Encrusted Galvanising

[John_Sims]

My launching trolley is beginning to show signs of rust and over much of the galvanised area is a layer of hard salt crust. I've tried careful chipping, wire brushing, caustic soda solution and "Limelite" to no avail. Any thoughts on treatment that will not damage the galvanised surface would be much appreciated.

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[AndrewB]

I don't have a trolley but there are a lot of galvanised steel deck fitting on my yacht, and the problems sound very familiar.

There seem to be two separate problems here: first rust weeps and second a crust on top of apparently good galvanising.

The rust weeps denote failures of the galvanising. Once these start, they get steadily worse and its best to treat them early. The crust is a zinc salt, powdery white, produced as the galvanised surface breaks down. This is not so urgent. Treatment of both will require some removal of the galvanising locally.

One solution is to take the trolley to a local galvaniser and have it regalvanised. That is very effective, but not cheap.

The other is to paint the trolley. The rust needs to be entirely removed: if it is not too deep a good quality power wirebrush will cut back to bare (silver-shiny) steel. The power brushes that fit small hand-drills up to 2800 rpm are not really up to this, get a bigger one that can be run at higher speed. Eye protection is an absolute must. The power wirebrush will also remove the worst of the white crust, leaving a light grey pitted surface. Alternatively an angle grinder can be used, with a light touch as the steel is thin. Both areas should be treated with red oxide primer, then the whole trolley painted with a good quality marine paint - several coats recommended. It will work fine over the remaining galvanising. For a showroom finish use a filler over the primer to smooth over the pitting. Avoid using the trolley for a few weeks after, to let the paint cure fully hard.

There is a treatment known as 'cold galvanising' which is a silvery zinc-rich paint which will match the galvanised finish. This is suitable for spot treatment without having to do a total repaint, but in my experience will not last very long if your trolley is exposed to sea water.