Polyester goof.

Discussion in 'Materials' started by member74761, Dec 15, 2021.

  1. member74761
    Joined: Aug 2021
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    Location: USA

    member74761 Junior Member

    Hello all.
    I’m going to admit guilt right out of the gate.
    I am an epoxy guy and just started dabbling with polyester and csm the other day. As csm isn’t too good with epoxy.
    I was trying to build up some bulk and radius for epoxy later. Well I goofed on the mekp ratio and ended up mixing at 1/2 %. 4 drops per oz.
    I think it will set or cure 1 day, month or year as I’ve seen poly start to set or quag left alone laying no catalyst at all. Especially around a heater, And this did have some, minimally..

    I’m really pre-coating stringers to help turn water or see if this makes a difference.
    Epoxy is the main cover or what will finish up with.
    Just killing time waiting on good weather.
    I know I could have gone with composite, but I have all this epoxy and lumber already taking up space and I am electing to use what I have rather than spend more $$ and just have more stuff left over.
    I’m probably at 5-6 coats right now and only need to encapsulate the bottom of stringers,
    I have only 1 stringer that I goofed on, I caught it by the time I made it to the 2nd. Well I did 2layers of csm and epoxy to follow.
    But like I said I’m just piddling and killing time and maybe someone in 20-60 years will say who did this.
    or not….
    It’s really my idea and peace of mind or making it mine.
     
  2. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    To start with, you're wasting your time and money precoating with polyester. Why start with a lesser product and rely on its comparatively poor bond for a base to put a better product over it.

    Now on to the actual question asked.

    In a thin film like you're applying, it probably won't cure very well, eventually getting hard is very different than actually crosslinking and curing completely.

    But, if it was just one thin layer it will probably cure along with any subsequent layers of properly catalyzed resin applied over it.

    Plus. Using drops to measure catalyst is a poor method at best, it leads to many avoidable failures.
     
    Last edited: Dec 15, 2021
  3. member74761
    Joined: Aug 2021
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    member74761 Junior Member

    Thank you ondarvr.

    I started out with epoxy and cloth,
    It rolled and buckled up on the radius and got several air pockets. The wood was already precoated with several coats of epoxy.
    and I get that polyester over epoxy is not the best, (at the very worst)but like I said I was building bulk after the fact.
    and will see how I do later with another layer of epoxy, over this radius.
    At worst I can throw all this away and start fresh,
    I’m still finding my way.

    Was only mixing an oz or 2 at the most, as I said I’m new with polyester and doing small steps.
    And it’s cold weather.

    again I appreciate the help and honesty.
     
  4. member74761
    Joined: Aug 2021
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    member74761 Junior Member

    And another thing.
    I had this polyester that had been just sitting around and was kind of thinking it’s going to go bad before I ever open it.
    So several things came into ply with me doing this.
     
  5. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Don't bother with the polyester, you aren't gaining anything by using it in combination with epoxy.

    And mixing an ounce or two of polyester correctly is almost impossible without extremely accurate scales.

    For lab use it's always 100 grams, this about the smallest amount you can mix and get reliable results.

    The only reason drops are suggested is that polyester chemistry appears on the surface to be very user friendly (idiot proof). Resin manufacturers never suggest or recommend counting drops.

    While even at catalyst ratios that are outside of recommendations it gets hard, getting hard and curing correctly are two very different things. This is one of the reasons for hate comments on polyester, people don't use proper techniques and then blame the resin for it failing.

    Epoxy isn't nearly as forgiving, any mixing ratio errors are more evident right away.
     
    bajansailor likes this.
  6. member74761
    Joined: Aug 2021
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    Location: USA

    member74761 Junior Member

    10/4. I’m using 20 Ml/Cc & 6Ml/Cc syringes for micro batches. 30 Ml being right at an ounce.
    I did sand the 2nd. Good stringer earlier today and added another layer of epoxy and glass. Seemed to work out well, for what I wanted.
    I guess now it’s a week of heat and indoors for the mishap mix.
    if it doesn’t do or cure to my liking it will get scraped and re-done.

    You know not to pick a fight or take away from the knowledge here or that you have given.
    But why,. Other than money do 99% of boats get built with polyester and we all seem to find rotted wood under this substance.
    But I must admit that I have found short comings with workmanship practices, meaning exposed wood, bare limber holes, etc..
    I’m still a rookie so my opinion isn’t very valuable.
    I just see plenty of room for production line quality,. improvement..,, But who am I to say or mutter such blast,foamy, lol
     
  7. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    There are a few reasons.

    1. Epoxy raises the cost to a price point where far fewer people could afford a boat.

    2. In a production environment epoxy is far more difficult and slower to use.

    3. In production epoxy has the tendency to be more toxic due to people becoming sensitized to it.

    4. With the all too typical poor attention to detail in a production shop it wouldn't make a difference which resin was used, the wood would rot away in the same amount of time.
     
  8. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    And there is no reliable way to mix one ounce of resin. Even the slightest variability in the amount of catalyst can drastically change the percent added when mixing so little at a time.
     
  9. member74761
    Joined: Aug 2021
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    Location: USA

    member74761 Junior Member

    Ondarvr, thank you for the reply and knowledge.
    I see the reasoning for your replies.
    All in all, providing this other stringer cures a little better,
    I think I can recover from my rookie error.
    And I probably still will end up with better than original after all is said and done.
    I can say with confidence that my epoxy coating is thick and thorough at this point.
    I’m over 5 layers not counting the 2 folly layers.
    And I still have the couple layers at install.

    thanks again
     

  10. redreuben
    Joined: Jan 2009
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    Location: South Lake Western Australia

    redreuben redreuben

    Stop pissing around with ounces and drops and go metric. 100 grams resin 1ml is 1% 2ml is 2%. Idiot proof.
    Existing stuff up.
    Hit it with a heat gun and see if it cures up hard, my guess is it won’t so rip it off and do it again. There are techniques to get a better bond on timber but if you can’t mix resin and catalyst it’s not worth bothering with. good luck.
     
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