alistairolsen
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| posted on 16/3/10 at 10:12 AM |
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GRP layup without gelcoat
I dislike gelcoat with a passion due to it being brittle, non structural, and its poor response to UV radiation and given that I need to paint the
alloy parts of the car anyway and to ensure a colour match will probably end up overcoating the car, can I dispense with it entirely?
I read somewhere many moons ago that model yachet builders were laying up hulls in mould sprayed with primer so when removed from the mould they were
l;eft with a primed surface?
I cant help thinking that even a thin layer of resin laid on instead of gel (which iirc is just a thickened resin) to prevent fibres on the surface
should be enough and then one could flat back, prime and paint?
Cheers!
My Build Thread
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coozer
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| posted on 16/3/10 at 10:27 AM |
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Not sure myself but how about the initial lay up with tissue? I was thinking about that myself for the impending attack of my Jago
1972 V8 Jago
1980 Z750
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StrikerChris
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| posted on 16/3/10 at 10:30 AM |
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I was under the impression the gelcoat was there to seal the fibres should you need to flat it etc.an exposed fibre could let water soak in and cause
issues?Just guessin,suppose neat resin would do the same.I used a thin layer of gelcoat when making my nosecone and just painted it on top,virtually
no prep work needed once it was out the mould,just a 5 minute rub with 1000 grit to key the primer....
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alistairolsen
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| posted on 16/3/10 at 10:35 AM |
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Thats partially its purpose, it also normally provides colouration, partial uv protection, abrasion resistance etc. If you are going to paint it
however its usefulness seems limited so if one sealed fibres by applying a think coat of resin to start with (and actually rolling it in properly
which seems commonly overlooked.....) Im wondering if it would be ok?
My Build Thread
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twybrow
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| posted on 16/3/10 at 10:44 AM |
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quote:
Originally posted by alistairolsen
I dislike gelcoat with a passion due to it being brittle, non structural, and its poor response to UV radiation and given that I need to paint the
alloy parts of the car anyway and to ensure a colour match will probably end up overcoating the car, can I dispense with it entirely?
I read somewhere many moons ago that model yachet builders were laying up hulls in mould sprayed with primer so when removed from the mould they were
l;eft with a primed surface?
I cant help thinking that even a thin layer of resin laid on instead of gel (which iirc is just a thickened resin) to prevent fibres on the surface
should be enough and then one could flat back, prime and paint?
Cheers!
I guess you have worked with some pretty pants gelcoats then... I spenmt some time working for the UK largest yacht manufactuerer, looking
specifically at gelocats, UV, weathering, impact etc, and I can tell you they do help. It is also about what you back the gelcoat with. As you are
painting anyway, you are right, therte is no point using gelcoat, but as chris says, you don't want to rub through into the fibre, so a good
layer of resin into your mould should suffice...
Primer is typically dissolved by most resins, so check compatability if you do want to go down the route of preapplying primer - personally, I would
do it afterwards......
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alistairolsen
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| posted on 16/3/10 at 10:55 AM |
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Yeah on something with a stiff substrate they are fine, and they do help to save the layup underneath, but they are fundamentally inflexible, so a
thickness of gelcoat applied to something as light a construction as a locost bonnet is bound to crack where paint wouldnt. As far as UV goes dark
colours tend to go lighter and chalky with time (as do light ones but its less obvious!) There is big money in "detailing" old hulls!
If there is no major advantage to preapplying then I wont, but if you reckon a light coat of resin would be enough to seal the fibres then that would
be a tempting proposition.
My Build Thread
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smart51
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| posted on 16/3/10 at 11:33 AM |
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What about a spray filler? I've used a spray polyester filler recently, though out the outside of GRP prior to paint. Spray it on your mould
and lay up on top of that. Test a small samples first!
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twybrow
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| posted on 16/3/10 at 11:41 AM |
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^
It would dissolve in the styrene (assuming you are planning on using polyester resin/gelcoats....
One big benefit from using gelcoat is the repair side of things - keep some original hel, and you never have issues with star cracks, chips, scratches
etc... Agree, Locost bodywork is thin, so the gel makes up a higher percentage of that thickness. Bulk up you layup, or put the gel on thinner - try
spraying it perhaps? Overly thick gelcoat causes all sort of issues to quality.
As for reworking boat hulls, yes lots of money - two of my mates used to do it in their spare time, and could easily make £800/day each with nothing
more than a bucket, a polishing mop and some Farecla pastes...
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alistairolsen
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| posted on 16/3/10 at 11:52 AM |
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quote:
Originally posted by twybrow
^
It would dissolve in the styrene (assuming you are planning on using polyester resin/gelcoats....
One big benefit from using gelcoat is the repair side of things - keep some original hel, and you never have issues with star cracks, chips, scratches
etc... Agree, Locost bodywork is thin, so the gel makes up a higher percentage of that thickness. Bulk up you layup, or put the gel on thinner - try
spraying it perhaps? Overly thick gelcoat causes all sort of issues to quality.
As for reworking boat hulls, yes lots of money - two of my mates used to do it in their spare time, and could easily make £800/day each with nothing
more than a bucket, a polishing mop and some Farecla pastes...
Yeah, the rework and colour matching is good, but if youre only having to do it because of gelcoat cracking then its counter productive. I think Ill
go with a resin layer to seal the fibres and paint as I can always respray panels but matching a paint colour to the gel initially is a pain, besides,
the gel is needless weight.
Yeah, I never got that well paid for it, but then I wasnt in the right place. lots of work around though!
My Build Thread
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twybrow
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| posted on 16/3/10 at 12:14 PM |
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The reason for the repair is stonechips. this will affect paint and gelcoat, so I don't think it is counter productive. you can apply gelcoat as
a spray no problem. In fact, you could spray your gel directly into the mould, and layup from there - now that would save a load of time and effort.
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Bobbyp
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| posted on 16/3/10 at 12:41 PM |
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Sorry for the slight thread hijack. I am looking to take a mould from my cars existing GRP front end (its a Morris Minor) to make a lighter version.
The front is sprayed in cellulose and I know that the styrene in the polyester resin will make a mess of this. Is there anything I can prepare (ie
spray on top of) the existing bodywork that wont react with the polyester resin? I guess that 2k paint would work, but would rather steer clear of
that an all of its safety issues. Any other suggestions?
Thanks
Rob
[Edited on 16/3/10 by Bobbyp]
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twybrow
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| posted on 16/3/10 at 02:04 PM |
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A well applied wax release agent will help stop this, but you can't guarantee it wont show... You could put a physical barrier, like cling film
down, but again, I would test your resin on it first, as it may well dissolve....
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Steve Hignett
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| posted on 16/3/10 at 02:11 PM |
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I've only scan read other people's replies, but I'd have to say that I would still use a gel coat, BUT simply apply it thinly rather
than a thick layer!
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twybrow
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| posted on 16/3/10 at 03:31 PM |
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quote:
Originally posted by Steve Hignett
I've only scan read other people's replies, but I'd have to say that I would still use a gel coat, BUT simply apply it thinly rather
than a thick layer!
Stop copying me! I suggested spraying the gel directly into the mould tool (thinner layers etc)... Should be the best all round solution as far as I
can see!
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clairetoo
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| posted on 16/3/10 at 04:40 PM |
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Resins is slightly acidic so that it bonds well to the gel coat - without the gel , it will bond quite nicely to the mold.........no matter what
release agent you use .
Its cuz I is blond , innit
Claire xx
Will weld for food......
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skinned knuckles
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| posted on 16/3/10 at 05:39 PM |
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quote:
Originally posted by clairetoo
Resins is slightly acidic so that it bonds well to the gel coat - without the gel , it will bond quite nicely to the mold.........no matter what
release agent you use .
i was just about to say that too. the gelcoat works well with the release agent to help release the mold, the fact that it leaves a nice finish and
can be coloured is simply a bonus
A man isn't complete until he's married, then he's finished
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BenB
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| posted on 16/3/10 at 05:42 PM |
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Gel coat is easy to use but it's not totally necessary. After all, they don't use it for carbon pimpiness. Okay that's epoxy (or
should be!!) but still... same difference.
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Fred W B
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| posted on 16/3/10 at 06:21 PM |
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I have read a procedure where Durabuild surfacer primer is used by spraying it into the mould and then laying up on the back of it, to give a released
part that is already prepared for paint.
Cheers
Fred W B
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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iank
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| posted on 16/3/10 at 06:25 PM |
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I've seen a number of kits (Mini Minus) for one produced without gel-coat. Bit disconcerting as they are translucent before paint.
Don't know if they have to do anything special to the mould to make release easier.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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clairetoo
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| posted on 16/3/10 at 06:39 PM |
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quote:
Originally posted by iank
I've seen a number of kits (Mini Minus) for one produced without gel-coat. Bit disconcerting as they are translucent before paint.
Don't know if they have to do anything special to the mould to make release easier.
Far more likely that they were made with clear gel coat - some like to work like that , but I find it very difficult as you cant easily see any missed
or thin areas in the gel .
Its cuz I is blond , innit
Claire xx
Will weld for food......
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hicost blade
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| posted on 16/3/10 at 07:26 PM |
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quote:
Originally posted by alistairolsen
I dislike gelcoat with a passion due to it being brittle, non structural, and its poor response to UV radiation and given that I need to paint the
alloy parts of the car anyway and to ensure a colour match will probably end up overcoating the car, can I dispense with it entirely?
I read somewhere many moons ago that model yachet builders were laying up hulls in mould sprayed with primer so when removed from the mould they were
l;eft with a primed surface?
I cant help thinking that even a thin layer of resin laid on instead of gel (which iirc is just a thickened resin) to prevent fibres on the surface
should be enough and then one could flat back, prime and paint?
Cheers!
The RC boats would have been made with epoxy......polyurathane (spray) paint works very well when sprayed into the mould first and laid up on with
epoxy.
I am going to try this with polyurathane varnish and my carbon mods fun kit tomorrow night.....wish me luck
[Edited on 16/3/10 by hicost blade]
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Fred W B
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| posted on 17/3/10 at 11:38 AM |
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Found a bit of info as below
Cheers
Fred W B
IN-MOULD USE OF DURABUILD SURFACE PRIMER FOR POST- PAINTED PARTS
Durabuild Surface Primer has been successfully used for years as an in-mould gel coat replacement for post-painted parts in the automotive
aftermarket. Recent successful conversions from gel coat in the transportation and automotive industries have shown that this is a viable and proven
concept. Note the following benefits versus gel coats:
Porosity-Free Surface
No post-priming prior to top coating is necessary.
Labour and Material Savings. The de-moulded part requires one sanding process. No post-priming or primer sanding is necessary. An entire finishing
step is eliminated.
Smoother Surface Profile
High gloss finishes actually lay out better over the Surface Primer vs gel coated / primed substrates
Higher Heat Distortion Surface
Reduced post-curing (shrinkage) of primed surface vs gel coated surface;
very important if the top coat is elevated temperature cured.
Higher Elongation Primer Surface Improved impact resistance vs gelcoated surface.
Lighter Weight Products
Spray 200-300 microns thickness of Durabuild Surface Primer vs 400-500 microns thickness of gel coat.
Cost Differential Reduced
Less of the higher cost Primer is used vs gel coat.
APPLICATION
The Durabuild Surface Primer is sprayed into the mould as is the gel coat - catalysation is @ 2% with MEKP50 catalyst. The lamination process begins
within 20-40 minutes depending upon how thick it is spayed and the ambient temperature. Heated curing generates faster primer flash-off and quicker
lamination
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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Neville Jones
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| posted on 17/3/10 at 08:59 PM |
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That's a good sales pitch from Durabild, but it's still a resin system( filled vinylestar) applied in place of a resin system(gel). The
only difference being that Durabild Primer has a filler added(talc or similar), so you just sand and paint. The big clue is in the '2%
mekp'.
Good practice would still be to use a primer, for a proper job. All been done before, and the mistakes learned from.
Durabild, and the Scott Bader equivalents and the Gloss coats that go with them are brilliant products, but don't expect miracles from them.
Nev.
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coozer
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| posted on 17/3/10 at 10:04 PM |
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Bit of a hijack here, I'm going to be needing some flat FG panels for the floor in my Jago. I was intending using a piece of glass as a
mould/surface and don't really need gelcoat as carpets will be on top and underseal underneath. Once I have all the panels in place I will be
glassing over them to form a single piece floor pan.
Whats the best way to produce panels and release them from the glass??
1972 V8 Jago
1980 Z750
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Triton
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| posted on 17/3/10 at 11:00 PM |
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Dude If you lay glass on glass so to speak it will release no bother but just in case wax it first.
Mask off the size you want then lay up the glass, the tape will be highlighted on the laminate once released so you will have a guide to cut
to...simples
As for not using gel as going to paint the part made thats a bit daft as you will rub thru into the fibres..gel is easier to flat down than resin
anyway.
Some folk specify a ral code for their parts then flat it then use some wobbly laquer to give a groovy finish. Much cheaper than a full spray job as
you get the grp supplier doing the base colour..
Spraying gel can give some groovy effects too especially if you use more than one colour and do it while still curing as they blend and do spooky
things, even dragging a brush through it all after spraying can have weird effects...
My Daughter has taken over production of the damn fine Triton race seats and her contact email is emmatrs@live.co.uk.
www.tritonraceseats.com
www.hairyhedgehog.com
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