Help For Vacuum Bagging

Discussion in 'Materials' started by rangebowdrie, May 20, 2022.

  1. rangebowdrie
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    rangebowdrie Senior Member

    Ok, a friend of mine is building a houseboat, the hull is what may be called scow shaped, flat bottom with vertical sides, ends on a slope.
    The bottom and sides are glassed already, but due to construction method the joint at the chine is not covered.
    He wants to put a couple of layers of glass over that joint, perhaps a 2' wide swath equally divided between sides and bottom.
    The total perimeter around the hull is ~100'.
    As the hull is upright there is only ~1.5'>2' or so between bottom and the ground.
    His idea is to vacuum bag the glass work by using my little pump that is for refrigeration service.
    My question is: Is such a method feasible in some way? What kind of alternatives exist for doing
    such a project, (keep wetted out glass against hull bottom against gravity)?
    I'm thinking that my small vacuum pump would be overwhelmed, not to the amount of vacuum, but mostly because of the small cfm capability.
    You guys with experience have any ideas?
     
  2. fallguy
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    fallguy Senior Member

    Yeah. The pump will fail; almost certainly because it needs 6 hours service time.

    It will be rather difficult to keep the wetted glass against the hull to close the vac bag. Once the tabbing is done, it will not easily come down. But getting it to stay home is a crapshoot. Don't try it. It is a not for semi-pro's even idea.

    Typically, one of the things to do is to minimize the glass. On what basis have you decided a 2' wide piece is needed? That sound excessive on its face.

    Then what glass are we talking?

    1200db through 1708 will not wet easily and are generally table wetted

    If I were doing the job, I'd want to try infusion, honestly. I'd use some 3M spray adhesive and apply the tabbing and then bag the job. Find a better pump for continuous service for 6 hours. Then pull the resins while the bag is already on.

    I can't tell you enough about how, but this is the easiest way. You can't spray the tabbing on and wet it conventionally because those heavier types of glass won't wet through, and hot tacking it might work, but not for 2' widths. It is a can of worms, infusion is best.

    I'm pretty good with glass and this is a nightmare job. I've watched a few videos of glassing upside down and I've done some. If you won't do it the easy way, I can tell you how the hard way, but it is horrid. You basically wet the glass on plastic right under the job, then hotcoat the substrate. Do not rush the hotcoat, it must tack up. Then a crew of people lift the plastic and glass up into position wetted. The Rutan videos used tinfoil and I can't recall the reasons. I used jigs for my upside down work. I will tell you; some of my glass ended up in steaming piles on the floor because it tends to stretch and move; perhaps the tinfoil prevents that a bit.. once my glass was deformed beyond reason; I had to shitcan it and make a new piece; that sucks if you have a stack of 3 pieces and lose the first one cuz you have only a few minute to cut out and wetout a new piece...etc
     
    Last edited: May 20, 2022
  3. rangebowdrie
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    rangebowdrie Senior Member

    Thanks for your reply Fallguy.
    I only got into this when I was called and my friend says: "Can I borrow your vacuum pump?"
    So I started asking about how it would be used, and that led to me seeking some answers here.
    I knew his "method" of construction would come-back to bite him in the end, now its trying to
    find some way to "make do".
    I will find out more about the amount of overlap, and agree with you that a 2' swath seems excessive.
    Thanks.
     
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  4. fallguy
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    fallguy Senior Member

    I updated my post to reflect a hack method, no vac. He could try it say on the stern or bow, but compared to infusion; it will be a nightmare.

    The glass doesn't move much hot tacking it, so you have to use a ton of reference marks and make sure they get made..right away.
     
  5. rangebowdrie
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    rangebowdrie Senior Member

    Oh boy, I've always thought that this was going to be a nightmare.
    Perhaps small overlapping sections done one at a time might work?
    Moving along the perimeter a few ft. per day?
    Another concern: I'm not so sure about using my basically new pump, (older but barely used,) to spend hours/days sucking-in epoxy fumes.
     
  6. fallguy
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    fallguy Senior Member

    The hack method is no vac. I doubt your pump is rated for continuous service.

    You need a resin catchment system in line, but one of my pumps got some epoxy anyway and would stop running. There is a trick a great guy from the great state of Pa told me. Put some atf in the vac pump with epoxy and it'll break it loose. And it worked, that pump, with vac oil now, does not stop.
     
  7. rangebowdrie
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    rangebowdrie Senior Member

    I'll report to him what I've learned, (enough to give me pause about proceeding).
     
  8. fallguy
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    fallguy Senior Member

    It doesn't need to be bagged to stay up. Hotcoating works, insurance is peelply, good bubble buster consolidating rollers, and masking tape over the peelply.
     
  9. kapnD
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    kapnD Senior Member

    Narrower strips are more manageable, I’ve done it solo with 1’ wide strips wetted out on plastic and a 1’ roller.
    Very messy, plan your PPE carefully and invest in a tube of barrier cream!
     
  10. fallguy
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    fallguy Senior Member

    Once it is up there good; it doesn't really fall down when you hot tack. Just getting it in place wet is the hard bit. Impossible alone. My location was only big enough for one person and my good friend Ray did all he could to hold a corner up.

    For this job, one person is the anchor. Has to support the original placement and not allow it to slide. Another one or two for the rest. Three people would be best.
     
  11. Howlandwoodworks
    Joined: Sep 2018
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    Howlandwoodworks Member

    rangebowdrie,
    Sounds like you came to the same conclusion that I did.
    I have been doing vacuum bag work on wood veneers for 25 years. Mostly desk tops and curved cabinet door panels. I think this type of system has a very steep learning curve.
    I was exploring the possibility of vacuum pressing some cold molding veneer to a sailboat scale model of 6.5' LOA.
    Here was a poorly done attempt. I didn't get the pump to draw a vacuum. I came to the conclusion that this is just a bad idea and it would take a long time to set up the first time.
    Getting a project to draw a vacuum is harder than it looks even with a good bagging system and I couldn't think of a way to use a bag this project without crushing the hull. So I would be using double sided tape and that is very hard to get a seal on irregular shapes. You wouldn't believe how small of a hole will keep the system from draw a vacuum.

    My system was around $1000 w/ bags and is Suitable for a vacuum bag max size of 4'x15'.
    • Maximum Vacuum: 25.5" Hg at sea level
    • Maximum Bag Pressure: 1,785 lbs/sqr ft
    • Air Evacuation: 5 CFM @ 0" Hg
    • Port size: 1/4 NPT
    • My largest bag is 30 mill polyurethane 52"x148" also have a 26'x104' and a couple smaller ones.
    upload_2022-5-22_9-34-36.jpeg
     
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  12. rangebowdrie
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    rangebowdrie Senior Member

    After much perusal and cogitating I think I came-up with a solution to the owner's problem.
    I went to to project today to get a firsthand close-up look at the job.
    The sides of the hull are straight as an arrow and the bottom is smooth, the chine joint is fair with a nice radius.
    I laid-out a plan and he agreed to make up a test section.
    My plan: Take a 4x4 of length desired, with a radius on one edge that matches the chine radius.
    On opposing sides, cut a rabbet that will allow a 1' wide panel of plywood to be screwed to the "corner post".
    Cover this with plastic.
    Now we have a male mold over which a fiberglass panel can be laminated, a fiberglass "angle iron" section if you will.
    He has several hundred ft. of heavy Bi-Axial cloth that is 12" wide.
    So, a laminate can be made that is ~5" on each side, with allowance for the corner radius.
    These sections when removed from the mold will produce an "angle iron" of fiberglass of whatever thickness desired.
    Then the sections can be coated with thickened epoxy and placed over the hull/bottom joint.
    They will be held in place by a heavy plastic covered panel that can be pushed up against the hull bottom with a few small jacks, (which he already has,) and held until cure is achieved.
    The sections of "angle iron" fiberglass can be overlapped a few inches as work progresses along the length of the chine.
    Work is easy, stand-up work laying-up glass on a mold, and with little waste of product.
    Anyway, that's my plan, he likes it.
    No pump, no "hot-coating", no tape, no plastic, no runs/drips/errors, no backbreaking upside down epoxy application.
    I'm not an engineer, more of an "Imagineer", and the simplest of solutions sometime are the best.
     
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  13. fallguy
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    fallguy Senior Member

    The solution you propose will work, but it will use more resin than others.

    For your epoxy putty, I recommend 1/16" vee trowels, but two of them, apply to both the prefabbed part and the hull.

    I think you'll need to probably stagger two tapes as one will be rather flimsy.

    And make sure the prefab panels have any blush removed.

    You can probably step the pieces on ends to allow the others to fit over tops.

    Epoxy use will be high, but the wirk will be cleaner.

    1/16 vee trowel both sides is volume of 9 cuin per running foot...using fumed silica at a rate of say 2.2:1 by volume is 3.2 parts or about 3 ounces epoxy per running foot and about 6 oz silica per running foot extra...my math is a hair short, but cost is about say $3 a foot more this way versus struggling..
     
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  14. rangebowdrie
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    rangebowdrie Senior Member

    I agree, and (thankfully for him at today's prices,) both the glass tape and epoxy are already on hand in more that sufficient quantities, along with plenty of filler.
    Just looking at the Bi-axial tape, I suggested to use a 3-layer laminate to start out with on a test piece so as to gage strength/rigidity, the tape is quite heavy.
    Ya know, in the beginning I was quite certain that a bag-job could/would be a nightmare devolving into disaster, and by starting this thread I could get professional validation of my concerns that he would acknowledge, as I've had no firsthand experience with that type of work.
    I told him: "I'll ask the pro guys at the forum about this idea of vacuum bagging the job".
    He does good work and without any compound curves or running bevels I've no reason to believe that my idea of "pre-fabbed"
    sections of fiberglass-angle cannot work for him.
    Edit: I like your idea of the notched trowel, and as the boat is going to be raised up higher above the ground the application of product should go easier.
     
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