How to repair failing paint & fairing compound

We’ve got some areas of very neglected paint that should have been addressed a long time ago. Not entirely sure what is happening here but it appears the fairing compound below the paint is cracking peeling and chipping off. My plan was to sand it and remove anything loose, fill with 2-part lightweight fairing compound, sand, high-build prime, sand, paint (spray, LPU). 
 

- thoughts as to what is going on with this failure?  Normal or anything seem weird here?

- is that the right set of steps/products?

- I could pick a long board out of a lineup, but that’s the extent of my fairing experience. How do I sand and fair these detailed areas with compound convex and concave curvature?!  I hope the answer does not include hand sanding until my fingers are bleeding nubs. 

- what else am I missing?

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billsreef

Anarchist
659
331
Miami
Not unusual in an older boat. Unfortunately, the answer always involves sanding your fingers into bloody nubs. Your approach is correct, sand it all down and fair. I would go with a random orbital sander for as much as possible. Save the hand sanding for the areas you can't use a sander. 

 

longy

Overlord of Anarchy
6,793
1,139
San Diego
Dealing with the aluminum corrosion will be the most work. Unless properly done, all material over that surface will fail again

 

SloopJonB

Super Anarchist
68,723
12,370
Great Wet North
Dealing with the aluminum corrosion will be the most work. Unless properly done, all material over that surface will fail again
The only primer (actually a tie coat) I've ever found that sticks to alloy is zinc chromate - the chartreuse coloured stuff you see inside airplane structures.

http://zenair-uk.weebly.com/uploads/6/8/8/1/6881136/342738.jpg?316

 

Startracker

Member
407
107
Van Isl.
Looks like an area I'd hit with chemical strippers, wire die grinder bit in a good 1/4" die grinder, or one of those little cheap sand blaster guns and a shop vac, I have bought one for just such areas I'm contemplating, anything to make my fingers hurt less  Anything to reduce the amount of fairing after filler.  Step 2 would be to invest in GOOD filling tools, like flexible applicators, the better you put it on, the less you have to sand off by hand.   https://flexisander.com/ comes to mind of course.

I love zinc chromate, Alodine seemed to work decent too.  Both are supposed to be getting harder to find, alodine due to hexavalent chromium I think it is being one of the best forever carcinogens with no known safe exposure limit apparently, that humans have invented, zinc chromate because it's still not good for you.  The zinc chromate is often easy to find as a lower unit primer. 

 
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silent bob

Super Anarchist
8,706
1,286
New Jersey
Here we go, again!  
 

A simple solution:  

4 Gallons of Kerosene / 16 Litres Parafin

1 Gallon of Gasoline / 4 Litres Petrol

Mix well, apply liberally, light match.  Viola, bad paint gone!   
 

If that doesn’t work, the José method works too!  

 

Fleetwood

Member
216
58
Sydney, Oz
I have a sailboat and a raceboat. Everything on the sailboat is as fair as I can make it, on the raceboat, the hull is fair, the decks, not so much....

 

MiddayGun

Super Anarchist
1,179
442
Yorkshire
If you want to restore it to as new appearance then I wouldn't mess about with sanding, some sort of media blasting is the way to go if you want it done this century. 
 

 
Many thanks all, very much appreciated.  

  • We're actually glass and carbon, not aluminum.  
  • Definitely going to remove the stantions and hatch (see related post ;)
  • Any product recommendations on fairing compound and/or high build primers?  
  • Any tips on sanding those inside corners?  The outside corners I'm ok with, but there's really no tool that works on those inside corners?  I would def susceptible to buying some as-seen-on-tv crap right about now....
 

Grande Mastere Dreade

Snag's spellchecker
Many thanks all, very much appreciated.  

  • We're actually glass and carbon, not aluminum.  
  • Definitely going to remove the stantions and hatch (see related post ;)
  • Any product recommendations on fairing compound and/or high build primers?  
  • Any tips on sanding those inside corners?  The outside corners I'm ok with, but there's really no tool that works on those inside corners?  I would def susceptible to buying some as-seen-on-tv crap right about now....
millions of youtube videos..  start with the west system ones..

 
Not unusual in an older boat. Unfortunately, the answer always involves sanding your fingers into bloody nubs. Your approach is correct, sand it all down and fair. I would go with a random orbital sander for as much as possible. Save the hand sanding for the areas you can't use a sander. 
A Dremel tool with lots of replacement sandpaper rings for the rotary drum bit helps getting into nooks and crannies. The sandpaper drums are not cheap when you are using lots of them so use sparingly.  But they help.  And remember to start with the speed way down.  At high speed they can cut through dry/frail material a bit too fast.  Might want to wear a respirator as well, there's no dust control and periodic smoke... 

 

2airishuman

The Loyal Opposition
  • Any product recommendations on fairing compound and/or high build primers?  
The good ones are good.  I've been using Awlgrip primer and fairing compound.  Works great, easy to use, expensive.

  • Any tips on sanding those inside corners?  The outside corners I'm ok with, but there's really no tool that works on those inside corners?  I would def susceptible to buying some as-seen-on-tv crap right about now....
I use a Milwaukee right-angle battery die grinder with a 1" ball burr.  You can get the burr from McMaster-Carr and the die grinder from home despot.  Straight grinders are cheaper as are air and corded electric if those tradeoffs make sense in your situation.

https://www.mcmaster.com/4238A143/

After you've used it you'll wonder how you ever got along without it.

 

2airishuman

The Loyal Opposition
A Dremel tool with lots of replacement sandpaper rings for the rotary drum bit helps getting into nooks and crannies. The sandpaper drums are not cheap when you are using lots of them so use sparingly.  But they help.  And remember to start with the speed way down.  At high speed they can cut through dry/frail material a bit too fast.  Might want to wear a respirator as well, there's no dust control and periodic smoke... 
I've sent a couple of Dremel tools to an early death doing this kind of thing.  They're for making jewelry and carving duck decoys.

A die grinder with a selection of suitable rotary file type tools works better when working at larger scale and is cheaper in the long run.  I have sanding drums too, smaller ones are OK at low speed on a die grinder, larger ones on a cordless drill. 

 

CaptainAhab

Anarchist
847
230
South Australia
1/4" electric die grinder. Buy the lowest cost good one like a Makita or yellow or red($100). Do not buy a cheap generic one(They don't include the bearings).  The die grinders work great with carbide burrs, flap wheels, small sandpaper drums. They also have small screw on sandpaper discs(2"). Also a variety of the different Scotch brite abrasive drums & discs.

Amazon carries an assortment accessories. They are very cost effective. 

They are like a big powerful dremel tool that won't stop spinning. 

 

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