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Proper Mixing of Plaster

This document provides instructions for properly mixing plaster by volume and weight. It explains that the volume of water should be half the needed volume of mixed plaster. The water weight is then divided by the typical water to plaster ratio of 0.70 to determine the plaster weight. The plaster and water are mixed manually or with an electric drill until the consistency is like heavy cream and air bubbles rise to the top. When a finger trail leaves a slight wake, the plaster is ready to pour into the mold in a smooth, steady manner.

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Jeremiah Jared Gascon
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84 views1 page

Proper Mixing of Plaster

This document provides instructions for properly mixing plaster by volume and weight. It explains that the volume of water should be half the needed volume of mixed plaster. The water weight is then divided by the typical water to plaster ratio of 0.70 to determine the plaster weight. The plaster and water are mixed manually or with an electric drill until the consistency is like heavy cream and air bubbles rise to the top. When a finger trail leaves a slight wake, the plaster is ready to pour into the mold in a smooth, steady manner.

Uploaded by

Jeremiah Jared Gascon
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Proper  Mixing  of  Plaster  by  Volume  and  Weight  


 
1.Determine  how  much  "mixed"  plaster  is  needed  (Volume)  
 
2.Weigh  half  that  volume  of  water  (adding  the  water  to  plaster  does  not  substantially  increase  the  
volume  as  the  water  is  absorbed  by  the  plaster  and  the  air  in  the  plaster  is  displaced).  
 
3.Divide  that  water  weight  by  the  water  to  plaster  ratio  –  typically  .70  
 
4.  The  result  of  3  above  will  be  the  weight  of  the  plaster  needed  
 
Note:  as  a  check,  the  volume  of  plaster  and  water  should  be  close  to  the  same  
 
5.  Sprinkle  plaster/gypsum  into  water  until  smooth  mounds  of  plaster  peak  above  the  surface  of  
water.  Allow  the  mixture  to  sit  undisturbed  while  the  plaster  soaks  up  the  water,  about  3  or  4  
minutes.  
 
6.  Manual  Mixing  (not  generally  suitable  for  batches  over  10  pounds)  –  using  a  spoon  or  wood  
trowel,  mix  from  the  bottom  using  a  side  to  side  motion.  Circular  motion  will  cause  bubbles.  Mix  to  
the  consistency  of  heavy  cream.  
 
       Electric  Mixer  –  Use  an  electric  drill  with  a  Jiffy  Mixer  attachment.  "Stir"  at  no  more  than  1750  
RPM  while  holding  the  Jiffy  Mixer  at  15  degrees  off  vertical.  
 
     7.  The  mixing  container  should  be  solidly  tapped  or  even  dropped  on  the  floor  several  times  to  
help  air  bubbles  rise  to  the  top.  
 
     8.  The  plaster  is  ready  to  pour  when  mixing  is  complete.  "  Marking"  is  a  way  to  determine  when  it  
is  ready.  It  is  the  moment  to  pour  when  a  finger  is  trailed  over  the  surface  of  the  plaster  and  a  slight  
wake  is  left  in  the  plaster.  
 
       9.  Pouring  should  be  done  in  a  comfortably  quick,  smooth,  steady  manner  directed  towards  the  
center  of  the  base  of  the  mold.  Avoid  allowing  the  slip  to  run  down  the  side  of  the  mold  as  "hard  
spots"  may  occur.  
 
 
By  Eye  
 
1.Those  with  sufficient  experience  sometimes  us  a  method  called  "Peaking"  or  "Island  Method"  
whereby  the  plaster  is  sifted  into  the  water  until  it  forms  a  mountain  of  plaster  in  the  water  with  
the  "peak"  rising  above  the  water  surface.  
 
2.  Follow  steps  6  through  9  above.    Adapted  from:  http://www.clay-­‐
planet.com/ceramic_central/info/plasters.htm  
 
 
Accessibility:  If  you  need  this  document  in  another  format,  please  email  Emily  Bush  at  
Emily.Bush@UNG.edu  or  call  706-­‐867-­‐2832  
 
 

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