How To: What are the Efficient Techniques for Mixing Lightweight Filler into Epoxy Resin?

Are you used to standing in a dust cloud when you mix lightweight filler into your epoxy? There’s a handy technique to avoid that. David Johnson tells all.

I have to be honest – no-one ever asks us how to go about mixing a filler into epoxy. In fact, I wondered briefly if it was worth writing about this at all, as it seems so simple. These days, however, people are quite rightly concerned about breathing in dust. If you don’t mix our fillers correctly, there’s a good chance you’ll create a dust cloud which you could end up breathing in.

If you don’t mix our fillers correctly, there’s a good chance you’ll create a dust cloud which you could end up breathing in.

When you’re using WEST SYSTEM 407 Low Density Filler® or WEST SYSTEM 409 Microsphere Blend® (*409 only available for EU customers*), you’re adding roughly twice the filler to the dense epoxy. If you stir this too roughly, you’ll have a problem. Even WEST SYSTEM 406 Colloidal Silica®, which uses a 1:1 ratio, is lightweight and tends to fly away.

Now I should point out that our fillers are inert. However, whenever you’re grinding, sanding or blending, you should always use the appropriate protective gear and safety techniques. So here’s a tip to help you avoid standing in a filler cloud next time you’re mixing.

How to Mix Lightweight Filler into Epoxy

You’ll obviously start off by adding your hardener to your resin at the correct ratio, blending that together. Then you’ll add the filler on top.

If you use your mixing stick like a paddle, the filler will fly everywhere. Yet if you use it like a blade – chopping and slicing through the filler as it sits on top of the epoxy mix – you can blend it enough to then fold everything together.

That’s really all there is to it! Hamish and I made a short video of the process which you can watch below.