gel coat problem

Discussion in 'Materials' started by harrier spiro, Aug 3, 2010.

  1. harrier spiro
    Joined: Aug 2010
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    Location: melbourne australia

    harrier spiro Junior Member

    hi guys have recently finished a mould for a 5.4 mtr boat everything seemed to go well until....:confused:

    tooling gel coat problem...was sprayed on in three wet passes to build up .8mm thickness with 30 mins breathing time in between in a temp controlled room of 25 degrees celcius with a pressure pot and a 2.5 tip at 55 psi air pressure thru the gun...2% catalist

    ok...all was going well removed the mould from the plug that all went well until we sanded the orange peel
    have wet and dried from 400grit to 2000 grit wet and and dry to what seemed to be perfection could see all the fluro lights around us in pretty much hd..

    ok now heres the problem after buffing and polishing it looks like it brought the orange peel back up from a distance????? on really close look it seems the gel coat has got tiny tiny creators and hills... that create the visual effect of orange peel????...ok i thought maybee i havent sanded proper so hit it very lightly with 200 again...could actually see the tops of the orange peel[or the visual effect} come off...buffed and polished again.....same deal

    very confused...any body come accross this b4? or can explain were ive gone wrong?..
    .not very impressed alot of work has gone into this project and disapointed to see less than a perfect glossy mirror finish...
    please help
  2. tunnels

    tunnels Previous Member

    These creators are tiny bubbles in the gel coat on the first coat .
    Causes mainly are The wrong catalyst , gel coat layer to thick , catalyst ratio to high , initial coat sprayed on with high pressure and the force of the air/spray moving the gel thats already on the mould . Because this also causes the pigment particals to separate from the clear Gelcoat it is held in suspension in .
    Thick is not best !!! :confused:
    When you catalyst gelcoat the reaction starts to gas and produce microscopic bubbles of gas , there bubbles are possible what you are exsperiancing and the more you sand the worse it could get . Its impossible to sand them out as they could go quite deep and even to the very back of the coats . Also in reality if you had not sanded the mould Those tiny bulles would only be visable but thats all because the bubbles were completely closed so would have had a clear side that you were seeing . If you had buffed lightly and waxed they would never have shown up on the product you made , by sanding you opened the bubble and now you have a hollow !! this will be there forever ! need to find a hard mould release wax to help fill the voids and stay there .

    When spraying you need to dust a very fine coat over the area first alowing the gas to surface and bubbles to burst , then a minute later another dust coat but a little heavyer than the first , you need to have and use an wet surface thickness gauage and have a wet film or 20 thousands of a inch . when hard this will have shrunk to 15 thousands of a inch .
    The viscosity of the gel is another factor in all this along with the temprature and = the gel time of the gelcoat . Slower ,thinner, catalysed to the manufactres recomendations gel coat , a lot of this is the operators problem and not haveing the product knowledage . Combine all this and you get what you have got !!
    Gelcoating is a art form and takes a very knowledgable person to completely understand all thats going on and the potentual problems and the causes .

    With the time lag between each coat its a wonder you didnt get lats of other issues as well , I question the catalyst raito and type of catalst used ?? In that time the first coat should have gelled !!

    When you make your artical out of the mould you will need to 1200 grit sand and buff/polish each time .
    I prefer tonever sand a new mould just cut/buff and polish only then wax and for the first 2 or 3 pulls out of the mould use PVA release wax and wax each time till the mould is broken in and then very lightly wax each time from then on !!

    Check this and see if you get the answer --
  3. tunnels

    tunnels Previous Member

    Something to look at
    Another place to help identify you problems :confused:

    Applications Guide

    This site has some good pictures for you !!:eek:

    Just remember if you never have problems to solve you will never learn anything !!
    The problems you have is the same the world over !! and even companies that have been making boats for a long time still dont understand what causes most of these problems !!
  4. tinhorn
    Joined: Jan 2008
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    Location: Massachusetts South Shore.

    tinhorn Senior Member

    Sounds like alligatoring to me. Y'see, when you apply a layer of gelcoat, it has to cure THOROUGHLY before adding resin or--worse, in my experience--more gelcoat. Sounds like your first layer started to cure, then you sprayed the next layer which caused alligatoring. Tsk, tsk.

    Your entire gelcoat layer should go on in ONE operation. You want 18 mils in three passes. Then you go find something else to do for the rest of the day, like dope-slapping the guy who told you to wait 30 minutes between passes.

    Because you managed to force gelcoat through a 2.5 tip, I'm guessing you thinned it a lot. Bummer. Even worse if you thinned it with acetone. Find a primer gun with a huge tip. Seems I bought mine years ago from some elcheapo online tool site. Seems the tip was 3.5, but it was a long time ago.

    You should only thin gelcoat with styrene. (It's okay to use acetone, but never admit it.) I used about twice as much acetone as catalyst, so that would be 4-5%. Shot it through a primer gun out of a pressure pot.

    I also made my first layer of 'glass as hot as I dared so that it would kick before it could soften and alligator the gelcoat, just in case.
    1 person likes this.
  5. tunnels

    tunnels Previous Member

    See what you have then you could get the answer !

    Before you get to far down the track look at what i have posted and identify what you have . then we can work on the answer to maybe fixing it !!:confused:
    Theres also a possability of more then one problem !!
    There are no pictures or photos so we are all stabing in the dark .
    What i wrote are some of the most usual things that most every one gets if you dont spray gel coat for a living .
  6. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    From your description of it looking like orange peel (returning), it sounds like either the skin coat or the gel coat isn't fully cured. When you sand it smooth it looks fine, but the heat from buffing will cause further curing and shrink, the shrink causes the orange peel.

    Now if you see tiny bubbles or pin holes in the surface, then its porosity, not much you can do to fix it other than refinish it.
  7. tunnels

    tunnels Previous Member

    Thinning gel coat !!! there lots a theorys on this subject , Personally i always use acetone !! Reason is because it thins and mixes quickly but there are limitations as with all things . After it leaves the nozzel of the spray gun and heads towards the moulds surface carried in a stream of pressurized air 80% of it is evapotared into the air and a good 10% of what gets to the mould also evaporates out of the gelcoat during the times its sitting there waiting for the gelcoat to gel .
    Same principle when you use Styrene BUT the evaporation rate is much less so you get a softer finished gel on the surface of your product .
    The company that supplied all the gel coat for the boats we were building would pre mix up to 5% of acetone with the gel for us . The chemist totally agreed that acetone was a better choice than styrene.
    Another company i worked for always used styrene and the mould always went dull very quickly, but once we changed to Acetone the shine stayed longer and we never had to wax the moulds as often . Even doing mould or product repairs i always use acetone in the gel and blow lots of air across straight after the spraying has been done .
    This is only my personal veiws and exsperiances , Styrene causes Gel to yellow quickly in the nz sunlight , we have one of the highest UV sun light in the world .
    When all things are done correctly in the right order and the right quantities of products are used everything works like its surposed to and you never have any problems !!!
    Most gel coat problems are a dirrect result and or ignorance of the operator thats spraying the gel, Very little is the fault of the product its self . :confused:
    The nozzel size has never been a problem ,be it a paint gun or a gel coat gun! as long as its on a pressure pot the flow pressure to the gun can be adjusted to suit the conditions of the day when you are using it .
  8. harrier spiro
    Joined: Aug 2010
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    Location: melbourne australia

    harrier spiro Junior Member

    No thinners was added the correct amount of catalist was added as well and the dwell time between coats was sugested by our fiberglass/ gelcoat rep
    to let it breath ... How wrong he was...
    Anyways there is a couple of diff problems I can see now ranging from entraped gasses to tinny pin holes to divets and an overall orangepeely look from a distance after buff and polish the first two passes were very thinly atomized can't understand why it went so pear shaped when we did everything to manufacturers spec... Except now looking back the breath time was well in access.... As well as putting too much on for the third pass..
    Hmmm this will be a lesson that I won't forget...
    Anyway... Is it posible to wet rub to 2000 grit aply the release agent and pull a. Few boats out b4 going back and possibly making a new mould off one of the hulls produced?...not likeing this idea but it might be the only thing I can do for now.... This hurts...
  9. tunnels

    tunnels Previous Member

    Sales men are there because no one else wants them and they like to look important when in reality they know very little.
    The orange peel is the look or is it rough like a orange skin??
    If it was rough it was one of two things , one the gel was not proprely cured and second the brew of glass over the top did not go hard quick enough and the resin /styrene attacted the undercured gel coat !!
    Catalyst needed to be higher !!
    Did you see the sites i posted with pictures to help you identify the problem and has a list of causes with it !!!
    Lessons in life never come cheap !!:D
  10. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Resist thinning gel coat if at all possible, because whatever you add will degrade the product.

    The first layer (every layer for that matter) needs to form a continuous film that flows together and levels, no fog coats, depending on the gel coat this means the film needs to be from around 6 mils for standard products and up to 11 mils for low VOC products. Use a mil gauge to ensure its correct. If the gel coat is applied too thin it tends to trap air because too much styrene is lost and this leaves the surface rough and dry. When the next layer is applied the rough pitted surface can hold air resulting in porosity. On the other hand if you apply too much at one time the air can't escape which can cause porosity also. On a mold you normally apply much more gel coat than on a part, 30 mils and up isn't uncommon.

    If the backside of the gel coat is rough with orange peel and pits, you are more likely to have orange peel issues on the mold surface even after sanding and buffing. Typically the surface will distort after a few parts and need to be sanded and buffed again.

    On small parts the gel coat should be left to breath for a couple of minutes between layers, on larger parts by the time you’ve finished the first pass you can start over and put on the next pass.

    As for going to 2000 grit paper, it sort of depends on the gel coat, the buffing compound, buffing pad and quality of the sand paper.
    On some gel coats you won’t see a difference after 1200, so going further won’t help. The buffing compound needs to be a very fine grit too, a coarse compound won’t yield a high gloss, you need to use the right buffing pad with the compound too. Uniformity of the grit on the paper will also affect the result.

    If the surface of the mold is poor you will need to rework the parts made from it and going to 2000 grit on a porous mold won't help much.
  11. harrier spiro
    Joined: Aug 2010
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    Location: melbourne australia

    harrier spiro Junior Member

    To the touch it's hardly noticable but if you go over the suface with 2000 grit wet rubing you can see th tops coming off the orange peel ... So going off that I think you are bang on with the bleeding thru of the styrene... Thank you for your help very much appreciated I'm by no means an expert but I've gathred alot of information and poblem solving info for later use I'm pretty stuborn and will not give up until I can reach what I'm after.. Saying that if you could post up in your opinion what the proper steps would be from the start to skin layer I'm petty confident there after that our practices are pretty spot on haven't experianced any other problems in the past in the lay up that's all gone smoothly... Thanks again your knowledge is beyond what I've come across so far here in aust
  12. tunnels

    tunnels Previous Member

    Any chance of getting some one with a good camera to take some detailed pictures ?? It sure would clear up a mass of speculation :confused: .
  13. harrier spiro
    Joined: Aug 2010
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    Location: melbourne australia

    harrier spiro Junior Member

    Yea I'll get on to it this afternoon ;)
  14. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    .....just my two penneth worth, I would prefer that the gelcoat never be thinned, we have only ever had problems the times the fellas decided in their wisdom to thin the product. Styrene certainly is the solvent of choice, but tunnels is also right that acetone does cause less problems when used instead of the styrene, , so I would follow the fella that does the work the most. I have only built dozens of boats, not hundreds, in GRP, so I am sure that anyone that has done that many (try tunnels for instance) certainly would have sorted out a lot of the little things that stuff up. for reps, never trust a white man.......I saw a mould gelcoated in China that had no catalyst added, I questioned the gauges when he was "demonstrating", he went on as if he knew all, but we soon found out he had NEVER used the GlasCraft gun at all that he was trying to sell the yard....
    well it took nearly a week to fix the poor mould again to be able to use it, plus all the waxing over and over again.

  15. tunnels

    tunnels Previous Member

    Me i cut my teeth on Venus guns a lllllooooonnnngggg time back . Not completely fool proof when some one forgets to put the pin in the catalyst pump push rod . To get uncatalysed gel off and mould mix a hot brew of resin complete with extra cobalt and give every one a big paint brush and go like hell , work the brush round and round and do the whole lot from gunwhale to gunwhale sten to stern !! . In a couple of hours it peels off and if you lucky there could be just bits here and there that need to be redone !!,then do the same thing again all over again and its completely clean and a good wax and all is ready to go again . only took 3 guys 4 hours to do a 36 foot launch hull once ,There is no other way to do it !! Ive seen people try and wash it off with styrene and a mountain of rags what a mess it made , nothing like uncataysed gel coat !! gets on everything !!!. A total waste of time .:D

    Where in China were you ??
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