Working Time, Pot Life, Open Time, Gel Time... Huh?!

Discussion in 'Materials' started by CatBuilder, Jul 21, 2010.

  1. hoytedow
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    hoytedow Wood Butcher

    That kind of temperature may be difficult to achieve in a tent. Would a heat gun be feasible?
     
  2. hoytedow
    Joined: Sep 2009
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    hoytedow Wood Butcher

    I guess you could build the tent out of Nomex. :p
     
  3. CatBuilder

    CatBuilder Previous Member

    So how do you achieve the temperatures? Put a heater into your tent in FL in the summer when the tent is already going to be 130F?
     
  4. hoytedow
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    hoytedow Wood Butcher

  5. Herman
    Joined: Oct 2004
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    Herman Senior Member

    Make an insulated tent (bubble wrap and tarpaulin) and use a gas heater. (Andrew's Heat For Hire, I believe they are now called Sykes Andrews)

    Also insulate the floor.

    One of my customers reaches 80 degrees C easily with 2 heaters, heating 12-15 meter boats.

    Oh, these radiaton lamps only heat a small area, their effect is limited. Good to sit under, but not much of use postcuring boats.
     
  6. apex1

    apex1 Guest

    Let me second that, and add:

    use a ventilator too, to get the temperature as even as possible.

    Regards
    Richard
     
  7. CatBuilder

    CatBuilder Previous Member

    Ok, I will find out the proper HDT and Tg for epoxies I use and do this as you say at the end... one big final post cure.

    I reach 48-50C no problem in the sun anyway with the doors of the building closed in the FL sunshine. I'm not sure I'll need all the insulation and to re-build my building. That's just too expensive. I'll go with what I currently have. Remember, this isn't a production facility, it's a one-off, so any money not spent on the boat itself is wasted.
     
  8. apex1

    apex1 Guest

    You should be able to reach 75°C easily with a gas heater and a ventilator in every sort of tent under the FL sun. I doubt you need any insulation to ramp up from say 45°C to 75 for about 6 hrs in the afternoon. And that might cost you a big bottle of gas, thats it.

    Especially for this reason some of us have been voting for building in FL, and not in the north.

    Regards
    Richard
     
  9. Herman
    Joined: Oct 2004
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    Location: The Netherlands

    Herman Senior Member

    Indeed, remember that when the guy is postcuring in NL, outside it can be freezing temperatures, and inside 15 degrees tops. (celcius). That is when you need insulation.

    However, some makeshift tent should not set you back much. It is no design contest!

    Keep in mind that you can (and will) get some print through, so save the last sanding job for after the postcure.
     
  10. kroberts
    Joined: Mar 2009
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    kroberts Senior Member

    I read the whole thread, but somehow I didn't see anyone recommend practicing the actual layup?

    Are you experienced with epoxy or is this a first project?

    I've done epoxy but nothing this big, and so far no boats. I know one guy who tried a relatively large layup on his first go and ruined the project. I would strongly recommend some practice and planning. I saw the recommendation about practicing the vacuum bag arrangement, which is actually really important. But the layup might need some too if you could be ruined by a lack of experience.

    I might suggest making a mock-up project with an example of all your basic shapes, say a cross section of the hull from center to edge for 8 feet or so. Could be out of anything, but just to give you an idea of how epoxy actually goes on with the tools you're using. For that matter it wouldn't actually have to be epoxy and glass, it could be anything similar and be useful for you.

    I might also recommend that you get a bunch of different tools to lay everything up and practice different approaches. Try a roller, brushes, a squeegee and whatever else you might imagine. Have cutting tools and scrapers and waxed paper handy when the final project happens. On my larger layups I use a paint roller. Definitely one thing that will make a huge difference on how long your epoxy is workable is the speed at which you get it spread out on the project. I would try to have 2 guys and maybe 3 to help, and maybe consider doing it at night unless the lights would cause too many bugs to be there.

    I would use a paint mixer on a drill, and have one guy whose job is to mix epoxy in relatively small batches. Then have another guy pour the newly mixed batch out on the hull, followed by the others spreading it down the side as quickly as possible in an even layer. Once it's there it should be workable for awhile. The epoxy guy needs to time his batches so he knows how long it takes, then watch you so the new batch gets ready right as you need it.

    The trick is learning to work your glass so the fibers don't get moved around, and learning the limits and techniques of your tools.

    One thing that some folks do for homebuilt aircraft wings is to work from one end and put down all the layers at once. They work to get a properly wet out project and have a region of workable epoxy on the wing. They wet, glass, wet, glass, wet glass and so on until done, the first layers slightly in front of the next and so on. The part they've finished is too gelled to work, and the other end is not even started yet but they have a workable region in the middle.

    That doesn't really give you much opportunity for the vacuum bag, but maybe it will give you an idea that can be managed.

    Good luck.
     
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  11. AndrewK
    Joined: Mar 2007
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    AndrewK Senior Member

    Richard makes a good point about use of ventilators to ensure the heat build up is even as possible. I get a whole bunch of $5 fans from charity stores, make sure there are plenty of them inside the hulls as well. Infra red thermometer ~$80 is also worth having as you can scan all of the surfaces very quickly to make sure there are no hot spots.
    I also prefer to use 4 small heaters rather than one or two larger ones.

    Because of your high humidity I would not recommend you do the glassing at night time, longer gel time hardener is a better option.
     
  12. hoytedow
    Joined: Sep 2009
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    hoytedow Wood Butcher

  13. CatBuilder

    CatBuilder Previous Member

    Good ideas on the fans, Andrew and Richard.

    I understand about not glassing at night. That makes sense when doing layups. How about my plywood bonding at night? No problem there, right? 3 plies of 3mm, scarfed, bonded and vacuum bagged at 3AM.
     
  14. apex1

    apex1 Guest

    I don´t see a problem.
     

  15. tunnels

    tunnels Previous Member

    With any kind of resin be it epoxy , polyester or vinylester warmth and heat play a really big part in the whole process of how quick it gels and goes hard and how quick it cures , Just because it had gone hard does not mean it has cured !!
    Progressively over a period of 24 hours the curing takes place and could get to 90+ % of it eventual hardenes but the full portentual hardness is only achived to if you heat cure the resin for a period of time , specifications can be got from the resin supplyer !!
    The types of hardeners used also play a big part in this whole gel and cure process as well , each can be speed up or slowed down , low time to get with quick cure , short gel time with a long cure time and so on , Need to get friendly with your supplyer / manufacture and tell them what you are looking for !!. Dont at any time start mixing you own hardeners
    Working and open time can be lengthened or shortened by what ever hardeners you use . If you mix a big quantity then you need to be able to get it on the job very quickly , Resin in bulk that has been mixed with a hardener begins to go off (harden ) and this chemical process produces heat , the heat begins to speed up the process and its a chain reaction till eventually you have a great hard smoking lump of sold very hot resin that is wasted and need to be taken outside .
    Its better to use a slower hardener and bigger diameter but shallower containers that will disapate the heat from the resin better . :)

    Something else that very few people take any notice of also is humidity . If you have high humidity the moisture in the air / glass /part you are glassing will slow the reaction of the resin also will slow and could kill the cure of the resin . Link temprature and humidity together you can get a quick geling , slow cureing rubbery disaster on you hands . :mad:
    70% relative humidity and below is ok !! The less the better . Once you start to get into the high 80% and above then expect problems of resin not and never curing properly !! Simply uping the hardener is not the answer as this leads to other problems of crystalizing the resin and making it weaker .
    Lots to think about !! But its not all bad news . :confused:
     
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