Curing & layup times

Discussion in 'Fiberglass and Composite Boat Building' started by hardguy007, Jul 13, 2019.

  1. hardguy007
    Joined: Jul 2012
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    Location: Ballymoney

    hardguy007 Junior Member

    Hi all. I’m for making a few small 10ft tenders. I’ve been advised by a very reputable builder that 1 layer of 450csm and 2 further layers of 900csm will be more than enough on top of 2 coats of gelcoat.ive build a few 16ft cabin cruisers a few years ago so have an idea of what I’m at.

    Firstly I’m wondering if it would be any benefit doing 5 layers of 450? I assume that would also increase overall layup time but I suppose I could do 2 layers at once.

    Second, could someone more qualified than me (wouldn’t be hard) advise of curing times. It’s been so long since I done any layup I’ve half forgot.

    Gelcoat first. Is applying it with a small 4” roller feasible? How long should I expect to wait before applying the 2nd coat and then before the first layer of 450csm?

    With the csm. How long should I wait before applying the next layer. When it’s tacky? When it’s hard? The next day?

    Basically I’m trying to work out how long it’s going to take me to complete the moulding from the first coat of gel to the final layer of 900csm. Would it be totally unrealistic to do it in a day or would that not allow long enough curing times?

    Thanks in advance.
  2. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    CSM has very little strength, so either some stitched or woven fabric should be used.

    Gel times for gel coats and resins vary a great deal depending on the exact resin and the ambient temperature.

    Normally you need to wait about an hour for gel coat to cure hard enough for a second coat, or to laminate on it. You will need at least two rolled on layers of gel coat, you probably need three.

    You can apply multiple layers of glass at one time. But depending on the gel time of the resin, and your skills, this may or may not be a good idea.
    fallguy likes this.
  3. KD8NPB
    Joined: Mar 2018
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    Location: South Carolina

    KD8NPB Junior Member

    Gelcoat; "coats". Sprayed gelcoat is best to control thickness and ensure consistency, but I assume you are brushing gelcoat.

    You should brush your gelcoat for an application thickness of approximately 0.5mm, +/- 0.1mm.

    After the gelcoat has cured and is only slightly tacky (it should no longer stick to a gloved finger), you can apply the skincoat.

    The skincoat is typically done with ISO polyester resin, ISO/DCPD, or vinylester, or blends to ensure osmosis resistance, and is done with either 300g or 450g CSM. At 25c, most manufacturers will call for about 2% MEKP9 at that temperature for a coating that thin. Most resins will gel off in about 30 to 50 minutes at that temperature, thickness, and initiator ratio. The mold should be pre-wetted with resin, before the CSM is applied. The CSM stuck in place, then wetted with a paint type roller. Then, the bubbles should be rolled out with a bristle type roller. Application should be wet-on-wet. Overlap a minimum of 50mm. Work from back to front, or front to doesn't really matter.

    After the skin coat is applied, it should be allowed to rest, exotherm, and cool down, then harden to a minimum barcol 35 hardness. This usually takes 4 to 8 hours.

    Once the skincoat is hardened, the surface should be lightly sanded with a gritty sandpaper (36 grit approximately) to remove hairy bits. Any air bubbles underneath the skin coat should be ground out with a dremel type tool, then puttied in.

    After which, you can bulk the pieces. At this stage, up to about 6 layers of 450g CSM can be applied without negatively affecting the gelcoat finish. 8 layers on cooler days.

    I recommend applying no more than 900g at time. Any more, and it is difficult to wet out and roll out.

    I have a 15 ft production boat that is made of 6 x 450g for bulking. We wet out 2x450g at a time, and give it a rough rollout, then another 2x450, repeat. Then after they're all applied, the piece is rolled out with bristle rollers and paddle/fin type rollers. Excess resin is then removed with the paint type rollers, and the rollers are "rung out" on to a waste collection box for "hot mix trash".

    here is a good video for you to watch using techniques common in your area. It's making a mold, but the process is the same as you. Brushed gelcoat to 0.5mm, followed by a thin skin coat, followed by bulking coat of 4x450g CSM after the skin coat is fairly hard. They use a pressure fed roller to wet out the 450g csm, but the technique is the same when working with a brush.
  4. KD8NPB
    Joined: Mar 2018
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    KD8NPB Junior Member

    For the European builder I work for, 30+ years of building boats from solid CSM laminates with no major structural failures. The tensile strength is poor, but if you stack enough, it makes up for it. Best of all, when you stack up a lot, you get stiffness without a core at risk of shearing. Most people confuse stiffness and strength. They go hand in hand.
  5. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Isn't the penalty clearly a heavier layup?
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  6. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Yes, you can make just about anything out of a solid CSM laminate, but it makes for a comparatively weak and heavy laminate when compared to using the proper fabrics.

    This was an old school “build it cheap” method of construction.
    Last edited: Jul 15, 2019
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  7. Tom Huckery
    Joined: Jul 2019
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    Location: 33880

    Tom Huckery New Member

    New member here. I have sprayed gelcoat before with a mini sprayer and would wait at least 4-5 hours. I have put the
    skin coat on earlier then that and had gatoring on the gelcoat from trapped styrene.

  8. KD8NPB
    Joined: Mar 2018
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    Location: South Carolina

    KD8NPB Junior Member

    4-5 hours maximum.

    My mainstay is a 10-12 min gel time gelcoat. It is ready for skinout in 45-60 minutes when catalyzed by temp at manufacturer recommendations.

    The other color I use is 20-24 min gel time, it's ready in about 90-120 minutes.

    Alligation in my experience is usually caused by lack of gelcoat thickness or insufficient catalyst.
    redreuben and ondarvr like this.
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