Polyester resin problems.

Discussion in 'Wooden Boat Building and Restoration' started by zoso, Jul 29, 2006.

  1. zoso
    Joined: Dec 2005
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    zoso Junior Member

    HI, I have made a good start on fixing my little sailboat but today I went out and got myself some polyester resin to coat the repaired sections where I had sanded back to timber. I made up a small batch and the instructions said add 1ml catalyst to 100g of poly on a warm day, 3ml catalyst on a cold day.

    So I added 2ml to 100g because it was warm(ish) thinking I would put a bit extra in to be safe but now its something like 6 hours later and it hasnt set yet!! How long should I have to wait before it sets?? what do I do if it doesn't set?? can I make up another batch of poly with like double the catalyst and paint that over the top to try and make it all set?? do I have to clean it off and start again?? help!!
     
  2. hansp77
    Joined: Mar 2006
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    hansp77

    no no no,
    don't coat over it.
    same mistakes have been talked about here somewhere very recently...

    I am not sure of the setting time with poly resin,
    but if it hasn't set in that time, you gotta clean it off and start again.
    If it is still recent, you migh be able to try to heat through the whole area..
    but I use epoxy- not poly- so I don't know..
     
  3. hansp77
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    hansp77

  4. zoso
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    zoso Junior Member

    bugger...

    Cheers for the reply, I had feared that might be the only solution :(

    Oh well its night time now so I'll wait till the morning and have a look. I get the feeling this will be a messy job tommorow :(
     
  5. lewisboats
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    lewisboats Obsessed Member

    Hit it with a hair dryer, if it doesn't jell in a few minutes, break out the gloves and acetone and clean it off. Suggestion: go online and browse for epoxy "tester" kits, get one of those.
     
  6. marshmat
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    marshmat Senior Member

    If it doesn't gel after a few minutes of heat as the others have suggested, it's shot. You gotta get it off, all of it. This is pretty common- even if you think you've mixed enough, remember you're mixing at a ratio of only 1-2% and that ratio must be perfectly uniform through the entire mixing cup. If it's not, it won't set right. As usual, epoxy is a helluva lot easier. But poly does work, if you're patient and take the time to mix, mix, mix for ever. (Tip- add 1 drop, mix, add 1 more drop, mix, etc- this makes it mix more evenly than adding all the MEKP at once).
     
  7. zoso
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    zoso Junior Member

    Poly, many thanks

    Ok, I woke up this morning and it has set in places, gone tacky in others but at least it has begun to set! I think it was colder than I thought yesterday and last night was freezing so probably not much happening. Today is much warmer and it appears to be setting ok. I might try the hair dryer trick though just to finish it off. I think perhaps the catalyst wasnt mixed well enough, I mixed and mixed for ages... oh well I'll just let what sets set and try to clean anything that doesnt set off.

    Thanks for all the help guys!!
     
  8. lewisboats
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    lewisboats Obsessed Member

    Next time, try warming up the resin before adding the catalyst, it will thin down a bit and mix better.

    Steve
     
  9. ernie
    Joined: Aug 2006
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    ernie Junior Member

    I mixed some poly once to do some repairs outside, hoping I could get it to kick before it got too cold that night. I didn’t, and the cold snap lasted for a couple of weeks. I also happened to work a lot of OT during that time and didn’t get back to cleanup and redo the work. On the first day of warm weather the gel kicked, it had only sagged a little, so I was lucky.
     
  10. roy marine
    Joined: Sep 2006
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    roy marine New Member

    fiberglass polyester resin

    The original question is almost a year old, however I read many questionable responses.

    The writer may complete the curing process by simply mixing a "hot" batch and painting over it. I write this without knowing all the details but I have used old hardener and/or old resin and corrected a slow cure with this technique.

    If the uncured batch had contact with water or moisture from working late in the day or above 75% humidity the resin may not cure.

    Also when polyester resin is used as a "paint process" the layer may be too thin to produce enough heat to cure. Here a second 'hot' batch may save things.

    Remember polyester resin never completely cures. It is always reactive and hence great for secondary bonding, typical of repairs.

    Epoxy has advantages in the presence of moisture and as a barrier below the waterline. Epoxy will cure anywhere but polyester will not cure if anything 'attacks' it during the cure period when it is highly reactive and vulnerable.
     

  11. mobhaid
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    mobhaid Junior Member

    Polyester requires three chemical components

    There exists the polyester resin and the polyester hardener and not well known is the accelerator chemical
    If you mix the accelerator chemical and the polyester hardener together first you risk to get an explosion from the high heat chemical mix .
    To reduce the risk of this type of accident it has been common practice since the 1980s era to only sell polyester with or without accelerator mixed in . The term is when purchasing polyester is to request slow set or fast set polyester .The slow set polyester is often hard to get will have little or no accelerator in it and is best suited for large molding such as large boat hull molding .Fast set polyester is the majority sold and suits small molding and repairs. The polyester will often set in to rubber state in about 30 minutes and hard set in few hours where its hard to cut off the rough edges and very hard after 24 hours .Many boat molders these days even use high speed polyester in molding hulls
    Some how i suspect you got polyester that has no accelerator pre mixed in often if the polyester is purple type color it often is rapid set polyester .If in dought ask the shop to sell you accelerator separately. In cold weather add more accelerator . Polyester shrinks 5% so many repairs will peel off due the shrink problem .Epoxy doesn't shrink .However there are times when epoxy is too soft and flexible compared to polyester so I have often done sandwich of the two materials .I might do thin layer of epoxy glass or carbon to be the sticky agent and then layers of polyester with some thin layers of epoxy in between .I find that reduces the risk of the repair peeling off and keeping the more rigid qualities of the polyester .The problem with epoxy is is unless the material is under pressure to squeeze out excess material in woven glass or carbon tows it tends to be too soft and then you have use lots more of it to get the needed strength.As a rough rule the slow set polyester risks to never set if the molding is small as there isn't enough heat made to set of the polyester .High level accelerated polyester isn't to critical to mix the hardener as slow set polyester .Unless your doing some large molding i can think of no advantage to ever use slow set polyester .However the shops will try to sell it as its much cheaper .

    David
     
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