I have a number of walls that have a mix of old lath+plaster and new drywall (parts of walls are plaster, other parts new drywall). The old plaster walls have paint on them but they have not been painted in a long time (like 6 years).
I am aware that there is Glidden Duo primer+paint mix which saves time (2 vs total of 4 coats with priming and painting separately). However, given the nature of the walls and the integration of the old and new technologies, as well as the fact that the old parts already do have paint but the old ones do not, I am not sure if I can go with Duo or if I should prime it first and then paint it.
Best Answer
Not all primers are good sealers for new drywall and tape joints. The new paint and primer combinations are great for covering existing paint, but are not a good substitute for a PVA or shellac/alcohol based primer on new drywall or patches. When sealing new drywall, it is important to seal the pores so latex/water based paints are not absorbed. Once the surface is properly sealed, paints will cover better and color will be more consistent and the finish texture will be the same from painted areas to newly primed areas.
Here is a good article that describes the difference between different types of primers and proper selection. http://www.finehomebuilding.com/PDF/Free/021161060.pdf