Painting GRP

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richardpope50
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Painting GRP

Post by richardpope50 »

I'm toying with the idea of painting my (Dax Rush) Gel coated GRP panels since they are off the car and I have sprayed a car before (albeit probably not very well and it was a good many years ago too). I've also made a few mods to some panels that are finished with filler. I have an air compressor sprayer so feel like tackling this.

Has anyone done this and / or have some links to 'how to do it' pages?

Thanks.


Richard.
Dax Rush 5.0l TVR V8, EFI with Megasquirt ECU and wasted spark, Racelogic Traction Control and Quaife LSD ....... Now nut and bolt restoring a TR6

kiwicar
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Post by kiwicar »

Hi
This is really one for Mr Gelmonkey, as he is the expert on this stuff, however I have a little experience,
I am assuming you will be using a basic colour coat top coat, not a colour coat and clear coat system
first thing is to get it all sanded down much as you would any surface you wish to paint, take it down to about 180 grit finish, don't go too fine you need a good key, however the surface needs to be even. do the classic sand at 22 degrees motion you would for any body work (first stroke at 11 degrees off to one side to the direction of the pannel front to rear of the car, second 11 degrees the other side, so you get a sort of herring-bone effect in the sanding marks. Use a guide coat to help find any low spots and use a long sanding block, at least 8" long more if it is a long flat panel. Give the panel time do dry fully and use an electric fan heater to get it really free of moisture, when dry (did I mention you need to get the panels dry :shock: ) wipe off with thinners to degrease it. Put down a high build primer/ filler with the spray gun using 2/3 wet edge overlap, again sand when dry as before but this time take it to 240 grade, again high build filler/ primer again sand, this time to 600 grit put down a nice thin coat of colour, 1/3 overlap on a wet edge, when tack dry put down a second coat the same way, leave to dry thoroughly (couple of days) block sand starting at 600 grit, then 800 then 1200 grit, but very lightly on the 600 and 800. Let it dry, give it 3 more coats of colour as before 1/3 overlap, leave it to dry, at least 72 hours preferably a week, then colour sand using 2000 grit, then polish and hay presto nice shiney panel.
That is a very old fassioned way of doing it and assumes cellulose type paints, or modern equivilent water based acrilic colour top coat systems. I have never used urathanes, cyanoacrolate 2 packs or epoxy systems and I have not used colour plus clearcoat systems (the latter are meant to be much less work and give very good results.
Basically it is like repainting any car, all in the prep, and provided the gell coat is stable and a good key surface is used then you need nothing special.
Best regards
Mike
PS there are loads of how to articles on the carcraft archives.
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unstable load
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Post by unstable load »

Be careful not to sand through the gel coat into the underlying fibres. This will give you untold headaches....ask me how I know...
Cheers,
John

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Post by Alley Kat »

With 1k aka 'basecoat' (solvent based like celly, DIY friendly), finish sanding to 800 grit and go with topcoats. 1k doesn't like lots of coats, there's no point anyway, and it's likely to crack/craze. Just need enough to cover, then you clearcoat it. Don't sand and polish the colour coat, the clearcoat gives the gloss and finish.

2k needs positive-pressure / airfed masks really for safety. It's top stuff but can be nasty for your health. People will say chuckaway masks are OK, and they are for many people, but for some it goes badly wrong.
I'd 2k epoxy primer as it has some build and is an excellent sealer, this is what your hot-rodders mostly use on their grp bodies. Then 2k hi-buld primer wet-on-wet. Guide-coat and sand to 600, then topcoat.

You'll need a decent water separator/regulator.

Might be well to nab some scrap/spare bits to try colouring in before trying on the real thing, to get used to the gun etc. Could save some sweary moments :) .

gelmonkey
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Post by gelmonkey »

Hi Richard
Just seen this post and can add this to your thoughts.
Once everything is prepared for primer use an acid etch system.
Upol do a superb etch primer which is the No8 range.
You will not go far wrong with this stuff and it can be bought in rattle can form if you are only doing small areas
What you can do if possible is to warm the areas first with an IR lamp.
This gets rid of any slight surface moisture and helps the primer to bite into the gel coat surface.
I think it was john who said not to sand through to the laminates and he is totally right on this.
Build this up with a few coats and then final sand with, as has already been mentioned 800grit paper.
Allow this to air dry and then wipe down with a panel wipe and then blast dry with an air blower/nossle.
With regard to painting there is better advice available from those in the know.
I have only done small areas myself albeit with fairly good results but cetainly not of professoinal sprayers standard.

If I can help you in any other way and you want to talk to me then pm me and I will give you my phoner number.

Cheers
P

DaveEFI
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Post by DaveEFI »

Would an acid etch primer do anything on GRP? I'd have thought not. Ages ago I spayed some GRP in cellulose. Just used exactly the same primer etc as I used on steel. Obviously make sure it is clean first. It seemed to last ok.
Dave
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Alley Kat
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Post by Alley Kat »

Believe the acid kills something given off by fresh resin? Otherwise it's not doing anything grip-wise above a straight primer.
Most epoxies are non-isocyanate so OK for DIY/non-airfed masks (but check MSDS for the hardener of each one), stick really well, give sealing, aren't reactive like etch can be so is good for going over old paints etc.

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richardpope50
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Post by richardpope50 »

Thanks all for the very welcome detailed advice. Much appreciated.

I've yet to digest this and will copy / save it but a couple of comments:

The GRP panels are 9 years old and have been stored in a dark garage for the early days and then fitted to the car for about 3+ years but the car has been mainly in a garage albeit with windows whilst it is being built. I presume this is not a problem and GRP is stable enough.

I was thinking of standard cellulose paint or modern equivalent and probably etch primers. Basically whatever is easiest - yet to chat with a paint supplier but above advice appreciated.

I was going to use P3 disposable masks as I do not have any other type. Possibly spray outside else make a simple spray booth in double garage (with door open(!) - I've just sprayed the chassis with POR 15 paints that way). All panels are off the car so all manageable.

I know that where I modified some panels (cut down wheel arches and extended nose cone) I need some more work to make them correct profile and was hoping to test spray primers to see where flats are.
Richard.
Dax Rush 5.0l TVR V8, EFI with Megasquirt ECU and wasted spark, Racelogic Traction Control and Quaife LSD ....... Now nut and bolt restoring a TR6

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