Gel Coat reactions

Discussion in 'Boatbuilding' started by Leon01323, Jan 24, 2011.

  1. Herman
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    Herman Senior Member

    You said the wax was going all sticky when wiped with acetone. What was going on there?

    The wax should be applied as thin as possible, a small tin of wax can last a very long time. If your moulds are good, as in a shiny surface, then you can apply a layer of wax (Meguiar 8, 16, 88 or 87). Follow the directions which if things went well were included in a small booklet taped to the can. (brown paper).
    Otherwise ask for it. It goes something like:

    -apply wax as thin as possible.
    -leave for 2 minutes
    -"break surface" by wiping with a cloth
    -leave to cure for 15 minutes
    -use clean cloths to polish the mould to a high shine
    -let cure for 1 or 2 hours (do not remember)

    -repeat above steps 4-8 times. After this, you can maintain the mould with one or 2 new applications of wax. You will get a feel for it.

    On the part:
    Try and get a sanding gelcoat, this could be useful for this part (I presume it gets sprayed after installation on the car). Ask for brushable gelcoat, and brush it on in the recommended layer thickness. Check this thickness with a wet film thickness gauge. Your supplier should give one to you, they cost near to nothing.
    Brushable gelcoat is slightly more forgiving than sprayable gelcoat, this should help you. After the gelcoat has reached enough cure, you can laminate your reinforcement behind it.

    Above directions should quickly generate commercial quality products. After mastering this, ask your supplier for a sprayable gelcoat, and experiment with that. You can use a normal spray gun for applying it, although it is a bit cumbersome. Clean it immediately after spraying, you can use aceton for this without any problem. (make sure the seals can handle acetone, or replace them with viton seals)

    Moulds with deep cavities (boat shaped): put them on their side after gelcoating, so the styrene fumes can flow out. Otherwise the gelcoat might not cure.
     
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  2. Leon01323
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    Leon01323 Junior Member

    Thanks Herman some very good stuff there. Not sure what is going on with the wax but I've not risked cleaning them since with acetone invade it ruined them before I made a piece.

    I found info on the wax and followed it as I thought it said but will have another look. I'm learning as I go so it is slow progress but getting there I think.

    Thanks guys
     
  3. Herman
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    Herman Senior Member

    After the mold is waxed, do not touch it with acetone anymore. Acetone can be used to remove the wax completely (still a tedious job).
     
  4. Leon01323
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    Leon01323 Junior Member

    Ah that would make sense. Yer not tried that one since I did it the first time.

    Thanks
     
  5. rxcomposite
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    rxcomposite Senior Member

    You have some problem areas. Those screw holes have sharp edges and the fiberglass mat will not conform. It will either be resin starved areas or void areas.

    After the gel coat has cured (tacky enough that you can touch it with your finger but the color will not transfer to your finger) apply a mixture of bog (resin + cotton flox,or micro baloons or cabosil). The bog mus have the consistensy of a paste. Apply with a popsicle stick or your fingers. This will kill the sharp radii and will enable te mat to conform. The popsicle stick end or your fingertip is a good radius. Also, no scissors at this point. Just tear the mat so that the ends are frayed and will mesh easy. If the mesh becomes thin, add an overlap with another torn patch.

    The screw points are stress areas and most likely to break first. I usually double the layers here or add a WR reinforcement. Just a patch on each area.

    It is also a good practice to cut the excess part with a sharp knife or spatula while the laminate is "green" (cured, but still soft enough to trim). Saves time on grinding and itchy fiberglass dust. With practice, you can trim accurately.

    Beause the parts are small, I usually use 2 layers of CSM 300 plus a WR 450 on patches. If you want it thicker, CSM 300 first, CSM 450 second, the WR 450 for patches. Experiment on what is acceptable in the market. Racing parts are so thin because of weight requirement but cost more. They have the money to pay for it anyway. That is one avenue for you. Commercial parts need to be thick to be perceived as good quality and has to be "cheap".

    You migh want to "peel ply" the inside for a good quality smooth finish. But this will add a little to the cost.

    Herman is spot on with a sanding gel coat. It is supposed to be cheaper. You said you are going to prep the part anyway by sanding it before painting. No need for tough and glossy gel finish. Brushable gel coat is good. Saves on electricity.

    Your part is an aesthetic application. Look for "Ortho resin". It is much cheaper than "Iso resin". Both are polyester resin, Iso is just a better grade.
     
  6. Herman
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    Herman Senior Member

    Or in the UK DCPD resin, which tends to be cheaper even, with better chemical resistance, and better final cure.

    For these parts I would not bother with peelply on the inside. For for instance a bonnet (for the US guys: a hood) I would probably do so, especially if you have to glue or putty in the inner reinforcing part (you can use polyester glue for that, but I would opt for MS Polymer putty, cheap, 1 component and has a dampening action. (way off topic now)

    Even if the parts are to be sanded, the surface of the mould should be top class. This prevents a lot of problems with demoulding. (you can easily pop the parts out, painless job)

    Good sanding gelcoat is Nord Composites GC514 (hand) or GC511 (spray). Ask the UK rep for Nord Composites for these numbers. Both are othoftalic, and should be sprayed (in the cars colour) for best protection.

    The reinforcement hints and the bubble prevention tips by RXC are good, follow them. This will give you top level parts.
     
  7. Leon01323
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    Leon01323 Junior Member

    Ah awesome stuff that is such good info that I've been after for ages. With the screw holes and the sharp bits I've been using a cheap body filler which I did apply with my finger to take the edge off because like you say I've had problems bit the resin leaving air bubbles and this lead to the gel coat cracking after. Since I used the body filler not had that problem at all. I will ask what type of gel coat I have as I don't know if it is brush on or spray on. Gunna have a look for these types of gel coat and resin.

    Once again thanks guys the info is priceless.
     
  8. rxcomposite
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    rxcomposite Senior Member

    Herman,

    Is the GC514 something you sprayed on after the part is finished or a replacement for regular gel coat?

    I used to use a gray sanding gelcoat before (forgot the brand) which I spray in lieu of the regular gel coat. Comes out smooth and glossy after demolding but easy to sand after. The tech rep says it is regular gel coat loaded with microbaloons.

    Is it the same stuff in terms of mixture, or is it a different mixture nowadays?
     
  9. Herman
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    Herman Senior Member

    It is the same stuff. It can be used as a regular gelcoat. Very handy for car parts that need adjustment, sanding, etc.

    You could use it as a topcoat as well, by adding some parafin.
     
  10. tunnels

    tunnels Previous Member

    Sounds like fish eyes its called , Little like painting over silcone !!
    When i worked in Tahiti we used Silicone car wax as a mould release , worked a treat!! The trick was to use multilays of fine spray over the top untill it accepted the correct amount and thickness and it came out perfect everytime . It happens if you freshly wax a mould and polish and try to gel straight after as well !!. Try spraying a thinned coat of PVA release agent over the top and let it dry!! Thin the pva with water! yes water and thats all !!Ratio 60% to 70 % water the rest PVA , Spray very very lightly and blow it dry with the compressed air !!, Trick is if you can see it on the moulds surface you have to much on . Other trick is thin coat is best !!!!
    The pva acts as a barrier between the wax and the gelcoat . Simple AH !!:confused::D;):):p
     
  11. Leon01323
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    Leon01323 Junior Member

    Ah that makes sense.. i would not really fancy spraying pva over the wax all the time..

    can i not just wax a piece and then buff it off leave it for a while and then spray on the gel coat... you must obviously be able to get around the alligatoring.
    ;)
     
  12. ondarvr
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    ondarvr Senior Member



    Alligatoring is a completely different issue and is totally unrelated to what's been discussed so far.

    The situation Tunnels described is a frequent issue we run into in the field, a company uses a product not designed for a purpose (this time a silicone auto wax used as a mold release) thinking its the best way to go either due to its availability or its low cost. Then they need to dance around other issues and end up spending more time and money building the part with their low cost substitute product.

    A mold release wax would not need PVA, nor would you need to apply mist coats of gel coat to build it up to the correct thickness. Mist coating gel coat, or even applying layers too thin can create problems in the finish, these problems don't always show up right away, but can in the future.

    Mold release wax is easy to buy, is low in cost and can be purchased almost any where in the world, worst case you order stuff like this from the states and need to wait for it to show up. My distributors have locations all around the world, including Asia, plus they load shipping containers with products that are sent directly to larger customers.


    Yes you can apply the wax as per the directions for that product, then apply gel coat directly over it with no fisheyes or other issues, its done thousands of times per day all over the world.
     
  13. ondarvr
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    ondarvr Senior Member

    While they could use micro-balloons in a sanding gel, they aren't the norm, typically talc and a couple other low cost fillers are used. Micro-balloons can separate out of the mixture and float, needing frequent mixing. Sanding putties do use them though. Most sanding gels are ISO's and since they don't need to have any UV resistance they can be designed for a little more flex to resist cracking.
     
  14. tunnels

    tunnels Previous Member

    You are a little confussed here !!
    As long as the mould has been waxed pva can be sprayed to help prevent the fish eye effect when you gelcoat !!!OR when you wax allow 4 hours or more before you try to gel coat over the waxed surface !!!:confused:

    Alligatoring is something else !! Its usually caused by slow gel coat undercured and slow resiin used to glass the first layer onto the gel coat. :?:
    Its the reaction of the styrene in the resin attacking the gel coat and acts like paint stripper .:eek:
    Something completely differant , dont be confused between the two !!!they are not the same :(

    Gel coat needs a minimum of 1.5% catalyst to go hard and semi cured for 8 hours , the resin for laminating on your first skin of glass needs to be gelled in 20 minutes or even less if its possible .:) from there on out you can do what you like , becasue you have sealed the gelcoat with a layer of glass.:p

    Thats as simple as i can explain this :D:p

    Just as a Matter of interest== A company i worked for in Brisbane never had any wax in the factory !! we used PVA for everything !!
    They bought pva in 20 litre pails and mixed 60% water with it !! had a spraygun set up hanging on the wall , clipped it on a air hose at max pressure and sprayed pva!!, then blew it dry with the compressed air and gelcoated!!, all happened within minutes !!!, the time i was there we never had one single gel coat problem, ever !! 90% of the time the pva comes off with the product and because it easy to wash off with water its clean and easy to use . Theres a lot of funny thoughts about PVA and how it should and shouldnt be used, but its save my *** many times believe me . Its wonderful stuff !!
    When its sprayed correctly its a barrier coat mico thin and you should not be able to see it !!! If you can see it you have to much on !!! Makes you thing dont it !!! spend hours or even days rubbing multi coats of wax on a mould of just one coat of wax and pva and dry and into it !!
    I love showing guys where i work how easy it is to use and how clean non skid pattern on decks always comes out each time and its never got wax to be cleaned out .Its like all things !!we should never stop learning ! took me more that 10 years to see it for myself and be totally convinced . Have handed this on in a lot a places iv'e worked since then !!.
     

  15. rxcomposite
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    rxcomposite Senior Member

    Thanks for the tip Ondarvr. Microbaloon is sometimes hard to get so I am looking for a substitute.
     
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