Finishing treatment for external wood

[Jimk]

+1 :>)

[petek]

I have just made a pair of garden gates in Iroko and I'm intending to use Sadolin Classic (1 coat) and Sadolin Extra (2 coats) to finish them off. On reading the small print on both products it states that only non-ferrous screws nails and fastenings should be used. I have used some zinc yellow passivated screws on my gates to fix the T&G facing boards to the gate structure. I would be happy to change the screws for brass, but can't find any on t'internet. I need 4 x 45mm countersunk, posidrive preferably. (In a reasonable quantity, say a couple of dozen!) What will be the effect, in the short term and long term, of leaving the screws in place and just going ahead with the Sadolin? Only the screw heads are showing, so there is minimal contact area between the screws and the finish. Unfortunately because of the virus, Sadolin have temporarily suspended their technical advice line.

Cheers Pete

[charles]

At the end of last year I got some brass screws from "Bit of Brass".

They might have something suitable

[petek]

Thanks for the link. Unfortunately the size of screw I need isn't listed. Really interesting site though!

[Dave Plowman (News)]

It's because Sadolin is water based. If you can't get brass screws, put a dab of thinned clear spirit based varnish over the screws. Make sure it is thoroughly dry before using the Sadolin.

You might find stainless steel screws easier to find than brass these days.

[Dave Liquorice]

Steel of any form is useless outdoors. Brass or stainless only, brass by preferance, stainless is a bit brittle.

Toolstation list 1 3/4" No 8 slotted brass, £8.84/200, unfortunately OOS for collection or delivery.

B&Q list 4 x 40 £5.37 or 4 x 50 £5.65 brass pozi packs of 25.

Irespective of the Sadolin they'll rust... Does iroko really need treatment anyway?

[petek]

Thanks to both Dave's for helpful comments. Yes, Iroko is a very durable hardwood (similar to Teak) but turns a grey colour with age. I want to retain the natural golden brown colour, hence the Sadolin treatment. I don't really understand why steel screws would be susceptible to rust as the length of the screw would be protected within the timber (Iroko is naturally oily) and only the top of the head exposed to air and water. Hence my question about short & long term effect. I thought there may be some possible discolouration effect similar to steel screws in oak, or perhaps some other obscure chemical reaction would affect the screws or timber. If just the top of the head turns a bit rusty, it wouldn't be too noticeable and I could possibly live with that. They're zinc passivated so maybe that would hinder corrosion a bit. Anyway, to be on the safe side, I'm going to get some 4 x 40mm brass from B&Q tomorrow in the hope they'll be long enough. The gate frame is 30mm thick so that leaves only 10mm to enter the facing boards which themselves are 18mm thick, but maybe with a deep countersink that will be OK. If that fails I like the idea of a drop of clear lacquer on the head of each screw. Cheers Pete

[polygonum_on_google]

Perhaps I have been extraordinarily lucky, but I really have not had any issues with stainless screws being brittle. Indeed, I have generally found them pretty good.

[Dave Plowman (News)]

I'd be amazed if you could shear an SS screw before brass?

[Smolley]

Counterbore the holes and fill them with putty.

[Tim Lamb]

Now try undoing a few!

>

[Martin Brown]

Iroko is almost as good as opepe in terms of surviving in the weather. Unless the screws are stainless steel they will rust and expand which will damage the wood. These oily hardwoods are brittle so it is worth using either stainless or brass fittings.

They all turn grey eventually due to UV exposure but the weathering is only skin deep. I would seriously use an external use oil on it rather than modern water formulation of Sadolin which IME tends to be somewhat opaque and flakes off oily hardwood in a messy fashion after a few years outside - at least that it what it did on our outdoors VH furniture.

The best outdoor system I found was some spirit based Dutch stuff from a Dulux decorator centre - I forget the exact name. It was expensive but it was also the only one that really stood up to continuous outdoor exposure really well. It doesn't seem to be available any more :(

But they do still have a decent range of outdoor oil based stuff.

[nothanks]

+1 (or that should probably be about +10, the bu&&ers break very easily and it's a pain to get the end out, plug the hole and start again)

[nothanks]

I agree. I'm a great fan of Osmo.

[petek]

I've been looking at Osmo as you have mentioned it, and I'm now thinking of using this instead of the Sadolin system. It's much cheaper. According to their website, the Sadolin system with 2 coats is expected to last about 4 years before a fresh maintenance coat is required. Have you any experience how long Osmo will last? Still need to use non-ferrous screws with Osmo!

[nothanks]

How long will it last? - it depends on exposure, wood and other un-knowables, but one of the nice things about oil is it's very easy to top-up or repair the finish. The oil isn't going to protect the screws. However, as you're using iroko, you could counterbore the hole for the screw head and then plug it with a bit of iroko. If you do this you wouldn't need s/s or brass screws and, if you get the grain in the right direction, the plug will almost disappear once everything's sanded and oiled. In case you're wondering, if you try this in Oak you'll eventually get dark marks around the plug; s/s or brass screws are essential.

[Dave Liquorice]

They went in OK but the failed in use fairly clean break. They were holding a bit of wood with a gutter bracket attached so there would be some movement. Replaced with brass of the same size they haven't failed, well I haven't checked recently but the flapping gutter is a bit of a give away. B-)

Vague memories of other breakages. Enough that the stainless are only used for non-critical things. Brass being used for everything else.

[PeterC]

When I built my shed I used st. st. fasteners as much as I could. For the main members 6mmx100mm Turbo Ultra. Even with a 4mm pilot hole in softwood a Powercraft 14.4V drill, bought about 12 years ago, so low torque, would shear some - had to go to clearance and 5mm pilot. Also I don't like 'machining' threads - OK 'til need to remove then replace a screw then a load of wood comes out. However, when I replaced the roof on another shed I used st. st. round-head screws in place nails, reasonable pilot hole and no problems. Perhaps the screws are better quality - the weren't from SF or TS.

[Brian Gaff (Sofa)]

Personally depending on whether the screws were scratched during insertion, the plating should be fine I think. Maybe find something to dob on the screw heads which will serve as an undercoat, but look inconspicuous. Brian

[Vir Campestris]

I've used SS on my boat for years, and never had a problem with them shearing. In fact the only time I've had trouble with screws shearing was when I bought some cheap ones from a shed... Never again.

Andy