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The Background
GYPSUM / WATER BASED; TWO-PART ACRYLIC POLYMER COMPOSITES HAVE BEEN AROUND FOR NEARLY 40 YEARS. THE MOST WELL KNOWN, AND POPULAR OF THESE, JESMONITE, WAS INVENTED IN THE UK IN 1984.
PRIOR TO THAT TIME, THE MOST FAMOUS GYPSUM BASED PRODUCT, PLASTER OF PARIS WAS APPARENTLY SIGHTED, BY HENRY THE III ON A VISIT TO PARIS IN 1264. HE LIKED IT SO MUCH, IT SOON BECAME USED IN ENGLAND. HENRY III WAS NOT REPUTED TO BE A VERY GOOD KING, NOR WAS HIS FATHER KING JOHN, (THE WELL-KNOWN ARCH NEMESIS OF ROBIN HOOD).
THE DIFFERENCE BETWEEN “PLASTER” AND “RENDER” IS THAT THEY ARE USUALLY FOR INSIDE AND OUTSIDE RESPECTIVELY. SO WHERE DOES A MODERN ACRYLIC POLYMER COMPOSITE BELONG? IT CAN BE USED IN EITHER PLACE.
ACRYLIC POLYMER COMPOSITES ARE MADE FROM A BASE OF POWDERED GYPSUM. GYPSUM BEING A COMMONLY FOUND MINERAL. IF YOU LIKED READING ABOUT KING HENRY, YOU MAY ALSO LIKE TO KNOW “GYPSUM” IS DERIVED FROM THE GREEK WORD “PLASTER." IT WAS ALSO KNOWN IN “OLD ENGLISH” AS “SPEAR STONE”.
GYPSUM HAS A SOMEWHAT CHEQUERED HISTORY, INCLUDING ITS USE AS A FERTILISER CENTURIES AGO, A PRACTICE THAT STILL OCCURS TODAY. IT SEEMS ALMOST INCOMPREHENSIBLE THAT GYPSUM WAS IN SUCH DEMAND FOR THE SOIL IN 1820 IT CULMINATED IN THE “PLASTER WAR” BETWEEN OFFICIALS AND SMUGGLERS AT NOVA SCOTIA AS SMUGGLERS SOUGHT TO FEED AMERICAN DEMAND.
Composites
THE WORD ‘COMPOSITE’ CAN BE MISLEADING. THE BASE POWDER REFERRED TO BELOW IS A COMPOSITE, (A MIXTURE). THE LIQUID THAT IS ADDED TO THAT BASE IS ALSO A COMPOSITE. WHEN COMBINED THEY FORM… WELL… A COMPOSITE. IT’S A CHEMICALLY COMPLICATED, PROPRIETARY COMPOSITE MIX.
IT’S NO WONDER THE SECRET RECIPE FOR JESMONITE REMAINS A SECRET TO THIS VERY DAY. IT WILL BE INTERESTING TO SEE IF THE RECIPE FOR ECRYLIMER CAN BE AS WELL GUARDED OVER THE NEXT FOUR DECADES!
The Now
HAVING SAID ALL THAT, LET’S GET BACK TO PLASTER OF PARIS, (SOMETIMES CALLED GYPSUM POWDER). GYPSUM IS HEATED TO 120 DEGREES C FOR ONE HOUR. THIS TRANSFORMS THE CHEMICAL COMPOSITION OF THE MINERAL TO FORM CALCIUM SULPHATE HEMIHYDRATE. THIS POWDERED FORM THEN MAKES UP THE MAJORITY OF “BASE”, TO WHICH IS ADDED A LIQUID ADDITIVE IN A SPECIFIC RATIO, (ECRYLIMER USES A RATIO OF 2.5 BASE TO 1 PART LIQUID, AS DOES JESMONITE).
THE LIQUID IN ECRYLIMER COMPRISES A PROPRIETARY ACRYLIC POLYMER. THE MEANING OF POLYMER, ISN’T THAT DRAMATICALLY DIFFERENT FROM COMPOSITE. BOTH ARE A TYPE OF MIX. IT’S SLIGHTLY CONFUSING…
ECRYLIMER, BEING THE MOST MODERN OF ACRYLIC POLYMERS (INVENTED 2021), PROVIDES A MORE LIBERAL WORKING TIME OF 10-15 MINUTES, GREATER THAN OLDER ACRYLIC POLYMERS. IT CAN DO THIS, USING ITS MORE ADVANCED FORMULA. SIMILARLY, IT GENERATES LESS BUBBLES, IS MORE DYE FRIENDLY, AND BOTH SIDES OF YOUR MOULD WILL BE SMOOTH, AMONGST OTHER ADVANTAGES.