Outdoor wood preserver and finishing product?

[efunc]

Hi all,

I'm coming to the final stages on this bench project. I'm new to woodworking and this is my first project like this. This is primarily a question about Osmo WR Base Coat. The seat is comprised of a couple of new scaffold boards made of an untreated rough sawn white softwood I picked up at my timber merchant. I'll be sanding them down, but not too much, because it's pretty rustic looking. The bench is located under a canopy roof, so it will not be rained on, or in sunshine, however will be subject to seasonal humidity changes and temperature swings, etc.

So, as I've not made anything like this before I need to know what products to apply to finish the wood, which let's face it, is pretty cheap and cheerful! My goal is to protect the boards from twisting and bending and stabalise them as much as possible. I don't want to colour it too much really. A slightly golden colour or light oak is fine, and it adjoins a cedar clad garden room. I also don't want a glossy or plasticy look. I like the idea or an oil or wax, but I'm not sure if they do much in terms of long term protection. One thing I do have in my shed is some Barrettine Clear Universal Wood Preserver which I bought for the garden room:

• Contains Tebuconazole, Permethrin & IPBC.
• Protects uncontaminated timber against wet rot, decay and wood boring insect attack.
• Suitable for use on all types of timber, rough, sawn or smooth.

Barrettine

I've also come accross a similar product, OSMO WR Base Coat, which actually sounds similar, but more suitable:

1. Extremely water repellent
2. Resistant to blue stain, rot and insect attack
3. Reduces wood swelling and shrinkage
4. No future application necessary
5. 4001: Oil-based, brush or roller applied only

WR Base Coat

Both of these are just a base product requiring the use of an oil or other finishing product. The OSMO specifically mentions that it "Reduces wood swelling and shrinkage" which appeals to me, but I wonder if it really excels at this or it's not it's main USP? I emailed Barrettine and they made no claim of having similar properties.

Does anyone have experiance of WR Base Coat? And what of recommendations for a low sheen product to go over the top for a bit of depth and protection? Osmo oil, Tung oil, Boiled Linseed? My plan is to probably opt for Osmo Decking Oil. It ought to remain dry and will be shaded, it's primarily stabalisation I'm after. Low maintenance would also be a bonus.

Thanks for any advice

 

[Cabinetman]

Hello and welcome to a less fractious place, can’t help with your question I’m sorry.
Just wondered why you didn’t tie the big metal brackets into the front rails somehow?
Ian

 

[Dr.Al]

I'm afraid I can't help with that either, but I will also say welcome efunc.

 

[efunc]

Thank you both for the welcome, that's much appreciated! I did search the forum before and found some great information and tests on various finishes, but not quite the use case I have. So I'm hoping someone might be able to point me in the right direction.

Regarding the design of the bench, I did think long and hard about it before starting. It's not conventional and it's based entirely on the geometry of its location, so I just designed it around how I wanted it to look and how much load it should bear ( but I've got no special knowledge and am just figuring it out as I go!)

The metal brackets would normally be supporting cross bettens attached to the frame. I didn't want the brackets to be visible underneath so I mounted them independently. They would have had to be positioned 4cm lower otherwise and would be seen as the bench is approached and obstruct the lighting which will be mounted underneath too. The frame shouldn't move independently I don't think because ultimately it'll all be braced with the scaffold boards which will straddle the whole structure. I will also install another 4 cross battens to complete the frame and these will be positioned between the current metal brackets.

When I started I set out to first build a ledger plate and timber frame as strong and stable as possible capable of carrying the load on its own. There are 15 chemical anchors secoring this to masonry and 4 150mm screws into a reinforced timber panel in my garden room. Once I was satisfied that it would be independantly strong I added supplimentary metal brackts using a further 12 chemical anchors to provide additional support. Each of these adds 150Kg of supporting capacity.

The final and most important element is to tightly secure the boards over the top, because they will brace everything, unify the structure and hold it all togther. This final point I'm still debating though because I've realised that wood outdoors must ultimately move with moisture absorbtion and temperature, so perhaps the bracing aspect is ill advised. I'm not sure at this stage. And that's why the finishing product is important, if indeed I can "reduce wood swelling and shrinkage" as Osmo claim.

 

[AndyP]

Welcome from me too.
Will you be sitting on those as is or with cushions?
For a wood preserver I prefer Cuprinol Shed and Fence preserver. It does not form a skin so easy to brush clean and reapply when needed. I’ve used it on all of the external shutters (pine) that I had to replace and re-coat about every 3-4 years. i also use Cuprinol on chestnut picnic table.

 

[efunc]

Welcome from me too.
Will you be sitting on those as is or with cushions?
For a wood preserver I prefer Cuprinol Shed and Fence preserver. It does not form a skin so easy to brush clean and reapply when needed. I’ve used it on all of the external shutters (pine) that I had to replace and re-coat about every 3-4 years. i also use Cuprinol on chestnut picnic table.

Thank you Andy. They are quite comfortable to sit on as is. However I may leave cushions on it too, or see if I can find a long bench cushion in exactly the right size. (I'm not sure if my skills/time would extend to making a bespoke one!). I spent quite some time calculating the height of the saet to be perfect for me, or an average person - I'm 5ft 9". Deep cushions can really throw those calculations off.

Thanks for the recommendation of Cuprinol Shed and Fence preserver. I've taken a look. I guess this is an all in one product with no base or primer needed. Could I finish it with a wax over the top, or does it already leave a mild sheen or something? I was also trying to avoid staining or adding much colour because I just like natural wood as it it with just a slight enhancement. However I've come to realise that all the UV and weather protections seem to be present in coloured finishes, not clear.

 

[Cabinetman]

Thank you both for the welcome, that's much appreciated! I did search the forum before and found some great information and tests on various finishes, but not quite the use case I have. So I'm hoping someone might be able to point me in the right direction.

Regarding the design of the bench, I did think long and hard about it before starting. It's not conventional and it's based entirely on the geometry of its location, so I just designed it around how I wanted it to look and how much load it should bear ( but I've got no special knowledge and am just figuring it out as I go!)

The metal brackets would normally be supporting cross bettens attached to the frame. I didn't want the brackets to be visible underneath so I mounted them independently. They would have had to be positioned 4cm lower otherwise and would be seen as the bench is approached and obstruct the lighting which will be mounted underneath too. The frame shouldn't move independently I don't think because ultimately it'll all be braced with the scaffold boards which will straddle the whole structure. I will also install another 4 cross battens to complete the frame and these will be positioned between the current metal brackets.

When I started I set out to first build a ledger plate and timber frame as strong and stable as possible capable of carrying the load on its own. There are 15 chemical anchors secoring this to masonry and 4 150mm screws into a reinforced timber panel in my garden room. Once I was satisfied that it would be independantly strong I added supplimentary metal brackts using a further 12 chemical anchors to provide additional support. Each of these adds 150Kg of supporting capacity.

The final and most important element is to tightly secure the boards over the top, because they will brace everything, unify the structure and hold it all togther. This final point I'm still debating though because I've realised that wood outdoors must ultimately move with moisture absorbtion and temperature, so perhaps the bracing aspect is ill advised. I'm not sure at this stage. And that's why the finishing product is important, if indeed I can "reduce wood swelling and shrinkage" as Osmo claim.

Sounds like you’ve got it well in hand and have it well fixed!

 

[fuse]

I use raw (cold pressed) linseed oil on my bee equipment after an initial two coats of cuprinol wood preserver ( the non insecticide one for obvious reasons)
After a few coats its pretty much impervious to moisture but the downside is in damp shady conditions it blackens.
It takes a long time to dry in uk climate and I recoat it once yearly

Boiled linseed oil is horrible stuff and forms congealed crusts like an old chip pan.
I believe its a way of achieving a second yield from the previously pressed pulp.

Price has risen sharply in the last three years almost to the same as chemical treatments.

Incidentally I have chopped linseed on my morning cereal and its dramatically reduced my high blood pressure

 

[Lurker]

Welcome.
I have used the Barrentine on my double side gates and I am pleased with the result. A little goes a long way and I have given it a coat every spring for three years. Easy to apply.

 

[RogerS]

I use raw (cold pressed) linseed oil on my bee equipment after an initial two coats of cuprinol wood preserver ( the non insecticide one for obvious reasons)
After a few coats its pretty much impervious to moisture but the downside is in damp shady conditions it blackens.
It takes a long time to dry in uk climate and I recoat it once yearly

Boiled linseed oil is horrible stuff and forms congealed crusts like an old chip pan.
I believe its a way of achieving a second yield from the previously pressed pulp.

Price has risen sharply in the last three years almost to the same as chemical treatments.

Incidentally I have chopped linseed on my morning cereal and its dramatically reduced my high blood pressure

That’s why I loathe it. If you really do want to continue using it then make sure you get sLOP with zinc oxide which should reduce the black mould

 

[efunc]

Thank you for some great suggestions. I went back an fourth over all the myriad options thinking I wanted a natural tung oil look or something at first but then feeling the need to weather seal as much as possible instead considered some matt polyurethane lacquer. In the end, I jumped the gun and just ordered the Osmo WR Base Coat for my primer. I probably wouldn't have if I was ordering it now and not last week since I've been learning more and more each day! But I'm sure it won't be a bad choice, just quite pricy and maybe unnecessary. In any case, my choice of top coat may end up being Osmo Natural Oil Woodstain in 'Light oak' or 'Larch' tint. I didn't think I wanted a stain, but this will be fairly light and have a matt look. Osmo Hardwax (Polyx) was also a consideration. It's not recommended for exterior use of course, but I'd say this is sufficiently sheltered from elements to qualify perhaps (?)

I think key to stain absorption and appearance is prep and sanding. I hit the boards with 40 grit to get rid of the splinters and rough sawn look a little bit. Then I went 120 and I'll finish with 180 so that it won't be too fine a surface. I've also figured out that I mustn't screw the boards down. Instead I've devised a way to use metal brackets with slotted holes which I'll use to screw the boards on to so that they have space to swell and shrink. More soon once I've made some progress...