Funny pimples on keel

[tartan30cirrus]

Last fall at haul out I noticed little pimples (maybe 1/4-1.2 cm in diameter) on my keel ONLY in the places I patched up the previous spring. I believe the pimples had fluid in them but can't remember 100%. They are dry now and feels like there is a slight void underneath. Last spring I grinded large patches of my keel with 36 grit, cleaned it, epoxy coated it (2 coats...not much), sanded and then applied the bottom paint. In these areas I now have the pimples.

The patching was temporary as a full scale keel strip and recoat is likely to happen after haulout in the fall.

Would appreciate folks' thoughts on the cause of the pimples.

Cheers,
Clint Chase
Tartan 30 #388 Cirrus

[Figment]

just a shot in the dark.... How much time elapsed between the application of the epoxy and the application of the bottom paint? Was it only a day or three?

If so, then it's possible that the epoxy wasn't totally cured yet, and that some amines were still making their way to the surface, and that this caused an adhesion problem with the bottom paint.

[tartan30cirrus]

[quote="Figment"]just a shot in the dark.... How much time elapsed between the application of the epoxy and the application of the bottom paint? Was it only a day or three?

I think you are right. It was only a day or two between epoxy application and bottom paint.

[Figment]

A little tidbit I picked up from the Interlux rep at the Defender warehouse sale: Just because epoxy has cured stiff enough to sand, don't assume that it's done curing. Depending on temperature, full cure can take much longer.

Kinda like concrete... You can take the forms off after a day or so, but it takes weeks to cure to design strength, and months to cure completely, depending on mass and atmosphere.

To be filed under "Generally Useless Knowlege":
When the romans occupied/built London, they built a big wall around the city. Being roman and all, concrete played a big part in this. Over the centuries, London sprawled out far beyond this wall, though some sections remain. In the 80's (I think), part of this wall was encountered while constructing a station for the Underground. As the workmen carved deeper and deeper into the base of the wall (over 20' thick), they enountered centuries-old concrete that still hadn't cured beyond a putty consistency. They thought it was just mud, until the next day when the mud (now exposed to fresh air) had cured hard onto all of the tools....

[tartan30cirrus]

Fascinating tidbit.

I have since learned this about epoxy the hard way last fall when I was using it as a primer to build up my deck for a new section of non skid AND when i came across it in the WEST manual on p13 where it says it can take up to 2 weeks for the epoxy to cure to the point where it will accept a surface coating like deck paint, bottom paint. I understand now that the epoxy is in its thirf cure phase where the reaction is very slow but still producing the amines which cause the issues.

On my keel I am betting the amines caused te pimples but why does the bond seem fine except in these sporadic little pimples? How sis water get back there under the pimple or was it just gas or a product of the paint and uncured epoxy reacting.

[Shark]

Hi gang,

I am hoping to grind, prep, epoxy coat, fair & epoxy coat my cast iron keel in the next week or so ... waiting for the warmest weather possible.

I may not have 2 weeks time for the epoxy to reach "final cure" before I must paint the keel. Launch date May 13th. Also the overnight temps are in the 40's or cooler. Am I likely to have the same problems? Suggestions?

Lyman

[George ( C&C 40 )]

Hi Shark,


I have a cast iron centerboard on my boat. Cast iron can not be ground with any great success. It needs to be sandblasted then immediately wirebrushed with "Ospho" to get down into the cracks and convert any remaining rust into a solid -- only then can it be sealed. The wirebrushing with Ospho needs to be done while the keel is still warm from sandblasting. Wear eye protection when doing this. One day later it may be coated with epoxy.

I'm not sure what Tim's feeling is on successfuly coating cast iron keels but my own opinion is that it's impossible to get a permenant fix no matter what process you use. Cast iron and water just don't mix.

It does make a wonderfully stiff centerboard that will not deform under pressure though.


Good luck,

George

[Figment]

I don't know much about sealing cast iron, but as far as speeding the cure of the epoxy goes, it's all about temperature.

I'm having trouble coming up with a method that won't give the yard manager a heart attack, but if you can conjure a way to get some heat onto that keel for a string of hours, you'll accelerate the cure considerably.

[Tim]

Simple heat lamps will greatly accelerate your cure time, but you probably don't even need them if daytime temperatures are well up into normal epoxy-working range.

I'd just get the epoxy on there ASAP and wait as long as you can before painting.

Grinding and epoxy coating is within the reach of the DIYer and is the best hope you have for anything approaching decency. George's sandblast/ospho method is assuredly a more effective treatment, but opens up the door to expensive yard time, and even then there's no promise that it's going to do any better in the long run.

I don't think there's ever a "forever" treatment for cast iron, so this won't be the last time you're doing this. It's sort of like varnish: there is no such thing as a "last" coat.

Cast iron is used on any boat for one reason and one reason alone: it's cheap. It's a poor choice, but that doesn't stop many builders from using it. Do your best with it, but you'll never get it perfect, and even a perfect job will not last forever.

[Shark]

Thanks for the feedback guys.

I've already bought the materials so I'm committed to giving this thing a go no matter what.

Man, this epoxy stuff is expensive!

Lyman

[grampianman]

Good luck with your keel. I am going to be soon having to do the same thing on my boat. The keel has a great deal of scale on it, plus some areas of body filler which I plan to grind off. I am just wanting to get a surface which is approximately smooth, which will be light-years better than what I have now.
Regarding your comment on epoxy, yes it's expensive, but I couldn't imagine being where I am now without it. The workability and flexibility of the product is great. I am using the WEST system epoxy and have no problems or complaints.