More info about fillers and epoxy

Fillers are used to thicken epoxy. The epoxy will then be suitable for different applications. Thickened up to a ketchup type substance, epoxy can perfectly be used for glueing differtent parts. When you add more filler you will get a pinut butter type substance which does not drop and which you can use perfectly to make a putty.

There are many different types of fillers, each with their own applications (and price). To name a few: woodflour, cotton, chopped glass strands, stewathix, microballoons, aerosil and copper powder.

The choice of a filler depends on the application. The first difference can be made among fillers with a high and low density. Fillers with a high density are usually the strongest but also the heaviest. A low density filler means a light mixture that is somewhwat at the expence of strength.

A combination of fillers is also possible. Then you will get an excellent hard putty that 'sticks' very well, is fairly light but still well sandable by mixing 50% microballoons with 50% aerosil. An Overview of commonly used fillers and their qualities. (click for a magnification)




Fine cotton fibres make a good and cheap filler for glueing or making fillets and is well sandable. Cotton fibres thickens epoxy very quick. The fibres absorb epoxy but decreases under pressure, whereby a good suture is obtained when glueing. Cotton fibre is white and the cured mixture has an off white color. Cured has a somewhat less smooth surface. Add 5-25% (weight).



Fine chopped glass strands of about 3.5 mm. Suitable to sfuff big holes and spaces where weight is less important. Provides a fibre structure to the epoxy mixture.



Very fine and light powder. Stewathix has similar qualities as Aerosil, however a little less strong, but sprays a lot less. Therefore it is more enjoyable to work with and it gives less dust and clutter in the workplace. Mix 50% cotton and 50% stewathix for a relatively light but strong result. Add 10-40% (volume).



Aerosil is a very fine material, when mixed with epoxy results in a diehard epoxy after curing. Specially suitable for strained connections. However the disadvantage is that it is hard to sand. Add 1-8% (weight). Aerosil is also used to thicken epoxy somewhat, so that the epoxy will be less runny but still stays smooth. 



White microballoons are used to make easy to sand pastes for making putty. As a basis you can make a mix of 1 part white microballoons and 1 part aerosil (volume). The sanded surface of white microballoons should be coated with epoxy or a fine putty before finishing with a varnish.



Very fine copper powder. Is mixed with epoxy to make a diehard, algae resistant antifouling. Add about 80% (weight).


Very fine sawdust makes a outstanding filler suitable for many applications like glueing and making fillets. The wood flower gives the epoxy a licht brown color which is perfect for applications where wood remains visible. To obtain freely out of the bag of your sanding machine;)



Coarse powder is used for heavy applications like bridges etc., Fine grit for semi heavy applications like horse trailers.
PP powder is used for light applications like skateboards, surf boards and boat decks. Friendly for your bare feet.

The non skid grit can be mixed through the epoxy or sprinkled afterwards.

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