Fiberglass body prep - initial stages - help?

Ron Earp

Admin
Okay, you body guys, please educate the uninformed neophyte.

I've got the Lola body off the car, and, it fit pretty well on the car. Naturally one of the things I need to do is get the car prepped for paint work. I spoke with Al, admin here on the forum a long time fiberglass guy with Corvettes, to help me through the body prep before painting the car. He gave me some things to do and then I'd check back in with him when he was back from vacation to get further directions. Problem is, I'm not sure I'm on the right track.

Basically, what I did was clean the body using a dewaxer cleaning agent to make sure the gelcoat was free of release agents and other assorted things. Then, I sprayed the body with a grey sandable primer making sure I covered the gelcoat entirely.

Next step was to sand the primer, hoping that I'd remove primer on high spots and it'd lie in the low spots indicating where I might need to build the body up somewhat.

The problem is I'm not sure if I'm on the right track.

Jeff and I sanded the body, the front clip, for a good hour with very little progress. Using 220 grit sandpaper on blocks not a heck of a lot happened. I got out an electric orbital 6" sander and used it some, with 220 grit, with somewhat better effect but still not a lot of progress. Yes, the primer gets smooth but it takes a long time to get down to the blue gelcoat again. I didn't put the primer on extra heavy or anything, but just made sure that it covered the body as uniformly as possible.

At this rate, it'd estimate about 80 hours to get this first stage of body work done - and then I suppose there is a lot more I need to do.

So, am I doing something wrong? Is there something I am missing? Do I need better tools to accomplish the job, or, did I screw the process up? The paper appears to get loaded up with primer and stops working pretty quickly. For a short time it cuts and removes material, but the effectiveness really drops off and at that rate I'll be an old man when done.

Thanks much,
Ron
 
Hey Ron

Have you tried wet sanding the primer as this will
stop the sand paper from clogging?
When I sprayed my cobra I keyed the fibreglass
first with 90 grit then sprayed 2K primer filler.
 

CliffBeer

CURRENTLY BANNED
Ron, having done a bunch of this type of work in the past I may be able to help.....

1. You want to make sure the primer is good and hard before attempting to sand. Doing so will help to ensure the sand paper doesn't foul. Most home body guys don't have a hot room so the best way to go is to let the car sit in the hot sun for a full day or two before sanding.

2. There are different types of "primer" out there. There's a sealer primer which isn't meant to be sanded, rather, it just provides a barrier coat. The primer you want for this type of work and conditions you have is the quick build primer - typically comes in laquer in either grey or a rust red (from PPG). This primer sands easily and is excellent. Again, as per above, make sure it is good and hard before sanding.

3. Hand blocks are OK for dry sanding, but, if you really want to find the high and low spots use a long board. Long boards are about 18 inches long and take a paper which is specifically sized for them. The long board will find the highs and lows much, much quicker and more effectively than a hand blocks. 220 is probably OK for a long board but you might want to try 150 with light pressure for a first pass. Stay away from the electrical orbital sanders - these are just as likely to create highs and lows as find and remove them.

4. Once you've found the major highs and lows, and filled and sanded appropriately to level these out, you'll find it's better to then switch to wet sanding. Wet sanding, with appropriate grit, will not leave the sanding marks that can show up in a final color coat if you're not watching what you're doing. First wet sand should be with 320, then 400 and then 600. Some guys say you should go to 1,000 but I think that's wrong as 600 is very fine and the color coat needs some surface texture to bite to.

5. Depending on how good the surface is (level and finish), you'll likely have to prime a couple or three times, particularly in any areas where you find imperfections. You can use spot putty for small chips or dips and the like rather than breaking out a new layer of filler.

6. Ultimately, once the car is final sanded to 600 in prep for paint, anything that you can feel with your hand will certainly show up in the final color coat. This means both waves in the panel and any surface imperfections. You'll get better at feeling these out and taking appropriate corrective measures with (lots) of practice.

Good luck and be patient and persistent!
 
Hi Guys
I have found with most of the fibreglass work that I have done in the past, the first coat of paint should be an etch primer, this will key it's self to the gelcoat, then you need an easy sanding high build primer, this will this should be left for about 24 hours and then using a cheat matt black paint spray a dust coat (very light patchy coat) over the areas to be sanded, this will give you a visual idea of where you have sandes and also if you are using block sanding will show up the low points.

I hope that helps, happy sanding

one more tip before I go
sand diagonally one way on curves and then the other way or sometimes you end up the rubbing groves into your work

Bud
 
Hi Ron,
What products are you using? What equipment do you have? What level of finish do you require? If you like Ron I can call you for a chat and go over a few of the processes.

Steve
 
body prep

Ron, CliffBeer is right on! I might add, use plenty of light! I use a hand held light to see reflections. The light held low near the surface will show all the hights, lows and all the imperfections. You may not want to put all the work into a show quality paint job. For a race care I would prime, wet sand with 400 and shoot the color. A show quality paint job can be destroyed loading onto the trailer going to your first race. Two weeks after I put my Daytona Coupe on the road, someone backed into the nose. There went the show quality paint job!
 
It does sound as though the primer is not cured yet. What brand, name and type is it? And what were the mixing instructions? Wet sanding will certainly help the clog problem.

One goofy thing I recomend to do ... (better if the car is a darker color) scuff the body down and then in the shade I spray the body with an even coat of water, I then look for waves in the finish. It's a way for the less skilled/experienced to see it there is any defects from a ripple/wave standpoint

From what I have seen of Fran's other bodies, they are plenty straight for race track use. If the Lola is to the same quality level then I would check the mold seam areas for needed attention, level those, scuff, prime, scuff, paint. And then wait for all the rock chips on the nose to start showing up :)

A separate question, we make the assumption that the gel coat was sanded before priming, Yes?
 
Oh one other thing Ron -
If it can be determined the body is straight enough not to need blocking with a long board, or any other block for that matter .... One can actually do more harm with a board than good by digging scratches in the finish with the hard edges of the board if one is not careful. If the body is straight enough not to actually need blocking, I recommend, guide coating and wet sanding by hand only. As mentioned a DA sander is faster but if used improperly it can dig holes in the finish too (although not as badly as the edge of a longboard).

I spend my days developing products for the paint finish industry (aerospace, automotive, shipping) so if you need more help give a call.

too much to think about huh?
Rob
 

Ron Earp

Admin
Guys, I really appreciate all the help. I'm not much on bodywork and painting, just haven't been exposed to it much. Let me see if I can provide some more feedback based on suggestions and questions and go from there. And, upfront, we're not going for a show quality finish. We intend to use the car on street and track, and enjoy it without worry of spoiling mucho $$$$ when we have an off, which we invariably will.

I imagine Al thought I had more knowledge than I did when he made some suggestions and my ignorance has gotten me into trouble. I sprayed the body with a gray primer, just some spray bomb stuff from Rustoleum. I was under the impression I was to put a "throw away" coat of primer on the body to be sanded off. I didn't sand the body before spraying it on, but I did clean it with a auto paint store cleanser/dewaxer.

I think Cliff was spot on about the primer not being dry enough. It'd only had a few hours to dry and definitely didn't sand well. However, it isn't sanding well today either - dry sanding it loads up the paper so quickly that it becomes useless. I have not tried wet sanding yet, but I will.

In retrospect the body looks good enough that I might should have simply sanded the gelcoat up, used the gelcoat as the guide, and filled any low spots I found. Then, I could have nerfed the edges, cut things were I needed, and got my buddy to spray it in his booth.

So where to from here?

The primer seems hideously hard to get off the car. I also don't know if the car was prepped well enough before spraying the primer, therefore, that might cause big grief later. Should we remove the primer chemically, would that be possible, and start back over at square one?

Live and learn. I need to learn this stuff sooner or later!


Ron
 
Sorry to say Ron.....
Gel coat always needs some 'tooth' before priming. Quality primer will not hold onto a non-sanded surface for long.... uhh, bomb can stuff is .... well ... a total loss. All the primer must be removed. Many sad faces :-(

You could use a DA (Dual Action Air Driven Sander) but if the primer is being gummy it will probably eat dry sand paper faster than you would like.

Depending on your tolerance for chemicals Evercoat makes a 'fiberglass' rated paint stripper it shouldnt harm the gel coat BUT always test in a small area first. The drawback with this method is that cheaper primers will typically just turn into a liquid when subjected to stripper (instead of bubbling off in a sheet). So it will be a messy removal process for sure.

Another potentially easier way would be to soak a terry towel in laquer thinner and wipe, typically cheap primers won't hold up to this and will wash away. The sooner you get on this the better, again this is messy but if it works its less objectioable than stripper.

Last option you can go at the whole thing with an agressive wet sand paper say 180 or 220 grit. Keep the paper fresh don't skimp, keep it rinsed out and if it clogs up get a new piece and keep moving the sooner you get this over with the better :-( Use some gloves as the rough wet sandpaper will remove skin off your hands pronto.

I sent you my phone number, call me and I can give you some more tips.
At least the Lola is a little car.... Good luck

"Show me a man who has never made a mistake and I'll show you a man who has never accomplished anything"
 

CliffBeer

CURRENTLY BANNED
Ron, you're getting all the right advice here.

As mentioned above, spray bomb primers are a waste of time.... If you're going to prep the body for final coat (even just a basic non-show car coat) of color you need an air compressor and a basic automotive spray gun for priming. Practice spraying the primer on newspaper or something else before shooting it on your car. Use the laquer based high build primer (PPG is good).

So, yes, unfortunately, it looks like you should take that primer off. Better to do it chemically if you can rather than sanding it off with an aggressive grit because sanding it off in this way will most likely leave abrasion marks which will show in the final color coat. As suggested above, I'd try the terricloth towel soaked in acetone as the first tactic.
 
Hi Ron,
Have you thought about wrapping it? I believe car wrapping is huge in the US, I'll sponsor you if you place my website & logo on the side of your car. I'll kick in US $200 for a space either side of your car on the door or rear 1/4 panel, you could sell the rest of your car to help cover the cost of the wrap, no more need for painting. 5- 10 sponsors and your wrap could be paid for.

Steve
 

Ron Earp

Admin
Hi Fellows,

Sorry I couldn't get back on or call everyone back, but lots of folks called and emailed to help out with advice! Thanks much! The forum really works for this stuff......:p


So, the general concensus is the primer needs to come off and we plan to do that chemically. Once we get it off, we'll sand the body with some 120 and Scotchbrite, then spray it with Evercoat Polyester Primer, Ultra Easy. also in this procedure I need to cut out openings for lights, fuel fillers, and do any sort of nerfing work I need to on the edges.

Sooooooo, this is going to take some time because I have a fair amount of projects going on around the house at once. Once I get that far, I'll come back for more advice and we'll move to the next step!

Thanks again,
Ron


 

Malcolm

Supporter
Hi Ron,

I had to remove all the grey primer that had been put on my car (even though I had requested specifically no paint to be applied!) after the off I had some years back but it didn't seem to be as stuck on as yours is! We used wet paper with liberal amounts of elbow grease and got there in the end. If you are planning to use chemicals, will any residue effect the next paint you apply? Hopefully I will be back in proper colour within the next monthn or so. Its been a long time.
 
Ron

Before I tackled my Cobra I read up on painting procedures.
While everyone seems to have their own preferences...the consensus
was that bare glass bodies (after cleaning the wax off) should be
dusted/guide coated and blocked with 80-100 grit to reveal
the low spots and pin holes/air bubbles under the gel-coat.

In addition...all seems should be ground down (40 grit) BELOW the
surface...and then a nice THIN layer of glass filler applied to build back up.
Then the entire body can be shot with (permanent) 2-part epoxy primer...
left to harden...then apply the bondo as needed along with high build primer (different color) for the finish block sanding material.
Some people spray the whole body with sprayable bondo....but that's not
necessary unless the car is REALLY wavy or had lot's of body work.

It seems like a lot of work...but not too bad once you get the hang of it.
Long boards are helpful on flat surfaces...but on such a curvy body as the Lola you'll want to use rubber/foam round bars sold in any auto paint store.
The key is to use alternating diagonal motion on rounded areas....both rounded tops and rounded valleys. The key to a decent paint job is how well
you do the initial steps. You cannot fix waves with 220 grit sandpaper....
by then it's too late.

Also...since you plan to race your car (chips/damage/etc)...I'd suggest
a single step paint (no clear coat).....not only would it be cheaper...
but easier to repair when needed....just my 2 cents.
Also...buy the HVLP gun....$ 60 versions are fine for your project.....
so much less waste/overspray.
Regards.

MikeD
 
I am currently doing the finishing of my experimental aircraft which has a glass fuselage.

I use Superfil epoxy filler for the obvious fill work - very lightweight and sandable and can be added after the next two teps at any time. Then two coats of Pre Prime Sealer to fill pinholes, then six coats of UV Smooth Prime to further fill pinholes and to protect the skin from UV damage - this stuff rolls or sprays on (like putting Elmer's glue on) and takes care of some of the highs and lows. It uses a catalyst to crosslink and is pretty toug but very sandable. Then sand down with 320 grit or thereabouts and shoot the primer and paint. All products are from a company called Polyfiber and purchased through Aircraft Spruce.

I am ready for the final sand now and expect to shoot within a month or so (after it cools down around here).

Mike
 
Ron, whatever you do, don't sand all the gelcoat off ! and try not to sand through the gelcoat into the lay-up glass under the gelcoat. I doubt very much, that you will find any air under the gelcoat on Fran's bodies.
I don't know if most people know, that there is many types of gelcoat. There is a gelcoat called "sandable gelcoat". No explanation there needed! Most of us see the colored gelcoats used on boats. Impact resistance is a big property a getcoat has to have for the boat makers.It's finished properties have to look good and stay that way. But, both types of gelcoat work well under paint. Why take a beautiful gelcoat and paint over it? that's why the manufacturers came up with sandable gelcoat. It cost less, but it only comes in fifty five gallon drums.
The FFR Cobra guys go round and round on how to handle the seams and gelcoat. The must be five thousand cobra builders out there and five thousand ways to do body work. amazing!!
 

CliffBeer

CURRENTLY BANNED
One last note on this one.....

Best to use the finest grit that you can and still get the job done in moderate (translation: quite a while...) amount of time. Why? Because if you jump on the gel coat with 80 or 100 grit, unless you prime about 50 times thereafter you're going to have sanding marks in the final color coat. You'd be surprised how much these can show through and make what should be a good paint job instead look like a shop class project gone wrong.....
 

Alex Hirsbrunner

Lifetime Supporter
Mea Culpa

My apologies Ron. I really should have been more specific. My intention was to have you lay down a thin guide coat of contrasting quick drying (laquer based) automotive primer or paint to help you get the entire body to a 240 grit sanded surface, leaving none of the guidecoat remaining and finally laying down the dupont 2K primer filler we discussed to allow final blocking of any bodywork and minor imperfections that remained in the gelcoat.

Rustoleum primer is a nightmare as most of it's products are enamel/fish-oil based, intended for preventing rust on metal and take forever to dry, not to mention are not compatible with most topcoats and are not sandable primers.

On the positive side, you are sure to have cleaned off every last bit of mold release agent in the process so you should have a long lasting topcoat as a result.

A couple of things I would mention - if you are making slow progress on sanding, make sure you are using quality (e.g. 3M) automotive paper. It lasts longer, clogs less than the hardware store paper (and costs less if you buy it by the sleeve) and will help avoid the temptation to attack the gelcoat with a course grit which will sooner or later, end up showing up as scratches as the primer/sealer/paint films shrink over the course of a year or two.

I have seen a lot of corvettes that were stripped by shops with coarse abrasives (80-120 grit or worse) to get the job done quickly only to have the cars show up at our shop for another go at the paint 6 months later (this is especially true if you are going to use a metallic/clearcoat combo). There is no automotive primer/paint product that needs 120 grit to "grab on" The bond being formed is primarily chemical not mechanical.

120 grit paper will typically leave scratches that are 5 mils or deeper (if not using a DA) in gelcoat and most epoxy primer surfacers typically build up 6 mil or so in say 3 double coats, which does not give you much margin. Dupont recommends 240 grit (on FRP/gelcoat) for their 2k primer surfacers products. You can get by with 120/180 on metal panels because you will not be cutting very deeply into the steel with the abrasives like they do on plastic/gelcoat.

If you have already used 120, I think quickly going over it with 180/240 before laying down the evercoat/featherfill base would be the way to go, and would not take much time. You will also use a lot less expensive primer/surfacer.

Just like FRPGUY mentioned, this is just 1 in 5000 + ways of getting it done, but it has worked well for me in the past.

Regards,

Al (user in poor standing!)
 
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