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Frantically Relaxing
09-23-2015, 10:23 PM
Some of you may remember my post about our SkipperLiner, victim of stray current corrosion.

Here's the deal as of now. A lot of the steel is pockmarked by the corrosion, many areas are "light", much of it not very deep, certainly not deep enough to warrant hacking out the steel and welding in new pieces. And even where I will be hacking and replacing, as with the pockmarked areas, I've decided to use kitty hair epoxy filler to level these areas. I have several gallons of the stuff, and I also have several gallons of coal tar epoxy...

So here's my question(s):

I'll be sandblasting these areas, immediately followed by.... What? Can I coal-tar epoxy the bare metal, then do the filler,
OR,
Should I do the filler over the bare metal, THEN coal tar epoxy?

I'm thinking coal tar first, as it will definitely protect the steel, and since it and the filler are both epoxies, it seems to me that adding the filler over a coat of just-barely-set-up coal tar should work fine....

But I'm not sure? I'm pretty sure that the glass over bare steel should be okay, but again, not sure. The entire hull will get a couple or 3 coats of coal tar after all the repairs regardless...

And I'm also considering Rhino Lining after that, then Pettit Unepoxy over THAT...

??

OLD HOUSEBOATER
09-23-2015, 10:40 PM
If the pits are deep enough to require filler you should replace the metal. Coal tar will fill minor pitting. There is nothing better than Coal Tar on a freshly blasted hull. If you want it to be pretty squeegy the 2nd coat of Coal Tar in the rough areas then spray a 3rd coat for a finish. Filler is like putting lipstick on a pig. This may be a PITA process right now but it will probably outlast your ownership of the boat.

Did you ever find out what the root cause of your damage was?

easttnboater
09-24-2015, 05:35 AM
I agree with OHB. Either way, I would forget about the filler - it is just for cosmetics and the potential for problems is just too big. If you are going to Rhino line it, then I would have them spray the Rhino lining directly on the prepped steel.

Frantically Relaxing
09-24-2015, 09:07 AM
I've never messed with coal tar epoxy. The cans I have act like they're filled with grease, but I didn't think about it being thick enough to level out the pitting! As for it being a PITA, I doubt it can be worse than working with glass filler!

Haven't found the cause yet, mostly because I've been working on the Party Cruiser for the past 2 months. But in going thru old photos of the boat, clear back when it was on blocks at Lake Powell this corrosion was noticeably in progress, if just barely. I DID suspect the solar panel might be the culprit, but I was able to rule that out. Another possibility is the wiring running thru the davit mast... In researching this issue, they say bilge pumps are typical culprits because they're usually hot. My pump has no float switch so that's not it.

In the engine compartment, mounted to the steel plate that spans the transom:

http://www.engraver1.com/boatfixes/transom1.jpg

http://www.engraver1.com/boatfixes/transom2.jpg

--what concerns me is the battery isolators- should they be insulated from the steel, or not? I've had no battery charging issues, ever-- And second, that breaker box, which is actually used as a 12 volt main breaker box. Also on the breaker box hiding under the support beam is a pull-switch the operates the bilge pump. Pretty sure it's not 'marine rated', and I don't know who installed it, probably not SkipperLiner, but it was there when we bought the thing.

As for everywhere else in the engine compartment, everything appears kosher. If nothing on that steel plate proves to be the problem, I'll start looking at the nightmare of wiring under the helms...

For fun, I hammered in a ground rod right under the boat in back where it's blocked. Using a cheap HF meter, from the hull to the ground rod I was getting as high as 400mV of DC showing up on the meter. What I don't know is whether that's typical, or if it does indicate the hull is 'hot'...

Fun project I got going! ;)

easttnboater
09-24-2015, 01:45 PM
The coal tar epoxy will not level out the pits completely. It is not a PITA to roll on, I think OHB was referring to his suggestion that you replace the pitted metal. My question is - if the pits are not that bad and are not a structural problem, why worry about filling them?

OLD HOUSEBOATER
09-24-2015, 07:24 PM
Coal Tar Epoxy is great stuff HOWEVER once you start your committed. Every coat has to be applied NO LONGER than 24 hours after the previous to bond properly. so have enough help available so you can do a continous job.

Note the last time I didn't use Coal Tar I had the boat Coal Tarred 2 years later. On a 55 foot boat it was an expensive lesson.

OLD HOUSEBOATER
09-24-2015, 08:39 PM
Your replacing metal and have a welder on site. If you have a few deep spots in isolated areas weld them up and grind them off. Much better than filling and a quality repair. This was a standard repair procedure on River Queens back in the day in our area of the country.

BTW do you have an isolation transformer?