My cousin says I should leave 1/4" space between all edges of drywall so that mud can be pressed into it. Everything I've read online say to butt them tight. When is leaving a gap a good idea?
I think you run a pretty fair chance of pushing enough mud right out the back of a 1/4" gap that gobs of it will fall off inside the wall and be wasted.
You can (and should) squeeze drywall mud into pretty small cracks. Leaving a big gap just isn't a concern. Put a nice coat of mud under the joint tape, squeeze it into the joint, then put another coat over the top of the tape and feather it out. The mud will adhere to the drywall, fill the joint holding the sheets together, and the tape will be embedded inside the coat of mud strengthening the whole joint.
Regular drywall mud shrinks as it dries. The bigger the gap, the more times you'll have to go over the same seam with extra coats of mud to pull it out level with the wall. Otherwise, you would have a very visible groove running down the length of your wall.
Also consider that it's the paper on the front and back that holds a sheet of drywall together. The mud adheres well to the paper, to the drywall tape, and to any exposed gypsum on the cut edges of the panels when it is skimmed on.
But if you leave too large of a gap, you end up with bigger globs of mud, which you can knock loose in one chunk. You could actually bump that gap with something, like a furniture corner, and knock a line of joint compound loose from the edges of the sheetrock panels so that there's a flexible 1/4 strip of dried mud floating in that 1/4" crack, only being held in place by the tape on the front. I'm absolutely certain I've seen exactly that, at least once.
Set the sheets tight together. Like the other answerer, Jack, I've never seen drywall in any residential or commercial installation intentionally set with large gaps.
Though I have seen in commercial construction (where walls are often 50-500 feet long of continuous drywall) where there are deliberate expansion joints set. These help control cracking on long walls (similar to putting expansion cuts in concrete). Typically there is a small gap between drywall sections which allow a special expansion piece to be mudded into place (similar to typical inside/outside corners used at the edges of drywall). It is then finished like any other joint, except that the expansion gap isn't filled in which allows the joint to flex slightly without cracking the drywall.
Other than this, drywall sections should probably always be butted against each other and the joint finished with tape and mud.
After seeing the reference in a previous comment about the "Do's and Don'ts Of Drywalling" recommending a 1/8" gap, I decided to take a look at the reference. The gap is recommended for the edge of inside corner pieces that you need to cut. This is because if you cut it a little too wide, you can mess up the edge forcing it into place. It does NOT recommend gaps between full sheets. In fact is gives a photo of butt joints with no gap. The reference does have good points. If you are a novice, it is worth reading. Also, like several other people have noted, if you add 1/8" to every sheet, you're going to run out of studs to nail/screw to after a while.
Personally I have always hung drywall tight when butted or on outside corners. On inside corners I tend to leave a small gap, usually less than a 1/4 inch though. I do this because framing lumber, and framing for that matter, are never 100% perfect. Measurement to inside corner i usually subtract an 1/8 inch. Also i prefer mesh tape, always use hot mud (powder from bags) for my first coat. 2nd and 3rd coats vary by job between hot mud and joint compound.
ive been doing this 34 years and never heard of leaving a gap between sheets. just doesnt make sense. sheets are 4 x 8 typically and framing is 16 on center. like someone else said your run would grow even on just a few sheets across. i do alot of commercial drywall and we usually stand the sheets up so 4 ft 1/8 would grow fast in a big room. honestly never had a problem make them nice and tight , its a better job imo
Most houses are 70F year round so allowing for thermal expansion isn't really something you need to worry about. If the space is unheated (and -20F) for weeks at a time you might want to think about cracking coming from thermal expansion/contraction.
Similarly, the paper on the outside of the sheetrock and a coat of latex paint seems little it would inhibit moisture induced expansion (unlike a hardwood floor, where expansion can make a too tight floor push a wall out of plumb!)
There's no reason to engineer gaps between sheets. It just makes the taping slower .
I typically leave a gap about the thickness of the taping knife, so 1/16th or less.
I also use "hot mud", which is the dry powder mixed with water that sets via a chemical reaction similar to concrete. It's MUCH stronger, harder, and holds better. I also don't use paper tape - I prefer the mesh tape as the paper tape never seems to bond well at all, regardless of any gap or no gap between sheets.
According to The Do’s and Dont’s Of Drywalling. One of the biggest mistakes is not leaving a 1/8 in gap in your joints .