Surfacing/coating spoilboard?

[myxpykalix]

Couple questions. I have my plenum cut with holes in 3/4 plywood, next layer is going to be mdf. I need to shellac my plywood plenum board 2-3 coats then I need to shellac my spoilboard 2-3 coats too. I was told that i need to "skin" my mdf (surface it) which would allow for better vacumn by taking that top layer of paper off. I have to level the surface anyway, but do i need to turn it over and take off the top layer of paper from the bottom too?

[gerald_d]

Skinning on one side only makes no sense - surely you want to do both sides if your aim is to increase airflow? Why bother to remove only one flow blocker?

All MDF's are not the same - some don't have these dense outer layers.

[beacon14]

Do not shellac the spoilboard - thats the layer you are removing the skin from, and yes both sides.

You remove both faces of the spoilboard to increase airflow. You shellac the plenum to eliminate airflow.