Is it necessary to prime bare drywall before painting? And do we need to prime existing textured, painted walls before we mud over them?
Yes, you need to use a drywall sealer on bare drywall. Using a primer or a sealer would also help blend in the differences with the existing surface you want to cover.
In the UK, you don’t need to prime bare drywall or plaster before painting with normal emulsion paint. However the first coat will soak in and you will need a few more coats. (If you are using a very high spec paint that is thicker you may find that the first coat does not stick well without a mist coat, but I would always use a cheap paint for the first coat anyway.)
The normal advice is to use cheap MATT emulsion paint, watered down a bit, for the first coat as this will act as a sealer. Also if the plaster has been polished and is very smooth give it a quick light sanding will help any paint to stick well.
You do not need to use a Primer on bare drywall. I have painted numerous new houses, including mine, over the last 10 years and never have I primed the bare drywall. No issues what so ever. 2 coats of any good latex paint will be fine, no question.
If you were going to be painting over existing paint, it would certainly help and can save an extra coat or two of the new color. Also a good thing if you are painting over a wall that had wallpaper removed. Also good if you are paining on really old walls that are extremely dry and may soak up a lot of paint. But it doesn't sound like any of that applies to you.
People will argue that Primer is cheaper than good paint, so use the primer and save a coat of the expensive stuff. I can see that argument. But in my case, I would rather save time and stick to the same paint, rather than having to clean all the equipment and start over, especially if you are doing it the same day.
For your second question, primer might be a good idea before you mud over the textured / painted walls. Mud sometimes has a hard time sticking to painted surfaces. You could also give it a light sand that would help it stick. We reciently had to have our ceiling redone, and the drywaller had concerns about it sticking. Rather than priming it, he did a light sand, then used DuraBond to mud the ceiling rather than standard joint coumpound. DuraBond supposedly makes a better bond, seals out moisture/humidity, and reduce cracks/blemishes over standard compound.
My wife and I had our kitchen renovated just this past month and we told the contractor we would do all the painting of walls and trim as my wife is very meticulous, has a good steady hand, and an exceptional eye for detail.
We choose one of the best One Coat Cover paints on the market and figured we wouldn't have to prime/seal the drywall first. We were so wrong. Several coats of paint later we could still see different shades of the color over the seams and wherever else there was joint compound.
Then to make it worse, we splashed water from the sink sprayer onto the wall and when we wiped it off it revealed yet another shade of our color where the wall had gotten wet. So now we are in the process of repainting, first with primer/sealer and then with the original paint. Our mistake cost us over $100.00 and two week-ends. So yes, Prime/seal bare drywall!
Well you don't need to do anything -- in fact you don't need to put drywall up but you should prime drywall if you want a better finish on the wall. It seals the paper and seams. You often see a color variation or see the seams if you don't seal the wall. Sealing with a primer makes the whole wall the same surface that the paint can adhere to giving you a more uniform look. Have you ever gotten really close to a wall and looked down the side and you could tell where the seams were? They probably didn't use a primer.
you dont need to prime finished walls with paint on them if they are in good shape, but you should - it will save you finding out they arent.
as to priming fresh drywall, your answer is yes. but whats really interesting is seeing some of the answers that say no.
i cant figure out their logic. i have been in the general contracting business for 20 plus years, installed or had installed for me literally hundreds of thousands of square feet of drywall. i have seen every possible type of drywall installation and the one universal rule is value. you have to make a profit in a competitive market, which means giving good product at a competitive price. the only way to do that is 2 or even 3 coats of a good sealer/primer (depends on if you are going for a level 3,4 or 5 finish) and then 2,3,4,5 coats of paint (reds and oranges need a lot more paint). we almost universally spray paint on with a gun system and then overroll the very last coat with a very low knap roller. however, for the purposes of this discussion, it will make no difference as to how its applied, as labour is labour - however you do it you want to minimize it.
primer serves 3 purposes - promotes adhesion, reduces absorption of surface coats, and reduces surface changes and imperfections, particularly at the transition between surface paper and the fillers used.
primer by design is less costly but not able to have a sheen (too many coarse particulates). on the other hand, it has more polymerizing agents which make it seal the paper and fillers with less material. if you don't use primer, you will be using much more paint per square foot for the finished surface, or you will be using a much more expensive paint (essentially primers bonders and sealers mixed with paint and its pigments).
from a business perspective, it may seem logical to use a more expensive one-coat type paint instead of the standard primer and paint approach, but the economics of it dont work out. these paints are so much more costly than standard primer and paint, that it doesnt balance out in the labour savings. with the caveat that if you are really, really slow at painting or so meticulous it hurts, then you could make the argument that that type of paint is worth the cost. i would argue that its time to fire yourself and get some competent painters in.
from a finish perspective, its also vital that your surface be smooth and uniform. primer is a critical part of this. if you omit the primer step, you will have dramatic sheen changes on paper and on filler. thats a huge problem and will usually result in you redoing it for free.
hope that helps
This question depends on the situation. If the wall you are painting is the interior side of an exterior wall, it is a good idea to use a paint that provides a sealer for moisture. Brick and stone both have a tendency to sweat and under humid conditions your paint on interior walls that have not been “sealed” can bubble. Once moisture gets behind latex it can be troublesome and you may end up having to peel off the latex, repaint the drywall using Kills or a moisture barrier type paint, then repainting the area.
It is best to get into practicing quality work the first time around and I would recommend sealing your drywall and also caulking where needed. Do you have to do this? of course not, I guess it all depends on your piece of mind. For me knowing I went the extra mile to have a lasting paint job is part of the pride of doing good work. Trying to save time often can work against you.
We've prep-coated drywall, and even putty coated drywall, and checked it out with a 500 watt light sideways on the dry wall to show all defects and still primed the walls. If you don't the paint can burn though your prep coat and you will still halve to paint again or spray more prep coat.
Always use a good primer.
So many yes's and no's...
My advice is... Just prime it, even with a cheap paint at a ratio of 80:20 (paint:water), I also like to put a glug of PVA in too and mix it all up, especially on moisture resistant plasterboard in bathrooms/ensuites (To help the key)
The reason I add a bit of PVA glue (carpenters glue) mostly is that even after a flash coat on new plaster or drywall filler/cement joints (Or "mud") is that I find it does help against any suction when applying further coats, and thus, a more even application, whilst still achieving a masking effect over the contrasting board/mud colours.
It is ultimately something I like to do, be it drywall or new wet plaster finished walls.