Is it 2 pack or paint

[Astro2]

I have recently taken on a 1978 Adams 35 masterhead sloop refurbishment project. It is a painted/filled/fared Aluminium hull. I am currently sanding back, and in some areas back to aluminium, all of the cracked/weather paint. I sort advice on new priming/filling/painting etc. I was asked by suppliers "what is the existing surface - paint or a two pack system". I do not know and can not find out from previous owner. They stated you have to follow the same system or problems will happen down the line. My question is how can you tell. The suppliers said apart from paying $5000 for chemist to make a determination there was no real way. One suggestion was to put a turps soaped rag on the paint and see it it bubbles/smears etc but even that may not be accurate.
Have you got any suggestions?

[Benz]

Now's your chance to sand to bare aluminum and prime and paint with a good system that gives you confidence in the job. Or leave the alloy bare, which is the best thing for it anyway. If you must cover over unknown old paint, I suggest priming with 545 primer--it's my favorite primer for sticking to everything.

[model 10]

A single part paint will soften with a strong thinner like MEK. 2x probably not. Some people add hardner to single part paints to make them a bit harder, so you can be fooled but that pratice is not to common.

[HopCar]

Awl Grip published a simple test. It involves scratching a cross hatch pattern in the paint with a razor blade and taping a solvent soaked rag over it.
If you search the AwlGrip website, I'm sure you can find it.

I'm kind of with a Ben on this, it's a good chance to grind it bare and start over.

Use a 2 part paint and follow the manufacturer's instructions for priming and prep. Don't mix different manufactures products. If you use Awl Grip use Awl Grip primers and solvents..

I'm a fan of Interlux Perfection but I've never put it on aluminum. Talk to Interlux about how to prep the surface.

Down load this book for the best way to apply the topcoats. Instruction on rolling paint without tipping for spray like results...
The short version is thin it 15% and just roll it on. No need to tip it with a brush.

[hellosailor]

I'm with the others: grind it all off, start with a known good base.

Aside from the solvent tests, there may be some other ways to check, like scraping off some material and burning it. That's done in the plastics industries, the color of the flame and smoke and the way ti forms (soot or not, etc.) can sometimes identify what the material is.

I'd try calling a couple of the major manufacturers to pick their brains. They might even be able to test a sample for you.

But since you're doing extensive prep anyway...You know, if you go to bare metal you won't have to worry (as much) about having to redo the job in case the old stuff lets go next year.

[HopCar]

Here is the test: Surface Preparation and Priming - Previously Painted Surfaces Compatibility

[Captsteve53]

Since your in Australia i would suggest going with International INTERPROTECT

Interprotect Boat Primer | International

We use this regularly on Aluminium boats/masts etc and seems to have no issues at all, on previously coated surfaces we just roll on over a small area and check the next day for any re actions prior to coating the vessel.

Cheers Steve

[bsurvey]

why grind it all away, have it glass bead blasted to sp3 light sand sweep to bare metal and star with a complete system

[Cheechako]

Is the old paint stuck well? not blistering? If so, I'd think twice about removing it. Getting paint to last on aluminum is very difficult. My friends had their 48 ft cutter painted 3 times in 10 years. The first repaint was in a big luxury yard in E florida. That lasted 2 years.

[Scaramanga F25]

Sand to a fine finish. Leave it bare. It will self anodize.
Some yachties do not like the look. Far reaching cruisers a different story.

[Dougtiff]

Simple, scratch the surface, a 2 pack will be very hard, a single will scratch easily.

[David M]

Getting paint to stick to an aluminum hull long term is impossible. I have operated an aluminum commercial boat for almost 30 years. If the hull did not look like a potato, I would have had all the coatings removed from the hull a long time ago.

Some people do not like the dull color of oxidized aluminum and some are okay with it, it sure does save a lot of time and money not having it on an aluminum hull.

I say leave the paint off your hull unless how it looks would bother you.

[Cheechako]

I think he said it is faired so probably has a lot of filler in it.