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General: Tape/Joint plasterboard versus skim coat

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  1.  
    • CommentAuthorandyman99
    • CommentTimeMay 3rd 2018 edited
     
    I have applied IWI'd on my first wall and plaster-boarded over it, now I have to decide whether to skim coat or not. So my question is, how good is a taped and jointed finish on plasterboard compared to a skimmed plaster finish? Lets assume I do a first class job with the jointing. Also if skimming the wall, is the jointing process the same? Would a plasterer expect the jointing to be already done or would he do it himself?
    • CommentAuthortony
    • CommentTimeMay 3rd 2018
     
    Taping and jointing is an alternative so skimming with gypsum plaster.

    Top class tape and joint is common in the US a slurry coat is important to leave an even texture. Corner tapes are more tricky and generally substandard here.

    Taping and jointing is done on taper edge plasterboard, skimming on square edge. No need for both, both are best with sticky mesh scrim tape.
    • CommentAuthorandyman99
    • CommentTimeMay 3rd 2018
     
    Thanks Tony, seems my path is defined by my choice of PB. Will give it a go.
  4.  
    It's quite easy once you are used to it. Trowel if you are good with one, or spatula otherwise.

    I joint-fill because I can't plaster, but sometimes, if there's a bit of undulation, you end up more-or-less skimming with the joint filler, which is expensive!
  5.  
    Posted By: tonyTaping and jointing is done on taper edge plasterboard, skimming on square edge. No need for both, both are best with sticky mesh scrim tape.

    Over here no one skims. square edge PB has the joint filler feathered over about 15 -20 cm each side of the joint to make it invisible. Less than 15cm feathering also works but thats a cheaper (not so good) job. The filler comes in several grades but the usual one for jointing PB is designed for a thickness from 0 - 5mm
    • CommentAuthorFred56
    • CommentTimeMay 4th 2018
     
    Tape and joint taper edge board is great if done well but there tends to be a misconception that anyone can do it. It is still a skilled job. To me it is first choice because it reduces the dreadful mess that plasterers always make.

    The common defects are often due to poor practice in the boarding. Make sure the rules are followed around door openings particularly. You absolutely must use the correct drywall primer coat to get a uniform texture. Drywall primer is not contract emulsion contrary to popular opinion.

    I can recommend a contractor in Darlington who is so good you would wonder why anyone wants to skim.
  7.  
    Posted By: Fred56The common defects are often due to poor practice in the boarding. Make sure the rules are followed around door openings particularly. You absolutely must use the correct drywall primer coat to get a uniform texture. Drywall primer is not contract emulsion contrary to popular opinion.


    Good point. The proper primer is almost all glue and no pigment - if you use a roller you can't tell the difference in texture between the plain paper sections and those with joint compound.

    As Peter_in_Hungary mentioned, you still tape-and-joint square edges (you always have these on the short axis of the boards anyway). With the right feathering, these are essentially invisible. One trick is to use setting compound for the first couple of coats and then sandable drying compound for the final coat. If you're really good there's hardly any sanding required, but it's never zero, no matter how skilled.

    Over here in Canada, no-one skims the entire boards.

    Paul in Montreal.
    • CommentAuthorcjard
    • CommentTimeMay 5th 2018
     
    Not sure what you mean "would a plasterer expect the jointing to be done?"

    A plasterer, IME, would expect to see a plasterboarded wall, with electric accessory points made obvious and all drywall screws correctly flush or slightly subsurface

    He will tape the joints (if he doesn't use tape, get another plasterer)

    Tape and fill takes just as long as full skim by the time you've finished messing about with sanding and recoating so in theory the different is just the plaster price. When I as getting quotes, they were roughly the same price on a per job basis. Personally I'd go for full skin, and if you've got a lot of work, push for a per metre price. Anything less than a fiver a metre (materials excluded) is pretty good for one off builds site rates where there are acres of work are more like two quid a metre
    • CommentAuthorMike1
    • CommentTimeMay 6th 2018 edited
     
    As noted above, it's not easy making the joints truly invisible when taping & jointing - and it's very common to be able to see where they are. Having used both methods, and employed others to do them too, my own preference is for skimmed plaster.
  10.  
    From a DIY perspective I am happy to tape and joint and can get an acceptable result however skimming a wall is a whole different matter !
    • CommentAuthorandyman99
    • CommentTimeMay 7th 2018
     
    We were always intending to skim coat and I knew that was beyond my skill level. However having now put up boards more suited to taping and jointing, I've decided to have a go. I saw Paul recommended drywallinfo.com in a previous thread so I'm following the stages outlined there (blimey - a bit more complicated than I'd thought!) I was rather hoping to present the finished wall to my wife before she realised what was going on, but of course she has smelt a rat. Now this wall will be examined with great interest so we'll see if my skills pass muster. Some days away from the finished job, I will need to speed up considerably to make it worth while on a larger scale, but if its good enough, this should allow me to get a space completed without the need for outside trades. Paint comment noted - thanks to all as usual.
    • CommentAuthormarktime
    • CommentTimeMay 7th 2018
     
    The secret to good dry-wall finish is feathering. Make sure you understand what it means and how to achieve it. I finish off with a 50cm float so that and the primer yeilds invisible joins. Good luck.
  13.  
    Posted By: marktimeI finish off with a 50cm float so that and the primer yeilds invisible joins

    Yes on square edge boards but IMO a 50cm float is not needed on taper edge boards
  14.  
    Posted By: Peter_in_HungaryYes on square edge boards but IMO a 50cm float is not needed on taper edge boards
    Even on square-edged boards a 50cm knife is a tad excessive. The pro-taping knives here have two sides - one is straight and the other is slightly curved to allow feathering. Most pros stick to 12" or 16" knives for the final feathering. That and judicious use of a "trouble light" (until you get skilled enough not to need one until the very end).

    Another pro-tip if you want to do fast work - use a setting compound the sets in around 40 minutes. You can get the first couple of coats done all in one shot and then get the finish coat on the same day, ready for sanding/priming on day 2.

    Paul in Montreal.
    • CommentAuthormarktime
    • CommentTimeMay 7th 2018
     
    I call it my Buntline Special and yes, it comes out on butt edges and always on ceilings. :bigsmile:
    • CommentAuthorMarkyP
    • CommentTimeMay 8th 2018
     
    I would think that a typical 2 coat skim would improve both the fire and sound performance of the wall or ceiling relative to the same boards being only taped/jointed.
  17.  
    Posted By: MarkyPI would think that a typical 2 coat skim would improve both the fire and sound performance of the wall or ceiling relative to the same boards being only taped/jointed.


    I doubt it to be honest. How thick is the skim? A couple of mm? If you want fireproof you use the right boards in the first place as far as I understand. Sound performance also - there's special types of drywall available such as QuietRock® ( https://www.quietrock.com/ )

    Paul in Montreal.
    • CommentAuthorMarkyP
    • CommentTimeMay 8th 2018
     
    a standard 2 coat skim is typically 4mm in two passes. I reckon you'd be adding a 3 or 4 kg of mass per m2 based on a quick fag packet calc using typical plaster coverage, maybe 8 or 9kgs of mass added to the board overall. A 12.5mm board comes in at something like 23kg, so a very significant amount of additional mass is added with a skim. I think I read somewhere a 2dB sound reduction for 2mm of skim. Not sure if that scales in a linear way. But if you had a stud wall, both sides skimmed, you add around 8kg of mass per m2 and 8mm to the build up. if this achieved 4dB reduction then that would be significant based on typical system specs for the whole wall.

    If you have a 60 min fire rated board and add 4mm of gypsum mass, I think the fire rating has to be improved. compare the fire performance of a 12.5mm and 15mm board.

    agree you can achieve fire and sound ratings without skim using denser boards, but I'd bet all would do even better with a skim.
  19.  
    Taped & jointed can be fine depending on circumstances. In some cases the imperfections will be more noticeable than others. For example, if it's a wall that will be washed downwards with lighting that's close to the wall, then any deviations from perfect flatness will be much more noticeable than on a wall that's lit in a more horizontal direction.
  20.  
    Posted By: MarkyPa standard 2 coat skim is typically 4mm in two passes. I reckon you'd be adding a 3 or 4 kg of mass per m2 based on a quick fag packet calc using typical plaster coverage, maybe 8 or 9kgs of mass added to the board overall. A 12.5mm board comes in at something like 23kg, so a very significant amount of additional mass is added with a skim. I think I read somewhere a 2dB sound reduction for 2mm of skim. Not sure if that scales in a linear way. But if you had a stud wall, both sides skimmed, you add around 8kg of mass per m2 and 8mm to the build up. if this achieved 4dB reduction then that would be significant based on typical system specs for the whole wall.


    Smallest discernible difference in sound level is 6dB - so 4dB really makes no difference. That QuietRock product I mentioned achieves a 60dB reduction!

    Paul in Montreal.
    • CommentAuthorMike1
    • CommentTimeMay 10th 2018
     
    Posted By: lineweightTaped & jointed can be fine depending on circumstances. In some cases the imperfections will be more noticeable than others. For example, if it's a wall that will be washed downwards with lighting that's close to the wall, then any deviations from perfect flatness will be much more noticeable than on a wall that's lit in a more horizontal direction.

    Yes, it's illumination that often makes joints noticeable - but that can include horizontal light from a window too, especially when looking along a wall from a doorway towards the light.
    • CommentAuthorDarylP
    • CommentTimeMay 11th 2018
     
    lighting perpendicular to the surface will hide any small imperfections, whereas lighting close to parallel will serve to highlight any imperfections..... :cry:

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