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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.

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2 Answers 2

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

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Primer is a sealer. You are using it to save the underlying materials from the elements of the room - mainly temperature changes and moisture.

If you have walls that are not primed (new drywall) you want to prime them (with a real primer - not your Duo). Also if they are next to already painted walls you may want to make the surfaces even from a paint standpoint.

Since lathe/plaster is not a measurable finish it is going to be really hard to tell at what level your drywall is compared to it... other than eyeballing it. We are talking fractions of inches. If your plaster is dead even with the drywall but had several coats of paint on it then I would want to prime the drywall to the thicknesss that makes the two materials "even".

There is no use in priming over paint unless there was sort of damage/stain. Also primer is thinner than paint so priming the already painted sections would be a bit of a waste of time. Painting would cover faster.

So prime the bare sections to "even". And then paint the whole room all at the same time. Use the Glidden Duo if you want to paint it with that - it isn't hurting anything... but you don't need that Duo part.

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