Best clear finish for exterior mahogany door in direct sun?

[mardinor]

We've got a beautiful old mahogany door, circa 1880, bought from a reclamation yard. Sanded and finished meticulously with several thin coats of International Yacht varnish, left to dry indoors before hanging. Looked fantastic...for less than a year.

Varnish peeled and cracked after one season.

Now resanded and looking for advice on alternative clear finishes that can be maintained without removing previous coat. Leaning towards either pure Tung oil or something from Osmo.

Anyone have any practical experience?

 

[biffvernon]

I suspect you're trying to achieve the impossible. Polyurethene varnish (and still expect regular maintenance) or build a porch to keep the sun off?

 

[andrew gayton]

strip back and use raw linseed oil. in my opinion the best treatment for external joinery.

 

[biffvernon]

Agreed, but the oil won't keep the finish that mardinor seemed to want.

 

[Nemesis]

I wonder if this was once an internal door from a 'grand' house (or maybe a bank)?

An external mahogany door left unpainted isn't anything very historically correct and I think it will not be easy to try to maintain the finish.

 

[mardinor]

Thanks all.

The door was originally from Bond Street in London (with fancy real wrought iron over openable glass panels) so suspect it has always been external. But it was painted in a dark brown glaze/varnish which we thought was a shame for such a nice wood but now understand perhaps why!

I will try the oil approach. Not looking for a glossy 'varnished' appearance, just to stop the wood going grey as it doesn't suit the fancy gilded ironwork.

If I go for oil, is the consensus Raw Linseed? Any votes for Tung? Or is there actually any benefit in one of the blends that add UV filters in this sun-exposed situation?

 

[Andrew Bodenham]

In my experience linseed oil is a poor finish for external joinery. Having experimented with raw linseed applied to some parts of my boat last year I found that the wood quickly weathered to black and under the heat of the summer sun oil oozed from the end-grain - a complete mess.

I'm a great fan of Osmo products, though I haven't tried any of their external coatings. I'd feel more inclined to trust one of their mixtures over a raw oil approach.

Classic Boat magazine has a long-running test on clear finishes. To date the best resluts have been with Sikkens Novatech and Coelan, a flexible polyurethane which is gaining quite a following in the marine world, despite being appalingly expensive.

Having said all that, any good marine varnish should be good for at least 2 years. The fact is that to maintain a high gloss clear finsh you are going to need annual maintenance, i.e. rub down & re-coat. That assumes that the initial prep and application conditions were satisfactory. UV is the big killer for varnishes and the like, which is why woodstains like Sikkens last longer - they are contain filtering elements. But they don't give a true clear finish or gloss.

Be aware that the stuff marketed as Yacht Varnish is not intended for marine use - it's just a good grade DIY varnish. Genuine marine products such as Epifanes are in a different league.

Wood finishing is a real nightmare. So much choice, so much conflicting advice, so time consuming, so expensive if you get it wrong.

So, what are you going to choose.....?

 

[wobs]

Following on from AB's post, I did a bit of a search and found:

http://www.premapro.com/PDFs/ClassicBoatVarnishTestMarch2008.pdf

Would any of these be advised on a new hardwood exterior door (eg. Sikkens Novatech)? Not bothered whether its a matt or gloss finish. More interested in it lasting.

 

[SBJ]

Hi

Sikkens finishes have a good reputation, why not have a look at Sikkens Cetol Filter 7, which is specifically formulated high UV exposure.

This might sound like heresy to you but have you considered painting it? As mentioned before an unpainted mahogany front door doesn't sound historically correct although I am quite happy to be corrected on this.

rgds


SBJ

 

[wobs]

Cheers SBJ.
Followed your suggestion and used the Filter 7. Well, will do after the HLS has dried. And its forcast to stopped raining for a day.

It looks good so far though.