Thinning Epoxy?

Discussion in 'Materials' started by Frog4, Oct 17, 2011.

  1. DGreenwood
    Joined: Aug 2004
    Posts: 722
    Likes: 40, Points: 28, Legacy Rep: 507
    Location: New York

    DGreenwood Senior Member

    Did you ever wonder why the two biggest suppliers of boat building epoxy products (Gougeon Brothers, Inc. and SP) don't sell a thinned epoxy for the market? I mean they have enough market clout to annihilate Smith Bros and their ilk!

    Par you are a very patient man but I am afraid you are up against "True Believers"--- If they wanted evidence they only have to call Gougeon. They have done so much testing that has been of benefit to us all and they are happy to share their knowledge.
     
    1 person likes this.
  2. TeddyDiver
    Joined: Dec 2007
    Posts: 2,585
    Likes: 125, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    So from 2mm to 2.3mm.. it's 15% more. You should do the same test with uncoated sample. Any quesses what's the difference? :p
     
  3. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 481, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    That's not testing Teddy. There's no base line, no encapsulation, no procedures and he wants my data too, but hasn't the bother to look up the industry leader's data.
     
  4. CC Guy
    Joined: Sep 2011
    Posts: 12
    Likes: 2, Points: 0, Legacy Rep: 20
    Location: UK

    CC Guy Junior Member

    Hi par as I thought just your opinion,from one part of the world which you apply to the rest, I fully except I have gone beyond my epoxy manufacturers recommended thinning limit and have been clear on what I done,I see this may not fit some parts of the world thinking and as you can see something has happened to the Ply with only 75% thinned epoxy coating.

    My simple test was see how thinned epoxy holds up should it come in contact with moisture for long period.

    TeddyDiver, think your missing the word "Ply" and the % is 2.8 from that you should be able to work out how many layers and glue line.
     
  5. TeddyDiver
    Joined: Dec 2007
    Posts: 2,585
    Likes: 125, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    And you are missing the point it's not watertight.. (the % is just irrelevant) ;)
     
  6. ancient kayaker
    Joined: Aug 2006
    Posts: 3,497
    Likes: 147, Points: 0, Legacy Rep: 2291
    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    Interesting thread: as usual I come late into the discussion but I still manage to find a few comments to make.

    This works, but . . . Several years ago I was interested in how strong a plain, unreinforced butt joint between ply planks could be, using epoxy. The trick of pre-heating the ply significantly increased the resultant joint strength - but still not equal to the strength of the ply. Not only does the heat reduce epoxy viscosity but - as PAR noted - it causes the air in the open pores of the wood to expand; then as the wood cools the epoxy is drawn into the wood cells. Very absorbent woods like Okume have longer open cells so it works best on them; Oak maybe, but I doubt it is as effective on most hardwoods. I assume the additional area of the bond was responsible for the increased joint strength, which is probably not irrelevant for coating purposes despite contrary opinions expressed above.

    It was such a hassle to do on an entire hull that I didn’t go ahead with the idea. Basically for consistent results with either bonding or sealing the entire hull needs to be baked, coated evenly while the hull remains hot, then moved to a cooler location and recoated, all before the epoxy hardens.

    The bond is stronger than the cross-grain strength of the wood which is how it is usually used. End-grain is typically 10x stronger and joints are handicapped by the tendency of the epoxy to be drawn away from the joint, leaving voids and reduced bond area. Since the edge of ply is partly end-grain I found it next-to-impossible to achieve full bond strength. Again, not irrelevant for coating purposes, but noted here for interest.
     
  7. sabahcat
    Joined: Dec 2008
    Posts: 792
    Likes: 28, Points: 0, Legacy Rep: 273
    Location: australia

    sabahcat Senior Member

    Actually, West System / Gougeon Bros. used to have articles on thinning their epoxy resins and if you search you will find many links to west system sites (which no longer work) saying to do it for extra penetration.
    Here is one http://westsystem.com/ewmag/14/ThinningEpoxy.html

    If I had a dig through my reference books I am sure that my old "Gougeon Brothers on Boat Construction" also made reference to it.
     
  8. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 481, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    West System did open their thinning discussion with the understanding that they don't recommend it and that other techniques work far better, but for those that wanted to play with diluted epoxy, isopropyl alcohol as was xylene.
     
  9. Frog4
    Joined: Oct 2011
    Posts: 150
    Likes: 2, Points: 0, Legacy Rep: 12
    Location: Arizona desert

    Frog4 Proletariat

  10. sabahcat
    Joined: Dec 2008
    Posts: 792
    Likes: 28, Points: 0, Legacy Rep: 273
    Location: australia

    sabahcat Senior Member

    Thanks
    Like I have said earlier, tests I performed on ply samples with a thinned epoxy coat followed by a layer of unthinned epoxy and glass showed it was far more difficult to peel off the glass than it was on a straight epoxy glass sample, which peeled quite easily

    To me, that showed that the former had more strength due to increased penetration.

    As for moisture resistance, you need more than one coat of resin for an effective moisture barrier anyway, so the following coats can be unadulterated.

    In all my ply surfaces in wet/humid/unable to be accessed areas have added this product to the resin for the first coat, for my own piece of mind and to aid in penetration
     
  11. ancient kayaker
    Joined: Aug 2006
    Posts: 3,497
    Likes: 147, Points: 0, Legacy Rep: 2291
    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    - per your post #38 you thinned the epoxy with only 2% alcohol so perhaps that explains why you had good results. Those who plan to use thinned epoxy should bear this in mind.
     
  12. tunnels

    tunnels Previous Member

    Have you been working with the guys here in China ??
    thats the sort of stupid things they try to do and wonder why stuff falls apart .
    Think boy !!! :mad:
     
  13. sabahcat
    Joined: Dec 2008
    Posts: 792
    Likes: 28, Points: 0, Legacy Rep: 273
    Location: australia

    sabahcat Senior Member

    Think?
    I did, I even did real life testing to confirm my thoughts.
    The results, I had, speak for them self.
     
  14. ancient kayaker
    Joined: Aug 2006
    Posts: 3,497
    Likes: 147, Points: 0, Legacy Rep: 2291
    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    If you're responding to Sabahcat's posts I see nothing stupid about actually testing to see what is true and what is opinion or mythology. I thought you had a better opinion of the Chinese in general based on some of your posts -

    http://www.boatdesign.net/forums/materials/marine-plywoods-china-revisited-39870.html#post489404 - post #7
    - also posts #9, 12 and 23 in the same thread :confused:
     

  15. tunnels

    tunnels Previous Member

    I was witness to some guys using uncatalysed resin to roll down some chopper gun overspray fibres half way through a hull lay up . I went off the deepend for even thinking of doing such a thing !! what about the secondry bond strength of the next laminate that goes on !, is it 100% or just 50% ??
    If you work in a factory manufacturing enviroment and have 20 workers all watching each other and they start doing dumb things like that what would you do ??
    Living by the seat of you pants you leaving to many things in you life to chance !,when dealing with any part of a boats manufacture you all ways do things 110% right never leave anything to chance because it will cost you or some one you love there life !!.
    What works today may not work exactly the same next time .
    If your boat comes apart at the seams 100 miles off shore in a rought sea its not only our life thats at risk its the souls that will hear you cryes for help and come to rescue you!!Simply because of not doing something properly .
    So remeber as you walk towards those pearly gates in the sky ,watch for that slippery patch of uncatalysed resin you left on your path !!:)
     
Loading...
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.