# External iroko - Osmo UV Oil or Sikkens Cetol Filter 7 Plus



## RogerM (18 Mar 2012)

Nope - I haven't a clue either, and I've had enough conflicting advice to convince me we need a test, so I've set one up.







I've used an offcut of pale iroko, and from the left I have 3 coats of Osmo UV Oil, then one coat of Sikkens Cetol HLS Plus light oak stain covered by 3 coats of UV oil, and finally on the right one coat of Sikkens Cetol HLS Plus light oak stain followed by 3 coats of Sikkens Cetol Filter 7 plus light oak. The test piece is out in the open facing due south in full sun so we'll see what happens. I'll update the thread at approx 6 month intervals, or when I remember or when asked.


----------



## squowse (3 Aug 2012)

Hi Roger, (I'm also a Roger)
Will watch this with interest as like you I have been making windows from iroko. In my case it is the reclaimed stuff ex school chemistry labs. The stuff I have is mostly a bit darker. I've finished it internally in tung oil, but ended up running out of time in winter to finish the outsides. It's gone quite silver already but I think it will spruce up quite easily. I don't want a "perfect" shiny finish, I am quite happy for it to look aged but not completely silver and I want to look after the wood.
I saw you mentioned Owatrol Deks Olje D1 before. Did you end up trying any? I just saw they have started selling Owatrol at my local finishes shop and ended up here after googling it.


----------



## RogerM (3 Aug 2012)

squowse":khr6kg26 said:


> Hi Roger, (I'm also a Roger)
> Will watch this with interest as like you I have been making windows from iroko. In my case it is the reclaimed stuff ex school chemistry labs. The stuff I have is mostly a bit darker. I've finished it internally in tung oil, but ended up running out of time in winter to finish the outsides. It's gone quite silver already but I think it will spruce up quite easily. I don't want a "perfect" shiny finish, I am quite happy for it to look aged but not completely silver and I want to look after the wood.
> I saw you mentioned Owatrol Deks Olje D1 before. Did you end up trying any? I just saw they have started selling Owatrol at my local finishes shop and ended up here after googling it.



Hi Roger. I did try the Owatrol on a test piece of oak but it didn't fare well at all. It seems to work better with teak when I compare it to my neighbours boat. At the moment both the Osmo UV oil and the Sikkens Filter 7 are bearing up well. There has been some darkening of the wood but it is still looking good.


----------



## RogerM (23 Oct 2012)

All 3 seem to be standing up well. Predictably, the wood has darkened so that the difference between the far left and the centre panel is less marked, but all seems fine so far. The test piece has been in full sun and open to the weather.


----------



## RogerM (11 Jun 2013)

Latest update is that they are all standing up well. However, as you can see, there is very little difference between the UV oil over the stain compared with the UV oil on its own. There is a narrow line of grey along the top edge which may be due to UV getting to the wood from both sides near the edge. The Sikkens is still looking solid and if this were joinery I wouldn't feel the need to repaint yet. The position remains facing due south in full sun


----------



## sereneblue (5 Oct 2013)

RogerM":2m1ukm6r said:


> There is a narrow line of grey along the top edge which may be due to UV getting to the wood from both sides near the edge"MBB



I think your experiment successfully demonstrates issues with edge-film thicknesses. If the edges are sharp, the coating tends to pull back from them leaving the vulnerable to what its being tested against.

Speaks volumes for leaving a radius or knocking off the edges with a piece of sand paper before coating.


----------



## RogerM (17 Jan 2014)

sereneblue":216hwvpp said:


> RogerM":216hwvpp said:
> 
> 
> > There is a narrow line of grey along the top edge which may be due to UV getting to the wood from both sides near the edge"MBB
> ...




Getting a bit scruffier! Now nearly 2 years old - including 2 summers. 











The section of the left which is just 3 coats of UV oil is showing severe breakdown along the top of the specimen, and it's starting to show signs of grey along the front as well. 

The centre section, which is one coat of Sikkens Cetol HLS Plus light oak stain covered by 3 coats of UV oil is slightly better, which seems to indicate that a bit of pigment does help, which is hardly surprising given that sunglasses help as well.

Finally the one on the right has one coat of Sikkens Cetol HLS Plus light oak stain followed by 3 coats of Sikkens Cetol Filter 7 Plus (light oak), and this is still holding up well. There is slight greying along the front edge, but the front face and top is generally looking good. I reckon that if I had chamfered the edge, or rounded it slightly that would have held up as well. 

Ignore the white spots - back in the summer some silly person  sprayed his kitchen doors nearby and the overspray drifted over the test piece. 

Incidently, the back of the speciment which was treated in exactly the same way and is in the shade, is pristine, and it is slightly disappointing that a product that is marketed specifically as UV Protection has come out the worst. Whilst Osmo would probably claim with some justification that this is not a scientifically controlled test, and one specimen is not enough, this IS a real world test based on how people actually use the product in real life.


----------



## marcros (17 Jan 2014)

interesting comparison. It is a real shame that the sikkens isnt available in a sample pot- I have a small item to do that doesnt justify a litre of each coat. What would need to be done to the Osmo UV oil for maintenance, based on the above- 3 coats every 18 months or does the old stuff need stripping/prep?


----------



## JJ1 (30 Sep 2014)

Any update on how the finishes are holding up now?


----------



## RogerM (30 Sep 2014)

JJ1":1or385up said:


> Any update on how the finishes are holding up now?


Currently cycling from Bruges to Amsterdam - about 180 miles. Will post new photo upon my return at the weekend!


----------



## JJ1 (30 Sep 2014)

Thanks Roger. I'm away for a short while myself so will catch up with the thread on my return. Enjoy your cycle ride 8)


----------



## RogerM (11 Oct 2014)

A quick update.











This piece has been in full sun and salty wind ( we live on the coast) for 2 1/2 years now. This is the end of the 3rd summer. The left side (3 coats of Osmo UV Oil) is faring worst, particularly the top edge where not only has the wood discoloured, but the finish is peeling. The centre panel (one coat of Sikkens Cetol HLS Plus light oak stain covered by 3 coats of UV oil) seems to be holding up a little better. By far the best though is the right panel (one coat of Sikkens Cetol HLS Plus light oak stain followed by 3 coats of Sikkens Cetol Filter 7 plus light oak). Whilst this is beginning to show signs that it is weathering, I think it will probably last another summer before it would need repainting if it were a piece of joinery. However, I'll just leave it to continue weathering to see how it lasts.

Ignore the white spots on the front of the piece. Some dipstick sprayed his kitchen doors on the driveway and the overspray drifted onto it!


----------



## JJ1 (12 Oct 2014)

Thanks for the update Roger, much appreciated.


----------



## sereneblue (12 Oct 2014)

Thank you. This is getting dire, I have LOADS of Osmo oil and Osmo treated products at home. Thankfully they are mostly interior. Talk about getting sold on advertisements!


----------



## RogerM (12 Oct 2014)

sereneblue":x5p8s2zn said:


> Thank you. This is getting dire, I have LOADS of Osmo oil and Osmo treated products at home. Thankfully they are mostly interior. Talk about getting sold on advertisements!



The performance of the UV oil has been disappointing. On the other hand I've found Osmo PolyX Oil for interior use to be absolutely bomb proof. I test treated a piece of oak veneered mdf with it, then spilt some red wine, tomato ketchup and coffee on it, placed a hot mug of water in the middle of the mess and left it over night. The following morning it just wiped clean without leaving a mark.


----------



## JJ1 (13 Oct 2014)

I was planning to use the UV oil for a project but have since been informed by Osmo that their Teak Oil would be a much better option for my purpose so I'm just literally off out now to pick up a can of that.

I've also been very pleased with the results from the Osmo Polyx Oil and find it an excellent product.


----------



## RogerM (16 Mar 2016)

Can't believe it's 17 months since I reviewed this.
















This test piece has now been exposed to the weather for exactly 4 years. The left side -  3 coats of Osmo UV Oil has continued to deteriorate and there is little sign of any protection left. The centre panel (one coat of Sikkens Cetol HLS Plus light oak stain covered by 3 coats of UV oil) seems to be holding up a little better, which demonstrates that you do get some extra UV protection from pigment. The best though is the right panel (one coat of Sikkens Cetol HLS Plus light oak stain followed by 3 coats of Sikkens Cetol Filter 7 plus light oak). The vertical part is remarkably good, although the top/horizontal edge is showing signs of weather. After 4 years in a salty environment facing south in a particularly sunny spot, this is hardly surprising and if it was external joinery I would be redoing it this year. It case there is any doubt as to whether it is the sun that is doing the damage, I've also posted a pic of the back of the piece which is in permanent bright shade, and none of the finishes have been affected to any noticeable extent.

This is the same Sikkens finish on a sapele post box which gets full sun for half the day, applied about a year ago. No sign of any degradation yet.


----------



## JJ1 (17 Mar 2016)

Thanks for the update.


----------



## eniacs (6 Apr 2016)

This is a very useful test. Thanks for the information. 

I have a oak front door which needs redoing and looks like I'll be using cetol 7's light oak!


----------



## Skeety (7 Apr 2016)

Must admit that this post made me decide to use the Sikkens over Osmo Poly X.

I used the Sikkens to treat an Iroku garden table I completely took apart and rebuilt, was originally 6ft in diameter but now 5ft as that was the size we wanted and the easiest way to remove all the damage where the finger joints had expanded and broken.

Back to topic. It's been outside in a South facing garden all year round and all it needs is a quick wipe with a soapy cloth to bring it back to the condition it was in when first finished. So glad I cam across this thread back then. £50 for the Sikkens was well spent IMO as I doubt it will need touching for another 3-4 years at least.

I did a test on one of the chairs with Osmo Poly X, epic fail after a few months. Sikkens all the way for them as I rebuild them this year!

Cheers to Roger M for the original post. I'll add a pic of the table when I can.

Jon.


----------



## JJ1 (7 Apr 2016)

> I did a test on one of the chairs with Osmo Poly X, epic fail after a few months.



Isn't Osmo Polx oil designed for indoor use only? I was always led to believe the Osmo Teak Oil was a better choice for outdoor use, i.e. decking, outdoor furniture, etc.


----------



## yetloh (19 Apr 2016)

A really interesting and useful thread which I had not spotted until now.

The performance of the Skkens product doesn't surprise me at all. The painter and decorator who I have used for painting my house for many years was a dedicated Dulux system man but switched to Sikkens products about three years ago and would not now go back to Dulux because he thinks the Sikkens lasts better. He reckons to paint houses about as often but because there is less deterioration it takes less time which keeps the price down for his customers.

I don't tend to use exterior varnishes much, but protection from UV is something that has long interested me in the context of interior finishes and the possiibility of preserving the natural colour of hardwoods used in furniture making. Some years ago I carried out an experiment using various finishes on samples of sycamore, American cherry, American black walnut and padauk. The finishes were a finishing oil, a water borne acrylic lacquer (no longer available), Osmo UVwax, Morrells pre-cat lacquer, a further set of samples with the Morrells lacquer but where the bare wood was first spayed with a factor 30, non-greasy clear sunscreen and I also had a control set of samples to which no finish was applied. The samples were all left outside in full sun over a good summer - the equivalent in terms of light exposure to many years of indoor domestic use where, even in a relatively sunny spot, much of the UV would be filtered out by window glass.

The results were both clear and interesting. There was little difference between any of the finishes and none in terms of the amount of colour change. This included the Osmo which in addition to offering no noticeable protection had the disadvatage that the opacity of the product in the tin translated into a finish which reduced grain clarity and quite obviously reduced lustre - both effects which are the last things you want on a piece of wooden furniture where the beauty of the wood is an important part of what the piece is all about. The only exception to this uniformity in results was the sample of sycamore which had been sprayed with sun screen, this had barely darkened at all. My conclusion was that sycamore must be susceptible to a particular part of the light spectrum which the sun screen was efective at screening out. I have been meaning to experiment some more with other pale species such as ash, maple and holly but have never got round to it.

Since carrying out this experiment I have discussed the issue of UV screening with a friend who is a professor of chemistry and has spent some time looking into this in the context of conservation. From this, some points have become clear. In exterior finishes, UV protection is primarily about protecting the integrity of the finish itself rather than maintaining the natural colour of the underlying wood. It is therefore no surprise that in Roger's experiment all the samples have ended up much the same darkened colour. That the Sikkens finish has superior UV protection is apparent from the fact that the finish itself has broken down very little, so preventing the weathering and oxidation of the underlying wood apparent from the greying of the other samples. My professor friend also said that the difficulty with preventing normal colour change (as opposed to greying from weathering) is that the necessary level of screening would entail such a high level of screening agent that the finish would no longer be clear, so the holy grail of maintaining original wood colours in clear finished furniture is a distant and probably forlorn one. He wasn't aware of my sycamore exception and thought it would be worth experimenting with other pale species. Given that maple is so closely related to sycamore it might be the best bet for good results. If or when I get around to some more experimentation I will post the results on here.

Jim


----------



## Beau (20 Apr 2016)

Nice test and thanks for sharing.

Not surprised as saw a similar test in a yachting mag some years back with lots of fancy varnish's and stains tested and Sikens beat them all hands down for longevity. Think they were testing the Sikens HLS but I admit to getting confused with all there different offerings which seem so similar. Have used there finishes on various jobs over the years and never regretted it.


----------



## EdK (11 Mar 2017)

Thanks Roger - I followed the advice in this post and finished a back garden gate (oak) with Sikkens 1 & 3.
Salty environment/sunny.
Coming up for three years and the front of the gate facing the sun is starting to break down - mostly on the top rail.
The reverse of the gate (shady side) is pretty much looking new.

# How do you re-finish?
I was going to rub down the front of the gate and then reapply 1 & 3 coats but then thought that I might be able to get away with just giving it a quick sand in the worst areas and just apply, say, 2 coats ?
Do I need to go back to bare wood and start again?
Thanks,
Ed

(original gate - garden-gate-oak-work-in-progress-t80647.html )

Also...
How did you get your post box finish so even?
I had issues with my oak gate and it felt like I was applying brown streaky paint.
Is it a case of much thinner coats? Foam brush?


----------



## RogerM (11 Mar 2017)

EdK":2c9or8oj said:


> # How do you re-finish?
> I was going to rub down the front of the gate and then reapply 1 & 3 coats but then thought that I might be able to get away with just giving it a quick sand in the worst areas and just apply, say, 2 coats ?
> Do I need to go back to bare wood and start again?
> Thanks,
> Ed


Thanks Ed. When I'm recoating my bifold doors, I just wash them down, and then when dry wipe it with some 120 grit aluminium oxide paper to key the surface and give it two thin coats of the top coat. It is important to have a rounded edge to top surfaces as the finish will be excessively thin at sharp edges. I think 3mm pencil round is what the manufacturers recommend.



EdK":2c9or8oj said:


> Also...
> How did you get your post box finish so even?
> I had issues with my oak gate and it felt like I was applying brown streaky paint.
> Is it a case of much thinner coats? Foam brush?



I think it really is a case of mixing well and brushing it out thinly. Recently I have started using a Sikkens Walnut for sunny positions as it has a darker pigment which should be more UV resistant whilst remaining impressively translucent. I may set up a test comparing the Oak with the Walnut and also with Sadolin Ultra which also seems impressive.


----------



## RogerM (2 Nov 2017)

Anyone who has found this thread useful may be interested in the new one I've just posted that compares Sadolin Ultra vs Sadolin Classic vs Sikkens Cetol Filter 7 Plus.


----------



## RogerM (8 Nov 2017)

It's been a while since I updated this one. The UV oil only section doesn't look as though it's been treated at all, and the Sikkens part is in need of refreshment, but still not too bad considering that it has been in the sun for 5 1/2 years, including 6 summers.


----------



## On top of the hill (11 Jan 2019)

Ok i feel anxious and need some very basic help. Im new to all this. 

I bought some fantastic 6 foot iroko gates.
But they have been installed in the winter...months after I ordered them.

I have taken them off...after 2 months hung outside...allowed them to dry in situ by covering them with a tarp for two weeks unhung them and allowed to dry in garage for a week

I saw the sikken experiment so have plumped for
Sikkens Cetol HLS Plus light oak stain followed by 3 coats of Sikkens Cetol Filter 7 plus light oa

I have applied the one coat stain.
Q1...Might be a stupid question...how do i know its dry?
Q2 Should i just do 1 coat or two. And how do I decide?

Q3 i am now panicking... were the gates ‘dry’ before i added the stain? How can i tell this? Im concerned because its been so cold....was i too anxious to get them done before the winter weather.
Q4 What should i do now? Go ahead with starting the cetol filetr?
Q5... is it ok to do one side and then the other in the filter?
Q6.. they are in my garage but its only 5 degrees...how long should i wIt between coats ? How can i tell its dry.
Q 7 do i sand between any of the coats and if yes what do i need to do?

I am disappointed they were not hung in sept as promised...which would have enabled me to have done all this hing outside in warm weather.

Can you knowledgeable folk help me reduce my anxiety? I love my gates and just want them to be perfect...and hence all my efforts in trying to do the right thing!


----------



## Mike Watkins (16 Dec 2019)

Excellent stuff and many thanks for doing this experiment, I was about to buy Osmo for my newly made oak window frame but I will definitely go with Sikkens now. Cheers, Mike.


----------



## Farm Labourer (18 Jul 2020)

This has been really useful, thank you!


----------



## RogerM (20 Jul 2020)

It's 2 1/2 years since this was last reviewed, and over 8 years since it was started, and any finish left in full sun for that time will be showing severe deterioration by now. Only the Sikkens shows any signs of giving continued protection. The Osmo UV Oil has all but disappeared. 






The back of the test piece is in permanent shade and both the UV Oil and the Sikkens continue to give protection, although I question whether a product called UV Oil is correctly named if it only provides protection when shielded from UV.






This is of course only relevant to this particular product, and I remain a fan of Osmo Polyx oil, Osmo Raw and Osmo TopOil for protecting interior surfaces. I'm tempted to retire this particular test now as I think it has run its' course, but the more comprehensive test is still ongoing *here*.


----------



## Kinz (1 Apr 2021)

+1 for RogerM's original posts, and likewise sereneblue, I have Osmo UV oil, but am now going to order sikkens based on those test results!


----------



## JonOuk (3 Apr 2021)

I’ve always used just clear external uv Osmo on Iroko doors and windows. Never had any complaints/issues with the finish.
Did some recently that the customer wanted left in the white, so would go grey over time .
My opinion on it was, that we should really finish with something...for one the outside would weather a thousand times faster, if at all on the inside!
And a few years down the line when they start having expanding/warping/rotting issues and complain, we had done everything to mitigate such issues!
Not that I was listened too, customer always being right and all that!


----------



## JonOuk (3 Apr 2021)

Had recently made a (requested) green oak conservatory, again against advice...
What happened? Had dung loads of issues with it 
Still I got paid anyway


----------



## JonOuk (3 Apr 2021)

Isn’t it recommended by Osmo, to refinish every 3-4 years anyway?
And even more frequently on extra exposed, high weathering areas?


----------



## Paul-Saltcote (12 Oct 2021)

RogerM said:


> It's 2 1/2 years since this was last reviewed, and over 8 years since it was started, and any finish left in full sun for that time will be showing severe deterioration by now. Only the Sikkens shows any signs of giving continued protection. The Osmo UV Oil has all but disappeared.
> 
> View attachment 89262
> 
> ...



Roger, I wanted to say thank you for the persistency you have shown here. After a fire at my place the balustrade was replaced at a cost of £201k of which over £10k was on the top oak handrail.

Osmo was specified and it's not performed over the last three years so I have been looking at the way forward and your post was an absolute pleasure to find. Sadly the person who did the work described himself as an artist and fitted kiln dried oak in a coastal facing elevated position. The image I attach was taken one year after the work was completed at Saltcote Place, it's now in need of a very serious cuddle and your article was just what the Dr ordered.
Many thanks
Paul


----------

