Is there a SMC paint guru on the forum that would be willing to exchange some pm's to help me through my paint project on my 79'. I need someone that knows what he's doing and can give me a definative answer to my questions. The paint is sanded to the smc and blocked, has new front and rear fiberglass bumpers as well as a new fiberglass hi-rise hood which have all been fitted to the car. I would perfer to use PPG products. Thanks for any help.

 

Ask away right here for all to learn from! Lushdrunk and Zwede like PPG stuff, and I'm certain others here have good experience as well. I'm putting PPG topcoat on my current project myself... we can all share.

 

O.K. here we go. The car is bare smc right now. What should my next steps be, Epoxy sealer and 4 coats of 2k V-Prime then block sand?

 

Let me preface this answer with an observation... there is no "one and only correct way" to refinish a car. All of us who post here have different methods, and all are valid because they work for us. I like this forum because most of the time there is excellent "give and take" discussion; no absolutes, no name calling. Read and distill all answers you get here to formulate a plan which seems best for YOU. You'll likely find a consensus of sorts to guide you.

I personally am using an epoxy primer as both an SMC sealer, and "build" material. I will not use a seperate high build product because my body is straight enough after the seam and filler work not to need great correction... only "perfecting". I have had some issue with fisheye in my second coat, I WILL invest in a proper "sealer" between my last coat primer and first coat paint. Cheap insurance, and I hate the way fisheye eliminator makes stuff flow.

I think you should spray no more than a wet double coat of primer between sandings... "solvent pop" can ruin your final paint after you finish the job if trapped solvents from excess film thickness/insufficient flash bleed out after the car gets in the sun.

 

SMC fiberglass is only picky when exposed. Body fillers and non-approved smc fiberglass resins have a hard time sticking to bare SMC panels because of a mold release agent that is used in the resin during the manufacturing process. It don't effect primers, But will effect Gel-coat since gel-coat is nothing more then a sprayable polyester resin.

SMC Fiberglass panels where not used by GM until the 84 corvette. But aftermarket and replacement panels have been found on the C3's and can be quite common. Since their is little differences between the prep of SMC vs normal fiberglass I strongly suggest you treat it as if it was SMC.

Gel-coat would be the best option as a base for your 79, Gel-coat is a sprayable fiberglass resin and it will help to smooth and seal the old fiberglass found on your car. Their are some disadvantages to gel-coats. Special spray equipment is needed. You will need a gun that is no smaller then a 1.8mm tip. 2.4mm would be ideal. But guns like this are hard to find and tend to be pricey.

Although I like a smooth gel-coat for bare fiberglass, A good primer/sealer would perform just as well. Epoxy primers like you mentioned are used more for bare metal then fiberglass but they will work just fine. I like Urethane primers better for bare fiberglass because they are more flexible then epoxy primers, They can be thinned to spray smoother on final prime and when mixed with a urethane reducer they are a sealer as well.. Either one you choose will be fine. The only primers you want to stay away from are RTS (Ready To Spray) primers that don't mix with anything other then a reducer. You want a primer that mixes with a catalyst.

Primer is the single most important step to automotive refinishing. Even if you spend $1000's of dollars on high quality top coats, They will only have the quality level of your primer. Your primer don't stick, your base coat and clear coat don't stick. Ive seen a lot of people over the years buy very high quality top coats to use over $50 primers.


Your more then welcome to PM me any questions you may have. Im more then happy to take the time to answer any questions.

 

BillyTz06,

I sent you a PM.

"DUB"

 

Thanks for the replys. Returned DUB's pm. Back to original question, what step is next. If I want to use an epoxy sealer, should it go on the smc before the primer? My reasoning for this is that epoxy sealer is non sandable so if you shoot it first with the epoxy sealer, the car is sealed with a good adhesion product and should have no issues with anything bleeding through and then shoot a couple of coats of primer which you can block and reprime and block again if necessary. This is just my reasoning as I am not a painter

 

I don't happen to have a can of PPG epoxy sealer here to read, but it would surprise me very much if the manufacturer forbade sanding any of their refinish products. All those I can recall being involved with over the years offered a time "window" for recoat without sanding, with the caveat that outside that time recoats required a sanding and reapplication. Check your label and let us know.

My research led me to choose an epoxy as sealer, but it's not PPG. If you have chosen the exact products you hope to use, run your lineup past PPG tech and see if they agree, then let us know as well. Others who follow can benefit from this thread too.

 

Why exactly do you want an epoxy primer? If your body is bare 'glass there is nothing to bleed through. An epoxy sealer makes sense if you're painting over old paint (which of course is not recommended for other reasons), but over bare 'glass? ON my '71 we used PPG K36 (urethane 2K primer) straight onto the 'glass and then blocked it. That was followed by base & clear.

But as mentioned above, there is no "only way" to paint a vette. Several different ways that all give great results.

 

What primer/sealer are you planing on using?


The PPG Deltron DPLF series, Shopline JP series and Omni MP series epoxy primers are all direct to metal primers. The Deltron DP epoxy primers are a non sanding primer, and can be used as a sealer if mixed with DTV reducer. The other two will not preform as a sealer.

To answer you question, A sealer should be used first. But if your down to bare fiberglass then you don't need a sealer.

My question is, are they a reason your hung up on epoxy primers? I don't understand why you would want to use a direct to metal epoxy primer and a sealer and another unnamed primer, When you could just use a 2k urethane primer that is better suited for fiberglass and will work best for all three coatings?

 

[QUOTE] SMC Fiberglass panels where not used by GM until the 84 corvette. But aftermarket and replacement panels have been found on the C3's and can be quite common. Since their is little differences between the prep of SMC vs normal fiberglass I strongly suggest you treat it as if it was SMC. [QUOTE]

Not so by either 73 or 74 all body panels was a SMC makeup. Epoxy is a good choice due to the release agent in the SMC.

http://www.corvettepartsblog.com/vettetag/smc/

 

Note that the C3 SMC is nothing like the C4-up SMC. The C3 SMC does require SMC compatible resin if you do repairs but contrary to the C4-up SMC, there are compatible polyester resins (for example Dynatron has one).

As for primer, a 2K urethane primer works fine on C3 SMC. My rear deck is a NOS replacement and it is SMC. Same with my NOS left quarter panel. PPG K36 urethane primer worked fine.

 

The later C3's are a form of SMC, called BMC or "Bulk Molding Compound" It is made in a very smiler process and shares alot of the same materials. Both SMC And BMC are a form of compression molding. The only major difference is the release agent. SMC uses an incorporated release agent in the fiberglass resin where BMC uses a release agent on the mold it's self.
Regardless of where the release agent is used, it still finds it's way mixed in the resins.
And both BMC and SMC panels should be approached in the same way.


The whole release agent issue is only an issue when repairing exposed (cracked) SMC with other types of resins. Any automotive grade primer will stick to SMC fiberglass just fine. Be it epoxy, urethane or ploy primers.
Epoxy primer is not going to offer any benefits over urethane primers for SMC fiberglass.

The reason people recommend epoxy primers for SMC is because back in the day their where only epoxy primers (2K) and single component (1K) lacquer type primers. Two component primers far exceed any single component primer.
But now we have a few choices for 2K primers, Urethane being the industry leader.

 

It seems that the consensus here is that I don't need an epoxy primer/sealer at all. The paint store advised me not to use the epoxy also. I was going to use Deltron DP w/reducer for the sealer because a painter with not much Corvette experince recomended it. The new game plan will be to use PPG V-prime, a 2k ureathane primer which is the newest, greatest PPG primer out. It is similar to PPG K36 but has a little better adhesion and has a little less shrinkage plus it is available in a few colors. Now the next question is how many coats of primer and which grit paper to use to block sand and in what sequence. Remember I already used a dry guide coat on the SMC with no primer and blocked it with 220 grit so it is pretty straight already.

 

I use a double wet coat/dry 24 hours followed by 180grit dry sand. Double wet coat/24 hour followed by 220 wet with guide coat. Repeat at 220 until the lines are sharp and all low areas are filled. Single wet coat/ guide coat and 320 wet then you're ready for topcoats if you don't cut through. Keeps film thickness at a minimum.

 

Perfectly said.

The 305 series (V-prime) Primer is fantastic, You will love it. They only thing not to love about it is the price tag.

 

Sounds like we are on the right track now. Before I prime I have to fix a problem. On both rear quaters the bonding strips have a 4 inch long crack at the rear where the bumper attaches. What product should I use to fill in after I grind the crack out? What is the prefered grinding method?

 

I'm a little confused.. Can you post a picture?
Ive only had the opportunity to paint two C3's and both where 81 models and both had urethane bumper covers.

If it is urethane, You can use a urethane adhesive. Evercoat and Eastwood co. sell it. Although it is called an adhesive, It works like a body filler as well. It's meant to bond cracked urethane (black or yellow) back together and be finished sanded without the use of any other type of fillers. It is an epoxy that comes in a tube like caulk. Very strong stuff.

If it is fiberglass, Then you want to repair it with fiberglass.

As far as grinding goes, Anything that will do the job will be fine. You can use a high speed sander with a 60 or 80 grit disk, or a sanding drum on a die grinder.
I like to use carbide burr with a die grinder because they are small and don't leave alot of dust like sanding. But not everyone has carbide burr's laying around and they can be expencieve. I believe I paid $100 for my set of five, 5in long burrs.

The biggest thing to remember when repairing fiberglass is to clean it good. You can use a surface prep cleaner, or I like to use compressed air and MEK (Methyl ethyl ketone) It's cheap and can be found at any hardware store. just wear a mask it is very strong stuff. Stay away from lacquer thinners and acetone, they can leave a slight film behind that don't do well with fiberglass.

 

If the cracks are at the bonding seam area where the bumper joins the quarters...there should be a curved metal plate ( kinda looks like a hockey stick end) that is somewhat bonded in that area on the inside of the flange of the quarter and upper rear body panel...and curves up and starts to go across the top for just about an inch or two...so that the screw that holds the bumper at the top of the horizontal line is going through this metal plate....and then the studs on the bumper retainer go through the other two holes in the quarter flange. This metal plate is important. If you have them...GREAT...if you do not...I can fax or e-mail you a drawing outline so you can make some...or try to find some used in good condition.

These cracks in the seam will more than likely need to be re-laminated together...and might cause you to remove these plates if you have them. You will want to get a hold of some West System epoxy resin or something similar. "Others" have there own likes in this area...so I am sure they will "chime" in.

The main thing to be aware of is the extent of the delamination. Chase the crack until it stops...because if you do not...you can possibly have a problem in the future. Just remember that getting to the end of the crack may cause for you to do some intense grinding...but I always tell my guys...get it right the first time...because I do not want to deal with it again. SO try not to keep you grinding to a confined small area. I am not saying to grind your quarter off...but make your prep so that when you go in and laminate....you can effectively repair it.

Your SMC panel is layered. So it cracks entirely different than that of earlier press-molded fiberglass Corvettes....which usually crack clean through the panel. SMC will distress the layers..thus causing you to pay careful attention to how the SMC reacts to your prep tool. If the SMC "chunks" off while prepping...than that is a indication that the SMC was distressed and needed to be removed. SO do not be surprised if the area gets quite larger(wider) than the crack. This is why it is important to get all of the damaged SMC removed to the BEST of your ability...because if you leave some behind. Then that distressed area will hold moisture and can be structurally weaker (depending on the area left un-prepped). This moisture can come back and haunt you when it expands due to increase temperatures, such as direct sunlight. ESPECIALLY if the distressed SMC is close to the surface of the car where the paint is going to be applied.

Professional response:
with using MEK....and staying away from lacquer thinner when doing prep for fiberglass laminating...BUT acetone is an awesome material to use.

Because if acetone can not be used...then I have about 400+ Corvettes, 5 Funny car bodies,3 jet ski's, countless saddle bags for Harley's and one Cobra kit car to be worried about.

I have made enough molds and parts over the years to know that acetone will not do any damage and it flashes off so fast and is a virgin solvent...unlike lacquer thinner (which we agree on) which is a blend of many products. Acetone and MEK fall into the same "family" of worthy products to clean fiberglass/SMC/carbon fiber. NEVER have I had a failure in delamination...and much of this testing is done on 300+mph funny car bodies.

"DUB"

 

I use a 5 inch diameter air powered high speed grinder with either a 24 or 36 grit oxide disc. You want to grind the actual crack nearly all the way through, and go that deep for as long as "chunks" not powdered material comes out, like DUB said. Then "feather" the surrounding area getting shallower as you go away from the damage. I like to make this "trough" at least twice as wide as the damaged glass, wider if it's convenient. Repair the damage with fiberglass mat and a good quality epoxy resin... do not use auto parts store polyester resins on your SMC (or semi SMC) car.

Cut a piece of mat a bit wider than the bottom of the trough, and at least two more wider yet, (more is better) ending with one as wide as the ground area. Using a cheap bristle paintbrush with the hairs cut down to about 2 inches long, mix some resin per the label instruction... MEASURE the quantities, do not simply guess. There are graduated "Dixie Cups" available cheaply which are perfect for this. Wet the area to be laminated with the brush, and using the brush and more resin dab (like stencilling a wall) the resin into the mat until the mat is translucent and fully adhered. You can then do the next layer and the next without waiting for it to set until the area is filled. Once hardened, I grind any excess resin and glass as close to level as I can, seal with the epoxy primer you're not going to use, then add Bondo (I like Evercoat brand) to even the surface; and block smooth. Prime, block etc.

A bit of time spent planning the lay ups, precutting the mat and masking the areas below the repair to keep resin from running where you don't want it will allow you to production line the patches after the panels are prepped. It can go quite quickly and not be a chore to neaten up after if you're methodical about it.