Good evening folks.
I've been tasked by my daughter with making/fitting two window boards. Each
56" x 16".
The only option is to use thin oak faced plywood. This will be well
supported to front and rear with, I hope, adequate support in between. The
ply is 5mm and of good quality.
My intention is to very lightly hand sand this and apply three or more coats
of Sadolin.
Do I remember correctly that thin ply should be treated on both faces, or am
I thinking of something else? Or am I losing the plot?

Also, Sadolin has been my preferred finish for years. Has technology now
overtaken this? Thoughts/suggestions would be appreciated.

Many thanks,
Nick.