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I'm fitting square edge 1/2" sheetrock to a ceiling. I've not been able to find any best practice for how this should be fitted.

When the plasterer comes to skim it, some mud will squish through the mesh tape into the gap between the boards. Should the boards be butted tightly together to minimise the length of the tape/mud bridge between them? This also minimises the amount of wet mud below the board surface, that will presumably shrink as it dries.

Should I aim for a 1/16" or even a 1/8" gap between the boards, to encourage a 'fill' of the joint, thus perhaps stiffening the joint between the boards, helping to prevent any movement and the possible development of hair-line cracks? There is now even more wetness below the surface which could exacerbate shrinkage issues.

If I do aim for a significant gap between the boards, is it worth filling this gap with either mud or caulk and allow to dry well before the plasterer skims? This would stiffen the joint, and reduce the amount of wet mud below the tape.

I probably can get a tight joint between the papered long edges of the boards, but with cutting irregularities, that's going to be less possible on any cut ends.

Neil_UK
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  • Very relevant. The question is different, but the answer very specifically addresses this question. – FreeMan Apr 28 '21 at 11:32
  • I think it matters whether your plasterer is a professional or a DIY friend. If a pro, go with the pro advice here. If DIY, personally I find some pro tips don't apply to me because I simply don't have the speed and accuracy of a pro, and I look for techniques and materials that fit my style & mistakes, and still leave a pro result. This might explain the diversity in opinions regarding mudding/plastering. – P2000 Apr 28 '21 at 16:17
  • Where are you based? Your username suggests a UK connection, but you're using US drywall terminology. You also mention skimming, which is (I believe) very much a UK technique. – NMF Apr 30 '21 at 22:54
  • @NMF I'm in the UK, but have spent so long working for US-owned companies that I tend to think in dollars and use language randomly from either side of the Atlantic basin, and never write numerical dates in anything but ISO (yyyymmdd). Always spell colour and related words like that though. – Neil_UK May 01 '21 at 07:15

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Tight. Sheetrock doesn't "move" like wood does. Fit it as tight as you can, but don't go overboard on the labor. I've seen some pretty sloppy jobs of hanging rock that got muudded and taped and turned out OK. Problem is sometimes if the gaps are too large, the mud eventually shrinks and they open up and you get some cracks. Best practice is as tight and clean as possible when hanging rock.

George Anderson
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    Yes you want tight. If the joints aren't filled they should be prefilled before taping. Taping works best with solid surfaces behind it. Voids behind tape can easily allow the tape to move, be dented into this void or allow cracks to develop. – Fresh Codemonger Apr 28 '21 at 22:43
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There is a new procedure for hanging drywall in which butt joints are made between joists! The joints are backed by backer strips 6" or 8" wide to which the drywall ends are screwed. I have seen videos of this in Australia and I believe the US.

Google Buttboard. https://youtu.be/XNJWPDW-mzE

https://youtu.be/Lr5v3EblafA

EDIT https://youtu.be/UBVtU3XXUrU

Jim Stewart
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    I was doing similat in Australia as per manufacturers instructions, but we were just using off-cuts and a space-filling plaster-based glue by screwing near the end the glue would form a wedge shape resulting in a recessed end. – Jasen Apr 29 '21 at 03:20
  • @Jason off-cuts of what material? The videos on YouTube I saw were of work by Maxkil Australia. They were applying mastic to the backer boards and laying them over the edges as they were hanging ceiling drywall in very long sheets, almost 16 ft. – Jim Stewart Apr 29 '21 at 10:44
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! UK-specific answer - OP is in UK.

For plaster (e.g. Thistle multi-finish) skim over plasterboard, you would usually leave a small (less than 3mm) gap. The British Gypsum site book says Lightly butt boards with a max. separation of 3mm. Don't butt them tightly together!

The joints will be taped (often with fibre-glass mesh) then 2 coats of plaster applied in quick succession, although I have seen plasterers give the joints a quick coat to fill them first, although with small joint gaps that isn't needed, the first coat will fill them.

To avoid cracks, it is important that all board edges are well supported (well-fitted noggins) and fixed with sufficient screws of the correct length (driven so that the head is just below surface level - don't split the facing paper).

Source: British Gypsum site book

NMF
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