Best ways to make external steelwork rust-proof?

[AL_n]

Hi All,

I want to build a structure onto my house made of heavy-duty angle iron. What is the most maintenance-free way of treating or painting steel so that it will be best protected an resistant to rusting? I would use galvanised steel, except that I already have a bunch of suitably sized (ungalvanised) steel beams, so I'm thinking of using thise. The beams are not badly rusted. In fact much of the orginal grey promer is still in place, even though the steel has been sitting in my outhouse for over 25 years.

I livenear the sea so the air is particularly salty here and things do tend to rust badly if not suitably protected.

Many thanks,

Al

[Tricky Dicky]

Getting it galvanised is the way to go. Look for any local firm doing it I do not think it is that expensive. I had a metal gate frame made up by a lo cal small railing manufacturer. It was galvanised after fabrication and alt hough I cannot remember the figures now I do remember at the time that the galvanising did not add much to the cost.

Richard

[Huge]

POR15

[Scott M]

About 5 years ago it was a £1000/tonne to get things galv'd and the price was only going up at the time (scarcity of zinc IIRC.)

@OP, check out powder coating. Long lasting, tough and, cheaper than galv.

[Tim Watts]

hot dipped

- as opposed to painted on or electroplated. When you think of galvanised iron, it's the hot dipped variety and it does last forever...

But it's worth knowing that's what you are supposed to ask for because I dare say there are plenty of rip off merchants out there.

[Martin Bonner]

[snip]

Make it out of stainless steel or aluminium.

[snip]

In that case I'm not sure I'd trust stainless. How does ally react to damp salty conditions?

[The Natural Philosopher]

very badly indeed. It destroys it faster than steel

[Justin C]

Actually, it does quite well:

This is almost thirty years old:

And these have been producing ocean-going yachts for years.

And these produce expedition yachts, that is yachts that spend weeks at a time heeled to the wind with the aluminium top-sides immersed in the briney, they're not designed to sit on their bottom paint as a marina caravan.

And these people have circumnavigated their own designed aluminium boats for decades:

All, apart from Morgans Cloud (the first link) are bare, untreated aluminium.

Stainless does fine in a salt environment too providing it's not in contact with dis-similar metals when galvanic corrosion can become a serious problem very quickly.

Justin.

[Bill Wright]

Galv is the way to go, but you would have to get the steel completely clean. Powder coating is a poor substitute.

Bill

[The Natural Philosopher]

It does well IF and only IF you can eliminate all possibility of galvanic corrosion.

That's a matter of design and build discipline.

[alan_m]

But make sure that you drill all the (oversize) fixing holes first or they will become the weak point in the protection regime.

[alan_m]

Would not the company galvanising do that in a bath of acid? I watched a day-time TV program where someone had made some (crap) furniture from scrap metal parts (two fire extinguishers and a water tank) and had the whole lot hot dipped galvanised after a dip in acid to get rid of the rust and old paint.

[Nightjar]

316 stainless steel in commonly used in marine fittings, but it is an expensive option.

Badly, unless at least as well protected as steel needs to be.

[Nightjar]

+1.

I used that on an old corrugated iron garage and it was incredibly effective.

[LumpHammer]

Will the steel structure actually be exposed to rain, or will it be protected by plastic/wood/etc. cladding of some kind?

In my limited experience, painted (but ungalvanised) steel beams last quite well if they rarely encounter liquid water.

[tony sayer]

Yes and this structure was done around 1958 and its still fine after all that time:

Enjoy, about 4:30 in...

[Martin Brown]

Right grade of chloride resistant stainless will be OK but you do have to get it right! Hell to work with stainless steel for DIY though.

A serious mistake was once made with a reaction vessel for a once household name UK chemical industry player. Their original specification said that there was no need for chloride resistant steel - unfortunately they were wrong and it dissolved away in no time flat.

Badly. Aluminium chloride is acidic, forms fairly easily is deliquescent and will take the protective oxide coat off the bare metal.

Zinc chromate primer would be one choice that might hold up on mild steel but in a chloride rich environment steel almost always rusts.

[The Other Mike]

Used it numerous times on various substrates both rusted and new using grit blasting/bead basting and their metal prep beforehand and would not use it again. One or two pin prick holes from road debris , a bit of road salt and the stuff can be picked off in flakes or sheets. The clear stuff yellows even when not in direct sunlight, hidden behind a wheel and a brake disc, not to worry it'll soon be falling off.

Getting accidental splashes off skin or other surfaces is impossible and the 'replacing the lid on the opened can and then removing it few days/weeks/months later' problem is a real PITA

If it were as good as the claims it would be used on major bits of infrastructure, bridges, trains, pylons etc. It isn't.

[The Other Mike]

Can vouch for Alubat, our Ovni 43 has been around for well over 20 years and corrosion (touch anode) has never been an issue. I've seen more 'corrosion' on a tupperware boat.

[AL_n]

LumpHammer wrote in news:552a4536$0$3714 $ [e-mail]:

It would be difficult to protect the structure from rainwater. It might however, be possible to make it all out-of-sight, say by encasing the girders in upvc.. (Not easy, but just about doable. But probably cheaper than galvanizing). I'm just a bit concerned that where the angle-section steel will project from the painted wall of the house, there would be a constant rust stain projecting downwards that would constantly need painting-over. But perhaps that's a price worth paying to avoid the cost of galvanizing.

Many thanks to all for the other advice here.

Al