Corvette Image Body Panels

[65TripleBlack]

How are these best prepped for paint?

Thank you in advance.

 

[paintdaddy]

I agree,whats your desired end result?

 

[65TripleBlack]

Because of the manufacturing process involved, Image panels will cause the baint to blister, unless they are prepared in a very specific way, prior to paint. The Image instructions specify AT LEAST 20 mills of gelcoat before applying primer, sealer, and paint.

I would like to know, whether anyone has had a problem with blistering. Has anyone NOT had a blistering problem, and if so, EXACTLY how did you treat these panels prior to paint.

Thanks in advance.

 

[78 L82 4spd]

Sorry for butting in... Is "Image" the name of a company or style of panels?

Website?

Thanks,
Stephen

 

[65TripleBlack]

Corvette Image is the name of a company.

 

[paintdaddy]

The Image instructions specify AT LEAST 20 mills of gelcoat before applying primer, sealer, and paint.

Ive never heard of anything like this.Normally ,If there is gel coat on the part at all it is applied by the manufacturer.
Usually new fiberglass has to be sanded with 180 or finer and then primed with epoxy primer and a primer surfacer .Then block sanded and painted.

 

[Ron Miller]

Because of the manufacturing process involved, Image panels will cause the baint to blister, unless they are prepared in a very specific way, prior to paint. The Image instructions specify AT LEAST 20 mills of gelcoat before applying primer, sealer, and paint.

If you already have the panels & plan to use them, I"d for sure go with the manufacturer's recommendations regarding preparation. Manufacturers usually know what it takes to make their items work.

If you don't already have the panels, or are willing to change, I'd consider c5d's comment to look at some press molded or other panels with the gelcoat already applied.

rlm :cool

 

[JohnZ]

Production Corvette body panels (since mid-'54) have never used ANY sort of gelcoat, either in the panel manufacturing process or in the assembly plant body shop. The outer surface of production press-molded fiberglass panels is simply the cured polyester resin (with the mat/pre-form underneath it), and its surface mirrors the surface of the steel upper mold half.

The original press-mold process was as follows - with the press fully open and both mold halves sprayed with a light film of mold-release compound, the resin-coated fiberglass mat pre-form was placed on the lower half (which formed the inner surface). Then two operators poured measured amounts of the resin/hardener mixture all over the pre-form, covering its entire surface, and the hydraulic press then was closed. Both mold halves were heated internally with circulating hot oil at 200* to speed curing, and the press was opened after three minutes, revealing the fully-cured panel. The panel was removed from the press, taken to a trimming fixture to cut off the excess edge material, then to a drill fixture to drill any holes required, then any areas that would be bonded later were either sanded or shot-blasted to prepare the surface for good bond adhesion, and the panel was racked for shipment to St. Louis. Corvette body panels were molded by numerous outside suppliers, including MFG (Molded Fiberglass Corporation), A.O. Smith, Rockwell, GenCorp, Goodyear, and others.

 

[Ron Miller]

Production Corvette body panels (since mid-'54) have never used ANY sort of gelcoat, either in the panel manufacturing process or in the assembly plant body shop. The outer surface of production press-molded fiberglass panels is simply the cured polyester resin (with the mat/pre-form underneath it), and its surface mirrors the surface of the steel upper mold half.

The original press-mold process was as follows - with the press fully open and both mold halves sprayed with a light film of mold-release compound, the resin-coated fiberglass mat pre-form was placed on the lower half (which formed the inner surface). Then two operators poured measured amounts of the resin/hardener mixture all over the pre-form, covering its entire surface, and the hydraulic press then was closed.

John, wouldn't the measured amount of the resin/hardner mixture placed all over the pre-form function as what is commonly referred to as the "gel coat"? If I understand you correctly, this was only placed on the side of the pre-form which was ultimately to become the outer surface of the panel. Just wondering . . .

rlm :cool

 

[paintdaddy]

True,ultimately that is what gel coat is ,resin.I would think the manufacturing process is kinda like the repair process.First thing to be applied is a coat of resin,and then yes when released from the mold it now becomes the outer surface.

 

[BLACK MOON]

Thanks for the clarification John. Not vettes but in the boating industry gelcoat is a polyester colored mixture that is first sprayed in the mold before applying the fiberglass mixture. :cool

 

[BLACK MOON]

Off topic but Mr. Bush is in town today. $1,000 for lunch. I may have to run out and join the protesters for awhile.

 

[BLACK MOON]

Triple Black,
Who told you the paint would bubble? No one that I know sells gelcoated panels. NOS panels aren't and plenty of those are still available and used with excellent results.

 

[JohnZ]

John, wouldn't the measured amount of the resin/hardner mixture placed all over the pre-form function as what is commonly referred to as the "gel coat"? If I understand you correctly, this was only placed on the side of the pre-form which was ultimately to become the outer surface of the panel. Just wondering . . .

rlm :cool

Ron, the pre-form was just a flimsy "veil" of glass strands in the general shape of the finished panel; it was placed on the lower half of the mold, then all the resin was poured over it - the finished panel was the same composition all the way through, from top to bottom, with the pre-form of fiberglass strands becoming the internal reinforcement; polyester resin by itself is very brittle and has little strength, which gives rise to the industry definition for fiberglass panels as FRP, for "fiberglass reinforced plastic".

Gelcoat is a separate substance (also a 2-part polyester resin) that's sprayed into the open mold half (the only half) before laying fiberglass mat or cloth, later saturated with resin and "rolled", when "hand-laid" replacement panels (or boat hulls, etc.) are made in open molds. The gelcoat on hand-laid panels is applied to the mold first to provide the desired "smooth" outer surface when the part is removed from the mold (the inner surface is quite rough and "hairy" on hand-laid parts).

Press-molded parts are smooth (on both sides) as removed from the mold due to the polished steel upper and lower mold surfaces and the intense pressure under which they are molded, and don't require any additional resin addition prior to prime and paint.

 

[BLACK MOON]

Triple Black,
I've got gelcoat in med red or black if you need some. I get it at cost from a friend if you need some. I was thinking about doing my 63 in red and giving it a sanded/polished (boat) finish. Looks great and if you scratch it you just sand and polish.

Might sound crazy but I thought about it.

I can send you a cup/ pint or quart if you need it just let me know, or most corvette suppliers have it in original gray and white.

 

[Ron Miller]

Ron, the pre-form was just a flimsy "veil" of glass strands in the general shape of the finished panel; it was placed on the lower half of the mold, then all the resin was poured over it - the finished panel was the same composition all the way through, from top to bottom, with the pre-form of fiberglass strands becoming the internal reinforcement; polyester resin by itself is very brittle and has little strength, which gives rise to the industry definition for fiberglass panels as FRP, for "fiberglass reinforced plastic".

Thanks for the clarification John, I assumed the pre-form was already impregnated with an amount of resin. I'm familiar with the rest of the process, hand laid v.s. press molded, etc. Thanks again!

rlm

 

[JohnZ]

Re: Next ?

John, so then why would a press-molded panel require application of a gel-coat to prevent paint bubbling?
ID

I can't speak for current aftermarket panels that are press-molded, but I suspect their process differs from the original, which used solid steel dies (molds) and HUGE hydraulic presses with oil-heated molds. The current aftermarket panels most likely use unheated reinforced epoxy molds and MUCH smaller capacity presses, and may require unique surface preparation.

 

[studiog]

"The Corvette Image manufactures parts as original using only fiberglass and correct color resins to reproduce the original color and texture. These press molded panels are bare glass like OEM and are the most faithful reproductions ever made. "

This is a quote from the Corvette Image web site. I am no expert by any means but I have read in several different publications that the "bare glass" must be gel coated to insure that no "errant" fiberglass particles are allowed to contact, and thus ruin, the finish and that only gel coat will accomplish this satisfactorily. I am very interested in any comments as I will be painting a restored car this summer.

:confused

 

[paintdaddy]

I have never heard of this ,Im not saying it isnt true.As far as sealing off the fibers ,I dont see any difference in using gel coat vs a polyester primer filler.They both have the same basic chemical make up.You should probably call the manufacturer and ask if that would be acceptable.Im still amazed that they would produce these panels knowing they will need to be gel coated before painting.

 

[65TripleBlack]

Thank You For The Offer, Black Moon.....

.........but the problem is not availability of the product, but EXACT application methods.

The blistering problem is due to the relative density of the panels as compared to OEM. The paint on OEM panels will also blister if exposed to extreme conditions, because moisture permeates FROM THE BACK SIDE, then migrates through the glass/resin, and blisters the paint. This is why non OEM panels, which are gelcoated (or suitably sealed) on the BACKside, as well as the outside, do not blister the paint.

The reason for the gelcoat (or any other suitable barrier), is to prevent the moisture from lifting the paint.

1. OEM panels were NEVER gelcoated, from 1953, until SMC came into use in the mid seventies.

2 Gelcoat is NOT polyester resin.

2a. Polyester resin is NOT gelcoat.

3. OEM (and "Image") panels are made from fiberglass and pigmented polyester resin.

4. "Image" panels are produced in the same manner as OEM panels EXCEPT that, the presses used are not as powerful as OEM type, and do NOT produce the same density of the composite that OEM does.

5. OEM panels are also porous, and will also not fully prevent paint blister under very extreme conditions.

5a. STEEL is NOT porous, and therefore will not allow paint to blister due to moisture intrusion.

6. "Image" panels are considerably more porous than OEM, and will blister in MUCH LESS EXTREME environments.

7. Gelcoat, or ANY OTHER SUITABLE BARRIER must be applied, to prevent 6. above from happening.



NOW, BACK TO MY ORIGINAL QUESTION.

Thank you.