Shellac as glue

Discussion in 'Lost foam casting' started by garyhlucas, Jun 24, 2019.

  1. garyhlucas

    garyhlucas Silver

    I bought some shellac and tried laminating some 1” pink foam. Clamped for 12 hours and still wet inside. Do you need to sand the skin off the pink foam first?

    I finally got some 2” green foam material from Lowes. They had 2”, 1-1/2”, 1”, 3/4” and 9/16”. I got a sheet each of 3 sizes.

    I used to hate Lowes worse than Home Depot. Both local Home Depots had NO foam board at all. Looks like they might not carry it anymore. I see that some idiot in purchasing thinks that fully threaded bolts in all sizes are all they need to sell now! Looks like they are working hard at giving us even less choice than when they wiped out all the local hardware stores!
     
  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    When you say shellac, do you mean just a can off the shelf at Lowe’s or did you buy flake and mix your own?

    I’ve used just the retail stuff. I brush on a very thin coat with a foam brush on both surfaces. Let it dry. Then do it again and let it dry. A fan can accelerate drying to just a few minutes. After you apply the third thin coat, let for it dry until it gets tacky. At this point you can usually stick the pieces together like contact cement.

    The third coat reactivates the first coats. Sometimes just two coats will do it. Don’t laminate any larger area than needed because it’s tougher to get the entire surface at the same tackiness.

    Experiment with a couple small pieces. It only takes a couple minutes if you have a warm air stream from a hair dryer.

    I don’t think shellac burns out as clean but you can keep the joint very thin which is a bonus. The surface of the foam boards arent always uniformly flat which is unhelpful. Shellac is still a lot harder than foam so it doesn’t sand evenly but when dry it won’t load up you router cutters.

    Best,
    Kelly
     
  3. Melterskelter

    Melterskelter Gold Banner Member

    Shellac is a purely evaporative “setting” adhesive. From the first post I am concluding the parts were coated and immediately pressed together. There was nowhere for the solvent (ethanol) to go, so the glue line just continued to be liquid shellac. Shellac is the exact opposite of cyanoacrylate glue which polymerizes in an anaerobic environment. Used the way Kelly nicely outlined, the shellac is allowed to become almost dry, but will still cross link between two nearly dry surfaces. It will not bond if the surfaces become dry-hard before pressing them together. I’ve used it as Kelly recommended in machining thin flat pieces on a lathe faceplate and that is classic common watchmaking technique.

    Denis
     
  4. garyhlucas

    garyhlucas Silver

    Ah, the devil is in the details I did not know about.

    I was thinking about trying Loctite Go2:
    https://dm.henkel-dam.com/is/conten...ue-Carded-Bottle-1.75-oz-3.5-oz-2016-09-12pdf

    Says it works on polystyrene foam, moisture gives off methanol during cure and can be cleaned up with alcohol before curing. It is repositionable for about 5 minutes. Question of course is how hard to sand and will it burn out cleanly.
     
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Haven't used that one but the other important quality may be whether it loads a high speed cutting tool or abrasive. Since I recall you have a cnc router, if you are laminating stock where joints will lie in a tool path, you'll appreciate the importance of this quality. Once the cutter loads, you wont like what happens in the tool path from that point forward.

    When I see "elastic" in the cured description I take pause in this regard, but any chemically curing adhesive that can be thinned, or applied thin, and wont attack PS foam, is worth a try. High melt temp and hardness usually bodes better.

    Best,
    Kelly
     

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