The stuff I use is like a foam. Very lightweight but hardens like a rock. On the sashes and molding there were chunks rotted away, where I was able to take a mold of existing matching pieces and create replacement spans really easily. I was so shocked at the first sight of the trim I thought there was no way I could do it myself. But I wasn’t willing to lose the character of the old woodwork and a call to a historic restoration firm in a nearby city yielded an estimate of $1200 per window.

So I figured it out 😅