Dezincification.

Hostage

Hostage

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Hi all

I have just painted my prop with zinz rich paint to see if it has any merits as
an eroding antifouling agent. I see that a special zinc paint for the same purpose is available at about £ 30.00 per aerosol. This stuff is called ZG 90 and comes at £7 per tin.

However my question is - would zinc paint, applied to bronze skin fittings and attached seacocks, act as an anode and offer them some protection from dezincification.

Sounds too simple. Any thoughts?
 
Hostage said:
my question is - would zinc paint, applied to bronze skin fittings and attached seacocks, act as an anode and offer them some protection from dezincification.

Sounds too simple. Any thoughts?
Click to expand...

I would leave all skin fittings alone. If they are electrically isolated you shouldn't have any galvanic corrosion and I would be vary wary of spraying them with zinc as it may just intoduce a small current.
 
It's an interesting idea that might work. I would be very interested to hear how it goes. There is a risk, pointed out by Graham376, that the results might not be what you hope for! I'm not sure that a zinc-rich paint conducts electricity, in which case it cannot act galvanically. So it might do nothing that any paint could not do.

Of course, on bronze it cannot improve the situation, as that metal contains no zinc anyway. On brass it might.
 
I treated my prop and shaft with zinc based primer once (with a layer of antifoul on top). At the end of the season prop and shaft were covered with thin globules of what I assumed was zinc from the anodes. My guess is that the primer provided a key for which the anode zinc could adhere?
 
Hostage said:
Hi all

I have just painted my prop with zinz rich paint to see if it has any merits as
an eroding antifouling agent. I see that a special zinc paint for the same purpose is available at about £ 30.00 per aerosol. This stuff is called ZG 90 and comes at £7 per tin.

However my question is - would zinc paint, applied to bronze skin fittings and attached seacocks, act as an anode and offer them some protection from dezincification.

Sounds too simple. Any thoughts?
Click to expand...

I've tried the polish-to-gloss and lanolin option in the past, and for a sailing yacht I don't find it works well, though it seems to be good on fast powerboats.

For years I have wet and dry sanded back my prop to about a 600 grit finish, and then primed with a coat of Seajet underwater zinc rich paint before 2 coats of Seajet antifouling. It seems to help the AF stick, and usually the prop comes out fairly clean each year. The interesting thing is that each year when you wet-sand back to bare bronze, the "silver" colour of the primer has disappeared, and you are left with a creamy layer under the blue AF. Where the same silver primer is used to touch up other areas of GRP underwater, sanding back the next year still shows silver.

The prop is protected by a shaft anode and a tip anode. As yet no sign of dezincification.
 
Dezincification

Thanks all for the replies folks.

The prop sprayed has taken a very smooth finish which cant be bad. Any little blemishes have filled in. Its worth a try and I will report back at the end of the season with pictures for what its worth.

Last year I used boot topping on the prop and it was not a success. Quite a few small barnacles with an iron grip. As it does not erode it was hard work removing it

I havent persued as yet the idea of spraying the skin fittings but if I do I will report back.

Re the ZG 90 the speck does say as already reported that it IS harmful to aquatic animals and then goes on to state that it is NOT harmful to the marine environment. I'm confused - but not for the first time.
 
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