Could someone please tell me about fiberglass gelcoat?

Discussion in 'Replica Props' started by Westies14, Apr 16, 2002.

  1. Westies14

    Westies14 Master Member

    Trophy Points:
    2,580
    A tutorial or a step by step process would be awesome. I can lay fiberglass matte just fine- but I want to be able to start with that nice, clean, smooth outer layer! Thanks in advance!

    -Douglas
     
  2. Lan Jenn

    Lan Jenn Well-Known Member RPF PREMIUM MEMBER

    Trophy Points:
    816
    There are a world of possibilities with gelcoat. If you want to email me: blandon@millenniaboats.com I can help you on your way. I can get you books that put you through EVERY step of the way and I can help you with your questions as well. I work with it every day in mold processes and boat repair. There is even epoxy gelcoat but we won't go there. Anyway, let me know if I can help.

    Brett
     
  3. hydin

    hydin Sr Member RPF PREMIUM MEMBER

    Trophy Points:
    2,305
    i remember a guy on the old board making a capn america shield with colored gelcoat?. i remember it was gelcoat.

    man, it was SWEET. seriously a great skill to have in a hobby like this.

    cept maybe the hobby of getting the occasional lotto ticket that wins. then that can fund this hobby [​IMG]

    chris
     
  4. Westies14

    Westies14 Master Member

    Trophy Points:
    2,580
    Brandon, I'm definitely going to drop you an email, but if you'd like to post some general info here as well I'm sure some other members would appreciate it!

    -Douglas
     
  5. natty15d

    natty15d Well-Known Member

    Trophy Points:
    716
    Hi Douglas

    The big thing with Gel coat is what ever you do dont apply it in thin coats. If you use too thin a layer the heat from the curing fibreglass will cause it to crack or craze. Also if the coating is too thin it will leave bare patches in the mold. You want a GOOD covering of gel coat & you wont have any problems. [​IMG]

    Nathan
     
  6. Westies14

    Westies14 Master Member

    Trophy Points:
    2,580
    Thanks Nathan,

    I need to start at the beginning though, I'm afraid. Is gelcoat just a layer of liquid fiberglass resin brushed in without the matte, or is it a completely different product? If so, where do you buy it? I can lay down fiberglass matte well enough. The shape I am casting is fairly complex though (proton pack), I need the detail and smoothing help of a gelcoat layer...

    -Douglas
     
  7. natty15d

    natty15d Well-Known Member

    Trophy Points:
    716
    Gel coat is a completely different product from Fibreglass resin.
    For a start you can get it in different colours, ususally grey, white & clear can be obtained off the shelf from suppliers. Coloured ones can be made up by adding dyes to white gel coat. Your supplier should be able to sell you these along with the gel coat.
    Gel coat is like a thick gloss paint & takes longer to cure than fibreglass resin, or at least the stuff i use does.
    You want to really LOAD the brush up with gelcoat & use a 40/50mm brush. Use a cheap brush with white or clear bristles as if they come out they wont show up in the gel coat. Once your done just bin the brush.
    Work the gelcoat well into the corners as air bubbles can get trapped there.
    Gel coat is that thick it will even stick to vertical/inverted surfaces but it sometimes starts to come awat from sharp edges. Dont worry if that happens the fibreglass resin will seal it.

    Once the Gel coat has hardened give it half a day to fully cure as the fibreglass resin will start to break it down if you apply it too soon.

    Hope this helps
    Nathan [​IMG]
     
  8. Skyler101

    Skyler101 Sr Member

    Trophy Points:
    1,242
    I know that some people on the board mix body filler and resin together to make a cheap version of gelcoat. I have done this, and it worked very nice...

    -Skyler101
     
  9. Lan Jenn

    Lan Jenn Well-Known Member RPF PREMIUM MEMBER

    Trophy Points:
    816
    Nathan,

    First of all I don't want this taken the wrong way. We have had far too many wars here lately and I don't want you to be offended by my corrections to some of what you have written. We all want the best from our work so I hope you understand.

    First of all, you are correct about not wanting gelcoat to be too thin, but some of the reasons listed are incorrect. Gelcoat is a resin, only it is higher grade, has longer elongation, has pigments and resists UV rays much better. Both resin and gelcoat are made the same way, polyesters and styrene monomer. Both use the same catalyst with the same percentage to cure it and both, when done correctly, will take the same amount of time to gel and cure if their gel times are compatible. Even with varying gel times they will cure in about 2 hours at 77 degrees F.

    Cracking of gelcoat comes when it is applied too thick, not too thin, in excess of 25 mils. Optimum thickness is 18(+/-2) mils. Below 12 mils and it will under cure and will have fiber print through. Resin will not break down gelcoat when it is cured, thick or thin. Paint on a car is 4 mils thick for reference.

    Crazing is something that happens in resin and not gelcoat. Cracking or checking (mud cracking) occurs in gelcoat and is caused by gelcoat being too thick, blistering, evaporated gasses behind the gelcoat that expand and blow out the surface, and stress. If gelcoat is too thin, it will flex with the fiberglass easier. But thin is bad right? If thicknesses do not exceed 22 mils it will still flex with the glass well enough and not crack, otherwise the stress of the flex will crack the gelcoat. Fiberglass must flex, otherwise a boat would shatter the first time you take it out.

    I recommend spraying gelcoat onto a mold. Brushing can be done but the results will not be mirror of the mold surface. And if you want an even coverage then spraying is the way to go.

    After I spray gelcoat onto a mold I start my skin coat of fiberglass about 45 minutes to an hour after spraying. You can start in as little as 35 minutes after applying gelcoat if you are in a well controlled 75 degree environment. The norm is when the gelcoat cools back down to room temperature. Waiting too long and the skin coat will not adhere well enough and delamination will occur down the road. I always follow that rule. If I wait for a long time between coats of fiberglass I can always sand it to rough it up. The gelcoat should be tacky when you start laying the skin coat.

    A supplier can provide any color of gelcoat needed. For exact matches, like boat matches, I use a place in Washington that supplies factory colors.

    I think some of the reasons your gelcoat is taking too long is either the amount of catalyst you use (should be 1.8% at 77 degrees), room temperature at application, applied too thin, not mixed well enough before mixing catalyst or old gelcoat. You might also have incompatable catalyst.

    Hope this helps. Happy prop making!


    Brett
     
  10. natty15d

    natty15d Well-Known Member

    Trophy Points:
    716
    Hi Brett

    Dont worry i didnt take it the wrong way.

    Im no expert with Gel coat, i was just trying to help out by pointing out things that i have found while using Gel coat.

    What i meant about the longer drying time is that Fibregleass will start to go off very quickly without much warning where as gelcoat has a longer usable time and gives you more of a warning when it starts to solidify. Living here in sunny Scotland things take a little lnger to cure.

    Thanks for the advice though its helped me understand gel coat a bit more. [​IMG]

    Nathan
     
  11. Lan Jenn

    Lan Jenn Well-Known Member RPF PREMIUM MEMBER

    Trophy Points:
    816
    Yeah, living in an environment where there is higher humidity will definately effect applications with plastics. I live in the second dryest (is that spelled right) state in the US, so I don't have that problem, fortunately.

    But what sucks about living here right now is 2 days ago it was 79 degrees F. Now it's 36 degrees and snowing! Just north of me, about 35 miles, there is 9 inches of snow on the ground. Hey, we could always have the winter olympics again! I'm sure all our venues are stacked up with the white stuff. <g>

    Brett
     
  12. Got Maul

    Got Maul Official Licensee RPF PREMIUM MEMBER

    Trophy Points:
    1,980
    hey Westies-er Douglas [​IMG]

    Why are you gel coating your proton pack ? I think the effect would look great BUT unless you want that darth vader look to your pack, it would look waaaay to glossy for a proton pack. I am from the school that the packs were low sheen at most, at least from my observations of seeing the real thing in D.C..

    For my Fiberglass packs I simply brushed on 1638 (or master cast) resin first, mudded it (fiberglass resin and cabosil) and fiberglassed it. The end result was beautiful as the 1638 really picked up on just about EVERY surface detail of the silicon mold (even light dust !). Best part was, glassing the pack only took 3 hours and about 2 hours to dry if on a sunny day !
     
  13. Westies14

    Westies14 Master Member

    Trophy Points:
    2,580
    Nathan, Brett:

    Thanks so much for your input. What kind of equipment do you use to spray the gelcoat into a mold? What is the cost of the gelcoat supplies, on average? This is a great quick education for me, I really appreciate it!

    -Douglas
     
  14. Lan Jenn

    Lan Jenn Well-Known Member RPF PREMIUM MEMBER

    Trophy Points:
    816
    Actually, whatever your surface on the mold is, that is what you get on the part. So, if you have a satin or dull finish on your mold, the part will be dull. You can spray PVA on a shiny mold, though, and it will pull dull (those two words look funny together like that).

    Douglas, I use a pressure pot, gravity feed, siphon feed, or my gelcoater (It's a big piece of equipment that takes the gelcoat directly from the drum and mixes the catalyst in at the gun tip-very expensive).

    I recommend a pressure pot or siphon fed gun. You can get really cheap ones from Harbor Freight. Make sure your pressure is at 35-45 psi at the gun tip. For the pressure pot, no more that 10-15 pot pressure is needed. You need good atomization or you can end up with porosity. The tip should be no less than size 18 on the siphon gun. You'll need lots of fluid coming out in order to get about 5-6 mils in each pass.

    Gelcoats usually run about $50-$100 a gallon. If you are going black, it will be closer to $100. One thing you need to know is black must be catalyzed at a higher percentage than light colors. Catalyze at 3-4% by volume. Catalyst comes in 1 gallon containers and usually runs about $25 a gallon. Clean up immediately with acetone. If you need to thin the gelcoat, reduce with about 5% styrene monomer.

    Brett
     
  15. Westies14

    Westies14 Master Member

    Trophy Points:
    2,580
    Hi GotMaul,

    The gelcoat was not intended to be the final exterior of the pack. The surface can only pull as smooth as the master, and the shell is to be painted when it is pulled from the mold. A brush on resin would be just as good, better even if it is an easier application and just as durable... I am "exploring my options!" Please send me some more info on the products that you used if you get a chance! Thanks Jose,

    -Douglas
     
  16. Got Maul

    Got Maul Official Licensee RPF PREMIUM MEMBER

    Trophy Points:
    1,980
    hey douglas, okay, I got your idea !

    If you are going to be painting over the gel coat, wouldn't you be defeating one of the main purposes of gel coating.

    As far as supplies go, the type of brushup resin I use is the 1638 or 1630 or Master Cast- all are the same thing, all can be had from any place that supplies this stuff. You might want to look up an FX place like F/X solutions (down here in CAli). The mudding process is a combination of Cabosil (dried silica) and Fiberglass Resin (which can be found in Home Depot or something place like it). The fiberglass can also be found there too.

    After that, there's not much to it. [​IMG]

    Jose
     
  17. kropserkel

    kropserkel Well-Known Member

    Trophy Points:
    706
    Now this is what I call contributing.

    Great information. Thank you very much.
     
  18. Got Maul

    Got Maul Official Licensee RPF PREMIUM MEMBER

    Trophy Points:
    1,980
    archive this * ! Good stuff from all around. I never knew about gel coating myself [​IMG]

    Jose
     
  19. Westies14

    Westies14 Master Member

    Trophy Points:
    2,580
    Jose,

    I'm not sure I understand what you mean? I want to use the gelcoat to have a hard and perfect surface layer on the casting... Am I missing something about the fundamental nature of gelcoats? From what I understand, the process you're describing would achieve the same surface. Would it be as hard and durable? Are you saying that this process is much less expensive than gelcoating, and gelcoat's finish is something that I should pay for if I'm painting it- that the rest of the properties will be the same fundamentally?

    Agreed, this is a great and educational thread. Thank you to everyone who's posted so far, and to those of you who have PMed with additional information!

    -Douglas
     
  20. kimncris

    kimncris Well-Known Member

    Trophy Points:
    931
    jose's method looks and works great! I have seen the finished pack- and it has a nice smooth gray resin outer layer and then a nice hard backing of fiberglass for strength!

    -cris
     
  21. Skyler101

    Skyler101 Sr Member

    Trophy Points:
    1,242
    You can prime and paint gelcoat right?

    I want to use it for undercut parts that trap bubbles...

    -Skyler101
     
  22. Lan Jenn

    Lan Jenn Well-Known Member RPF PREMIUM MEMBER

    Trophy Points:
    816
    Gil,

    Gelcoat can be painted but doesn't need primer. Just rough it up and make sure it is clean from release agents. The best and recommended paint for gelcoat is a catalysed acrylic urethane, single stage paint. I get mine from PPG and the finish is great. I did the entire bottom of a 28 foot boat with it 2 years ago. I am working on that boat again right now but not from paint problems. He keeps beaching the boat and * up his hull bottom. Even after 2 years if you weren't told it was paint, you wouldn't be able to tell. The PPG stuff is great.

    Douglas,

    If you are going to paint the surface, I would still gelcoat it or put a coating of good resin down and let it cure before any layup. The resins and products Nathan mentioned will work but you can also get some from distributors of composites materials that are a much higher grade. The main purposes of gelcoat are to protect the fiberglass as it is a much higher grade of resin, and for cosmetic appeal. Having fiberglass too close to the surface will ware it down and expose the fibers to the elements. Yes, even air is an element and will cause problems eventually. Water is the real problem. No other chemical on earth can do the damage to anything or corrode everything like water can.

    The Cab-O-Sil is an interesting approach. You must make sure, if you use this process, that it is mixed very well. Resin without the reinforcement of fiberglass is very week, especially for polyesters. It needs reinforcement. The term for fiberglass is FRP (fiber reinforced polymers/plastics). It includes all reinforced plastics, like carbons and Kevlar. Polyester has the lowest elongation of all resins, although you can upgrade to Isophthalic Resin (also a polyester) which is a tougher resin. When working with Cab-O-Sil, don't breath it. It's only purpose is for making paste like applications not for strength. If not done with attention, it will also trap air easily and that weakens the resin. If not done smoothly it will cause problems laying up against unlike a smooth coat of something that was sprayed first.

    Now all of what I have said is for industrial applications, but for all of it, it is fundamental to all areas of applications, even hobbies.

    Brett
     
  23. Double T

    Double T Well-Known Member

    Trophy Points:
    941
    Well, as Got Maul and kimncris can tell you, I've been learning a bit about the stuff over the past couple of months while working on Endoskeleton pieces.

    The stuff Jose is talking about is fairly affordable (about 65 bucks for a 1 gallon kit) and is really easy to use. Now, when it gets down to the specifics on what exactly it is, I couldn't tell ya. I just know it's a thick brushup resin, 1/1 activator/base, mix until it's grey, and pour in. Brush it up and around the mold, and keep working it until it thickens up and kicks, which on a warm day will take 5-7 minutes. Works really well, captures a lot of detail. If there are other products, I doubt I will ever try them.

    The cabo/resin mix, "mud".....I'm not quite sure what you mean by it being tricky. I fill a bucket partway with fiberglass resin, mix the cabo in cup by cup until it thickens. When I have it to the thickness I need, I seal up the bucket until I need it. Then I use it, kick it with the catalyst, and put it in my mold to round out 90 degree angles, fill areas that are difficult to get the glass down in, you know...essentially take care of the troublesome fiberglass areas. Never had any problems with it. Dries very strong. Don't think I'd ever make an entire piece out of it, but for filling areas and helping provide a sticky surface for your glass to lay on, it's really a lifesaver.

    Just always remember to wear your respirator! [​IMG]

    Tony
     
  24. Got Maul

    Got Maul Official Licensee RPF PREMIUM MEMBER

    Trophy Points:
    1,980
    Really interesting info Lann ! I always thought the main reasons for using Gel coating was for 1) layer before glassing 2.) cosmetic factors

    Great info ! So basically, if you want something to be immortal and withstand rainstorms and nuclear fallout, this is the stuff to go with ! Real interesting.

    As Tony touched on, the main reason for mixing Cabo with the fiberglass resin before glassing, is to get tough corners of the piece you are glassing up. If you try glassing up sharp corners, everyone will tell you,those * shards will only bubble up since they don't want to bend that way. Cabo/ Fiberglass resin has the great property of still being Fiberglass resin, BUT will stay where it is put. So what I do is stuff this stuff in the corners and small boxes...so when the glass is finally laid down, it falls over a moothen edged and not a hard one.

    Douglas, for your application there are a lot sharp corners and especially in teh cyclotron trench...I would highly advise using this stuff before glassing.

    Also, you can use either gel coating or brush on resin. from the sounds of it, brush on resin is a thinner than gelcoating, but I mean, are you really going to take your pack to the carwash ? I use the brush on resin to be outer coating to catch the smallest of details on my pack mold (even some I do not want caught !!! ). It is still strong enough to withstand my roughing it up as witnessed last night as I was cutting the poor thing up and even (get this) STANDING ON IT (don't ask me why, just had to do it !).

    In the end it's all up to you. I just wanted you to know that there was this other technique being used that dries faster and can get you to glassing a lot quicker But hey, if you want your pack to survive fallout, I am in complete support !

    Jose
     
  25. Lan Jenn

    Lan Jenn Well-Known Member RPF PREMIUM MEMBER

    Trophy Points:
    816
    Tony and Jose,

    Sorry I didn't read into what you are doing with the Cab-O-Sil. You are right about it being somewhat of a lifesaver. I also use it for the same purposes. I thought you were coating the whole surface with it. I should stop reading so fast once in a while.


    Brett
     
  26. Double T

    Double T Well-Known Member

    Trophy Points:
    941
    Hey Brett-

    No biggie, man! That's what all of us are here to do, right? Try to clear stuff up and inform each other!

    Tony
     
  27. yodaman

    yodaman Sr Member

    Trophy Points:
    1,231
    Archived...
     

Share This Page