Exterior clear wood finish

I used Osmo 420 on a new cedar feeder about 5 years ago and despite the promises of anti-mould ingredients, anti-blistering and anti-uv I have found it pretty useless. I understand that there’s maintenance to do, but trying to strip this is basically impossible and defeats the purpose of using it.

Here’s the 5 year old piece looking poor with the Osmo.

This is the Osmo.

This Ronseal 5 year woodstain is superb. I’ve used it on something and it’s still pretty perfect 8 years later with no new coats. However, it changes the wood colour to look like it’s painted, which I don’t want.

Does anyone have long term experience of any exterior clear wood treatment that works for at least 5 years, without repainting and even then it needs to be easily done (not stripping the whole layer off)?

I find Osmo oils exellent for interior use, but no way are you going to get protection for 5 years from any of their outdoor products, or any other low build wood finish for that matter. The point of oil finishes is that they are very quick and easy to re-apply so a recoat every year or two is simple.

I’ve had very good results from Barrettine Wood Protective Treatment, despite it being much cheaper. Also Sadolin works very well for outdoor timber and it’s available in a clear coat too.

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Well, that’s my point. They’re not very good then. As I mentioned, the Ronseal is a wax based product and is perfect after 8 years with no care.

Osmo oils are great if you want to keep wood looking and feeling as natural as possible, which would be desirable if you have timber cladding on a building, for example. I certainly wouldn’t use it outdoors on a non-vertical surface, at least not without recoating regularly.
The best results I’ve had for durability on external timber were with Sadolin Extra which you can get in a clear finish.

Thanks I’ll take a look at the Sadolin.

I guess it will take you a bit of time and elbow grease to get rid of all that greying and black mould which is going to show through a clear coat. Maybe worth trying one of those ‘wood reviver’ products to take away the greying, but I’ve never tried them myself.

Ahh this is for another small project. It’s hardwood and seemingly taken forever to make. I was just going to paint it with the Ronseal as I know it will last, but the hardwood looks lovely and it’s a shame to cover it with a pigmented coating. Completely ott for what it is, but who cares.

The cedar feeder was just an example of what I don’t want to happen again.

Interesting stuff as I use Osmo for internal wood but use either teak oil or boiled linseed oil for wood outside.

Go to your local marine supply store. Professional grade products made for harsh conditions.


Is there a need to use a preservative or varnish on cedar? I recently had a new cedar roof installed on my summerhouse and I was advised not to use any treatments at all because cedar contains naturally protective oils.
If left untreated, your bird feeder will go a beautiful natural grey colour. If it is kept in a well ventilated, sunny area there should be little growth of moss or algae, otherwise try putting a ring of fine copper wire around the finial. The slow leaching of copper ions will protect against mould, moss and algae

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Are you looking for a coating , or something that is absorbed by the wood and protects that way?
Coatings require reapplying, and require good surface prep before applying. And whilst they look good for a year or so, soon require reapplying. And that can mean going back to the wood again.
Whereas an oil that absorbs in, protects with a relatively thin " coating". And often requires less surface prep.

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Avoid yacht varnish or the like, they need regular maintenance in my experience. I used Sadolin Natur on my external pine window frames, it’s pretty good but like any product will require a bit of tlc every few years depending on uv exposure.

Have you considered a clear acrylic varnish topcoat? It might be a glossier finish than you’re after due to it being fairly thick but it provides a waterproof coating if done right.

IME it tends to deteriorate pretty quickly. Well, it does in the harsh NZ sun anyway. I applied a two-pot clear coat on a wooden kayak a few years ago, which has lasted very well, but it requires a lot of surface preparation.

I use decking oil on our hardwood deck every 2-3 years. It finishes beautifully and brings up the wood nicely.

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I’ve done the copper wire thing with a pitched roof, and it works well.

I agree with you about there being no need to finish cedar - that’s part of its appeal. We’re in the process of having our fence replaced, and one vendor who came to give an estimate says the only maintenance it should only need is a power washing once or twice a year, to keep mould / algae from growing.

my summer house is painted with clear protection from scewfix, but its a spirit based rather than water so is a bit fumey. Lasts well and just soaks into the wood like good old creosote used too so leaves no finish other than the natural wood.

Thanks for the replies.

Cedar is a beautiful wood, with stunning purple/pink/cream hues. I don’t agree that letting it go a miserable grey colour is nice. Also, it does contain it’s own natural preservatives, but that doesn’t stop unsightly mould forming and it will eventually rot like all wood. This natural preservative probably causes problems with anything painted on top too. Saying that, this project isn’t to coat cedar. It’s another nice piece of hardwood.

It is a tricky decision to choose an oil vs varnish/lacquer. Oil is easier to apply and reapply, but I do think a well maintained good quality lacquer will be better in the long term against the elements.

I’ve decided to go for Sadolin Extra Durable Clearcoat. From the research I’ve done, it seems at least to be somewhere at the top. The problem with reading online product reviews is that 99% are just people saying “Goes on great” “Does what it says on the tin”, etc. Trying to find actual feedback of how a product has worked over 2-3 years is not easy. I’ve read a few long-term praises for the Sadolin and the fact that a door manufacturer recommends it too. Thanks @ChrisSU. There are some very specialist proper 2 part yacht varnishes, but needs further research, cost and that is going a bit ott for me on this job.

The key to successful wood coatings is first treat the wood with a clear non-waxed preserver. I have both Ronseal Multi Purpose Wood Treatment and Cuprinol Wood Preserver Clear. Both are very good and are for use under a coating. Not sure which I’ll use yet.

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