Taggart001

From experience, does anyone know if it is better to treat , varnish or paint exterior wood on an outbuilding in Central Portugal?

I wonder if the summer gets so hot it degrades varnished surfaces?

Also the constant sunshine may have an effect too?

BillBullock

From my experience in the Algarve, I would not varnish exterior wood. Use a good quality preservative instead.

liveaboard

Varnish looks great, but blisters in the sun far sooner than paint.
I've tried everything.
Basically, anti UV compounds break down after a couple of years, and then sunlight beaks the surface of the wood; the varnish is just fine, but falls off. Varnished surfaces that don't get direct sunlight do ok.

Paint lasts longer, but is variable. wet/dry cycling breaks it loose, and sunlight kills everything. Some paints are good for 20 years if applied properly, but 5 or 10 years between repainting is more likely. It's much less work to repaint than to revarnish.

Treated wood will last 10 years or more, but remember that it's impregnated with toxic compounds that leach out over time.

If your area gets good hard frosts in winter, you have far fewer wood eating bugs to worry about. Make sure the wood is isolated from the ground so it won't wick up water all the time. If water freezes in the wood, it breaks the fibers. Bugs, fungus, and bacteria all need water. Dry wood lasts, wet wood does not.

Wood shrinks when dry, and swells when wet; a lot. That's why it's difficult to maintain wood in the Portuguese climate. 5 months of hot aridity, followed by months of high humidity causes extreme movement, even cracking open in summer.

I hear a lot about wonderful coatings that last for decades; I've been disappointed too many times now and don't believe any of it.
Anyone with treated wood that's been exposed to sun and rain for 20 years or more, please tell me I'm wrong.

BillBullock

Well said liveabroad. That's my experience as well in the Algarve but we don't get hard frosts. I've come to the conclusion that wood preservative will do for a few years and then you replace the wood! Also, our house seems to need repainting every 5 to 6 years, no matter how good and expensive the paint. Time spent repairing and preparing the surfaces is important of course but the harsh climate wins in the end.

BlackBeardie

Yes, wood is difficult to preserve exterior woodwork in the Algarve due to the extreme heat. This evaporates the oils rapidly leaving the wood dry and brittle. Paint I think can work, if it is of sufficiently high quality as liveaboard said. The shorter periods of extreme wet weather doesn't do the wood any favours either. One chap mentioned slapping diesel onto the wood. Any idea on the validity of doing this? I am using teak oil at the moment by it's the first year so how long it will last is unproven. My guess is I will have to repeat biannually as a minimum. I find linseed oil works well for outdoor furniture and tool handles.

BillBullock

Linseed oil has not worked on my wooden sunloungers. I am going back to using teak oil again, reapplying it annually.

liveaboard

Diesel stinks, and is a pollutant.
Some people advocate old engine oil; that's even worse!
I have barrels of diesel in my garage, and engine oil too; I sure wouldn't use that for my furniture, or any wood. Indoors it's poisonous, and outdoors it's poisonous.

Those oils are good if you have the discipline to do it every year. Linseed oil not good in the sun I think.

It's not just the Algarve, it's everywhere. Even the feeble northern European sun will blister varnish after a year or three. Everywhere that's habitable has sun and rain.