07-29-2013 03:46 PM
If you are dealing with raw masonite - then you will need to prime all sides with a high quality grade product like 1-2-3 or Gripper. Keep in mind that masonite will swell if too much moisture is present - so only lightly prime up to two coats - sanding between coats.
07-29-2013 04:13 PM
I actually peeled off some old walpaper and there has been some kind of white filler, pretty thick along the seems and nails - not sure what this product is, but it seems like what i need to apply to to help fill in the high gaps. do you have any idea what this product could have been? thanks
07-30-2013 01:48 PM
It sounds like someone in the past did a less than ideal repair before hanging the wallpaper I personally prefer an oil based primer whenever working over composite type wood products, i.e. OSB, Masonite, MSD, etc. Water based products tend to raise the the grain or fester up the manmade panels or boards.
If you are planning on leaving the Masonite and painting over it, seal it with oil primer after evening out the old patches as best as possible with sandpaper. Try not to break through the tempered surface of the Masonite. If that is done, the underlying surface is little more than pulpy sawdust! After the sealer has dried, you can treat the surface almost as if it were drywall. Tape the seams with the thin fiberglass tape and feather them out with drywall compound. After sanding with a sanding block, spot prime the seams. Then give at least two coats of the finish paint, either oil or water based.