Removing Polyester Resin

[Scott Rosen]

I'm trying to strip some 33 year-old marine plywood that was originally primed with what I think is polyester resin. The resin prime coat is cracked and checked, but is not peeling. I'm sure it's not epoxy. If it's paint, it's not like any I've ever seen before.

Since the stuff was applied 33 years ago, I don't think it could be a two part poly

The stuff really sticks. A heat gun works, but not very well. Unlike paint, this stuff doesn't peel off in flakes. The heat doesn't lift it from the surface, but just makes it very brittle, which I can then scrape off in a powdery mess. That's why I don't think it's epoxy.

Any ideas or suggestions? I can keep at it with heat, scraper and sandpaper, but I'm hoping for a better way.

[Jim H]

Have you been using a carbide scraper?

[Wild Wassa]

Polyester has a very strong smell, it smells like nothing else on the planet. Polyester I find sands off somewhat easily and isn't too difficult to heat strip.

Old polyurethane will powder (it doesn't have to be a two pack), with little to no smell. Old poly I find comes off at about a blade width by a 1cm at a time mostly, if it has been exposed to UV it is even more difficult. The primer is as bad as the paint.

If it is old polyurethane, there is a critical temperature. It is cooler than hot. Once you go over that temperature you will harden the paint/primer, it will then become even more difficult to remove. The powdering that you mentioned Scott, is the give away as far as my experience is concerned.

If it is poly, warm it up slowly. Don't put the heat into it too quickly. If I'm heat gunning old poly, I can strip it at a rate of just over 1sq mt per day and the real danger is scorching the timber underneath. That's why I use the sander ... come grinder.

I hope you haven't got too much to do.

Warren.

[ 08-09-2004, 08:21 PM: Message edited by: Wild Wassa ]

[JimJ]

I also have had to remove some type of coating from the inside of the centreboard case of my Hartley TS18.

I used a heat gun and the stuff seemed to crystalized and it came off easly with a carbide scraper.

I seem to have the same product saturating the glass tape over the chine joints, the transom hull joint and the layer of glass in the joint between the plywood of the hull (planned flat) and the exterior keel.

The boat was built in 1974. Resoninal seems to have been used as a glue elsewhere in the construction.

What puzzles me, if it is epoxy that is in the glass tape and inside the centreboard case, why wasn't used for gluing the joints in the frame and the plywood to the frame?

Any ideas out there?

[Scott Rosen]

The area I'm stripping is the interior cabin overhead. It's had no UV exposure to speak of. There is a camber, so I'm working on a curved, concave surface. That makes it difficult to use all but a small sander with a soft pad.

The stuff does have a fairly strong smell when it gets hot, like outgassing polyester.

Last year I stripped a large section, which was easier because it was more accessible. The areas I'm working on now are smaller, lots of corners, etc.

At first, I thought it might be MDO, some kind of resin-infused paper coating, but I don't think that's the case. The ply is good quality mohogany, at least 33 years old.

I like the idea of a carbide scraper. I've been using a steel Pro-Prep, which dulls quickly.

My plan is to strip and then refinish with Sterling 2 part LPU over an epoxy base. I've refinished other areas of the overhead in that manner with excellent results.

[Dan McCosh]

Polyester resin also reacts to ordinary paint remover. The powerding action doesn't sound like polyester, however. As for the age, 33 years ago still was some 15-20 years after polyester resin was in common use.

[Elco's]

To echo what Dan said, polyester resin will desolve under certain paint removers. Such as the marine finish remover made by McCormack paints. Read the label...when it warns you to NOT use it on plastics...it will desolve plastics.