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Achieving a Woodgrain Finish

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                                       © Smooth-On, Inc. (2005)
 

FAQ: How can I make my plastic casting look like wood?

A: A wood grain finish can be attained by mixing urethane resin with various colors of pigment and Ure-Fil™ 5 filler.   Finished castings will have the appearance of natural wood.  Different wood finishes such as oak, pine, maple and mahogany can be achieved by varying the color and amount of pigment and/or Ure-Fil™ 5.  Castings can be stained and finished by spraying with a clear coating.  Duplicating wood pieces with the following casting method offers the benefits of being fast, realistic and less expensive (labor, time, materials) than hand carving.

     Overview - A rubber mold (negative) must be made of a natural piece of wood to capture the wood grain.    The liquid rubber (Mold Max™ 30 Silicone or  ReoFlex™ 30 Dry Urethane) will duplicate the finest wood grain and yield that detail into finished castings.  For information on general mold making, visit www.smooth-on.com.   Once a working mold has been completed, we can begin preparing our casting resin mixture.  This mixture consists of urethane resin, pigment and/or

Ure-Fil™ 5. Once the desired color effect is achieved, the mixture can be poured into the mold. 

In less than one hour the casting may be removed from the rubber mold.

Materials Needed:      
A. Smooth-Cast™  320 Casting Resin         
B. SO-Strong™ Brown Tint*           

C. Ure-Fil™ 5                                                 
D.  Universal™  Mold Release

Our Smooth-Cast™ 320 Urethane Resin works well because it is inexpensive, has extremely low viscosity (pours like water), and sets up quickly.  Adding a dark pigment (brown or dark brown) to the resin/ Ure-Fil™ 5 mixture will give the final casting added definition and dimension. If casting into a urethane mold, a mold release agent is required.  Other items that are needed include the rubber mold, measuring / mixing containers, mixing paddles and an accurate gram scale for weighing components.

     Amounts of resin, Ure-Fil™ 5 and pigment required will vary depending on the desired effect.  Most customers will experiment by varying the amounts of resin, Ure-Fil™ 5 and pigment used in combination to attain a desired effect.   For this example, we will use the following:

         Part A of Resin:  100 Parts            Ure-Fil™ 5:  100 Parts
    Part B of Resin:  100 Parts            Liquid Pigment (Brown): 1 Part

      Apply Release Agent To Rubber Mold** - If using urethane rubber, you must apply a release agent to the mold cavity to prevent resin mixture from sticking to rubber mold.  Brush into all surface detail let dry and follow with a second coat.  Let dry

      Mix Ure-Fil™ 5 And Pigment With Part B Of Resin – If using Ure-Fil™ 5 in the urethane resin, it is necessary to bake the Ure-Fil™ 5 (150° F for 30 minutes) to eliminate any residual moisture. Let Ure-Fil™ 5 cool to room temp. before using.  To allow ample mixing time, mix Ure-Fil™ 5 and color tint thoroughly with Part B of Smooth-Cast™ 320 (Blue Label) prior to adding Part A (Yellow Label).  Dispense 100 parts of Resin - Part B into clean mixing container.  Add 100 parts of Ure-Fil™ 5 and 10 parts of brown pigment to Part B and mix thoroughly.  Mixture will be very thick.

3.  Add 100 Parts Resin - Part A to the Part B/ Ure-Fil™ 5/pigment mixture and mix thoroughly.  

4.   Pour Mixture into the mold cavity.  For best results, pour the mixture in a single spot at the lowest point of the mold.  Let the resin seek its level inside the mold.  A uniform flow will help minimize entrapped air.

5.   Entire casting should be thoroughly cured before demolding. Remember, the resin/ Ure-Fil™ 5 mixture or filled resin will take longer to harden than unfilled resin.  Cure time depends on size of casting, mold configuration, amount of fillers used, etc. Generally, 30 to 40 minutes is sufficient.  Applying mild heat will accelerate cure time.  Let cool to room temperature.

6.   Demold - remove casting from mold. 

7.   Post Finish – Remove release agent from casting with Cascade dish washing gel & water or acetone.  Dry the casting.  Next, lightly abrade casting with fine steel wool to promote better surface adhesion of stain and shellac.  Apply desired wood stain or brown shoe polish thinned with alcohol on to the surface of your finished casting.  Let this coat dry thoroughly and apply a second coat.  After drying, apply two coats of clear gloss shellac spray to prevent scratches or nicks on the surface of the casting.

*Liquid tint used for this illustration is Smooth-On SO-Strong™ Brown Tint.  Using other pigments may vary results.  Some experimentation may be required.

**  Use only a release agent specifically made for mold making and casting such as Universal™ Mold Release or Mann Ease Release™ 200 (both available from Smooth-On and its distributors).