I'm looking into repainting a classroom in an NGO facility (can seat about 80). Due to both time and budget constraints, I don't have freedom of spending too much time priming and painting the entire room. I suspect I can readily prime half the wall height and paint the whole room within the allocated time.
Would I create an odd mark on the wall if I only prime up to about head height? I plan to use a dry roller between the primer and bare walls to even out the edge so it doesn't get a sharp bump.
The rational for priming half the room is because the marks on the walls are all chest height and lower. I've already used a power sander and lightly sanded all the marked areas, and have sanded all repaired sections of the wall. I'll want to put primer on the repaired areas and the marked up areas to help with paint adhesion.
2020-09-01 Update: Wall material mixed. I can tell there is concrete and dry wall, with a layer of wall putty. Region is Hong Kong, which is typical to simply do Putty + Surface paint, skipping the primer. I know this doesn't work well and high humidity = putty failing, and paint peeling off.
Sanding wise, it is light sanding. It isn't past the paint layer. It is mainly to get the surface scuff marks off so the primer can attach better to the existing paint (instead of some random material). Any deep gouges are filled with wall putty and sanded flat.
If I had more time, I would sand past the paint and putty layer, and do a thicker sealer/primer layer onto the material. The current paint is not showing any major area failure, so I think it'll hold a repaint.
Best Answer
Just to answer a rather odd question the way it was written...
No if you plan on going to specific height and stop right there all the way around. You will create a paint seam and it might take a few coats to make it less noticeable.
Yes if you kind of go to a height and taper off randomly on both side of the height with less paint/pressure as you go up.
My advice would be to cut corners, in the corners (and to get more people to help). You can prime pretty quickly - and paint - open walls. If you are not worrying about the ceiling or edges painting is twice as fast. I would suggest you prime to ceiling but start tapering off as you go up and the top 6-8" need very little.