Transparent fibreglass over Mahogany - Pros + cons

Discussion in 'Boatbuilding' started by jake101, Oct 16, 2017.

  1. jake101
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    jake101 Junior Member

    Hi all

    All the kayak/canoe builds i have seen seem to use a light cloth with 105/207 west system epoxy then a few coats of varnish to finish. but you dont seem to see it too much on other bright work like on the decks of a J-craft for example.

    I want to build a boat with mahogany decks (around 30foot) but don't want to be varnishing every year and don't want any cracking around the joins in the wood (where it always seem to go bad). the decks will be developable surfaces.

    my plan at this stage is to go with Awlgrip's Awlwood MA. its almost perfectly clear and sprays well and seems to be abit more flexible than polyurethane varnishes. its also super easy to repair. and it can fill big dints in wood. and its a single pack.

    is it worth putting down a layer of glass first?

    will it add much goodness to the deck effectively making it a fibreglass deck (glass over ply like)?

    What are the pros and cons of transparent fibreglass over wood?

    why is it only kayaks and surfboards that glass over the wood and most other boats just use varnish/clear over wood.?

    is it a pain to repair dints/scratches?

    thanks for any help/advice

    I have done a search but not much came up except for some methods.

    Jake
     
  2. Blueknarr
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    Blueknarr Junior Member

     
  3. upchurchmr
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    upchurchmr Senior Member

    You might look at the recommendations from guys who have done this before.
    Gougeon Brothers on Boat Construction book - WEST SYSTEM Epoxy http://www.westsystem.com/the-gougeon-brothers-on-boat-construction/
    Its a free download of a book that has shown how to epoxy / glass construct boats for 30+ years.
    Some will say they are just trying to sell epoxy, but who would know how to do it right?
    Someone you never heard of or guys who made a living?

    No doubt you have to protect the glass with varnish or other methods.
    Personally on a kayak I have been using Automotive clear coat like on high dollar cars.
    It does scuff and leaves a whiteish mark - possibly not the best on a boat deck.

    The one thing the book says is if you want the wood protected, you need to apply epoxy to all sides of the wood, to prevent movement due to moisture. A layer of glass makes it easy to build up the epoxy, and adds strength - including abrasion resistance.
    I don't do real boats, so read the book, and West System has a hotline for questions. There are also lots of previous project reports available from them.

    Good luck.
     
  4. jake101
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    jake101 Junior Member

    Thank you for your input blokes.

    I've been doing some more looking and found this article - WOW 17 Years Later http://epoxyworks.com/index.php/wow-17-years-later/#more-5603

    Its written by Mark Bronkalla about his 20' runabout that is almost fully sheathed in glass (4 and 6 oz). hes been running it quite hard for the last 17 years including extended period in the sun and in the water. he does mention a small batch where the glass has blistered and some damage from the anchor bashing the hull. but that may have to do with using an oil based stain.

    this is the best selling point (from mark bronkalla) of using glass over wood - ''Some other builders had questioned my use of fiberglass on the deck. In another experiment, I coated the repaired section with epoxy without fiberglass. This was a mistake. The joints between the walnut opened up by the end of summer.'' my biggest dislike of brightwork is when a join or seam cracks and breaks the finish allowing water and sun to bleach the wood making it very difficult to repair.

    I have also found this test on a kayak making site - The Epoxy Test - six epoxy types tested for UV damage http://www.oneoceankayaks.com/Epoxtest.htm

    it seems to last at least a year even unprotected by any varnish. his greatest bit of advice that comes from the testing is to add a few extra coats for insurance. he did three coats of epoxy but where he had accidentally dropped a blob the finish was the best.


    Blueknarr - you say it won't add any benefit or goodness, and then you also say that they put it on canoes to help with abrasion resistance (which is part of what i am aiming for) --- also if it is so difficult to bond fibreglass to wood, how a stich and glue so popular?

    Upchurchmr - why do you go with automotive clears? have you used any of the 'marine' polyurethane varnishes?

    jake
     
    Last edited: Oct 17, 2017
  5. upchurchmr
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    upchurchmr Senior Member

    Jake,

    I am either ok at applying varnish (sometimes) or poor (usually, IMHO).
    I have used Minwax Spar varnish which is a "marine polyurethane" for kayaks.
    My poor application leaves me with runs, drips, etc. If I sand and polish to get a smooth finish, its not possible to be sure you have an even coat - which has resulted in local damage to the coating in less than a year.
    Really, the reason it showed up so bad was that I had a bad attitude and didn't cover the boats in the Texas summer sun. Didn't take long even where I didn't sand and polish before I had significant damage.

    Most people will tell you to re-varnish each year or two if not covered.

    Automotive clear will typically last for at least 10 years on a car (there are different grades of course).

    Beyond that, when I got the kayak back from the painter, the clarity of the finish was so significantly better than the varnish that people were really astounded. These are people who had seen my other varnished boats.

    Honestly, furniture like finish may not really be something you want. A boat gets used after all ( or should be).

    BTW, please don't listen to anyone who tells you un-protected epoxy will last a year. I have had West epoxy go bad in 4 months unprotected. If it is not totally destroyed, it still looks worse and would need to be sanded and polished to look new.
    Unfortunately, Epoxy tends to separate from the wood when it is sundamaged. In that case there is nothing you can do by strip it off.
    That is lots of time and expense to potentially throw away.
    My experience is limited to two epoxies, so "buyer beware" for others.

    You also can't expect anything but damage if you have an anchor bashing a fiberglass epoxy coating. It does not have superhuman strength.

    Good luck.
    Marc
     
  6. PAR
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    PAR Yacht Designer/Builder

    I have a similar environment to yours (subtropical) and varnish (real alkyds) only last a year, before needing some touch ups or recoating. Polyurethanes, like MinWax lasts about 18 months, but is much harder to repair or recoat without lap marks and obvious repairs.

    Some epoxies are using UV inhibitors to help them stave off break down, but these are the exact same inhibitors used in clear paints and just don't hold up that long. As a result the epoxy starts to turn darker in color, usually within a few months, though at a slower rate of non-UV inhibitors added formulations.

    Two pack automotive urethane and acrylic urethane coatings do last, but this is because of the base coat, not the clear coat. Again, it's the same UV inhibitors employed and these break down in time.

    Simply put, clear coats over wood are the hardest finishes to live with. You'll continously chase the coating with touch ups and repairs, with full up re-coats every few years. This is the nature of clear over wood, regardless of epoxy or fabrics used in addition to the clear coating. In short, be careful what you wish for, as you might just have to live with it.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    Window glass blocks UVB rays, does glass fibre do the same ? What kills clear coats, UVA or UVB ?
     
  8. Blueknarr
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    Blueknarr Junior Member

    Sorry, made some assumptions. Many think that adding cloth will increase strength of wood. It would take almost the same thickness of cloth as the original wood, to add significant strength.
    Cloth does add mucho strength to the joints in wood construction. With stich and tape many joints will not need additional structural framework, especially on small boats.

    I have a biased position, in that I repair boats for a living. I rarely come across cloth fully bonded to its underlying wood.
     
  9. jake101
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    jake101 Junior Member

    PAR- how does the base coat make the top clear coat last longer -re automotive clears? other than the fact that wood is not as stable as painted steel.

    Mr efficiency - that's also something I considered. how thick does it have to be to block the UVB? or is there a percentage per mm?

    a very large majority (almost all) of the failures i see on brightwork are at the joins between wood, i almost can't remember the last time i saw failure somewhere else unless the coating was not applied properly in the first place (thickness or poor prep). So if the fibreglass makes the brightwork stable, then it is a very good step ahead in reducing maintenance. therefore it must be worth doing???

    jake
     
  10. PAR
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    PAR Yacht Designer/Builder

    There are a number of chemical reasons the base coat protects the substrate and over coats, some absorption, others dispersion, etc. It's not so much the formulation of the coatings but the film thickness for effective coating performance, at least in terms of clear wooden finishes. 'Glass over wood doesn't make the wood more stable, only full encapsulation does and this is coating formulation (epoxy) and film thickness (10 mils minimum). Yes, joints and edges are common places for coating failures, usually from not sufficient film thickness in these areas also too crisp on the edges, to the film retracks a touch as it cures, dramatically thinning these areas, but flat surfaces are also subject to breakdown, from UV inhibitor break down. As a rule, if you want to increase the maintenance required in clear finishes on wood, just put a 'glass fabric under the clear, because you have to manage both the coating and the fabric. Unless you need the additional abrasion resistance of the fabric, it's generally wise to not have it under a clear coat. If you need additional abrasion resistance on the wood, you're far better off painting or incorporating the texture into the epoxy, rather than using a fabric.
    81.jpg
    This is a classic example of a textured epoxy coating on a deck. You can see the waterways, margins, etc. This texture was painted over, naturally, as clear texture coats can be awful looking though I have seen some try it. The nice thing about this system is there's no particulates to get knocked out of the coating and you can strip it or sand it if desired.
     
  11. pauloman
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    pauloman Epoxy Vendor

    best is an epoxy with bubble breaker in it, then a few coats of real marine varnish (for mil thickness and 'warmth') - then 2 poly poly with lots of uv blockers and absorbers. This is a 3 coat system - paul oman- progressive epoxy polymers inc



     
  12. fallguy
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    fallguy Senior Member

    Your question is a bit ambiguous, but you got mostly good answers.

    Mahog ply or mahog 2" strips, for example? Deck above cuddy or appearance deck?

    If you have a lot of seams; you might consider a 6 oz fabric and epoxy to hold the deck together some and help prevent ingress. I did a sailboat deck with glass and epoxy to prevent ingress. But the sun is mean.

    upchurch has great advice; epoxy will sun damage easily - I have a rarely used strip canoe and I neglected to varnish the inside and the boat spent maybe ?2 months of its 15 year life outside (otherwise upside down in a building) and UV has degraded the inside epoxy and I need to sand and reepoxy it and poly... upchurch also has good reality advice; you'll not get a long window of no maintenance on a bright finish; expect 24 months maximum between reapplication and in constant Austrailian sun; perhaps less.

    Paul-what is the bubble breaker? Previous nightmares with clear finishes and bubbles; never heard of such a thing.
    Also, for Paul, does the peanut butter and jelly rule apply? Are you suggesting varnish under with polyurethane above it? If so, why? Can the poly support more UV inhib? Thanks very much.
     
  13. Blueknarr
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    Blueknarr Junior Member


    Different Paul, I had to reread to see if you were directing at me. You weren't, but I'll still throw in 2 cents.

    Grooved rollers used when laying resonated cloth are often called bubble busters.

    I don't trust the polyurethane over varnish sandwich either.

    The average single part polyurethane is slightly more UV resistant than the average varnish. Polyurethane is also harder to touch-up. Two part poly more so on both accounts.

    I like the warmth the oils commonly used in varnish give wood. However, they must be applied directly to the wood to be effective. Varnish over epoxy will produce the feel of varnish, but still retain the look of epoxy coated wood.
     
  14. pauloman
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    pauloman Epoxy Vendor

    you cannot add uv protection products to thermoset resin systems like epoxies. That said some epoxy curing agents yellow less and slower than others.

    UV blockers and protection can be added to 2 part polys - not generally done as they are expensive additions. Exceptions are auto clear clear and our acrylic poly uv plus product (large amounts of uv blocks and uv absorbers were added at my request about 12 years ago. The web page on it shows some UV test exposure results. Best is epoxy base - spar varnish - then the 2 part acylic poly plus.... This is about as good as it gets.

    As per another question above - we are the only folks that add bubble breakers to our Basic No Blush Marine epoxy - this is because it also gets used on tables and bartops, as well as art works. A lot less bubbles than those other website table top epoxies that sell junk and have no control over the epoxy formulation.
    paul oman - progressive epoxy polymers inc
     

  15. Blueknarr
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    Blueknarr Junior Member


    Thanks for the clarification.

    Paul
     
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