How much prep work for painting interior walls?
March 21, 2011 10:50 AM   Subscribe

I have a big, big room I'd like to paint. Do I really need to sand and wash every inch of the walls?

I am fairly lazy, but I am a perfectionist. This'll be my first time painting an interior wall of a place that I own (I have painted rental apartments, but never did much prep except for filling nail holes) and I want to do it right. However, I have a LOT of area to cover. It's my entire downstairs, and the "room" measures something like 25 by 40 feet. From what I've read, to paint a room right you need to sand the entire wall, wash it with some mild detergent solution (or even just water to get the dust off), before painting. How necessary is this step? Could I get away with simply washing any smudges and doing hole-patching and sanding -- basically, spot-work? Or would I end up with some bad-looking walls?
posted by chowflap to Home & Garden (21 answers total) 12 users marked this as a favorite
There's a Dave Barry book about household repairs called "The Taming of the Screw." The section on painting/wallpapering addresses this, stating something along the lines of, "if my walls were clean, even, and free from blemishes, why the heck would I need to paint them?"

I have no idea if it's truly, honestly required, but in my experience with painting a huge room according to the rules, it went pretty quickly. Granted, my whole family was in on it, but still. And we started with blank, never-painted walls. After filling all the little holes and whatnot with putty, we took--well, I'm not sure what they are, but they're basically sponges with one sandpapery surface, and just sort of lightly scrubbed over the entire wall. It went pretty fast with the four of us working on it, taking turns.

My dad, who is really into home improvement stuff, insisted on the sanding. I don't think we washed anything, but we ran a stiff brush over it to knock off all the sanding powder.
posted by phunniemee at 11:00 AM on March 21, 2011

Wash yes, with TSP, but you don't have to sand the whole wall, just any bits you fix w. plaster.
posted by GuyZero at 11:06 AM on March 21, 2011 [1 favorite]

Depending on the condition of the wall right now, I'd go over the whole thing with a broom and then a slightly damp towel, and call it damn it.
posted by small_ruminant at 11:12 AM on March 21, 2011 [1 favorite]

You don't say, but i presume your walls are plaster. I have never done the sanding bit, but my walls have always been textured. I do wipe them with a damp sponge. It doesn't take long, just carry a bucket and rinse the sponge frequently. There does seem to be a big benefit to painting the walls with primer first. Why not paint a section with, and one without the prep work and see what works best for you?
posted by annsunny at 11:17 AM on March 21, 2011

Response by poster: I think they're regular ol' sheetrock. And I am already looking at priming -- the walls are a bright orange color (which I have enjoyed for four years, but I'm looking for a change).
posted by chowflap at 11:26 AM on March 21, 2011

spackle holes, sand spackle, wash walls (TSP or plain ol' water), prime, paint.

I've been known to skip the wash step when the room is pretty clean to begin with. People have been painting walls without sanding them for some several years now and I think it generally goes OK.
posted by that's candlepin at 11:29 AM on March 21, 2011

For DIY, with a decent starting surface, spot-fixing, sponging down and a good primer/undercoat is going to work better with much less hassle than, say, trying to skim-coat an even layer on drywall, where you risk compounding any existing flaws.
posted by holgate at 11:32 AM on March 21, 2011

Wipe the walls down, yes, but I've never heard of sanding painted drywall before repainting. Wood, yes, but not drywall. Unless it's painted with an enamel gloss or something.

Just sand down the imperfections (paint drips, filled holes), wipe down, and paint.
posted by torticat at 11:32 AM on March 21, 2011

Re: sanding -- Depends on what you intend to do to the walls after painting. I've only ever sanded down the putty to smooth it before painting. We put some wall stickers up for a while and the paint lifted when the stickers were removed, indicating the latex hadn't bonded very strongly between new and old layers (i bet the sanding is for improving adhesion between layers). Same with getting my clawfoot tub refinished in my bathroom - the painter's tape lifted the bright blue paint from the formerly white walls.

Lesson learned: keep some touch-up paint on hand.
posted by lizbunny at 11:48 AM on March 21, 2011

Best answer: If you're using water based paint, a small mark such as, oh, let's say fly shit, WILL smudge through and end up as a bigger but less defined mark in the new paint. This is why cleaning is necessary. If you're going for a serious colour change and need a few coats maybe it won't be as much of an issue ... but you really don't want to find out the hard way that actually, it was. I've never sanded internal walls though, as someone else said MAYBE if it was gloss, but not otherwise.
posted by Lebannen at 11:55 AM on March 21, 2011

If you can find a color you like --Behr paint and primer in one is a major work saver.

Granted some of the colors don't offer the rich saturation of regular paint. But they stick to not perfect walls pretty well. I've used it alot and its great.
posted by AuntieRuth at 11:58 AM on March 21, 2011

Seconding the TSP (tri sodium phosphate) recommendation. Get the real stuff (not the "TSP substitute" that's being sold at some paint stores), mix it with hot water following package directions, wear gloves because it's a corrosive base, and do a rinse-wipe with clean water afterward. Your paint will stick & cover so much better.
posted by squalor at 11:58 AM on March 21, 2011 [1 favorite]

Sheetrock painted with a roller will get a very light texture from the roller brush. As the wall is repainted without sanding, this texture will get more pronounced with each new coat.

Which looks perfectly fine as long as that texture was even in the first place -- if the person who painted it last did a bad job cutting in at the edges, or if you've done any patching beyond the odd bit of spackle and nail-hole-filing, you should sand -- not to a mirror finish or anything, just enough to even it out to whatever is your degree of perfectionism.

I usually skip cleaning unless it seems obviously necessary -- i.e. if I've just sanded, or I'm painting a kitchen or bathroom (cooking oil and smoke can interfere with adhesion), or if the walls are just plain dirty.
posted by ook at 12:04 PM on March 21, 2011

Nthing, Wash - yes, Sand - No
posted by bitdamaged at 12:47 PM on March 21, 2011

Yes, wash them. TSP and water solution in a bucket. sponge/rag, dunk squeeze out, and wipe. Dunk frequently or you'll just move the dirt around.

The only thing new I'd add is that if you've washed floor to ceiling about a 6-foot section of wall, and the water is still looking clean, this may be a step you can skip. Wall-cleaning required about 3 dump-and refill buckets when we painted our tiny tiny bathroom, but that grossness made it feel really worthwhile. If it doesn't seem like you're accomplishing anything, feel free to skip it.
posted by aimedwander at 12:57 PM on March 21, 2011

Paints nowadays are really good at sticking to non-washed walls, esp. if you get a higher-end version of whatever brand you are buying. I personally wouldn't bother to wash walls beyond just a quick wipe-down with a damp towel, mainly to catch cobwebs or other minor things. Maybe do this a little more thoroughly along the baseboard where you'll find more dust, dirt, marks, etc.

Also, don't bother to get primer...just use 2 coats of whatever paint you're using. Or if you've already bought the primer, you can add colorant to it to bring it "close" to the hue of the final coat. That'll allow the final coat to cover the orange color more easily.

Good luck!
posted by see_change at 1:20 PM on March 21, 2011 [1 favorite]

Best answer: A flat finish paint will show fewer imperfections than a glossier one.

Accept that there will be some imperfections, and that you are much more likely to notice them than anyone else.

Depending on the wall texture and climate, vacuuming may make a lot more sense than washing. I've never bothered with using TSP or soap unless the wall has grease on it (kitchens), as that adds the step of rinsing. You can wash with a clean mop instead of a sponge. In places that are less dusty than where I currently live I've skipped the vacuum/wash step altogether, but you still need to run something along where the cobwebs are, like a broom with a rag over it.
posted by yohko at 1:25 PM on March 21, 2011

Best answer: My recommendation: Wash with TSP and use a piece of scotchbrite as the sponge. You'll get the walls nice and clean and you'll get that important mechanical adhesion ("tooth" adhesion) that painters look for.

Use good paint. By good paint, I mean Benjamin-Moore or Sherwin-Williams.

If you have carried out repairs to the drywall that have involved sanding and if the wall is lightly textured and if your repairs have removed the texture, those repairs will stand out for their lack of texture. I suggest you use something like this aerosol texture to add some texture before you paint but after you wash.

I suggest using primer—spot priming—those repaired areas after you've washed. You can use a spray can primer for spot priming. Killz is a decent spraycan primer.

Finally, just before paint, I use a tackcloth to remove any dust that may have accumulated after the wash.

Oh, and don't attempt to wash a ceiling.
posted by bz at 1:38 PM on March 21, 2011 [1 favorite]

When I'm painting furniture or rooms for a client, I almost always clean, sand, and wash before the first coat. It really adds to the quality of the finish. My grandfather used to say 90% of a good paint job is in the prep work.

When I have skipped steps, most people don't notice it, but I do and it drives me crazy. So it also depends on how much you look at your walls and notice that tiny streak no one else can see.
posted by Nackt at 2:58 PM on March 21, 2011

I am fairly lazy, but I am a perfectionist.

Hire someone. Hire someone who is not particularly cheap.

How great does the drywall look now? After doing massive renovations on our house, we felt like our drywall looked pretty perfect after painting, even though we didn't always have time to sand to a perfectionist degree. And they do look great.

For the love of all that is good and holy, pay extra attention to your bedroom and to your view wherever else you sit most of the time. I don't give a damn about the imperfections in the dining room.

But above the bed, there's a slight bulge in the ceiling about four feet from the center of the room that follows the tape line for about a foot, and a scaly patch above the left side of the one radiator, and a bit of a sort of dent on the far corner that catches the light just so in the morning. We didn't notice this stuff until we looked up at it for a couple of months and started seeing the slight shadows.
posted by desuetude at 11:25 PM on March 21, 2011

Response by poster: Thanks everyone. It sounds like spot-sanding and then a full wash are the way to go here. The current coat of paint was put on without very much care, and I think anything I do to the surface will be an improvement. (It's a very flat color, not glossy, looks like it was put on with a roller.) And I may, after all of this, pay for someone to do it.
posted by chowflap at 10:33 AM on March 23, 2011

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