Nasty paint job problem

[reelfishin]

I acquired a rather solid Starcraft Starchief over the summer. It came from a freshwater area and therefore is lacking all the usually corrosion issues.
However, the boat was repainted at some point, apparently over the original paint, with what looks to be to be house paint or some other very thick paint.
The problem is that the finish is now cracking badly, the entire boat has the texture of alligator skin. The paint is cracked, shrunk, and lifting. I looks like when you coat something with paint stripper and let it sit, then forget it and let it dry.
What gets me is that even the original paint is affected, and it's all over, 100% of the exterior surface. If I take an old credit card, I can brush away nearly 1/2 of the paint, a blast with some high pressure air takes away another 1/4 of it, but I'm left with many stubborn spots that won't come off.
Where the paint comes off with air or by scraping, it leaves clean, shiny unsanded aluminum. Who ever painted it before most likely scuffed the original paint and painted right over it.
So far aircraft stripper has no effect on this paint and I don't really want to sand it and scratch the hull all up. My plan is to repaint the whole hull in white epoxy once all of the suspect paint is gone.

The paint on it has the texture of 26 grit sandpaper when you rub your hand over it. The last owner was running it that way.
What gets me is what caused it? I've seen paint deteriorate but never like this, and on multiple colors and all surfaces. If the paint they used was bad, then I'd have figured it would have lifted and left the original powder coated aluminum, but it sort of shrunk and curled up in tiny little 1/16" sections and lifted the old color with it. The boat is 18' with a 7' beam width, sanding it would take ages and being it's a lapstrake hull, getting it perfect could take many, many hours.

Has anyone any experience with soda blasting?

I have a guy nearby that says he can strip it all off in a few hours. My concern is denting the aluminum or warping it by blasting.

 

[fixb52s]

Re: Nasty paint job problem

Soda blasting, if done properly, will be fine. Ensure the person doing it knows his stuff. The warping comes from keeping the media blast on an area for too long, heating it too much.

As for that paint, something in it must have chemically reacted to the base paint. It can happen between laquers and enamels.​

 

[180shabah]

Re: Nasty paint job problem

Agreed, if done properly, soda blasting is a safe option.

 

[bowman316]

Re: Nasty paint job problem

a power washer will take a lot of the paint off.
that took off all of the paint on my fiberglass boat.
just get really close and really high pressure to get the stubboron spots off.
It won't hurt the alumimun either

 

[salty87]

Re: Nasty paint job problem

no telling what was used on it. if primer coats aren't done correctly, results will be bad. that could be why you're seeing so many layers too...original etching or primer coats, original paint, new layers...

for a new, good paint job you'll want to get it down to aluminum again. otherwise, you don't know what you're laying good paint on.

 

[reelfishin]

Re: Nasty paint job problem

no telling what was used on it. if primer coats aren't done correctly, results will be bad. that could be why you're seeing so many layers too...original etching or primer coats, original paint, new layers...

for a new, good paint job you'll want to get it down to aluminum again. otherwise, you don't know what you're laying good paint on.

I won't have any choice as to going down to bare aluminum, both layers are cracked and lifting.
What gets me is that I've known this boat for quite some time before owning it, it was stored in a barn for 15 years, I looked at it about 5 years ago and the paint was decent, not great but also not all cracked. What ever happened to this happened long after it was painted. There's no corrosion whatsoever under the paint, so it wasn't an aluminum problem or anything like that. It was most likely painted well over 30 years ago. I got it from the original owners son after he passed away. There's no telling what was used on it. It could even be latex house paint or even an old marine paint of some type.
I just can't imagine it taking the old paint up with it, I've stripped these hulls before, although smaller versions, and their original paint or powder coat is a real job to remove. If I could get all of this mess off, this thing would look like chrome, it's that shiny underneath.
I blasted away about two square feet of paint up front with a blow gun and just air, I was able to get 99% of the paint off that area with a few very well adhered specs here and there that won't even chip off. The metal underneath is like new. If I were to continue doing that way, I'd be old and gray before I finished. I'm afraid that maybe the soda blast won't be abrasive enough to brake through the adhered paint. I'd venture to guess that even glass bead wouldn't do much to this stuff. I'd rather not use the chemical striper since it's hard to neutralize and get out of all the seams and rivets. I'm afraid that it's too corrosive and might damage aluminum if not washed off completely.

There's a few local guys that do soda blasting, on site, but their prices are all over the place. I have no idea what a fair price should be. They range everywhere from $1500 down to $50. Each one claims the same results.
My biggest concern is that all of them say that it makes a huge dust cloud when blasting, but the result is harmless. I don't want to be digging soda out of every car and boat in the yard for the next 5 years either.

Is the equipment something special or just done with a pressure blaster? I have one of those, currently set up for sand blasting. Maybe I can retro fit my current blaster to use soda blast media?

I watched a demo at a trade show where a guy stripped the paint off a soda can but he explained that it was done with only 10psi. My pressure blaster normally runs at about 180 to 250psi, which would cut the can in half even with a soft media.

Does anyone have first hand experience soda blasting? What is the equipment like, what sort of pressure and how much media does it take to do the average 18' boat?