Will Polyester resin eventually cure fully if applied below 60 degrees?

Discussion in 'Fiberglass and Composite Boat Building' started by sbklf, Nov 26, 2007.

  1. sbklf
    Joined: Feb 2006
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    sbklf Junior Member

    The instruction sheet I picked up from my resin supplier says that "applying resin below 60* may cause resin not to thoroughly cure". I applied some yesterday in 50* weather and it seemed to harden OK but is gumming up the sand disc today.

    Is this a partial cure I am seeing due to the temp? If so will it harden up in time?

    If it does not harden enough to sand properly should I re-do it?

    I am use to working with epoxy not affected by temp. One more question about poly, How long can I wait between layers and still get a chemical bond with polyester resin?
     
  2. Frosty

    Frosty Previous Member

    Good questions!! I shall be looking forward to the answers myself.
     
  3. Fanie
    Joined: Oct 2007
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    Fanie Fanie

    I assume it's polyester resin ?

    It is a chemical process and should dry out but over a longer period of time in low temperatures. If the humidity is high it's going to add to the time it will cure properly.

    Adding more hardner will get the polyester to 'green' quicker and do dry out somewhat quicker since it generates more heat, it is however not desirable as the polyester may become less flexable.

    If you could heat the item up for a couple of hours it will cure (not gumming the disk). I have also found that getting it in the sun, probably more so the UV light, does wonders. Whenever I get impatient with the drying rate I drag it in the sun here.

    Subsequent layers should be applied as soon as the resin hardens.

    Storage or shelf life While pourable Up to one year if stored correctly
    Pot life or gel time 20-40 min Depends on age, catalyst and accelerator
    Hardening time 30 min (green)
    Fully cured Three weeks from addition of catalyst

    Avoid sandpaper (sand or gold coloured) as it will clog badly particularly if the resin is wet. “Wet and dry” (black colour) is the only suitable kind and it must be used with plenty of water. A small amount of liquid soap added to the water will reduce friction. For power sanding, a very open grade of disc will clog least. Resin bonded discs must be used.
     
  4. lewisboats
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    lewisboats Obsessed Member

    You might also have used laminating resin which stays sticky. The other resin has a wax that floats to the top and seals out the air for a proper cure. As you are looking to add additional layers you should be fine. You will probably want to use a finishing resin for the last coat. Check with your supplier.

    Steve
     
  5. the1much
    Joined: Jul 2007
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    the1much hippie dreams

    it will cure in time,,but its not going to be strong or reliable. chemicle bonds happen within 24 hours with poly. if its just a "cosmetic" fix,,then id leave it,,,,but put the heat to it. if its "structural" then i'd re-do it,, and when working in cold temps add more mekp. and if you sand it out,,,i'd use 36 grit or 24,,and have plenty.and as lewisboats says,,if it doesnt have wax in it,, it will always be "gummy"
     
  6. sbklf
    Joined: Feb 2006
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    sbklf Junior Member

    It is poly resin. After three days now it is still has an ever so slight tack on the top. It is not structurally important enough to re-do so I will leave it, sand it best I can and go over it. In the meantime I am installing heat in my garage. One step foreward and two back like always. Thank you all for the replies.
     
  7. Fanie
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    Fanie Fanie

    You have to make sure the hardner to polyester ratio is correct. If you've used less than required the polyester will take longer to cure and will dry out over a longer period of time, but will remain tacky untill it has reached a certain stage.

    The heat source is going to make a huge huge difference. Don't sniff too much fumes while you're cozy in the heated garage, it isn't really a substitute for beer ;)

    The polyesters that has wax in them is called gellcoat and flocoat. Gellcoat has the property to let the waxy appear inward (ie to the mold), flocoat has the property to let the wax to the outside, so this you paint on afterwards, ie like in swimming pools.
     
  8. ronc98
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    ronc98 Junior Member

    If you can get a halogen light shining on it that will help heat it up. I used this method when painting and it helped alot.
     
  9. Frosty

    Frosty Previous Member

    OK seeing as though this seems to be the place to ask stupid questions but did'nt dare to.

    When my 1/2 gallon bottle polyester resin starts to solidify I bung in about 1/2 a liter of Acetone and give at a shake. In no time its gone back to its usuall consistency. Have I done anything wrong? it still seems to work ok?

    AND will epoxy paint hardener harden epoxy filler? or the other way round?
     
  10. the1much
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    the1much hippie dreams

    i dont know about the epoxy hardener question,,,,but you can reduce poly with acetone and its o.k. the liter part messin with my head tho..lol,,but it sounds like you might be reducing a little too much,and not using your poly enough,,,get more work and it wont solidify on ya ;) hehe
    i would put as little as it takes to get it flowing again. and yes reducing does mess with it. it brings its tencil strength down the more you reduce it.
     
  11. Fanie
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    Fanie Fanie

    Aye, I agree with mr too much, Frosty. The acetone evaporates very quickly once you spread it in the open. Seems you need a new boating project or else you may lose that half gallon over time (and the new boat), which would be a bloody shame.

    ronc98, if I'm not mistaken those lights are infra red lights to generate heat...
     
  12. AroMarine
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    AroMarine Junior Member

    Lewis is right if you are using a nonwaxed, laminating resin, it will stay tacky. If you are using waxed resin ,finishing resin, 50 degrees should be fine. Just make sure you fully catalyse. To get rid of the tacky layer depending on size of project you can wipe down a small area with acetone and alot of paper towels. Using the acetone and the towels pick up the uncured resin not just smearing it around your project. I have cleaned 3x5 ft areas this way. Not time or acetone efficient but does work. If it is bigger area and decent laminate I have used a 4.5" grinder with a masonry grinding stone. Yes it sounds funny but the stone will keep sanding and not gum up like fiber discs and sand paper. This has saved lots of $ on laminating projects.
     
  13. ratrace2
    Joined: Dec 2007
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    ratrace2 Senior Member

    My resin won't cure:

    Dude, get a hair-dryer and heat up enough of the surface so that the resin kick will cascade through the whole part.........In other words, take your best hair-dryer (be prepared to answer to your wife for this) and heat up about a 8"x 8" inch section of the part your trying to cure. When that heated section starts to kick, the heat from the kick will travel across the entire part setting off a chain reaction......wow......:)
     

  14. Fanie
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    Fanie Fanie

    Even better still. if you can get a box fitted over or on the part and a heat gun you get it cured in a few minutes. Take care, the heat inside the box builds up and stuff gets hell of a hot, similar to an oven. There must be an air outlet or else the box will blow up ;) and the heatgun or your/wife's hair dryer will burn out.
     
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