Seawater in Lead

[Dockhead]

I've had my keel sandblasted today, blasting off all the work I did refinishing the keel 2 years ago


I was careful -- sanded off ALL the old antifouling and primer, wiped down well with the correct International solvent, painted with good Internatioal epoxy primer specifically recommended for lead. Yet it was falling off a year later.



Now it's blasted off, and the cause of the problem was not some defect in painting but WATER under the primer. The guy who's helping me with it, whose knowledge I respect greatly, says that the problem is that sea water soaked into the lead and made the primer fail. From the PREVIOUS failed coating. So we've now pressure washed thoroughly with fresh water to get all the salt out, then we'll sandblast it again on Monday prior to painting.



Just a heads up in case it might help someone avoid the same mistake I made.

[jamhass]

The water under the primer is a result of the paint failure, not the cause.

Lead is notoriously difficult to paint because it oxidizes very fast and the lead oxide is very weakly bonded to the lead effectively inhibiting anything from adhering for long. The trick is to fully prep the lead and then get primer on BEFORE the lead has a chance to oxidize.

One approach I have had luck with is:

Do a coarse sanding on the lead to bring up a good "tooth"
Follow with the appropriate prep solvent/oxide inhibitor
Apply primer with a wire brush, working it in to allow the brush to scrape the lead breaking up any oxide than may have formed.

It is important that these steps be done as quickly as possible, minimizing the length of time raw lead is exposed to air.

[SVHarmonie]

Like JAMHASS says....

It was a defect in paint (possible, but unlikely) or in painting (my high odds bet).

The first time, after the lead was sanded down to bright metal, how long was it before the primer was applied?

Saltwater "soaking into" lead is a new problem unique to your boat... Think about it... how many sailboats have NEVER scratched their keels enough to let water "soak in"?? How come we don't all have paint falling off all the time from this effect?

I call bogus.

Have you tried calling the international paint tech people? or local tech rep? Especially before you just repeat the process again?

[Dockhead]

Originally Posted by SVHarmonie

Like JAMHASS says....

It was a defect in paint (possible, but unlikely) or in painting (my high odds bet).

The first time, after the lead was sanded down to bright metal, how long was it before the primer was applied?

Saltwater "soaking into" lead is a new problem unique to your boat... Think about it... how many sailboats have NEVER scratched their keels enough to let water "soak in"?? How come we don't all have paint falling off all the time from this effect?

I call bogus.

Have you tried calling the international paint tech people? or local tech rep? Especially before you just repeat the process again?

Well, after the failure of the last job, I'm not doing it myself -- I hired a top marine coatings guy here in Denmark.


It was he who told me about seawater soaking in. Whether it is true or not I have no idea.



What we've decided to do now is to actually melt some lead to fill in the small voids -- the way car bodies used to be repaired in ancient times.



He also confirms what you've both said about time to coating. I wasted a batch of epoxy primer because we mixed it up PRIOR to sandblasting so it could be applied IMMEDIATELY -- my guy also says 1 hour tops, or the lead will oxidize, turn greasy, and coatings won't stick.

[RaymondR]

Interesting problem. I wonder whether the old trick of wet sanding with the primer would work?

[donradcliffe]

After unsuccessful tries to get my lead keel to stay sealed up in one spot, I really went after it with the grinder and found porosity in the casting. Water was seeping out tiny holes in 2 x 4 inch area. Maybe your keel pouring crew took a lunch break too.

I ground out a fair bit of lead, replaced it with bog, and problem solved.

[Dockhead]

Originally Posted by donradcliffe

After unsuccessful tries to get my lead keel to stay sealed up in one spot, I really went after it with the grinder and found porosity in the casting. Water was seeping out tiny holes in 2 x 4 inch area. Maybe your keel pouring crew took a lunch break too.

I ground out a fair bit of lead, replaced it with bog, and problem solved.

"Bog"?

[Chotu]

Originally Posted by Dockhead

"Bog"?

And interesting bit of etymology.

Bog refers to thickened resin. I think the word comes from Australia. The Australians call it bog when you thicken up the resin and apply it.

That term has stuck throughout the world in boat building.

It’s interesting that mud and bog have similar roots, I think that’s where it came from. I found this little link fascinating when I first started building boats.

[Wotname]

"Bog" = filler, previously a polyester based filler but now any filler.
"Bog it up" = cheap job by using a filler rather then replacing the base material as when using a filler on a rusted car panel instead of replacing with new steel etc.

Not to be confused with a Bog Roll AKA Date Roll / Dunny Roll / TP.

[RaymondR]

Originally Posted by Wotname

"Bog" = filler, previously a polyester based filler but now any filler.
"Bog it up" = cheap job by using a filler rather then replacing the base material as when using a filler on a rusted car panel instead of replacing with new steel etc.

Not to be confused with a Bog Roll AKA Date Roll / Dunny Roll / TP.

And it can just refer to a toilet.

Prior to the drive to attract tourists it was often an appropriate descriptive term for many public toilets which it was outright flattery to call disgustingly filthy.