Need Gel Coat Help - NCRS Discussion Boards

Need Gel Coat Help

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • Patricia Brown

    Need Gel Coat Help

    Hello,

    I have some questions as I prepare to gel coat my '72. I'm trying to decide between Eckler's that has the wax catalyst vs. Evercoat's that requires PVA be sprayed on.

    1) I've heard the wax is a pain to sand off, as it clogs the paper. Would the extra step of spraying PVA on and rinsing off with water end up being worth the extra step over the wax-catalyst type because it would then be easier to sand?

    2) I've read someone's warning that to spray more than one coat of the wax-catalyst type causes problems because the succeeding coats do not stick to the wax on the first coat, yet I also read one should do 3-4 coats... Is this just an issue of making sure to follow the directions and re-coat within the window of time and there should be no issues?

    3) So if I go with the wax-catalyst type, will the wax still "rise to the top" properly if I have sprayed the *underside* of the floor, such that the gel coat is upside-down now? Would the wax still migrate to the surface, even though the surface is *down* in this case?

    4) If I go with the PVA type, do you spray the PVA on with a spray gun, or is it a squirt-bottle type application? Is the PVA particularly dangerous/poisonous to work with?

    5) I've also heard that additives are used to help the gel to flow out, which can significantly reduce sanding time. Would those additives be in both types of gel coat, such that flow-out characteristics would be similar between the two products?

    6) OK. Maybe I'm being too anal here, but Evercoat advertises that their gel coat is made using isophthalic/neopentyl glycol polyester resins, while I discovered Eckler's uses orthophthalic resins. I was told that the isophthalic resins are more expensive and have slightly tougher mechanical properties. I am wondering if it is a big enough difference to bias my decision as to which brand to go with. I'm wondering if any of you have used both and have a preference or could tell a longevity difference?

    Sorry for too many questions. Help with any of them would be appreciated!

    Thank you,
    Patricia
  • Ralph Harlan

    #2
    Re: Need Gel Coat Help

    First, I have never used either Eckler's or Evercoat's gelcoats. I have used gelcoat on a 64 Corvette many years ago, but also spent almost a quarter of a century repairing sailboats before retiring 10 years ago. Perhaps it has been my comments you referred to in #2 when you said you heard that wax loaded gelcoats could give problems on recoat. I chose to always use #10 PARTALL - PVA - over freshly sprayed gelcoat rather than have the potential pleasure of doing a second repair on the same large area of a client's boat. The joy would be especially intense because it would not become apparent until well after I returned the boat and I would have to pull the boat back out of the water (a pricey proposition for boats much over 20 feet), remove the faulty gelcoat, remix a new batch of color matching gelcoat, and refinish the area - on my nickel. Er, no thanks!

    I have found that in a pinch PVA can be applied with about any sprayer - PREVAL, FLIT gun (you know - the old pump action bug spray from the 50's), HVLP, siphon cup, or even dip your fingers in the pot and fling it at the surface. The reality is that the finer the mist of PVA you put down on the wet gel, the smoother the surface of the gel will be when you do your follow-up, and the shorter the time for the PVA to dry. I have usually been able to do a wet sanding with 600 grit after a good misting of PVA (wait until the gel cures, tho). Or you can hose the PVA off the cured gel and then work it over with an air sander - you can start out without the water hose wash-off, and just start air sanding the area with 150 grit. So much easier than messing around trying to get past the wax.

    Reference your question #3 - the wax is actually more of a "blush" than a "float" - it does not know up from down or sidways. It will be there - maybe even when you least expect it or want it to be.

    The NPG/isopthalic resins are usually more resistant to blistering when left in the water for long periods; they also fade and yellow somewhat less when exposed to UV (sunlight); and they can be effective as a finish in slightly less thickness over laminating resins compared to the "old" orthopthalic formulas - which reduces the likelyhood of cracking. None of these factors is of much value to you in preparing the surface of your Corvette for an overcoat of paint. You are not worried about the potential of blistering unless you intend to (literally) have Corvettes "float your boat". The final paint will protect the gelcoat from UV deterioration, and since you are using the gel as a fairing compound it may go from none to 8 mils when you finish sanding it. (Too thick can still cause you problems with cracking.)

    I would expect both products will be similar in "flow" if they are properly prepared for spraygun application. Follow the mixing and reducing directions closely, whichever product you choose. Yes, there are other "additives" that can help the gelcoat "flow out", but talk with your supplier for recommendations for your product. Acetone has been used - as has laquer thinner - but much at all will cause "porosity" or "pinholes" in the cured gel begause of the outgassing during the cure period. Styrene monomer can also be used but can give other problems if you have a heavy hand - either in the adding of the monomer or in applying the coating.

    Gelcoats - indeed, any polyester resin - carry the responsibility of using them wisely. A good respirator is a must - forced breathing apparatus better. Do not wipe/wash off spills on your clothing/skin with solvents as the solvents are usually carcinogenic in their own right, and will dissolve the gel enough for you to absorb the mix through your skin. PVA is short for Polyvinyl Alcohol, another substance you are better off not breathing, ingesting, or absorbing. When using fluids of this nature it is better to treat them like you are working with hazardous chemicals in a chemistry lab - because you are. The MEKP that catalyzes the polyester resins (BONDO included) such as fiberglass and gelcoat is a hazard in its own right. Remember that it is a catalyst so that each molecule of MEKP enters the chemical reaction to accelerate the reaction and then is kicked back out as a molecule of MEKP - ad infinitum. This means that if you get it in your eye (it is an oxidizer, remember the P stands for PEROXIDE) it will oxidize the cornea (and other parts) of your eye. Repair for that is cataract surgery! So, when your nose itches or you get dust in your eye while you are (or have been) working resins, wash your hands thoroughly before touching your face! Wear goggles to reduce the inclination to put your hands near your eyes and reduce the likelihood of splashing/spraying MEKP in your eyes while mixing or spraying gelcoat. By the way - wear your respirator when you sand fiberglass. You know how it feels when you get fiberglass dust on your skin where it can be washed away with ZEST bar soap and a washrag; just think about what sort of vacuum cleaner you will need to get it out of your lungs!

    I hope I am of some help.

    Comment

    • Dennis C.
      NCRS Past Judging Chairman
      • January 1, 1984
      • 2409

      #3
      Please help... Why would you want to gel coat...

      ...a car that was never gel coated to begin with...???

      Comment

      • Howard K.
        Expired
        • November 11, 2011
        • 111

        #4
        Re: Need Gel Coat Help

        You guys have convinced me not to use gel coat EVER !

        Comment

        • Michael H.
          Expired
          • January 29, 2008
          • 7477

          #5
          Re: Please help... Why would you want to gel coat.

          I agree with Dennis. I'm not sure where all this gel coat stuff came from but I see absolutely no need for it on a Corvette. The best way I can think of to completely erase any trace of the true look of a Corvette is to gel coat and block sand all of the character away. My cars have ripples, waves and textured unsanded glass in many areas and I'm proud of every ripple.

          Comment

          • Wayne W.
            Extremely Frequent Poster
            • April 30, 1982
            • 3605

            #6
            Re: Please help... Why would you want to gel coat.

            I tend to agree, but if I turn out jobs like the factory, I wont last long in this business. I can also say that just gel-coating a Corvette, especially an early one, will not straighten out the body significantly enough to change the character of the body. You have to work hard at that. In my experience a gel-coated body and paint will last longer than one that is not. I agree that with the new urethane primer materials, that gap is not as pronounced. But even the new primers do not produce the level of fiber and seam shrinkage that the old lacquer primers did.

            Comment

            • Michael M.
              Expired
              • April 1, 2002
              • 149

              #7
              Re: Need Gel Coat Help

              if you read Patrica's post that appear slightly below this one, it appeears that she is planning to gelcoat the UNDERSIDE of her '72 - why - I have no idea.

              Comment

              • Michael H.
                Expired
                • January 29, 2008
                • 7477

                #8
                Re: Please help... Why would you want to gel coat.

                Wayne,

                I suppose the majority of current owners don't understand what the body/paint of a new Corvette looked like 40 years ago so they don't know how to prepare one for accurate restoration today. The body man/painter is in a difficult spot too because if he tries to duplicate a typical 50's ot 60's finish, the owner feels he didn't get his money's worth.

                Jell coating, or any other heavy coating, will definitely destroy/remove all of the character in areas that were never sanded originally at either the source of the panel or at the St Louis plant. A good example would be much of the front fender louvers of any C2 car. The glass strands show through original paint because not only was the louver not sanded, the primer wasn't either. Another area would be the small section between the top of the rocker mldg and the point where the body panel rolls out and up. Looks like a piece of that quilted aluminum foil. Glass strands are very pronounced and visible. The edges of doors originally had deep grinder scars on both ends that everyone sands smooth during restoration. There are dozens of areas that should have their own character when prepared and painted properly.

                Next time you have opportunity to inspect a car that still has original paint in the door jambs, note the absolute lack of any attempt to sand any of the texture off of the glass or primer before paint. Bet 98% of all restored cars don't have this look.

                I could never explain "the look" in less than a few thousand words (or pages) but it definitely looked nothing like most restored cars today. Just about every one is over restored when it comes to body/paint. Amazing the progress we've made on chassis/suspension restoration accuracy in the last 30 years but the body/paint accuracy has not improved at all. The quality has, but not the accuracy. In fact, I think it's gone the wrong way entirely.

                I can only hope that everyone has a chance to closely inspect what few original paint cars there are left on the planet before they're all gone.

                Comment

                • Patricia Brown

                  #9
                  Re: Need Gel Coat Help

                  Ralph-thank you for your help. Regarding the isophthalic vs. orthophthalic gels, is it correct to say that the gel layer is so relatively thin on a Vette application that either type of gel will have similar crack-propensity characteristics? I gather that isophthalic gel is "tougher", hense less brittle and prone to cracking, but if I understand correctly the amount one uses on a Vette would render that advantage negligible over an orthophthalic gel?

                  I am wishing to gel coat the underside of my car because I am having to make many repairs that I would like to seal over. I will also be installing aftermarket, press-molded panels that, while they are the best money can buy, are still not as dense as factory 'glass (from all I have read) and have less resistance to moisture working through them from the backside, threatening a paint job. I plan to drive this car, and we live in a very humid climate, so I am especially concerned with the moisture threat. Of course the panels come gel coated on the paint-side, but from what I have gathered it is good insurance to have panels that are *also* gel coated on the backside. I know it is thoroughly non-stock, but when I am forced to go with new 'glass it seems the safest thing to do.

                  Comment

                  • Chuck S.
                    Expired
                    • April 1, 1992
                    • 4668

                    #10
                    Re: Need Gel Coat Help

                    Any resin coating on a body surface, steel or fiberglass, is prone to cracking with too much thickness. I believe it has less to do with the type of resin than the total build thickness. Even your paint will have a tendency to crack if the total build goes beyond about 10 mils (0.010"). This cracking probably has to do with the relative difference in the materials' response to bending and flexing...as a type of polyester resin, gelcoat should be closer to the original panel material, but it lacks the fiberglass reinforcement that increases the fiberglass' resistance to bending and flexing.

                    Patricia, I'm impressed with your approach...you're learning the hobby thoroughly. On gelcoating the underside, if possible, you may want to limit gelcoating to only the repair areas. In practice, however, I don't know if "spotting" gelcoat works; I don't see why not. Judges will expect to see the character of the fiberglass if they look at the underside...I would try to preserve that appearance of fibers in the surface as much as possible. Gelcoating will cover and change the appearance of the fiberglass to a "painted" surface.

                    Comment

                    • Chuck S.
                      Expired
                      • April 1, 1992
                      • 4668

                      #11
                      Re: Need Gel Coat Help

                      In fact, even with repairs, gelcoating the underbody is probably not required and will only detract from the car's originality. I presume you don't intend to paint the underbody, so sealing the repair with gelcoat serves no purpose.

                      I have done minor fiberglass repair on panels that is virtually undetectable inches away by a super-anal, hyper-critical restorer (myself). If you use black tinted resin, it is possible to make repairs that are virtually identical to the surrounding fiberglass surface. (There may be a change in the way the glass fibers appear in the repair.)

                      Once the laminations of mat and resin are fully cured, you block sand with progressively finer grit sandpaper all the irregularity out of the repair surface until it is flat and smooth with the surrounding area. This implies that you have to laminate enough layers of resin and mat to build the repair slightly above the panel surface. The finishing touch might be just a little semi-gloss clear to bring up the shine...virtually "judge-proof".

                      Comment

                      • Patricia Brown

                        #12
                        Re: Need Gel Coat Help

                        Chuck-

                        I think I'm still stuck with gel coating so I can have the moisture barrier for the aftermarket fiberglass. I must confess, I don't plan to have the car judged for originality. In fact, (and PLEASE don't shoot me!) I admit I plan to apply undercoating to the bottom of the car. Since I will be driving it I really want the impact protection, along with any added sound deading, plus the clean look of a fresh black coating. However, I am aware the solvents in the undercoating are rather agressive to fiberglass, and hence another reason to first seal off the 'glass with gel coat.

                        Patricia

                        Comment

                        • Chuck S.
                          Expired
                          • April 1, 1992
                          • 4668

                          #13
                          You Go, Girl! Sorry If I Harangued You... *NM*

                          Comment

                          • John M.
                            Expired
                            • January 1, 1999
                            • 1553

                            #14
                            Re: Please help... Why would you want to gel coat.

                            For all you guys that keep singing the "why would you do it if the factory didn't" song. I will remind you of that when you use anything but lacquer primer and lacquer topcoats! I use Gelcoat on almost every job I do including my judged cars. If you do not use it on Corvette Image panels, you can kiss any warranty on the panels goodbye! If you do not believe me than just read the disclaimers that come with their panels.

                            It absolutely amazes me when people will use K-36 primer, but then moan about gelcoat being non-original. I use gelcoat because I believe that it is unsurpassed in sealing repairs and rough 'glass. There is, in my opinion, nothing better on top of bare glass and body work to keep the repairs from telegraphing through, especially when lacquer topcoats are used. The lacquer thinner has a tendency to swell body work as it penetrates the primer. It is my experience that gelcoat will completely prevent this solvent penetration. If you guys all have pristine, never hit bodies, I envy you, but for those of us who have to put a car back together from bits and pieces, then gelcoat is a valued tool in our toolbox. I have been painting cars for over 35 years, and would never consider doing a bare-body repaint of one of my Corvettes without it. I have talked to dozens of people who have used CI panels without gelcoat who have had blistering problems, but I do not think that I have ever heard of a CI panel that was gelcoated that blistered. This particular point is moot for me since I use Semerscheims panels, but I am still a big fan of gelcoat.

                            You all can shoot all the paper-thin, poor coverage, orange-peeled lacquer jobs you want with bare spots down low on the body, but I will continue to put paint jobs on my cars that I can be proud of when I drive them somewhere other than off the trailer. I shoot lacquer on my judged cars, but there is always gelcoat under the primer. I will continue to take the 12-20 point hit that I get for my body being too slick, since there is a life off the judging floor. Even with my crappy, gelcoated body, and non-original looking paint, I can still get to 98% at flight judging, so I must be doing something right. I am not knocking your decision to fathifully recreate the crappy job the factory did on these cars, but I chose not to do so and would appreciate you all not looking down your noses at those of us who make a informed decision to have a car that we can be proud to drive to the local cruise.

                            Regards, John McGraw

                            Comment

                            • Chuck S.
                              Expired
                              • April 1, 1992
                              • 4668

                              #15
                              Re: Please help... Why would you want to gel coat.

                              What??!! They didn't have urethane primer back in the fifties, sixties, and seventies??

                              If you're applying 2-4 coats of K36 primer-surfacer, block sanded in between coats, you might as well use gelcoat under it...all of the short wave length ripples will be gone (cie la vie); only the major long wave length undulations will be left.

                              Before you turn your wrath on me, John, just know that I'm on your side...I would love to have a brand new, time-capsule Corvette just the way the General did it, but if I'm having to paint an old one, I ain't going to worry about making urethane look as bad as the General's lacquer paint jobs.

                              What can I say, John...We're Blasphemers!

                              Comment

                              Working...
                              Searching...Please wait.
                              An unexpected error was returned: 'Your submission could not be processed because you have logged in since the previous page was loaded.

                              Please push the back button and reload the previous window.'
                              An unexpected error was returned: 'Your submission could not be processed because the token has expired.

                              Please push the back button and reload the previous window.'
                              An internal error has occurred and the module cannot be displayed.
                              There are no results that meet this criteria.
                              Search Result for "|||"