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Thinning Bondo

Discussion in 'The Hokey Ass Message Board' started by blasted, Aug 11, 2008.

  1. blasted
    Joined: Feb 10, 2006
    Posts: 262

    from N. Tex

    Last edited: Dec 23, 2009
  2. Stude-sled
    Joined: Sep 24, 2006
    Posts: 678


    Evercoat part # 1249.
  3. Squablow
    Joined: Apr 26, 2005
    Posts: 14,406


    The guy who I've been working with uses fiberglass resin, the kind you buy with matting and the little drippy hardener tube. Don't use any of the hardener, just the resin (maybe that's what you're referring to as "poly resin"?).

    That's all I've ever heard of used to thin out filler. Also, if you have some old stuff and you let it sit on a shelf for a while, the solids sink to the bottom and the creamy goodness rises to the top, so you can scoop off some of the thinner stuff from the top of an old can.
  4. slddnmatt
    Joined: Mar 30, 2006
    Posts: 3,679


    ill thin it with some glaze coat by evercoat
    dan31 likes this.
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  5. overspray
    Joined: Jan 14, 2003
    Posts: 1,232


    That's about the best. The Evercoat glaze coat is an easy sanding nice viscosity in the first place, and you can blend it with body filler like their Rage and get the consistency you need and still have easy sanding. Thinning with too much resin alone could make the end result more brittle and harder to sand. It's easier to get a nicer sanding and more flexible mixture by blending the glaze coat and body filler.

  6. bobj49f2
    Joined: Jun 1, 2008
    Posts: 1,797


    I experimented with thinning filler to spray it, using it like a two part high build primer. I was able to thin it out using acetone.

    Look on the side of the can and find the chemicals it made of.
  7. 49ratfink
    Joined: Feb 8, 2004
    Posts: 17,696

    from California

    I wouldn't be messing with "thinning" bondo by mixing something else in there.

    I'm not sure what the problem is you are trying to correct. if you need a "light thin wipe of plastic" push harder with your spreader..
    The37Kid likes this.
  8. BigChief
    Joined: Jan 14, 2003
    Posts: 2,074


    Feather-Fill has been around for a million years and isn't that expensive if you want a sprayable polyester resin filler.
    seb fontana likes this.
  9. Skrayp
    Joined: May 31, 2008
    Posts: 197


    I use Ever Coat "Plastik Honey" #1249 in my Rage to help it flow out better. All it is, is the polyester resin that it already has in it. It really helps with pinholes and slows the dry time a bit on a humid day.
  10. bisquick59
    Joined: Nov 1, 2007
    Posts: 49

    from wahoo,ne

    acetone works great. just add a little, dont take much
  11. gotwood
    Joined: Apr 6, 2007
    Posts: 264

    from NYC

    Open any body shop supply catalog and there has to be about 50 different glaze type compounds. Anything from easy flow to almost as hard as regular.

    With that said why in the world would you go and be a chemist and start mixing different things together. If you can't spread a 2 part glazing putty to a thin layer you are doing something wrong. Try a rubber squegee.

    Don't blame the plastic when you have a problem later on down the road. Cost of can of bondo and acetone to make the home made so called sprayable filler vs just buying Featherfil??? Come on are you serious?? These are the exact reason why bondo has such a bad name.
    1934coupe likes this.
  12. 53floored100
    Joined: Apr 12, 2008
    Posts: 20

    from wichita

    I put a lil fiberglass resin in my body filler to thin it learned it at a body shop and makes spreading it easier to work with but I usually do it on a final coat I was told by old timers thats how they use to do it before glazecoat was invented
  13. BarryA
    Joined: Apr 22, 2007
    Posts: 643


    Do NOT use acetone to thin down polyester resin based fillers!! It will compromise the properties of the cured system.
    If you absolutely have to thin it use a sprayable polyester filler, straight polyester resin, or styrene monomer (in that order)

    Besides possibly affecting the sandability, these are also going to give more shrink to the system too ( but are at least likely to be compatible)

  14. eaglebeak
    Joined: Sep 17, 2007
    Posts: 1,120


  15. Misfit
    Joined: Sep 8, 2006
    Posts: 99

    from Upstate NY


    Thats what it's made for
    Joined: Jun 3, 2005
    Posts: 8,042


    Slick Sand. It's a more user-friendly version of Featherfill. It's a slower build and sands easier...waaaaayyy easier. If you don't get greedy with it shrinking is no concern. Good luck.
  17. weemark
    Joined: Sep 1, 2002
    Posts: 814

    from scotland

    cant you just use a couple of coats of high build primer then flat it back, that will more than fill in sanding scratches.
  18. Shaggy
    Joined: Mar 6, 2003
    Posts: 5,208

    from Sultan, WA

    Yep good stuff
    Tri-power37 likes this.
  19. Willy301
    Joined: Nov 16, 2007
    Posts: 1,426


    I have actually started using Marson Platinum filler when I need filler. It is made by Bondo, and is about 2/3 the viscocity of regular bondo. When I need it thinner, I put it in my paint shaker for about 2-3 minutes. This ensures it is mixed well and also thins it down because of the heat generated. Any time you use the "skim" that has settled or adding another chemical to thin it, you compromise the chemical make up and cause potential problems down the road. If I need thinner material than that, I use "Icing" catalyzed glazing compound, it has enough for the in between projects, but is not quite as thick as regular putty.
  20. blowby
    Joined: Dec 27, 2012
    Posts: 6,592

    from Nicasio Ca

    Yeah, old thread, and here's a good reason why I search them. Needed to do some minor repair work today. My auto body class is closed for the shelter order so I couldn't get some killer Rage Gold like I normally use. Didn't want to chance a trip to the auto parts, supposed to be essential travel only and I've made it this far without getting sick. Had a small can of Bondo brand filler on the shelf but it was too thick, not lumpy, just thick. I was about to dump acetone in it when I though I'd better check that out first and found this thread. Never would have thought of fiberglass resin, had a pint of that too. Man, worked like a treat, nice and creamy, dried and sanded as normal.
    Hombre and VANDENPLAS like this.
  21. Slopok
    Joined: Jan 30, 2012
    Posts: 2,551


    If you have access to a paint shaker put it on there for a while, makes it nice and smooth!
    Hombre and blowby like this.
  22. Kan Kustom
    Joined: Jul 20, 2009
    Posts: 2,553

    Kan Kustom

    Styrene is the thinner in body filler. It is the part that evaporates off to harden the filler in addition to the MEK hardener which is a radical to create heat. Styrene to polyester body filler is like paint thinner is to paint.
  23. bubba55
    Joined: Feb 27, 2011
    Posts: 316


    Good post @ Blowby
    I too have been miserably miserly with materials and supplies - writing down notes of things to get after it safe to go out - now where did I leave my pad
    Stay safe everyone

    Sent from my iPhone using H.A.M.B.
    blowby and Hombre like this.
  24. Roothawg
    Joined: Mar 14, 2001
    Posts: 19,718


    @K13 to the front desk......
  25. Moriarity
    Joined: Apr 11, 2001
    Posts: 18,112

    Staff Member

    I have successfully used polyester (fiberglass) resin dozens of times
    Kan Kustom likes this.
  26. Kan Kustom
    Joined: Jul 20, 2009
    Posts: 2,553

    Kan Kustom

    Polyester resin is thinned to viscosity by liquid styrene. Fresh resin will thin old filler to a point because of the styrene in it . The styrene is what has evaporated over time from the filler. Fiberglass resin, silica and styrene are what body filler is made of. The styrene is the thinner and is what needs replaced. It will take less styrene to bring it back faster than adding more resin which is thinned with styrene.
  27. It is NOT a good idea to use fiberglass resin to thin fillers. Thy are not the same as the resins used in filler hence the need for different types of hardeners to catalyze. Using resin can result in shrinking down the road because BPO style hardeners that come with body fillers are not strong enough to fully harden fiberglass resin. There are products specifically designed to do this (Plastic Honey, Supercharger).
    The "I've done it many times without problems" camp is the same as it is with anything else used improperly it great when it works but you are going to wish you hadn't done it if you get your painted car out into the sun and the areas where you have used thinned filler start to sink.
    Roothawg likes this.
  28. brasscarguy
    Joined: Jun 12, 2010
    Posts: 179

    from seattle

    I always put bondo in my rotary paint mixer for 5-10 mins depending on how long its been on the shelf. It comes out very creamy and easy to spread. Also I store my bondo upside down so the resin will go to the bottom of the can stored up side down. To use it I put it in the mixer as stated and then it is smooth an ready to spread easy.. Using a rotary mixer eliminates air bubbles.

    just sayin'

  29. GEET
    Joined: May 15, 2007
    Posts: 46


    Acetone works great !
  30. Kan Kustom
    Joined: Jul 20, 2009
    Posts: 2,553

    Kan Kustom

    I have been in the fiberglass industry for over thirty years. Have used both BPO (Benzoil Peroxide) and MEK ( Methyl Ethyl Ketone) hardened polyester. My information has came from Alpha Owens Corning, Ashland chemical companies and a direct line into the Corvette engineering department. I may be wrong but with my limited expertise on this subject, I think these are a pretty good source. I usually will stand down when I am not very sure of a subject but this has consumed a great deal of my life. I will stick with the done it for years camp.
    The37Kid likes this.

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