cleaned it manually, but the wood right underneath was OK. The only significant damage was at the ends of boards and sometimes between boards, where litter would hold water. Conclusion: if that deck had been mostly stored out of the rain like my canoes, damage would have been minimal. Similarly, the only serious damage I see or hear of on ash gunwales is where water can sit on them without drying out. Surface mildew is unsightly, but rarely comes to anything.



is the best then? Allright will keep using it and I have tried the bleach even ajax with bleach. The canoe is better protected than exposed in the summer. We do get sun but it rains daily from July - Sept

There are other drying oils, but
exterior Watco is as good as any, IMO. More frequent applications might help, especially if you scuff-sand first or rub down with mineral spirits and a Scotch Brite pad before re-oiling.

I use Scotch Brite
pad to apply the Watco…generally cleans everything up pretty well.

Yep. Scotch pads
work great for this application.


I’ve never seen mildew on spar varnish.

True, but it grows real nice everywhere
the spar varnish gets chipped or scraped off.

Varnish mildews too, most everything will if it’s kept warm and damp.

Bill H.