West System 404-45 High-Density Adhesive Filler, 43 oz

We recommend 404 High-Density filler as the most cost-effective and easiest-to-use filler for hardware/stud bonding. Even small amounts of this adhesive filler help reduce creep in the epoxy. Mix this filler into liquid epoxy to create a moderately loose slurry. It should be thick enough to stay in a horizontal hole, but not too thick. Blending too much filler into epoxy can trap air.

To increase the mixture’s load-carrying capacity, you can add chopped glass fiber or carbon fiber. However, the additional cost and application difficulty are usually not worth taking this step.

We typically use 800 psi as the ultimate shear stress when testing the filled epoxy mix. We base this conservative value on long-term fatigue data. At this stress level, the epoxy is the limiting component. The interface between the fastener threads and the epoxy is where a fatigue failure typically starts.  This is good. The fatigue failure mechanism for epoxy—cracking and the gradual destruction of the matrix—provides you with some warning.

A hardware bonding failure at the wood/epoxy interface or the loss of a bolt head is usually catastrophic. Proper use of this product helps prevent these things from happening.