If you’re painting new dry-wall, we have a post just for that.
Preparing Walls for Painting: Prepping Old Walls
Are Walls in good condition? Keep reading.
Problems? See the next section, but in both cases, you want your walls gently sanded and cleaned.
Many walls we work on were painted by DIY-ers who used cheap rollers that shed lint into the paint, leaving a gritty surface. We give that a sanding (mostly from eye-level down to knee-level), and then wipe with a damp cloth. Most walls have pin/nail holes and we write about that in #4 below, but generally, you can start to paint most pre-painted walls with little prep. The other DIY sites will not say this to cover their butts, but it’s true. Let’s not lose sight of the forest.
When do you need to prime?
When you are going to paint new walls, red walls or old yeller, uh, I mean yellow, or unless you are changing TO NEW red or yellow—you need a primer. Somehow the chemistry (pigments) in red and yello paints are problems. When you buy your primer for red paint: have it tinted gray. Primer for yellow: no tinting. Ask advice from the store. Read my post on paint-and-primer-in-one and when not to use it.
Other than that, you only need a primer coat when changing from a very dark surface to a much lighter one. The better lines of paint have no problem covering in 2 coats. Don’t believe the ads you have seen about how our great paint covers in one coat. Bunk.
Problems are not problems
“Problems” are not really difficult (except the last one in the list – oh boy.)
Problem #1: Water Stains. (Read this and #2) If you had a plumbing or roof leak (now repaired right?), you have to put a stain blocking primer on the water damage. such stains bleed through every single coat of paint you could apply. Amazon sells Kilz and so do most paint stores. Other products are called Bin, and so on. Use the knowledge of paint store managers, or talk to me here, and I’ll reply asap.
Problem #2: Water Damage. Sometimes water will ruin the ‘rock’ of your wallboard. It will turn soft and powdery. No worries. It’s messy, but it’s not rocket science. Just dig out the soft rock, and fill the hole with pre-mixed drywall compound (“mud”). (It lasts forever in a plastic tub if you keep the lid clean and tight). This stuff shrinks so we only use it when we have to. For deep holes, you’ll need several coats of mud. Sand between coats somewhat and sand well after the last coat. Use the rough grit sandpaper (about 80 grit) to go fast and fine tune with 150 or so. I’d recommend an assortment pack. For massive holes, sell the house. Not an option? It’s ok, you just need to do a patch. See the next ‘problem’.
Cut a scrap piece of drywall in something close to a square that’s just bigger than the hole. With a pencil (never ink) trace your new patch over the old hole. Cut the pencil line with a sharp knife and remove the old wall. If there is a stud, you can use it to screw in your new piece, but if not just find a strip of wood (a painting stir stick will work, but something bigger is better), and fasten it to the backside of the hole as you see in the photo (this is simulating a stud and will give you something to screw your new piece into). It is just a matter of holding the stick behind the wall as your screw goes through it: if you have a clamp or a teenager, that will help to hold it as you screw. Fit your new piece in and screw it in and lightly cover edges with ‘mud’. Then lay your tape of patch material over that and then another coat of mud over the tape. If you don’t use tape, the seam will crack later. That will probably shrink and maybe crack a bit as it dries, so you’ll need at least one more coat, sanding between coats. Save the fine tune-sanding work for the final dry mud. Whew. Done. Prime and paint. All too much? See my first short story at bottom of this page.
Problem #4: nail pops. The nails or screws that hold the ‘rock’ up to the walls frequently crack and pop out (mostly from temperature changes outside, not from ‘house settling’). Slamming a door will pop them too: vibrations from that loud music you play. Not really. Just scrape the loose stuff out with your putty knife (or 5-in-1) and hit with spackle. We use non-shrink, lightweight spackle because it dries in only hours, or less depending on the depth of the hole. (“Mud” takes overnight). Your wide knife from the above will work but a medium size knife is what we use, or if nothing is around I’ll just use my 5-in-1. Apply, let dry, give a quicksand, prime with regular wall paint (not proper!, but ok) if you have no primer handy, and you are done.
Problem #5: pin and nail holes. We don’t do much here, just like finger-painting in kindergarten, we just our finger, spread a bit of lightweight spackle (described above) and wipe with the palm of the hand. No need to prime.
Problem #6: glue type gunk. We just remove with a knife and use a little paint thinner on a rag. If you have a real problem, write to me.
Problem #7: paint beads up like water on a waxed car.
Ok, you have a serious problem. It is probably grease or even tar from a smoker. (See not so funny cavitation story below* ) This beading is known as cavitation. The paint cannot adhere. You are going to have to get your hands dirty, but as they say, if there is no solution, don’t worry. If there is a solution, don’t worry. Here the solution is a solution. Tri-Sodium phosphate (TSP) is your new best friend. It comes as a liquid or as a powder you mix with water. It’s not very toxic, but WEAR EYE PROTECTION and water-proof gloves. It is basically soap plus moxy power. Really, the phosphates are just something they used to put in detergent, but it was having a bad effect on the environment. If you have any mildew or mold, you can add a small amount of bleach to your mix and kill two, uh, jobs with one, uh, solution. But don’t use in bathrooms (near metal). For that try Moldex. Be sure to keep it off metal and other surfaces you will not work on as it can stain them. It will just leave a film on the glass that you can clean later. So scrub away a bit, let dry and test with paint to see if it is working. Not working? Write to me.
Short Story on Preparing Walls for Painting
That’s it but here is a short story: My father showed me how to just stuff a hole in a wall with newspaper until the paper was fairly tight, just keep pushing in the paper until there is not more room in the hole. With the paper just below the surface of the wall, he would layer the mud in coat by coat. It’s easy but slow. Works!
*A short story about cavitation: We were assigned a studio apartment in an urban setting (near NYC). We had done literally hundreds of these: 2 per day. This one was very different. Brown walls need 2 coats of off-white. Let’s go in. The stink, oh god the stink. Anyway, let’s start painting. Oh, the cavitation, the cavitation. We packed up and left. The cause? Smoker. 20 years in that hole. The brown walls? They used to be white. That what’s happen sometimes when you are preparing walls for painting.
If you have any comments or questions about preparing walls for painting, please write in the comment section. I’ll reply asap!