Advice Needed for Painting Prep

[Dave666]

Just wondering about the correct preparation method before painting in 2pac Poly. As you can see in the pics, lots of holes to fill and also have the hair line cracks.

Holes - Is it ok just to counter sink the hole surface and then fill? For the bigger holes I was going to put some glass behind the hole also.

Hair line cracks - can I just sand and paint over? Do I really need to gouge out each of these lines, fill, and sand. If yes, then I may as well grind the area out and lay some glass before filling, as the cracks are so close together. Don't want them to come back, but a major pain if I have to grind them out and glass them.

What's the correct prep for hairline cracks and filling holes?

Thanks
Dave

[Rip it up]

Hey Dave, I'll help you out with the info.

Some background info on gelcoat surfaces. The cracks you have shown are not a structural issue. Fibreglass is somewhat flexible in nature and repeated movements/ weight in certain areas cause the harder brittle gelcoat surface on top to flex at different rates to the glass underneath. Impacts on the gunnel edges will do the same thing. The glass underneath will flex and the gelcoat cracks as a result.

The lay up of gelcoat in the factory is not a scientific approach. More of a "slap it on" approach in the 70's and 80's. Hand brushed was not uncommon. So the thicker the gelcoat is laid on the more chance it will crack as it has no reinforcing in the thickness.

2 pac poly is a very thin coating compared to gelcoat. And flexes quite well as a substrate naturally. Which is my more boat repairs are done in 2pac now days. Less time consuming after it's applied and can be glossy straight out of the gun.

If it was my project this is how I would tackle the paint job.

Yes fill all screw holes and chips. An epoxy filler is my choice because it's water proof. But car bog can be used as well. Any hole over 12-15mm should have a patch made from the reverse side. If it is in a panel that is 6mm thick I would grind it back to 2mm thick. Tapered grinding. A few circles of glass stepping up in size on the back will make it solid again. Then you only have a 2mm disc of bog. Again epoxy will hold on better than a car bog.
Counter sinking the holes is a good idea and provides better resistance to that cracked edge around the hole that can happen down the track.

Hair line cracks are inevitable. These as usually created when the deck is popped from the mould when the glass is still too green. The corners get stuck in the mould and air pressure or wedges are used to release it. Certain areas flex and cause these hairline cracks, even when they are new. It's not until years of use or dust can collect in these crack do they show up.

The correct way to repair a hairline crack is to put a small (4mm) drill into the end of each crack. Deep enough to hit solid glass. Then Drexel/die grind out each line 2/3mm wide it's full length back to glass only. Fillers can then be used to build back to level surface. If you don't grind them out you will normally find that over the years oil/wax/dirt sinks into those cracks. And when the primer coat goes over them you will get adhesion issues with the paint. Fish eyes etc.

Give everything a good 240gr sanding. Gelcoat is a good surface to lay paint on. I prefer JOTUN penguard high build primer. But any epoxy primer works well. Lay on 3 coats wet on wet. Then more sanding. 400gr wet is the best I find.

Now spray your preferred topcoat.

Long post but I hope it helps. If have any specific questions just ask.

Enjoy.





Damo's dodgy boat building factory.

[Dave666]

Damo - Thanks very much for the great info, this will help me a lot. Can I clarify a few points.

Holes - I think we are ok on this one - counter sink all holes, glass behind the bigger ones, and glass front patch, in layers, the really bigger ones, then filler on the surface.

Hair line cracks - so it sound like the 2pack should flex and not crack on top of the flow coat, but I think you are saying 4mm grind out the cracks because of the shit in the cracks will cause fish eye / poor quality paint finish? - Is that correct? As you can see the hair line crack are less than 4 mm apart, so I may as well grind the area (flowcoat & gel coat) down to glass or at least when I think I have hit clean gel coat and fill with epoxy filler from here. Correct?

Seem strange to me, because I would have thought the epoxy filler would be as brittle as the flow coat. Away, I have put so much work into this resto, I cannot cut any corners now.

Any help appreciated - thank again.

Dave

[fandtm666]

if you are painting then where you have ground out the crack's - drilled out holes etc
make up a batch of resin mixed with q-cel for above the water line or microballons
for below the water line. Over fill the area then sand back and prime and paint .

if you dont have to many then just use epifill

when i was doing similar to you i just ground back all the gell coat in those areas and
gave the whole area a cover with the mix then sanded it back.

as for the paint i am also a fan of the jotun high build primer and paints.

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[Rip it up]

Hey Dave.

You have it under control. Those close hairlines can be tackled by removing all the gelcoat in that area. F&T has the correct gear for it. Q-cells are a powder that you add to the resin to thicken it up. Sands down really nicely.

Epoxy is definitely not as brittle as flowcoat. And the fillers that you add help bind it all together.

Good luck with it. Remember building boats is 80% sanding.


Damo's dodgy boat building factory.

[Keevers88]

Hey guys,
where do you guys buy the Jotun high build primer? and how much roughly is it? The chandleries up here (Townsville) are about $120 for a 2 litre kit. Seems a little pricey for not much...
Can you make your own fairing compound out of resin and talc? cause I have plenty of each.
Or if I have to get the "Jotun fair compound" or "high build primer" how far does it go? I will need to do the gunnels and the transom on my boat - 5m Mustang Half Cab convert to Centre console.
Keevers