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Sealing Plaster

Discussion in 'Molding and Casting' started by 1tahr, Jun 2, 2023.

  1. 1tahr

    1tahr Active Member

    hi guys has anyone used polyester resin for sealing plaster , i was told you could lightly paint resin into dry plaster fish molds for longer mold life , i have used shelac , but my molds deteriorate after a few casts , i like the detail of plaster and have been using shelac to seal the plaster
  2. You can kick iy up a notch by sifting in Durhams rock hard putty. its a very dense plaster. Are you using pl
    aster of paris?

  3. are you thinning the shellac with denatured alcohol the first few coats? when you start a fish do you use aluminum sulphate to remove the slime? then dry the fish and seal with a 10% lacquer to 90% thinner? then molding the fish?
    Last edited: Jun 5, 2023
  4. 1tahr

    1tahr Active Member

  5. Wash the fish in aluminum sulfate a cup no specific size in fresh water. place the fish in it. Use a toothbrush to gently scrub the slime off. gently dry the fish lacquer thinner and dry air. careful with the fins. Bed the fish in hi-fib. you may need to wrap or keep the fins wet while bedding. In a spray gun, a cheap one, mix 1 part of lacquer to 10 parts lacquer thinner. Now at as low and air pressure as yu can get a nice oval pattern. just barely wet the fish out with this. You will have to play ith it to learn just how much/ You will wet the bedding compound to. If you get it to wet with the thinned lacquer you can dry it with a hair dryer in seconds.

    Now take your plaster and mix a thin splash coat, Cover the complete fish.. It should set up in about 2 minutes. As soon as it is setup add a thicker coat for strength. you can add more coats if needed.

    Now if you want a solid hard coat. mix 1/2 Durhams rock hard plaster with 1/2 plaster of paris. do the splash coat or as you get more experience a slpash coat of Rock hard plaster. then back it with regular plaster of paris.

    now for the back side of the fish, apply Vaseline to the flange and repeat the molding.

    once you pull the fish carefully. clamp the mold and allow it to dry 7-10 days. once dry seal the plaster inside with thinners shellac. 50/50 denatured alcohol and yellow shellac.
    if it pools just wipe it around until is soaks in. repeat until you have zero flat dull spots. it should start glossing.. allow the shellac mix to total dry a few days. look for the inside to be shiny if not apply more shellac thats thinned. you can spray or use a soft brush.

    once the mold is prepped. usea good carnuba paste wax, wax the mold buff repeat several times. the wax is going to build and the buffing will fis=nish the mold very slick.
    Johnnyclyde likes this.