Painting - Painting plaster

We recently purchased a 12 year old home with WAY TOO MUCH wallpaper. We stripped off the old paper and cleaned the walls. We then had someone "butter" plaster the walls and ceilings. Some yellow shows through from all the chemicals...we want to paint, but what is the procedure? Do we need to prime first?

Primer is a must. But there are a couple of things you should know: if wallpaper was applied throughout the house it may be that the plaster is not suitable for paint (even with the topcoating of new plaster). You must wait at least 30 days for the plaster to reduce its Ph and moisture content before applying paint. When purchasing paint (at a paint store I hope) tell them you want to primer fresh plaster. That way you'll be provided with the proper primer for high Ph items, regardless of the brand.

If you meant drywall instead of plaster, prime then paint.