Preparing a futon for outside use

Question

We have a futon which we would like to use outside as summer seating(It will move outside permanently). I believe the wood is either rubber wood or some sort of pine. How should I go about preparing it for outside use? I have some teak oil which I can apply after sanding the surface, but I get the feeling teak oil by itself will not be enough and I need to seal the surface somehow to protect it from the worst of the rain and sun. I'm in the UK so a bit of everything weather wise is the norm.

Edit in response to some of the points raised below:

1. The wood is rubberwood - found a stamp on the piece and traced back from there. Wikipedia ( https://en.wikipedia.org/wiki/Rubberwood + others) does state it is a poor choice for outdoor use due to moisture absorbency. Defined as a hardwood, it is farmed for its sap and at end of commercial life, used for indoor furniture . However, money is tight and the futon was free and so even if I get just a couple of years use out of it, I will be happy.
2. After initial sanding back for product application, I would prefer to keep future maintenance to simply brushing on a protective layer( once or twice a year is perfectly OK ). Sanding furniture is a real pain!
3. We will add some rubber or plastic feet so it is not directly in contact with the ground. Also, the wife will make a cover for winter.

So it is really a case of how best to protect it. I did research before posting but most articles are are either about wood that is suited to outdoor use or construction timber. Rubberwood is a very poor choice for garden furniture but see point one.

Answer 1

As I mention in the Comments, doing nothing to this in terms of adding new finish is actually an option as strange as it sounds. We're programmed to think that wood must be coated somehow if it's in an outdoor setting, and various finishes do help protect wood and maintain looks, but the actions of rain and sun aren't so damaging that you have to coat everything that isn't pressure-treated to resist decay. And since you say you would be OK with just a couple of years the wood will almost certainly last that long with nothing done to it, although it will naturally weather and go grey.

But obviously you can apply various finishes that will ensure it lasts longer, and keep it looking better until the futon is at the end of its useful life. These include, in rough descending order of protection:

• Paint.
• Marine varnish¹.
• A penetrating finish such as "teak oil" ².

If the right paint is chosen in addition to providing the highest level of protection possible it will require the least intervention, since a good exterior-rated paint has a touch up/refinishing schedule of 5+ years, and possibly as much as 7-10.

Marine varnish as used on boats is of course purpose-made to protect wood in very challenging conditions, including much more water of course. There are a couple of downsides though, the major one possibly being the looks — marine varnishes need to be put on thickly, producing a slick glossy finish which you might not care for visually or find pleasant for skin contact; they're also usually very yellow-orange, and at typical coat thickness the wood will be made decidedly yellowish. It's not to every taste!

"Teak oil" or something similar provides the least protection, but I suspect enough for your purposes here. It's the easiest to apply to a high standard (no brushwork experience required) and it is the easiest finish type to touch up later, or if there's a scuff through to bare wood on a leg or an exposed corner. It will also alter the colour of the wood the least since there's essentially no surface film.

We will add some rubber or plastic feet so it is not directly in contact with the ground. Also, the wife will make a cover for winter.

Both very good ideas. I was going to suggest sealing the feet with epoxy to prevent water intrusion but rubber/plastic feet should accomplish the same goal.

One other potential worry
The wood itself, despite not being an exterior-durable wood, may not be the major concern.

As this piece wasn't intended to go outdoors the joints could be the Achilles's heel here. The glue might not be water-resistant and any fasteners (even if zinc plated) could readily rust. Adding a protective finish will help with both of these but might not completely protect so you'll just have to try it and see.

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¹ Not yacht varnish as sold in normal paint outlets, it's not typically in the same ballpark (hence the price differential).

² See Answer from yesterday with a little on that.