Epoxy repelling on mould


Epoxy repelling on mould
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AWOL
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AWOL
posted 7 Years Ago HOT
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Hey Guys,

We're playing around with a few moulds at home (Australia) but are having a consistent repelling issue from the Epoxy when we go to lay our carbon (240gsm 2/2 twill)
Pretty much pulling our hair out, we're convinced it may have something to do with our moulds but thought we'd seek opinion from the global community.
We're wondering if it is because of a polyester gelcoat mould vs epoxy problem? 
Anyway - here's what we have;

Mould build - the moulds always seem to be a good representation and quite solid
Release waxed mould - 5 times
Laid down polyester gelcoat (waited 24hours)
Laid down 1st lightweight fibreglass adhesion coat (waited 24hours)
Laid down 5-6 heavyweight fibreglass layers
Wait 2 days - pull mould - reverse mould looks great, detailed representation

Laying Carbon - temperature is approx 20-25C
Waxed mould - 5 times, waiting between coats
PVA release agent - light coat - wait 30 mins til applying epoxy 
Epoxy is West Systems with 205 hardener 5:1
Yet when we go to brush on epoxy it repels, ie doesn't seem to want to stick to the prepped surface

Note: when we skin items we have no issues with the epoxy

We're still noobs in this hobby, so will appreciate any input

kind regards
Justin
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AWOL
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posted 7 Years Ago HOT
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Dravis - 3/5/2018 5:00:57 PM
Hi!

I used to do hand  wet-lays with West Systems 105 and they never turned out well without vacuum, especially on moulds with a lot of contours like yours, 105 is simply too runny for that! (too low viscosity)

All surfaces that are  not almost horizontal will have the resin running off them and pooling in the low areas, even when laying up one layer at a time and. I do not think you will ever get a good result without vacuum bagging it.  where the resin runs off, there will be voids in the fibre, when cured these will not really let new resin bond to them.

You could try to use som way of mechanically compressing the layup in the mould, I've used plastic bags of hot water to do this, since they will conform to the mouls shape, and speed up the cure to boot :-)

Hi Dravis,
Thanks for the reply .. That helps greatly
I did wonder if it was a viscosity problem, but not having enough experience under me it is hard to compare
I do have vac bagging gear but have just been putting it off trying to perfect the disciplines one step at a time - but I guess its time to step up and improve the results - even if there's some trial and error involved
I do like the out-of-box thinking re: the hot water bags
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Epoxy repelling on mould
AWOL - 7 Years Ago
     Additional note: when we pull the part from the mould we have big pock marks, and yet when we try to sand back and fill we only seem to repeat the same issue It's like the Epoxy won't adhere to the.....
AWOL - 7 Years Ago
     Here's a pic - probably should mention we're doing hand layup, and its 480gsm 2/2 twill The areas where it has repelled the epoxy show up as great gaping voids :ermm: Hoping to resurrect it - o...
AWOL - 7 Years Ago
             Did you try using a plastic roller to remove air/spread excess resin. I see you add multiple layers of carbonfiber. I assume you wet the mould with epoxy, put down the first layer of carbonfiber, wet...
matthieutje65 - 7 Years Ago
                 Thanks for the reply Matthieu, No we haven't tried a plastic roller yet, we will source one out for sure, especially if it will improve our chances - I'm not going to pretend we are experts, still...
AWOL - 7 Years Ago
                     hmm strange! I would recommend you to try the same technique you are using on a glass plate! that way you can do every step and try to analyze now and then through te glass wat is happening on the...
matthieutje65 - 7 Years Ago
                         That's a great idea - I'll try that for sure (on a smaller scale haha) Thanks again for the advice .. stay tuned
AWOL - 7 Years Ago
                             No problem, hopes everything turns out ok for you!
matthieutje65 - 7 Years Ago
     Hi! I used to do hand wet-lays with West Systems 105 and they never turned out well without vacuum, especially on moulds with a lot of contours like yours, 105 is simply too runny for that! (too low...
Dravis - 7 Years Ago
             Hi Dravis, Thanks for the reply .. That helps greatly Idid wonder if it was a viscosity problem, but not having enough experience under me it is hard to compare I do have vac bagging gear but have...
AWOL - 7 Years Ago
     are you letting your pva dry completely? To fully dry pva over a mold of that size in 30 minutes, you have to have a lot of airflow going. If it is pooling up in corners/creases, it could be releasin...
M.R. - 7 Years Ago
             It is possible that I was a little hasty with letting the PVA dry I appreciate all the input so far, and will apply this information when next making the next 'test' carbon part
AWOL - 7 Years Ago
     We've had mid-30 degree ambients in Perth lately, so it wouldn't be impossible to PVA that mould inside 30 minutes. If the PVA was touch dry when you moved ahead then it wouldn't be a problem....
Hanaldo - 7 Years Ago
             We have just brushed on the PVA, although we recently picked up a Preval sprayer so will definitely be using it on our next attempt I like the idea of pre-wetting out the carbon on some plastic first...
AWOL - 7 Years Ago
     Hi, indeed just like a polished car bonnet in the rain by releasing your mould by the very nature of what that release is achieving is going to stop resin being able to wet out the surface and it wil...
CaveDweller - 7 Years Ago
     Defo wet the cloth out. Another possibility is to spray a clear gel coat into the mould first, its viscosity will allow it to stay where you put it and then you'll be able to stand a chance of...
CaveDweller - 7 Years Ago
             Thanks for the advice CaveDweller, It's definitely a learning curve - but the passion is strong so I'll run a few test pieces over the next few weeks, then hopefully drop a nice infused piece on here...
AWOL - 7 Years Ago

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