Painting over cut GRP

[mullet]

I'm in the process of cutting/grinding out a moulding from a locker (old gas bottle holder, no longer needed). I'm a bit lost about how to finish the cut surface to cover the GRP strands that are be exposed. Is there a benefit to using a 2-pack epoxy-based product like Flocoat, or something like Danboline suitable? Or is something else better?

The surfaces that will need refinishing are on both the inside of the cockpit and the inside of the hull; the locker contains a fuel tank (but far enough away/below that there is no risk of leaks onto the area being painted) and is otherwise mostly used for storing fenders and jerry cans of fuel. There's a possibility of one day putting in a diesel heater there but it's not top of the job list.

 

[V1701]

You could just gorilla tape the edge if it's all out of sight? Or a suitable filler & use greaseproof paper to get a smooth & consistent finish?

 

[Refueler]

First : 'Wash' with acetone and then fresh water .... dry.

You can use Polyester resin with catalyst ... quick setting (10 - 15mins) to seal the strands .... or a two pack Epoxy ...

Literally trowel it on but leave surrounding original slightly higher. Let set.

Now get a Gel Coat of suitable colour - but note that it is difficult to get exact match. You now use the Gel Coat to fill the area level to surrounding area .... get a clean stiff piece of plastic or glass and polythene sheet ... sheet covers the plastic or glass ... which is then pressed onto the area and taped in place .... this should give you a reasonable surface finish that later you can sand with varying grades to get final ....

 

[AngusMcDoon]

.... or a two pack Epoxy...

Now get a Gel Coat of suitable colour

Anything polyester, which gelcoats usually are, over anything epoxy is unlikely to give a good result. There are examples on youtube where polyester over epoxy has been shown to bond well, but it's an unusual and difficult process. Any epoxy amine blush remaining will prevent anything polyester bonding. So either all epoxy, or all polyester, or epoxy on polyester, but not the other way round.

 

[mullet]

Thanks for the replies. It’s inside a locker so aesthetics aren’t terribly important (and most of the rest of it is bare GRP anyway). I’m expecting the bits I remove to leave a flush surface of the backside of the cockpit/inside of the hull so think filling should not be needed. All I need to do is cover the rough surface.

 

[Refueler]

Thanks for the replies. It’s inside a locker so aesthetics aren’t terribly important (and most of the rest of it is bare GRP anyway). I’m expecting the bits I remove to leave a flush surface of the backside of the cockpit/inside of the hull so think filling should not be needed. All I need to do is cover the rough surface.

If thats the case - then down to a car shop and get some Davids Isopon Polyester .... smooth it one ... sand it flush.

 

[Refueler]

Anything polyester, which gelcoats usually are, over anything epoxy is unlikely to give a good result. There are examples on youtube where polyester over epoxy has been shown to bond well, but it's an unusual and difficult process. Any epoxy amine blush remaining will prevent anything polyester bonding. So either all epoxy, or all polyester, or epoxy on polyester, but not the other way round.

Generally I agree and is why many people advise Epoxy completely for repairs ............ but if you look back at what I wrote ... I specifically said about leaving the 'filler' part BELOW surrounding surface ... the Gel then keys in ...

Done it so many times .... and years later still in place.

 

[PCUK]

Drop of resin with pigment. Paint it on - Done.

 

[penfold]

Unless your boat is quite a high end product cut edges of mouldings are likely not finished at all other than sanded down to remove snags and smooth off. There's no real need to do so other than aesthetics.

 

[mullet]

Thanks for all the advice. The moulding I removed turned out not to have been as well bonded into the locker as it appeared (or indeed was intended to be). It was bonded over two large, flattish areas but only a few spots were actually well attached, once those had been cut the rest came away cleanly, so no painting needed. I’ve a few other spots that will need coating so will put the advice above into practice with them.