Thining Gelcoat question..

Discussion in 'Fiberglass and Composite Boat Building' started by boatdude, Mar 12, 2008.

  1. boatdude
    Joined: Dec 2007
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: california

    boatdude Junior Member

    Do you calculate the catalyst amount based on the original gelcoat amount or the final amount total after it is thinned?




    Also, what are the limits on catalyst % at 70 degrees?

    Is the same for gelcoat thinned 10% with acetone?

    Just doing small throw away tests I've found the thinning with acetone really retards the cure time at 2% catalyst. I need a faster cure when using gelcoat thinned with acetone.


    I know some guys are going to yell at me for thinning with acetone.





    Thanks.
     
  2. the1much
    Joined: Jul 2007
    Posts: 3,897
    Likes: 44, Points: 0, Legacy Rep: 696
    Location: maine

    the1much hippie dreams

    how come your not using styrene to thin?
     
  3. tinhorn
    Joined: Jan 2008
    Posts: 575
    Likes: 20, Points: 18, Legacy Rep: 310
    Location: Massachusetts South Shore.

    tinhorn Senior Member

    Acetone. Tsk, tsk. They say that if you need to thin it at all, you don't have a gelcoat problem, you have an equipment problem. Yup, my equipment problem was that I was too cheap to spend thousands of dollars on a dedicated system that would take up half my shop space.

    I was one of those guys who didn't keep a gallon of styrene around just in case I needed to thin some gelcoat. I read some guy's theory once that acetone evaporates between the gun and the mold, so it was actually preferred to styrene. Perhaps he was just trying to justify being a cheapskate.

    I wouldn't go much hotter than 2%, measured against the thinned gelcoat. To quicken the kick times, I used a 5000-watt electric furnace in a small shop to control the temperature. Spray, clean the gun, turn the thermostat to the max, go drink coffee...
     
    Last edited: Mar 13, 2008
  4. boatdude
    Joined: Dec 2007
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: california

    boatdude Junior Member

    Thanks guys.

    Does thinning with styrene retard the cure time?
     
  5. jim lee
    Joined: Feb 2007
    Posts: 368
    Likes: 20, Points: 18, Legacy Rep: 247
    Location: Anacortes, WA

    jim lee Senior Member

    Acetone has styrene in it. But it can contain other stuff as well and you can't be sure what the other stuff is. From what people tell me, its the other things in there that can cause unpredictable chemical reactions to your resin. Mostly it works, but some times your reaction times are way off or behave oddly. Hence using straight styrene is a the better choice.

    Anyway you initialte the resin at your 1% or 2% by weight of the resin alone. (At least thats what I was taught and what we do in our shop.)

    As for spraying unthinned gelcoat, like into a mold, have you tried a dump gun? They're only $130 and dead easy to clean up after.

    Hope this helps.

    -jim lee
     
  6. ondarvr
    Joined: Dec 2005
    Posts: 2,611
    Likes: 372, Points: 83, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    Small amounts of acetone or styrene can be used and may have few negative results that are noticable, but it can affect how well the gel coat holds up over time.

    While not recommended, if you stick with less than about 5% of either product you normally won't see any issues, the problem is, in the field that 5% turns into 25 to 40% and then there are major issues to deal with.

    Styrene is a very important component of gel coat, but it is not as water or weather resistant as the base resin used to make gel coat, plus it has little strength and can be brittle. These are not features you want in a gel coat, so that's why we recommend against using it.

    There are products designed for reducing the viscosty of gel coat so it can be sprayed easier, they will work better than acetone or styrene and will hold up better over time. You can get patchaid type products that will reduce the viscosity and speed up the gel time, or just one or the other.

    Gel coat can be sprayed through many different types of equipment and when done correctly they can all produce good results. For small jobs a dump gun or pressure pot will work, as the part gets larger and the volume of gel coat being sprayed goes up, then the specialized equipment becomes more important.

    It's best to stay around 2% on catalyst, but going up to three may be needed at times, more than that and you may start having problems with the quality of the cured gel coat.
     
  7. Roly
    Joined: Jul 2005
    Posts: 508
    Likes: 23, Points: 18, Legacy Rep: 222
    Location: NZ

    Roly Senior Member

    I haven't heard of patch aid here. What is in it?

    I guess you sell it, so that is a million dollar question. :D
    sorry.
     
  8. ondarvr
    Joined: Dec 2005
    Posts: 2,611
    Likes: 372, Points: 83, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    I normally refer to them as a patchaid type products. There are many different formulas for these products and several companies make them. Some have styrene and some don't, but they may also have other ingredients to lower viscosity and speed up the cure. Even these products which are designed for this purpose can have a down side, especially when too much is added.
     
  9. jim lee
    Joined: Feb 2007
    Posts: 368
    Likes: 20, Points: 18, Legacy Rep: 247
    Location: Anacortes, WA

    jim lee Senior Member

    Well I just went and asked the guru and the answer was Yes it does retard the cure time. And it does it in an odd way; The resin stays liquid longer, but when it does go off it does it much faster. I've seen this in person where a bucket of resin was runny then one second or two later was solid. It was older resin we'd thinned with either styrene or acetone.

    -jim lee
     
  10. fiberglass jack
    Joined: Dec 2005
    Posts: 463
    Likes: 16, Points: 0, Legacy Rep: 95
    Location: toronto

    fiberglass jack Senior Member

    resin and gelcoat contain promoters like dma and colbalt, this is what makes the resin go hard when the mekp catalist is added. you can buy unpromoted resins and gelcoat that you can mix with a lower ratio of promoters ie a summer or winter resin, by adding styrine or acetone you are reducing the ratio of promoters so it will take longer but the quality and propertys are lost some what, what i would do is thin your gel with styrine and add some colbalt say 1% this way the cure time wont long be careful and do some tests first for the pot life and what ever you do DO NOT MIX THE COLBALT AND HARDNER TO THE GEL AT THE SAME TIME the 2 will combust . its this reaction that makes the resin get hot and cure
     

  11. dereksireci
    Joined: Jun 2004
    Posts: 163
    Likes: 3, Points: 0, Legacy Rep: 37
    Location: South Carolina

    dereksireci Senior Member

    While not a self proclaimed "guru", this is my take.

    Acetone is a solvent which dilutes the material to be sprayed but does not participate in the chemical reaction. It can have adverse effects including changing the color of the gelcoat.

    Patchaid is a resin product sold by Cook Composites and Polymers. It comes in formulas to speed cure or to extend cure depending on the size of the repair. It also appears to contain wax so the resin will cure in the presence of air as well as light stabilizers to help the patch not dis-color.

    I've never seen gelcoat thinned with anything other than Patchaid or a similar product at a boat building plant. Out in the the trenches of the boat yard it may be a different story. I showed a "how to" video to my composites class a few weeks ago and the guy on the video thinned his gelcoat with acetone. There you go. Maybe he was a guru!

    In the world of manufacturing we don't take chances.

    djs
     
Loading...
Similar Threads
  1. JackyJ243
    Replies:
    8
    Views:
    529
  2. Nachtvlinder
    Replies:
    2
    Views:
    257
  3. Scuff
    Replies:
    12
    Views:
    819
  4. doogymon
    Replies:
    12
    Views:
    625
  5. wesley Sherman
    Replies:
    14
    Views:
    1,368
  6. bedfordd
    Replies:
    9
    Views:
    1,337
  7. E350
    Replies:
    7
    Views:
    2,449
  8. bch
    Replies:
    6
    Views:
    975
  9. Charlie A Bess
    Replies:
    13
    Views:
    1,613
  10. Crayolo
    Replies:
    5
    Views:
    1,433
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.