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View JSThoreau's profile

How often does exterior polyurethane need reapplication?

by JSThoreau
posted 08-04-2016 02:21 PM


2 replies so far

View mahdee's profile

mahdee

4286 posts in 2130 days


#1 posted 08-04-2016 03:20 PM

Hi Jacob,
I think it should hold up well as long as there are no sun exposure on it. I use the spar Urethane on the door on my shop which has direct exposure to the elements and it didn’t last for more than a year. I think your assumptions are accurate.

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View JBrow's profile

JBrow

1368 posts in 1283 days


#2 posted 08-04-2016 05:51 PM

JSThoreau,

A ceiling is a little different from the experience I can share regarding renewing Helmsman Spar varnish, but perhaps it can be helpful. We have a west facing covered patio. Setting on the patio is a coffee table and an end table both with a red oak tops (base is metal). When I finished the table tops I applied 5 coats of Helmsman Spar varnish on all six sides. This year, two years after being completed, I applied a renewal coat of the spar varnish. I did so only because the gloss sheen had become dull.

The table tops get far more weather than the ceiling of the patio cover, so I would expect the spar varnish to hold up a little better on the ceiling. Therefore a renewal of the ceiling I would think would be less often. I would be concerned that if not renewed often enough, the UV bouncing up to the ceiling could lead to cracking and peeling. A periodic renewal coat when the finish becomes dull therefore is probably a good idea. I would guess renewal would not be required more often than every 3 – 5 years, but annual inspection is probably better.

I would guess that the cracking and shrinking is due to only one side of the ceiling being finished. Had all six sides been coated with a sealer, the cracking and shrinking would probably have been less.

The dark moldy patches are a mystery to me. I maintain a red oak picket fence annually and notice what I think is mold in the wood. Bleach and soap does little to remove it. I have yet to figure out why it occurs on the sealed fence, how to prevent it, and how to remove it without deep sanding. My theory is that the sealers I have used are penetrating oils, thus leaving places where mold can get a foothold and then grow. If this is correct, then a film finish like a spar urethane should prevent its re-occurrence – but I really do not know.

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