Steel keels - proofing and painting

DGuthrie

DGuthrie

New Member
Joined
14 Nov 2006
Messages
21
Location
Newcastle upon Tyne
Visit site
I have a Kingfisher 30 with twin mild-steel keels which hld the fuel tanks (30 gals a side; eat yer hearts out) but on lift-out found large patches of the carefully Primoconned surface had just lifted, with rust blooms forming very quickly.
Maybe I need something a bit more chunky to prevent this happening too often. I've had Zingard (MG Duff) mentioned and something called VC Tar. I wonder about using some proprietory rust-curing product after grinding to as near bare metal as possible, then treating the patches with Primocon again. But if peopl know of a better way, I'd be delighted to hear about it.
David Guthrie
Mercilla
 
if you can get the keels shot blasted that would be better if you were going to recoat the whole keels and then i would go for epoxy paint.
 
No substitute for coating thickness. The best product I ever used was made by Leighs paint and was called Resistex.
 
As already said dry abrasive blasting is by far the best way to prepare. Ask the blaster if they know what Sa2.5 means and to show you the standard, then blast to it. Too many small scale blasters say they know it but don't really although that shouldn't be the case around the Tyne!
Before blasting pressure wash several times with fresh water to remove salts otherwise they will just be forced into the steel and cause premature breakdown of the coating.
If you can't blast then grinding is a good second best but still wash well first to get rid of salt.
Once steel is prepared get the first coat of paint on as soon as possible. I prefer a zinc rich product over an epoxy as it gives active protection rather than just a waterproof layer, especially important if the steel is pitted. Work it well into the surface to get good coverage. About 150 microns dry or 3 good coats with brush or roller will be plenty. Follow up with a good waterproof intermediate layer (micaceous iron oxide is good) and, as someone said, plenty of film thickness. Up to 500 microns dry will give good protection. Finally antifouling of your choice.
If you can prepare the steel well this will be far better than Primocon although that is a good basic product for lower standards of preparation. VC Tar is OK but no better than many other epoxies and only suitable for a blasted surface.
Avoid rust converters if at all possible. They're OK at converting rust but inhibit adhesion of subsequent coats and reduce overall life of the scheme.
Do you know how thick the steel is? If the keels are old and have rusted / pitted it may be worth getting a check done if they are your fuel tanks as well.
 
Can't agree on using a zinc rich product because it electrolyses and lifts subsequent paint. Agree if you want a decent job blasting is the way to go.
 
How does it electrolyse? I don't understand what you mean. Zinc rich primers are standard procedure for marine and heavy duty steel protection, especially where the steel is in less than perfect condition.
 
Not the same as an anode I'm afraid. There is no electrolyte present to allow galvanic (not electrolytic) action. While the coating scheme is in good condition there is no action between the zinc and steel whatsoever - it just acts as a waterproof barrier coat in the same way as a pure epoxy. If there is damage to the coating allowing an electrolyte (sea water) to get to the steel the zinc will become sacrificial and prevent the steel from rusting under the coating, blowing it off and letting damage extend to a wider area.
High performance anticorrosive schemes applied to steel in tough environments are designed this way to prevent steel degradation after mechanical damage
 
Pasarell
Many thanks - others too.
Shot-blasting isn't an option, have tried before, so grinding is it. When you mention 'zinc-rich' do you have Zingard (MG Duff) in mind. I've looked into Galvanifroid (?) but no luck finding a supplier in this neck of the woods.
David Guthrie
Mercilla
 
All on this thread
I'm overwhelmed by all your advice: what a great place this forum is.
My good friend Mike also did some research, and here are his findings and I thought I'd share them with you and anyone who comes on here looking for advice.
Once again, thanks all. I'll let you know how I get on.

David Guthrie
Mercilla
Syntema do an equivalent [to Galvafroid] called Tamazine EE, it is £15.82 per Litre but only sold in 6 litre tins. Can be rollered on (may have to thin it slightly) plus a barrier coat (like primocon) before putting on antifoul.
Syntema (North East) Ltd
Unit B8 Hamar Close
Tyne Tunnel Trading Estate
North Shields, Tyne & Wear
NE29 7XB
Tel: +44 (0) 191 258 4564
www.syntema.co.uk
I also spoke to International Marine paints in Southampton 01489 775050 who surprisingly did not do a bare metal primer.

They suggested to first put an International paints ‘Etch Primer’ on top of the Galvafroid then the Primocon then antifoul which would give better results. He also stressed the importance of pressure-washing the keels before applying anything to remove residual salts.
Helpful guy called Steve at NWE Paints Ltd in North Wales, Tel: 01745 334 746 he said Galvafroid is only sold in 800mm tins due to its weight and is £40.20 + VAT,BUT, he said although Galvafroid is the best it is basically a Zinc Rich Primer and they do their own equivalent at £40.20 +VAT but for 2 ½ Litre tins (1 tin should be enough), delivery is £10 + Vat
 
You must log in or register to reply here.

Share this page

Top