Thickeners & Anti Sag

Epoxy is not an “Old World Craftsmanship in a Can”. A tight joint is superior to a wide one in every respect, but when fill is required, epoxy can do the job.  To prevent resin from running out of the spaces before it has cured, an anti-sag agent must be used.

All of the agents, when mixed in sufficient quantities, can hold the un-cured resin in the desired position until a cure is reached. They are not to be confused with fillers, (such as micro -balloons or sawdust) which have a different purpose.

The quantity of anti-sag required varies with the job. Once you become experience you will be able to estimate the quantity required to suit your needs.  A rough rule-of-thumb is two parts anti-sag to one part of mixed epoxy and hardener.  Always thoroughly mix the epoxy and hardener together before adding the anti-sag.

After all the ingredients are mixed well, lift a small amount out of the container with your mixing stick, the amount remaining on the spatula will indicate how much gap filling is possible.  If all but 1/8th runs off, then it will bridge a gap of 1/8th or less.  If 1/4” remains, fill up to1/4” is possible.

One part mixed epoxy and hardener plus two parts anti-sag equal approximately 1/8” filling.

One part mixed epoxy and hardener plus three parts anti-sag equal approximately 1/4” filling.

Other powders such as talc, sawdust, flour or cornstarch can be used, but the anti-sag powder (made of dehydrated silicon) has the best holding power.  We here at Race Rock Yacht Services find talcum powder to be the best for our daily use.  We add the talc powder and mix with a triangular blender on a drill. When the talc has been fully added and thoroughly mixed, we lift the blending stick upwards and it should make the epoxy look like stiffened whip cream, making peaks in the container.  It usually doubles the liquid amount.