Plasterboard join to existing wall - scrim tape ?

Discussion in 'Builders' Talk' started by DIYDave., Oct 30, 2013.

  1. DIYDave.

    DIYDave. Well-Known Member

    Hi all, quick question please;
    Have a through lounge/ dining room that has a pillar each side where wall was knocked through
    Want to extend pillar by approx 200mm so I can build a cupboard behind it and so increase depth
    So build stud work frame, recess in to allow for PB and 3mm skim
    So where the new PB joins the existing plaster on pillar, do I need to scrim tape joint to avoid cracks
    If so, do I just knock off some of the existing plaster so tape sits below surface , ready to plaster over
    Also on pillar, edges have thin coat bead so would have to remove this to enable scrim to sit below finished level
    Hope I have explained ok, sure it's simple really , but I welcome your advice, many thanks
  2. Just as you say - knock off the existing edge beads, run a Stanley knife down the wall around a couple of inches from the edge of the existing pillar to score an 'end-line' a couple of mm into the skim - go in a wobbly line - and then use a scraper blade or similar to remove that bit of skim, which should hopefully stop fairly cleanly at your score line.

    Build your timber frame just as you've said, so's the p'board is a skim's thickness recessed. Make sure to plug and screw the frame very tightly to the blockwork of the existing pillar - you don't want any movement. Where the timber makes physical contact with the blocks, PVA it too - really :)

    P'board, and scrim across the join.

    (That's what I've done when DIYing...)
  3. joinerjohn1

    joinerjohn1 Screwfix Select

    I'd just build the frame out, plasterboard it and use scrim across the join, then skim both the old and new (putting a couple of mil thickness skim on top of the existing bit) No need to start scraping away bits of the existing pillar. ;);)
    FatHands likes this.
  4. Hmmmm, nice 3mm ridge... :p
  5. joinerjohn1

    joinerjohn1 Screwfix Select

    How do you work that out? If DIY Dave makes the framework correctly and plasterboards it, up to the existing wall, then the few milly skim should cover the join (without creating a ridge)
  6. DIYDave.

    DIYDave. Well-Known Member

    Thanks Satan for the advice, confirms what I thought was the correct method, along with a few tips as well. Will hopefully start this project in a couple of weeks time

    Cheers also JJ, kinda makes sense what your saying but this method is gonna give me more work as that would mean plastering pillars both side of room and also across ceiling where RSJ is boxed in. My plastering ain't that good so am trying to minimise the area so will go with my original plan
    As always, thanks guys for the help, great stuff
  7. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    One thing. If he removes the corner bead, he won't be needing to score any plaster. He could lose up to 2" either side of the corner anyway!
  8. DIYDave.

    DIYDave. Well-Known Member

    I don't get your reply David regarding a " 3 mm bump and wall like a seesaw"
    I'm going to extend pillar with stud work, plasterboard, bead the edges, remove existing beads from pillar and scrim the joint , setting the PB back 3 mm ready to plaster
    Thanks Handy, got what you mean about removing existing beads, that will remove enough plaster so I can scrim joint between old and new and give me the correct depth
  9. DIYDave.

    DIYDave. Well-Known Member

    Hi David
    I'm sure that you see plenty of bodges on site and I've also seen plenty of bodges in people's houses
    I'm a diy'er but always do a proper job even if it takes me longer to do. If I really can't do the job to a good standard, then no worries , I will get a pro in
    If I don't know how to do something, I will research and also use this forum frequently for advice
    My plastering isn't 100% perfect ( certainly is a great skill to have) so am trying to minimise area to plaster
    As I said in previous message, if I skim entire area as suggested by JJ , or PB area as you suggest, that means pillars on both sides of room and boxed in beam across ceiling. That's too much plastering for my abilities !
    I'm going with my plan of just extending existing pillar and plastering up to existing skim. That way I've only got an area approx 2000 x 300 mm to plaster (on 3 faces)
    I'm confident I can do that, even if I need to go over a few areas with sand paper and filler once plaster is dry !!
    Thanks for ideas though
  10. JJ, my apologies :oops:. I thought you were suggesting just skimming over the scrim - I've re-read your post and you were saying to skim the whole lot - which obviously wouldn't leave a ridge. Soz.

    The reason for the score line is just to give the strip of skim you're scraping off a place to stop! Sometimes the skim coat is a bit 'keen' to come off, so you can end up going further that you'd like, and end up with a rough, crumbly or slightly-loose edge.

    Something to watch out for when you apply the new skim is that the solid wall part with the exposed 'bonding coat' layer will suck your skim dry in seconds if you don't either thoroughly dampen down that exposed strip bit first, or else PVA it. Best to simply dampen - I use a hand sprayer, one of these pump-up types. Spray that exposed strip and see how it sucks up the water - if it's almost instant, it'll need a few sprays! Keep going over it until you can see that it remains damp.

    PVA has its uses, but best avoided here, I'd say.
    FatHands likes this.
  11. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    PVA is good for this!

    Mr. HandyAndy - Really
  12. joinerjohn1

    joinerjohn1 Screwfix Select

    Apology accepted DA. My younger brother is a plasterer and even he would recommend that the whole lot be skimmed rather than try to "feather" the plaster in to the existing. I've watched him try to feather a skim coat into the existing before, and it just never looks right (even with sanding down afterwards) ;);)
  13. Yes, it takes a bit of effort, although it's ideal for DIYers - like masel. And this is what I did when widening a couple of room openings.

    You think it's going to be easy as you have the existing wall to act as the guide for the trowel, which should in theory get the new skim dead flat. But even after sanding you'll often see part of the join after emulsion paint is applied. Mind you, this is where the emulsion itself acts as the finest of fillers - a couple of thick coats rollered on and flattened back with 120 grit - and it's all mirror smooth :).

    The reason I'd advise caution with PVA, is that if the PVA goes right on to the edge of the old skim - and you'd want it to - it'll then leave a layer of plastic (which is what it is) between the old skim and the new, and the very fine edge of this layer will be exposed as you sand it all flat.

    When you then roller on your emulsion, it'll often develop a very visible raised 'hairline' on the wall surface where the PVA is reactivated.

    Even worse is if you allow the PVA to go over the old skim surface. Have you ever tried sanding down plaster which has parts of it covered with PVA? A right 'mare.
    FatHands likes this.
  14. DIYDave.

    DIYDave. Well-Known Member

    Well, after the above advice and my original plan I got this job done at the weekend and now in the process of building two alcove cupboards and cupboards under the stairs

    Built out the pillar with CLS timber then PB. Removed existing beads where original pillar finished and this took off enough plaster so that the scrim tape covered the join between old and new pillar
    (this is what Handy and Satan were saying I guess) With a scrapper I feathered out the edge of the original plaster, ready to meet the new skim and used one coat plaster. Just plastered the extended section and not the whole area to be honest

    Once plaster had dried, just applied a little lick of filler here and there over the joint where needed, sanded and mist coated, followed by 2 coats emulsion
    Even though its just a small area, the joint between old and new was likely to give the most problems as suggested but, I'm well happy with the result

    Once again, many thanks for the advice offered
    FatHands likes this.
  15. DIYDave.

    DIYDave. Well-Known Member

    Tried to put couple photos on to show end result ( if anyone interested) ? but won't load up - file size too big
    Will get one of my kids to help me out with this, I'm not clever enough !! :(
    FatHands likes this.
  16. FatHands

    FatHands Well-Known Member

    yeah, load them up Dave.

    Open them in paint and save as .png and then save as a different name so it doesn't change the original photo.
  17. DIYDave.

    DIYDave. Well-Known Member

    Cheers Fats but I've got an even easier system....... 2 teenage sons

    Don't get me wrong, I can use the computer and think that the internet is a great tool but I don't get off on all these file sizes. .png (WTF) !! , high resolution, compressed files, j peg formats and etc

    Would rather boil my head but in tonight's case, its out for some beers and a carvery so can wait !

    Will post some pics eventually, cheers mate
    FatHands likes this.
  18. FatHands

    FatHands Well-Known Member


    Can't fault you. Carvery and beer, aw now you are talking ;)

Share This Page