Questions about epoxy & FG on house boat roof

Discussion in 'Fiberglass and Composite Boat Building' started by mudflap, Jun 17, 2020.

  1. mudflap
    Joined: Jun 2020
    Posts: 8
    Likes: 0, Points: 1
    Location: texas

    mudflap Junior Member

    Hello all-

    New member here seeking some expert advice.

    I am rebuilding an old pontoon "house boat" (shack boat???).

    Mechanically, she's in good enough condition, but the "cabin" has seen better days.

    The small cabin is 14'L by 8'W. The two side walls and roof have developed leaks. I stripped them off and re-decked with 3/8" exterior plywood (AC grade, not treated).

    I'm planning to coat the side walls and roof with epoxy resin and (in some places) fiberglass and thought I'd run my plan past you and perhaps ask a question or two...

    Plan is to fiberglass&epoxy all seams and corners on walls and roof. Roof will also get fiberglass. Sides will just be coated with epoxy only (everything will be painted eventually).

    Q: Is that a reasonable plan? Will a few coats of epoxy prevent the plywood from checking if no FG?

    Q: suggestions for pre-cut cloth for seams and corners?

    FWIW, leaning towards Raka or MAS epoxy.

    Next area of concern is how to tackle the roof. It is big enough to prevent me from applying epoxy and FG while standing (on ladder) to the side. I'll have to get on the roof...

    Plan for roof is:

    1. Epoxy and FG all corners and seams

    2. Epoxy entire roof

    3. lay out cloth and wet out

    4. apply one or two more coats of epoxy as needed

    Q: How do you suggest I do the above given that I'll have to be walking/crawling on the roof to do so?

    I'm guessing that I'll apply epoxy to entire roof in one step (many small batches of epoxy)...

    ... then come back after appropriate amount of time (???) and layout one run of FG, wet it in, then layout next run of FG, wet it in, etc, working my way across the roof as I go...

    ... then after the appropriate amount of time (???) apply epoxy to entire roof and repeat as necessary.

    Does this sound reasonable?

    Q: how will I know it is time for next step? Is it OK to walk on partially cured epoxy?

    Q: if I time it right, will I need to sand between steps? I'd like to do entire roof as a sequence of steps spanning a day or three to eliminate sanding if possible...

    Thanks for any advice you might offer.

    Bob
     
  2. bajansailor
    Joined: Oct 2007
    Posts: 1,243
    Likes: 340, Points: 83, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    Welcome to the Forum Mudflap.
    There are others on here who know a lot more than me about applying epoxy and fibreglass, so I shall leave it up to them to answer your questions.

    Re the roof (3/8" thick I presume?), have you climbed on to it already in order to secure it to the beams?
    If yes, were you happy with the strength, or did you have to walk on additional boards to help distribute your weight?

    Do you have any photos that you can post showing the boat and the work you have carried out so far?
     
  3. Blueknarr
    Joined: Aug 2017
    Posts: 927
    Likes: 186, Points: 43
    Location: Colorado

    Blueknarr Senior Member

    Epoxy alone won't prevent the plywood from checking any more than simple paint would. Epoxy is best used were the wood will have extended water contact.

    Epoxy recoat times are brand and temperature dependant. Look for a chart on the can you purchase. Or use the touch test.
    Wet or sticky is too soon. Scrape with 80 grit sandpaper:. If paper gums up ok for next layer. If it sands to a powder then sand before next layer.
     
    bajansailor likes this.
  4. trip the light fandango
    Joined: Apr 2018
    Posts: 418
    Likes: 75, Points: 28
    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Senior Member

    Hi mudflap, the slow cure[40 mins?] epoxies saturate best before they go off, it is always the cuts and edges where you have to be most careful, 3 coats are often recommended. The plywood edges suck up water like a sponge, you can't leave epoxy unpainted for too long it isn't UV stable. Standing the sheets in a shallow epoxy bath to absorb fully may be a good way to guarantee all edges get a good soak. Where ever you drilled holes through for the fastening also needs treatment. It will last for a long time done well. Around 77 degrees outside temp and better to start warm and then get cooler than the other way around.
     
  5. Will Gilmore
    Joined: Aug 2017
    Posts: 223
    Likes: 80, Points: 28
    Location: Littleton, nh

    Will Gilmore Senior Member

    You describe her as a houseboat (shack boat???). Just because she's a boat, doesn't necessarily mean you need glass and epoxy for a roof. If she will be on a lake or protected bay, used on nice days and on a trailer during stormy weather, maybe you could just roof her like a house? Plywood underlayment, rubberized water shield over drip edge, shingles. Cute look. Of course, I have no idea how or where you plan to use her.

    Good luck.

    -Will (Dragonfly)
     
  6. mudflap
    Joined: Jun 2020
    Posts: 8
    Likes: 0, Points: 1
    Location: texas

    mudflap Junior Member

    Thanks for the replies.

    Yes, the roof is 3/8" ply, supported 16" OC (2x4s), so it is pretty stout. I currently have the boat in a shop I'm renting that has 13' ceilings. Top of boat is about 9', so I'm pretty much forced to crawl instead of walk. In doing so, I spread my weight around enough that there is very little flexing of the plywood.

    A. Plan outlined above is to epoxy entire roof, then FG&epoxy entire roof, then epoxy entire roof.

    B. I've seen where others will epoxy one section, then FG&epoxy that section, then epoxy that section. Then repeat with next section.

    I guess an advantage of the plan 'B' is that I would complete one section before moving on. Then I could vacuum the next section and take care of it, and I'd never have to walk on partially cured epoxy. Would that be a better plan? If so, would I go all the way to waxed epoxy on final coat? And if so, I guess I'd then have to sand just the area where the new section overlaps with the old to help the mechanical bond between the two areas?

    Dang. I have quite a bit of experience in many types of construction, but this fiberglass stuff has me feeling pretty clueless!
     
  7. ondarvr
    Joined: Dec 2005
    Posts: 2,333
    Likes: 259, Points: 83, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    You don't put wax in epoxy.

    The easiest method is to start at the front or back and do full straps all the way across. Work your way backwards until you're done.

    I normally use 38" wide glass because I can reach the far side with a squeegee.
     
  8. mudflap
    Joined: Jun 2020
    Posts: 8
    Likes: 0, Points: 1
    Location: texas

    mudflap Junior Member

    Oh, that's right. What little experience I have with FG is with everybody's favorite: polyester resin, where wax is added to final mix. Thanks.
     
  9. mudflap
    Joined: Jun 2020
    Posts: 8
    Likes: 0, Points: 1
    Location: texas

    mudflap Junior Member

    Doing lots of reading and wondering if I might have messed up ...

    Is "PC Woody" epoxy wood filler compatible with epoxy resin?
     
  10. PROPGUNONE
    Joined: Jun 2018
    Posts: 24
    Likes: 8, Points: 3
    Location: Sharpsburg, GA

    PROPGUNONE Junior Member

    Always had good luck with RAKA through three builds now, so it gets my vote, but their surprise shipping costs piss me off.

    No amount of epoxy will prevent ply from checking if the ply isn't up to the task to begin with. I’d recommend at least a quality marine ply, or, better yet, a closed-cell foam roof. I’d also build some sort of crown into whatever I put up there to ensure water doesn’t pool on it. Paint is a must as epoxy isn’t UV friendly.

    For your project, expensive materials for the core might not be realistic. I’d do a boil-test on a scrap piece of wood and see how it behaves. You can google the test method or search on any boat building forum. Vinyelster resins and a mat layup will also work, but your work better be good and, again, paint it when you’re done.

    I’d do it like this:

    0 - shore the roof up to where I can stand on it with minimal flex
    1 - use thickened resin to glue all my seams. Let this cure and sand flat
    2 - Precoat surface with resin. Try to apply as smoothly as possible.
    3 - Sand flat and wash clean
    4 - 6-10oz glass layup. One layer unless you’re gonna be hanging out up there, then I’d work out scantling numbers ahead of time.
    5 - Let cure, fair it out and paint it.
     
  11. mudflap
    Joined: Jun 2020
    Posts: 8
    Likes: 0, Points: 1
    Location: texas

    mudflap Junior Member

    Many thanks for the excellent advice!

    I'm pretty clueless about all this, but I ordered up a good bit of epoxy, cloth, tape and other supplies, so I'll be a little less clueless pretty soon!

    I'm curious to find out how much sanding I'll need to do. This rig is pretty red-neck, so I don't want to make it look too good. haha. Seriously, if it ends up with a little orange peel or fabric texture, that wouldn't bother me. Q: Allowing for that low bar, and since I'm using slow-curing hardener, if I apply next layer in < 24hrs, is sanding necessary on the early layers?

    I bought 6" high density epoxy application rollers, plus a couple of the aluminum head laminating rollers, plus a 6" squeegee. Q: For large, flat areas, what is most commonly used to spread and remove air, the laminating rollers, or squeegee?

    Thanks again for the help and support. It's amazing what getting a little nudge can do to get one over the hump on a new project!
     
  12. Blueknarr
    Joined: Aug 2017
    Posts: 927
    Likes: 186, Points: 43
    Location: Colorado

    Blueknarr Senior Member

    Rollers vs squeegee is a personal choice. I think the squeegee moves the resin around more than it removes air bubbles. So I use both depending on what needs to be done. The rollers do have the advantage of being able to be extended. Also low nap paint rollers can apply lots of resin quickly.

    I do a simple coat of resin on wood, let it cure. Then sand any raised grain before laminating cloth. This prevents the wood from sucking the resin out of the cloth and creating a resin starved blister from forming.

    Touch testing epoxy:
    If wet or sticky, then wait.
    If gums up 80 grit then no sanding strong chemical bond will form between layers.
    If sands to a powder, then continue to fully sand to get a mechanical bond between layers.

    Household vinegar cleans up uncured epoxy.
     
  13. PROPGUNONE
    Joined: Jun 2018
    Posts: 24
    Likes: 8, Points: 3
    Location: Sharpsburg, GA

    PROPGUNONE Junior Member

    Exactly as stated above. I’d probably laminate width wise in shorts strips, maybe 36” cloth, versus length wise. Doing it that way would hopefully let me keep a “wet edge,” for lack of a better term. Lay one strip, wet it out fast, and lay on the next one with a slight overlap. If it cures, the edges at the seam will be rough and you’ll have to feather them with a grinder before you can lay the next piece down.

    I’m mostly a squeegee guy, but for big areas of resin wet-out, like plywood, I might be tempted to use a roller. Personal preference. Vinegar is great, but flood it, dont just wipe if you’re doing multiple layers. You have to wash the blush away, not dilute it and spread it around.
     
  14. mudflap
    Joined: Jun 2020
    Posts: 8
    Likes: 0, Points: 1
    Location: texas

    mudflap Junior Member

    Thanks very much for the great info Blueknarr and PROPGUNONE!

    Wow! The above perfectly addresses the next question I was thinking about! Goal is to work across short side, applying narrow enough strips to allow me to lay down next strip while previous is still wet. I ordered 30" cloth to help in this area and also allow me to easily reach far side of cloth when working on the top.

    Q: How much epoxy should I make per batch? I'll be applying with 6" roller.

    Q: Can I continue to use same roller tray and roller across multiple batches? Guessing "yes" on tray and roller, but "no" on mix cups due to residual epoxy in mix cups just sitting with thin layer that can dry quickly?

    Q: When I do need to let cure and sand before next layer, what are we talking about:
    a. sand lightly, hitting mostly just the high spots?
    b. sand thoroughly until entire surface has been roughed up?

    Q: Sandpaper grit? Block of wood by hand or recip elec sander?

    Oh, also...

    Q: Will I need to use the alum roller to remove bubbles on every layer, or just when I'm wetting out cloth/tape?

    Dang. My "one last question" sure turned into a lot more than just one...

    Thanks again for your excellent advice.
     

  15. bajansailor
    Joined: Oct 2007
    Posts: 1,243
    Likes: 340, Points: 83, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    Just a thought, for anybody else planning on doing something similar to mudflap - rather than installing the plywood sheets on the roof, and then glassing them up there, it might be easier to fibreglass the sheets at ground level, fit them on the roof, and then just glass the joints?
     
Loading...
Similar Threads
  1. schlever
    Replies:
    16
    Views:
    2,588
  2. ahender
    Replies:
    8
    Views:
    154
  3. Kmmcreynolds
    Replies:
    27
    Views:
    521
  4. what2be
    Replies:
    22
    Views:
    607
  5. Anthony212
    Replies:
    6
    Views:
    506
  6. fallguy
    Replies:
    2
    Views:
    458
  7. GP1998
    Replies:
    17
    Views:
    3,007
  8. freddagg
    Replies:
    15
    Views:
    1,593
  9. mike marchetti
    Replies:
    29
    Views:
    2,725
  10. CaptainObvious
    Replies:
    20
    Views:
    4,489
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.