Painting steel boats

How often do steel boats need to be re-painted a) below saltwater-waterline b) above waterline (that is, properly primed and epoxy'd surfaces)

 

I commonly see up to 25 year old quality base paint jobs on the exterior and interior of steel liesure boat hulls that still meet the adhesion tests. There will be a areas that have been touched up due to poor initial application or collision or poor manufacturing detail ( sharp corners etc).

Normally an exterior topcoat will be applied and this topcoat generally takes the weathering and minor knocks and needs a more regular refresh with a simple overcoat.

What usually compromises the epoxy coating is simply poor application of good materials. The initial base coat must go onto a warm, dry, clean, blasted surface. This then needs sufficient build applied to seal all possible holes through the paint. Above the waterline the first coat can be be a zinc rich epoxy but never below.

Try and find a high solids low thinners airless sprayable or roller appliable paint. We seem to get the best results from industrial polyamides rather than the marketed 'yachtie' brands. There is no difference in the chemistry and the yachtie brands often have more thinners for ease of application.

On some immersed structures we are now applying 3mm high build epoxies in one coat.

cheers

 

Dear Mike,
Thank you very much for that. Very informative. So are you saying that if properly epoxy'd, base paint could last for up to 25 years? What about the cover paint? How often would that have to be renewed? under and over waterline? Cheers Monika

 

Monika
Below the waterline its just antifouling over the epoxy layers.
Above the waterline hull topsides I like a glossy chorinated rubber based Dulux product over the epoxy , you'll find you can simply roll over the top every 3 years or so to keep things bright but not absolutely necessary. MAny people recommend a polyurethane top-gloss coat but it is harder to re-coat.

Steel decks are good overcoated in swimming pool non-slip paints, cabin tops same as topsides.

I know of one steel boat where the interior epoxy paint is still largely intact and in prime condition since being applied in 1974. Exterior the bottom has been blasted once but mainly only to remove the built up anti-fouling which they had not been rubbing down at each haulout. Much of the original base coat was left intact and we recoated over it. That had been 5 or 6 coats of Devoe/Altex well applied and well maintained.

I see you are in Australia. I'm an engineer in Hobart feel free to email me .

 

Thanks very much Mike, I am looking at possibly purchasing and doing up as a liveaboard a 20 steel barge cat (photo att). It has been primed with a Dulux Luxepoxy 66 2-pack primer all over by the now deceased owner. I don't think they added zinc-rich primer underneath that unless that is part of this particular primer. I don't know enough about such things. I've previously owned and renovated a 40' aluminium paddle-wheeler, and did its hulls, but that was different again. If I copuld contact you periodically with other queries, that would be swell! Best, Monika

 

Hi Monika, if I was looking at that barge it would be a good idea to get a surveyor or naval architect to have a look & do some calculations on bouyancy & weights/displacement, plating thickness, connective structure etc etc so you can proceed with confidence.... or not, as advised, it may well turn out to be a fine vessel for your needs but some of the detailing as exibited in the pictures suggests it may not be. I'd firmly recommend some professional advice, it may save you a considerable amount of trouble. Sorry to sound like a wet blanket but all the best in your boating from Jeff./waikikin

 

Thanks heaps, Jeff! Great advice.