In article O6LHe.27801$Tk6.7916@trnddc02,
"dadiOH" wrote:

Get a primer made for auto bodies...sands wonderfully.

I have used automotive spot-putty (is lacquer based) on the end grain of
MDF with great success. It is thin enough to crawl into the MDF a bit
and sands like a dream.
One of the brand names is 'Green Stuff'.