Q: I am in the process of finishing some MDF boards with clear varnish. The cut edges, the inner fibers of the MDF, are very porous and need several coats of sealer. Could you suggest other methods or different sealers that would have a faster buildup?
A: The quickest and, I think, best method is to seal the edges first with thinned wood filler or putty that is the same color as the MDF. Rockler sells a nice one called Wunderfil™ that you can thin with water and that dries quickly. Make sure you buy the type of putty that dries hard and must be sanded.
Another quick method is to seal the edges with hot hide glue, applied fairly thick with the excess wiped off. Like the filler, it should be sanded after it is dry.