Woven roving print-through

Discussion in 'Fiberglass and Composite Boat Building' started by Camino Camper, Jun 13, 2022.

  1. Camino Camper
    Joined: Jun 2022
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    Location: Spain

    Camino Camper New Member

    Hello!

    I am developing a truck camper prototype and have successfully constructed all the molds and pulled various parts. With the latest and largest part, I, unfortunately, am having some serious print-through from the Woven Roving.

    I will try and summarize the process:

    - Conventional hand layup on Vinilester tooling gelcoat (near perfect surface)
    - Temperature 25-28 degrees Celsius
    - Chemical release agent
    - White Polyester gel coat brush application @ 600 g/m2 @ 1% MEKP
    - Let gel coat cure for 16h
    - 2*100 CSM with polyester resin @ 1.5% MEKP
    - Let 2*100 CSM cure for 1h until slightly tacky
    - 2*combi mat CSM 450/roving 800 with @ 0.5% MEKP (CSM 450 side down)
    - Demould after 48h

    Print through and uneven surfaces worst at the overlap, see pics and drawings.

    At the workshop, I have CSM 100, CSM 450, and combi mat CSM 450/Roving 800, and ideally, stick to these materials.

    What am I doing wrong? Thanks so much in advance for your feedback!

    Best,

    Alex

    print_through_1.jpg print_through_2.jpg print_through_3.jpg print_through_4.jpg print_through_5.jpg
     
  2. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    @ondarvr is your best bet

    I'll go on a limb and suggest the csm layers are too light, but wait for him. He is the expert. I have not done polyester moulding much.
     
  3. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    Fallguy is correct,if you are only using 2 100gsm plies beneath the roving,it simply isn't enough of a barrier to prevent print through.I would actually have a hard job finding mat that light as 225gsm is about the lightest commonly available here.The other question is why woven roving?A biaxial combi would have less of a tendency to print as the crimp of the weave isn't present and thus there are smaller volumes of the resin within the layup to undergo shrinkage.The fact that the laminate is unbalanced might be another factor.
     
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  4. Camino Camper
    Joined: Jun 2022
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    Camino Camper New Member

    Thanks a lot @fallguy and @wet feet!

    I will do a test laminate with some heavier than CSM 100 as a barrier. Do you reckon reckon 1 or 2 layers of CSM 300 would be ok? I was also thinking about leaving this barrier layer to cure overnight before applying the woven roving.

    @wet feet I chose woven roving because I found it easier to source and knew it would work structurally. Could you help me with the approximate 90/90 biaxial equivalent to my 800g woven roving?

    Thanks!
     
  5. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    I don't have any knowledge of the local suppliers of reinforcement but I expect google will know much more.I found this page and they might be a good starting point Combi Mats https://www.castrocompositesshop.com/en/78-combi-mats A test panel or two would be a great way to determine the way forward.In fact a couple-one with a single 300gsm beneath the woven roving and one with two beneath the woven roving would give a very reliable indicator of the benefits.

    Since you already have a component with the print through,what are your plans for it?A single gel doesn't really leave you with much thickness to attempt to sand the pattern out,which means that perhaps a coat of high build primer,some serious sanding and a coat of 2K paint might be a salvage plan.
     
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  6. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Again, not my area, but the roving will print through most anything once the sun hits it hard. It is really probably just too much for the plan.

    If I were trying to bury roving from printing, I'd probably step up and down to it, which is a pita.

    But something like 100,450,200,100, combi would probably allow the lighter layers to flatten out into the roving

    Still like to hear from @ondarvr because the guy's expertise in moulding is remarkable.
     
  7. fallguy
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    fallguy Senior Member

    don't test anything until you hear from @ondarvr
     
  8. kapnD
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    kapnD Senior Member

    Try rolling or spraying the gelcoat—-THICK!
     
  9. fallguy
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    fallguy Senior Member

    I always thought thick gc cracked easier..but I can't argue it and it may save the part here.
     
  10. comfisherman
    Joined: Apr 2009
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    comfisherman Senior Member

    Had some problem with that as well being new to glass. Eneded up doing gel coat with csm until it was close to cured and then layed up the combi mat. Seems to have worked on my raised bulwark section. Wanted to do internal panels out of glass and hit the easy button with csm and 10.7 oz cloth (dunno what the metrics of it is.)

    Had a fair whack of material left over from a big boat project, 10% leftover is enough to make a decent little travel trailer. Going to probably go cloth vs roving on it. Roving might do the base panels, but it's kinda chunky when going for fair easily.
     
  11. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    The short version.

    Not sure of the gel coat you're using, but 99% of them recommend 1.5 to 2 percent MEKP, 1% will leave it under cured. And thin gel coat will cure poorly anyhow and lead to excessive print. Try for 20 mils of gel coat.

    Go thicker on the CSM skin, and let it cure until at least the next day.

    Don't under catalyze the roving layers, they need the full amount, .5% leaves it undercured and it will post cure, which again leads to print.

    But this part would benefit from using something besides roving, one of the big problems with roving is print through on cosmetic parts. If roving is used you need to pay even more attention to doing every step correctly.

    The exact resin plays a big part in this. Resins designed for good cosmetics need to thoroughly cure in a thin layer, and are typically blends of different bases.

    Then, leave the part on the mold for an extended period of time, the longer the better.
     
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  12. Camino Camper
    Joined: Jun 2022
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    Camino Camper New Member

    Thanks so much to the community @fallguy, @wet feet, @comfisherman, @ondarvr for the feed back!

    With all the comments, including feedback from my provider, I will summarize my next steps based on materials I have available to me at this moment (CSM 100, CSM 450, Combimat 450/Roving 800)

    - Apply thick gel coat catalyzed @ 1.5-2.0% (allow to cure overnight)
    - Apply skin 2*100 CSM in the morning (allow to cure during the day)
    - Apply additional skin of 1*450 CSM in the evening (allow to cure overnight)
    - Apply first layer of combimat 450/800 in the morning (allow to cure during the day)
    - Apply second layer of combimat 450/800 and finishing layer of CSM 450 in the evening
    - Demould after 24h

    What do you guys think?

    Regarding the piece that I have "lost", this will be used in stress tests and as a pattern for interior parts...

    Thanks again!
     
  13. fallguy
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    fallguy Senior Member

    I have one question.

    How does hot sun play a role in 'post-curing' esters?

    Is there any benefit to him baking this part in mould, for example; despite the headache? I have this notion a few hours at 130F would make a difference, too. Worse, that the part will print once the camper sees a hot sunny trip..after he thinks it is fine.

    All the stuff I post cured on my epoxy build, zero print through.

    Everything not post cured and suitable for printing, printed on a day here that was like 105F. Nothing horrible, but happened. I repaired a couple 1/4" holes on a part, for example, and all faired and looked great, and the heat got me..
     

  14. ondarvr
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    ondarvr Senior Member

    Polyesters are considered ambient cure resins, but can benefit from post curing, not typically to the same degree as epoxy though. Almost all epoxy will see a significant increase in physical properties after a post cure cycle(s).

    The physical properties on the data sheet for an epoxy are almost always after it has been post cured, and are significantly higher than without the post cure.

    Heating the parts while still in the mold can help to eliminate print, 120F for a couple of hours will normally be enough for an improvement. Not many manufacturers post cure their parts, but the truck part industry will frequently go to 200F or so for 30 minutes. This may induce some print, but they use sanding gel coat, so after sanding the part is smooth again and less likely to print after painting.
     
    Last edited: Jun 16, 2022
    fallguy likes this.
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