Handy Hints

Resin Powder Fillers

When filled Polyester Resin can mimic many different finishes such as Marble, Bronze, Wood and many more. A resins ability to accept filler powders, and its relative low cost, makes it a choice of many for a reproduction material.

A combination of filler powders is best. The main advantages are:

• adding bulk and reducing the amount of resin required (reducing the cost of a reproduction casting)
• reducing the exotherm of the resin during its curing process
• producing special finishes, such as a marble effect
• improving the post heat distortion of the resin
• adding or reducing the resins normal weight

To fill a resin with powder will make the resin much thicker and can effect the flow of the resin as a casting medium. To cast large pieces in filled resin will produce a great deal of exotherm which can result in warpage, greater shrinkage and in some cases cracking. To combat these effects, greater quantity of filler powder is required.

A common filler to add to resin is a Microdol powder, such as H100, H400 or H600. This is an ideal filler as it has a good cooling effect on the resin during exotherm but if added in very large quantities will make the resin very thixotropic because it is a fine particle filler. To increase the quantity of powder to a resin and retain the flowability, a second, or even third filler powder of a larger particle size should be used.

It is possible to increase the filler content of resin from 60% filler to 80% and some combinations even higher, without loss of flowability.

My preferred basic filler mix into polyester resin for Marble and general white castings is H600 and ATH (aluminium trihydrate) and for Bronze effect casting H600 + ATH + bronze powder+ Antique black powder.

This hint appeared in our January 2004 Broadcast Newsletter.