Efficient workflow on large polyester / glass layup?

Discussion in 'Fiberglass and Composite Boat Building' started by Jeff in Boston, May 14, 2021.

  1. Jeff in Boston
    Joined: Sep 2020
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    Jeff in Boston Junior Member

    Hi folks!

    As I mention in another thread I will be building a large (1 ' x 12' ) fiberglass keel insert for my sailboat to electric cruiser project.

    I've done small fiberglass jobs before, but nothing this size. I have seen lots of tips in videos that shows applying one "batch" of fiberglass, but nothing that really covers *how to do a big job efficiently*.

    Is there a book I should read?

    Here's my questions, and I probably should have more!

    * I understand I can go about 16 hours between layers without needing to sand. If I think I will be longer, should I put down peel ply to get a toothed surface to be able to restart without sanding?

    * I know I will need to keep my rollers, both layout and consolidation, clean. Any tips?

    * Can I re-use resin buckets? At least one video said so.

    * If I use a wet out table, what do I need to do to keep it clean between layers?

    * Can I use a infrared thermometer to verify I'm not adding too much at once?

    * It looks like I should use those cool MEKP squeeze dispensers?

    Any other tips?

    Thanks!

    -Jeff
     
  2. rxcomposite
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    rxcomposite Senior Member

    1' x 12' is not much.

    Lamination is supposed to be a continous process, that is when the 2nd layer is being added, the 1st layer should have cured to tacky dry. So even with 1 man on the laminating table, there should be a rest in between. Depending on your mix, it is about 30 mins (fast cure) to 1 1/2 hour for the resin to kick. Your mixture will be your window. Fast cure heats up quickly. Use MEKP dispensers for accuracy.

    Max 4 hours is allowed for long breaks. You need to sand to remove slivers. 8 hour break you have to do light sanding to abrade surface.

    If the lamination is simple and thin, you can go continous 2 layers and see if the tacky dry laminate is warm to the touch. If uncomfortably warm to hot, you are laminating too quickly. Take a break. The only time you need infrared meter is if you are laminating to strict enviromental conditions. What is important is you have a blower or air extractor to remove the lingering volatiles on the surface of the laminate. It is for safety and even cure. Those heavy volatile prevents full cure and stays on the surface.

    Use a bucket for large job. Measure the cloth, weigh and calculate only the resin you need between lamination. Mix only what you can handle. Several mix at staggered times maybe needed. We do reuse resin bucket but only if the resin has dried. In fact we remove the dried up resin before use. We don't mix a fresh batch if there is remaining gelled resin on the bucket.

    If you have to spray gel coat, all areas must be free from dust. The floor is sprayed wet with water.

    Waxing is needed in between jobs.
     
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  3. Jeff in Boston
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    Jeff in Boston Junior Member

    Thabks!

    For more context the mold will be between 4 to 12 inches deep and I want at least a 3/8" thick layup. This is replacing a 2200 lb deep keel with a 4" deep keel so I don't mind going heavy.

    I am thinking of alternating csm and 6 oz cloth (as that is what I have)
     
  4. rxcomposite
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    rxcomposite Senior Member

    12" deep you need extractor fans. No problem about CSM and WR. Just follow my recommendations and continously feel the lamination if it is heating up. I usually lay down my WR while the CSM is still wet as I have better control.
     
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  5. kapnD
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    kapnD Senior Member

    6 oz cloth and csm will be a slow,labor intensive way to achieve a 3/8” thickness.
    1208 or heavy woven roving would be stronger due to much less csm content, and take fewer layers.
     
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  6. Jeff in Boston
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    Jeff in Boston Junior Member

    Extractor fans and use hands to check temps. Got it.

    At this thickness and the low stress that will be on such a short stubby keel, I'm not worried about strength. If I did two layers of CSM to 1 layer of 6oz would it go faster? Or you think I should just get thicker cloth?

    I might be able to find someone who wants to trade cloth as I have WAY more 6 oz than I will ever need.
     
  7. rxcomposite
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    rxcomposite Senior Member

    Sorry cannot comment on that without knowing the lam schedule on adjacent layer like the bottom layup.

    Strength, in the true sense is a difficult to solve. If we go by the rule of thumb, it is 10% of the hull breadth and 1.5x minimum the thickness of the bottom layup. Afterall, the keel is just a reinforced portion of the hull bottom
     
  8. ondarvr
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    ondarvr Senior Member

    A few things.

    Cloth is close to worthless in any type of polyester laminate, use roving, typically 24oz, but 18oz would work.

    With a summer resin and the correct catalyst, 3/8" can be done all at one time. Your level of skill may limit you though. Two 1.5 oz csm and two 24oz rovings aren't difficult to put down at one time.

    You aren't limited to 16 hours for a second layup, you could go a couple of days and not have a problem (I've done bond testing in our lab, and customers have done it too, the bond is better than most people think for a longer period of time than expected). The exact resin has a great influence on the actual secondary bond timing though.
     
  9. rxcomposite
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    rxcomposite Senior Member

    Lloyd’s, probably the biggest or has an access to an independent lab continually monitors raw materials for approvals. It is also most prestigious and this is the rule.

    I assume you are using polymer resins. These resins form a chemical bond by crosslinking by the addition of a reactant agent. Once initiated by the reactor (MEKP for this) The resins starts crosslinking. It is technically “cured” once it has gelled or has attained its “potlife”, which is in the 30 min to 1 hour of mix. EXCEPT that it is not 100% fully crosslinked. The surface, unless covered by a moisture barrier does not attain complete crosslinking and may take sometime.

    To Lloyd’s, lamination is a continuous process “wet on wet” and when “interrupted” the surface is to be “prepared” to improve bonding. LR deems the laminate to be “fully cured” after 12 hours or when the laminate has attained the required Barcoll hardness. Anything after 12 hours is considered a secondary bond and “surface preparation” is required.

    You won’t be building to a class rule but these should guide you. You won’t reach a full chemical bond if you laminate the second layer after the resin has gelled/became tacky to touch but at least you have a fairly good mechanical bond. You are pressed for time as the crosslinking has started from the moment you add the catalyst.
     

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    Last edited: May 15, 2021
  10. rxcomposite
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    rxcomposite Senior Member

    The keel is the most critical part of the boat/ship as it handles extreme loads. Its strength is computed against the required modulus. The rule of thumb I gave you is just that, an approximation. From experience, keeping the keel width to 300 to 350 mm, its thickness is more than double the bottom laminate thickness. Strength also matters and the lamination schedule follows that from the original designed bottom laminate schedule.

    If building up the keel from one complete lamination sequence, the individual layers are just doubled up and overlapped to increase thickness.

    If building up bulk after the bottom lamination is finished, the layers must follow the original specifications. You don’t build up bulk by throwing in more CSM or using bulkier WR else the strength/stiffness calculated goes out the window.
     

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  11. Jeff in Boston
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    Jeff in Boston Junior Member

    Thanks all!

    You've convinced me to use roving. The extra cost is minimal compared to the increased strength and speed of layup.

    As for the keel strength, there is a keel slot where the cast iron keel used to be that is already reinforced: Keel and Keel Bolt Photos - Pearson 26 (pfeiffer.net)

    I'll be building an insert for that and then attaching with epoxy. I will make sure to go double the hull thickness, which I can verify when I pull the thru-hulls.

    I intend to use some fiberglass bolts in the existing bolt pattern to help with clamping the keel on during the epoxy process and then I can just leave them there.
     
  12. ondarvr
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    ondarvr Senior Member

    The guidelines put in place by Lloyd's are chosen to error on the side of extreme safety with the worst case resins.

    These resins are DCPDs and blends of them with ORTHO, ISO and VE.

    DCPDs are not air inhibited in the same way as other resins, so the window of open time is far less. These are the resins the bond windows are based on.

    Many/most boat and yacht builders use a higher quality resin for the skin, then much lower cost resins for the bulk of the build. These lower cost resins are typically DCPD blends.

    The other thing that greatly affects the bond window is temperature and humidity. Cooler temperatures and higher humidity extend the bond window dramatically.

    Comparing the bond window of a particular resin in Arizona in the summer will yield huge differences from Seattle in the winter.

    So recommendations are based on worst case scenarios.

    That's why I mentioned the type of resin makes a big difference in my prior post.

    We did this testing based on the actual resin used by the customer in the ambient conditions in the plant and/or our lab.

    We also formulate base resins for fast surface cure or a long surface cure as needed for particular applications.

    The elevation of the builder also comes into play, you will get different surface cure characteristics at sea-level compared to 7,000 feet.
     
    Last edited: May 16, 2021
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  13. Jeff in Boston
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    Jeff in Boston Junior Member

    I'm in Massachusetts and will be doing this over the summer. Do you have a specific recommendation for resin for me? I'm leaning towards using the Total Boat products.
     
  14. ondarvr
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    ondarvr Senior Member

    There are only a few manufacturers that make resin, retail outlets buy resin from these manufacturers and repackage it into smaller containers.

    Some change suppliers depending on the resin price every time they need more, so you have no idea what you may be getting.

    Some online suppliers do offer descriptions or information on the exact resin though, it's better to buy products from one of them.
     

  15. fallguy
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    fallguy Senior Member

    There is little reason for me to comment much. I keep all my rollers in a 5 gallon jug with 1/2 gallon acetone for epoxy. For polyester work, my guess is the other solvent.

    I line all my tables with plastic for epoxy work. The tables are also waxed, so little bonds to them.

    Best I got. You have a team of experts answering and you sort of hit the jackpot on good advice.
     
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