November 28, 2011 5:06 AM   Subscribe

DIYers: How anally retentive with joint compound do you need to be to prevent visibility of seams after painting?

I'm finishing sheetrock for a garage ceiling--a money-saving project that's also, well, a good indoors DIYer for the early winter. Running into a speed bump. Relevant details:

-The sheetrock crew taped and mudded the seams and screws, and also added a second skim coat. My job is to finish the mudding and paint the ceiling with a coat of primer and a coat of white topcoat.
-Using a 6" drywall knife, I added the third coat of mud, but because of my inadequate feathering skills, many 1/16" and 1/8" ridges and divots remained. Sanded, spot-coated with mud, sanded again. Now, only a few 1/16" or 1/32" bumps and thin knife-creases remain, but some of the seams are visible when viewed under direct light from certain angles.

My question is this: After a coat of primer and topcoat, is there any chance that these 1/16"-or-less flaws will be visible? Will two coats be enough to cover them up?

I realize that I've got more leeway in aesthetic flaws than I would with a wall, because it's a 9' garage ceiling. But I want to be satisfied with the final results. Also, I know that I could test my work by priming and topcoating a small section, but I want to see what your opinions are before jumping into this stage.
posted by Gordion Knott to Home & Garden (13 answers total)
Because you did the work yourself, you will always see every little, teeny flaw, because you know where to look. Since you have three solid coats of mud up there, wring out a large sponge until it's barely damp, and go over a few of the smaller ones with a few wipes and see if it "melts" them down enough not to be noticeable. If it's satisfactory when it dries, you can do this over the rest of them. It never hurts to do a damp wipedown on a ceiling to remove all the sheetrock/mud dust before you paint, anyway. Allow to dry for 24 hours before applying primer.

Ceilings are tough because they are large, unbroken planes. No windows or doors to break them up or cast concealing shadow lines. The up side is you may not have to paint it again for ten years, so do a thorough job now and reap the benefits.

Good for you for jumping on it, and good luck.
posted by halfbuckaroo at 5:19 AM on November 28, 2011 [1 favorite]

It won't be perfect. This is the reason why people do popcorn ceilings, because flat, unblemished ceilings are really tough to accomplish.

That said, it'll most likely be good enough for a garage, especially 9 feet up.
posted by xingcat at 5:25 AM on November 28, 2011

About the only flaws that solid colors of paint can conceal are tiny pinholes in the compound. Lines and ridges will be virtually as visible after paint as before.

If you're going to do more drywall finishing, get a wider knife - at least 12", preferably 18". You're making it really hard on yourself by using the wrong tool.
posted by jon1270 at 5:26 AM on November 28, 2011 [7 favorites]

Can you wet it and smooth it out that way? It's a garage ceiling right? It will be fine the way it is. Don't let it make you nuts. If it was in your bedroom, I might venture to say sand it down and try to do it a little better since you will lie on your bed and look up at the ceiling making you crazy, but you will never look at that ceiling the way you do right now again. Go paint and have a sandwich!
posted by Yellow at 5:28 AM on November 28, 2011

Seconding the wider knife. And try for a light, but deliberate, touch; overworking the mud (going over and over the same spot) hardly ever works out well.

And, like it was mentioned upthread, you'll see the mistakes much easier than anyone else, because you'll know where to look.
posted by Benny Andajetz at 6:17 AM on November 28, 2011

Whack a bit of primer on the bits you're not sure about and have a look. It won't look any better with topcoat than it does with primer, but if you've put on some primer and still see bumps you're unhappy with then you should be able to fix them with a bit more sanding, and if parts of your ceiling end up with multiple coats of primer that will be no problem at all.
posted by flabdablet at 6:21 AM on November 28, 2011

Before putting the paint on you could try to smooth them down with sandpaper. Two coats should cover most the blemishes up.
posted by melizabeth at 6:41 AM on November 28, 2011

Seconding the pole sander.
posted by beagle at 7:32 AM on November 28, 2011

It might, and might not, be visible. I'm pretty OCD with things like this myself, and I didn't notice a HUGE gouge in my mud job until years later.

Anyhow, the goal of mudding is to get to a point where there are no low spots (gouges, knife divots, etc.) You can scrape or sand down high spots, but if you leave gouges, you'll be at it forever. The basics are that the seams are high spots. You use progressively longer blades and bridge the gap between the ridge of the seam and the base of the drywall.

Given where you are at now, what I would do is:

1- Buy a 12 inch blade and gently scrape down any ridges. You want to hit it at an angle that makes sure you won't dig into the good parts.

2- Go out and buy some primer and add a tint to it. Maybe even mix in some drywall compound into it. You want something super flat and easy to sand. Paint the wall with it, and then sand it with the largest drywall sanding block you can find. (Larger blocks bridge gaps and take down high spots without taking anything off low spots.) When sanding, don't scrub, but sweep across. Anywhere you can still see your tinted primer, skim it with more drywall compound. Slap some compound on, and then drag the blade across it, scraping off the excess, like a squeegee. Repeat the primer and sanding process and you should see a marked improvement. If it comes off pretty evenly at that point, primer and paint.
posted by gjc at 8:20 AM on November 28, 2011

After a coat of primer and topcoat, is there any chance that these 1/16"-or-less flaws will be visible?

Yes, there's a reasonable chance they'll be visible in the finished product if you look at the ceiling and shine a light on them. There's a reasonable chance nobody's going to do that.
Also, unless you plan on priming and painting with absolute perfection, this doesn't have to be absolutely perfect, either. i.e. If you paint like I do, there's a reasonable chance they'll be mistaken for one of those little ridges of paint you get at the side of the roller when you press too hard.

Drywall tip that you probably know, but it doesn't hurt to say: Take a bright worklight and shine it along the surface (not at it, along it). Look for shadows created by the ridges and craters.
posted by aimedwander at 8:20 AM on November 28, 2011

Speaking from experience, flat paint on ceilings will help you tremendously. Not 'eggshell', but 'flat'. It is sometimes labelled ceiling paint, but not always.

Also, yes, a damp sponge can help with evening things out.
posted by alienzero at 9:50 AM on November 28, 2011 [1 favorite]

You need to get the right tools for the job and use the right technique.

First as mentioned, you need a wider knife -- 12 inches.

Second, you need a lighter topping compound. General purpose compound is denser and good for setting tape into the joint, but topping compound is easier to use for the finishing coats because is trowels easier and is much easier to sand.

Third, get a pole sander. It works well on walls and ceilings.

Use your 12-inch knife and use fairly strong pressure and a fairly flat angle. The divots you are seeing are because you aren't applying enough pressure. You use the smooth, dry surface of the drywall at the far edge as the guide for your knife so make sure that the knife extends off to the side of the joint. The outside edge of the knife should be on the smooth sheetrock as a guide. Press hard on that outside edge. This keeps you from making divots. This is also why you use a wide knife.

The tapered joints on the long edges of the sheetrock are the easiest because they have a built in depression you just have to fill. So just drag your 12-inch knife down the joint spanning the depression with hard pressure to make a smooth surface. Adjust the angle of the knife so that you don't leave divots. The best angle may be shallower than you are used to. The pressure should be enough to slightly bend the knife.

The butt joints on the ends of the sheetrock are a little harder, because they don't have a depression. You have to feather out the joint to avoid creating a lump. To do this, you extend your mud 10 inches or so to either side of the joint. You do this by using your 12-inch knife. Let's say you are doing the left half of the joint. You position your knife so that it overlaps the joint on the right edge of the knife about 1 inch. The rest of the knife is to the left of the joint. You apply hard pressure on the left edge that is on the smooth surface of the sheetrock and slightly less pressure on the right edge of the knife over the joint. This will give you a very slightly tapered joint, feathered at the edges and slightly higher over the joint. Do the same on the right edge of the joint and you have a total of about 20 inches wide.

When sanding, go with light pressure on the edges because you don't want to sand the paper and cause it to fuzz up.

It's just a garage, so you could just ignore the imperfections. On the other hand, if you want to improve your DIY skills, the garage is a good place to practice. I think you will find that using the 12-inch knife will make a world of difference.
posted by JackFlash at 10:49 AM on November 28, 2011 [1 favorite]

My question is this: After a coat of primer and topcoat, is there any chance that these 1/16"-or-less flaws will be visible? Will two coats be enough to cover them up?

Yes, they will be visible. No, paint will not cover them up.

In my experience, paint doesn't cover up anything except, well, the previous color. If this is to be a so-called "unfinished" garage (nobody living in it), I'd suggest just leaving it. Garages are usually not finished to the same level as interiors. Flat paint is actually *less* forgiving of imperfections under what are called "challenging" lighting conditions, so you could consider a semi-gloss or eggshell up there. Full gloss is probably a bit much.

Your other options are to improve the seams by taping, sanding, and repeating as your skill gets better (do obtain a wider knife, though), or to texture the ceiling. It doesn't have to be a popcorn ceiling to hide imperfections; even a spatter or orange peel does great at hiding everything (which is why they are so popular).

For the absolute best, most demanding finish it's recommended to skim coat the entire surface with compound so that the texture/porosity is the same over the whole surface. But the garage doesn't need that level of finish, and your skills are such that you'll actually make it worse (no offense. :-) ). If you're going to be doing this a lot, I recommend Myron Ferguson's Drywall; my copy has the pages falling out. It is frequently available in to check out in at least my local library; that may be an option for you if you don't wish to buy it.

My background: 12 year homeowner, 44 year old house, a 9 year old, a 6 year old, a 4 year old, and a 1 year old. I don't do drywall for a living (thank god), but I've done quite a bit of it on my house. I take much longer than a professional does to get similar results, but I do know a bit about how it's supposed to be done. I can't always get it right.
posted by RikiTikiTavi at 1:07 PM on November 28, 2011

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