How to stop timber soaking up resin filler

I knew there was a problem with timber absorbing casting resin when one tries to fill knot holes etc.

I dilligently sealed all these holes and cracks in some Blue Gum plank with Shellac, when dry poured in the casting resin. To no avail.

A 20 ml size knot hole soaked up at least another 20 mls of resin and kept on soaking for about 90 minutes.

What sealer works?

The casting resin is filthy stuff and I'd prefer to get it done in one go. Maybe I should put more hardener in to make it go off quicker? Then you get the problems with the bubbles getting trapped.

On the brighter side, once done it does look good. Its easy to tint with artists watercolours or brickies oxide. You get a translucent, deep fill which polishes up well.

maybe you can just fill half or more of the hole with a sawdust glue mixture putty, when that dries in a few days pour your usuall mix in and it won't need much cause the hole is only now half as deep...