When wallpaper is removed, there is often a good amount of glue residue left over. If this glue is not fully removed from the walls, it will interfere with the finish coat of paint. In cases where we cannot clean the walls fully of the glue residue, we must use a product to seal the walls before the finish is applied.
Oil Primer like Cover Stain used to be our go to. Now we usually choose GARDZ Problem Surface Sealer. Here are the main advantages:
1. Unlike oil, GARDZ does not smell horrible
2. Unlike oil, GARDZ is truly ready in one hour under normal conditions
3. GARDZ takes about half as long to apply
4. GARDZ spreads out almost twice as far
5. GARDZ preforms slightly better at sealing down glue residue, and has worked where oil has failed
Cover Stain would still be a better choice if you only want to paint only one coat of finish after the primer, because it can be tinted, while GARDZ is a clear. We always suggest two coats of paint, so for us this rarely applies.
There is a learning curve to applying GARDZ (which is also true of oil primer). GARDZ is extremely watery, and has a consistency resembling milk. You must be very gentle not to squeeze the roller, or it will run very easily. Once you get the hang, though, GARDZ will spread out far and easily.
Once the walls dry, give a light sanding, and they are ready for paint. The paint will go on easier, because your walls are freshly sealed.