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    • CommentAuthorselly
    • CommentTimeSep 13th 2010
     
    I'm getting conflicting advice on fixing insulated plasterboard (50mm + thick) to 1m thick old stone walls.

    Firstly I know its not the completely correct way to do things as external insulation or lime plaster may be but needs must...

    Anyway is it best to use dot and dab? Or nailable plugs? Or buy one of gyrpocs metal fixing systems which sounds ££?
    • CommentAuthorevan
    • CommentTimeSep 13th 2010
     
    From what I've read (here, mostly), some sort of mechanical fixing is a must as with glue alone there's the risk of the plasterboard falling off the insulation in a fire.

    The hammer fixings sound OK. Getting the boards level seems like the difficult part.
    • CommentAuthorwookey
    • CommentTimeSep 15th 2010
     
    If your walls are wonky then some kind of battening system is a good idea. If they are flat then gluing them on with PUR glue is fine. Dot and Dab is a bad idea as it allows too much air circulation behind the board.

    You seem to be aware already that fixing PUR boards to stone walls may not be the best plan.
    • CommentAuthorselly
    • CommentTimeSep 15th 2010
     
    Yeah i know pur isn't the best plan but its the best I think I have given that external insulation requires extending the roof and rafters and the walls are already 1m thick. Making it thicker on the outside again would look awful recessed around the front of the windows
    • CommentAuthorreefray
    • CommentTimeSep 15th 2010
     
    wookey

    If a continuous ribbon of adhesive is applied around the perimeter of the wall and also around any electrical boxes, door opes and windows that will ensure that there is no air movement behind the insulated boards.

    You are correct in stating if the walls are wonky the boards would be better off fixed to battens but only if there is more than 18mm between high points of most of the stones across all the face of the wall IMO.

    I'm in the drylining trade and it costs me about 300% more per m2 to buy the metal lining system selly refers to than drywall adhesive- and this is not the top branded metal either.

    For walls 2.4m high it would take slightly longer to dot & dab than to fit the metal framing but I assume selly is going to do the work himself so this is prob not a consideration.

    If selly chose the dot & dab route he could use the high points of the stones to place his dabs on and this would be economical with the adhesive.

    Selly, I have looked on YouTube for decent tutorials for Dot & Dabbing but there seems to be more clowns there than at the circus.

    If you are interested in trying this method the pdf available on this link would be really useful:

    http://www.british-gypsum.com/literature/site_book.aspx

    A printout of the Drilyner Basic section and you are off and running!

    If you have any other queries on this system I would be only too glad to help.

    Ray
    • CommentAuthorevan
    • CommentTimeSep 15th 2010
     
    Quick question for you reefray, all of the tutorials on drylining (onto battens) I saw on youtube were American, and they all use the boards horizontally. It never occurred to me to do that, I have always seen boards being placed long-way-up.
    Why is that, are there any advantages or differences?
  1.  
    <blockquote><cite>Posted By: evan</cite>From what I've read (here, mostly), some sort of mechanical fixing is a must as with glue alone there's the risk of the plasterboard falling off the insulation in a fire.

    The hammer fixings sound OK. Getting the boards level seems like the difficult part.</blockquote>


    This is correct
    • CommentAuthorreefray
    • CommentTimeSep 15th 2010
     
    evan

    To be honest I'm not sure why. Sometimes I see joiners fitting sheets in the same manner so maybe it's a throwback from the past.

    To get the desired fire rating for stud walls will involve the vertical fixing of plasterboard sheets so for us it's second nature.


    Ray
    • CommentAuthorreefray
    • CommentTimeSep 15th 2010
     
    jfe

    Two hammer fixings per board are required.

    It is easier than you imagine to plumb and straighten the boards, a combination of chalk line on the floor, accurate level and a STRAIGHT edge is all you require. 100mm box aluminium is perfect. The adhesive is not like jelly, more like stiff porridge and all you have to do is tap the boards into place checking vertically, horizontally and diagonally. Once in the correct place, they won't move a mm- unless you knock it while fitting the next sheet, of course!

    Ray
  2.  
    Posted By: evanI saw on youtube were American, and they all use the boards horizontally. It never occurred to me to do that, I have always seen boards being placed long-way-up.
    Why is that, are there any advantages or differences?


    Posted By: reefrayTo be honest I'm not sure why. Sometimes I see joiners fitting sheets in the same manner so maybe it's a throwback from the past.


    First thing to remember is that North American homes are generally "stick built" timber frame rather than the blockwork that's typical in the UK. Hence "dot and dab" is never used. Ever. Since the framing members are usually vertical, you want to run the drywall perpendicular to these, hence the horizontal orientation. Secondly, drywall comes in sizes other than 8'x4'. Since it's easier to tape and fill joints that are at chest height rather than running from floor to ceiling, this gives another advantage to running the sheets horizontally. For a room that's the standard 8' high, that's two sheets horizontally of 4' width - and since you can get sheets up to 12' or longer, then you can finish the installation much quicker (and with fewer joints) if you run the boards horizontally. Tape-and-fill is the usually finishing method here, skim coating is very rarely used.

    Posted By: reefrayTo get the desired fire rating for stud walls will involve the vertical fixing of plasterboard sheets so for us it's second nature.


    Surely the fire rating is based on the thickness of the drywall, not the orientation.

    I've personally used both horizontal and vertical installation, depending on the walls. In some places, I had horizontal strapping (holding the insulation in place as discussed in other threads) and so I affixed the boards vertically (for an 8' high ceiling height and this gave me only 'factory edge' joints, rather than butt joints) but in other places I used horizontal - where I had ceiling heights greater than 8' and didn't want the hassle of having to handle larger (and heavier) sheets. In our new house, with 9' ceilings, they used boards that were 12' long and 54" wide so they could do the two horizontal sheet installation method.

    Paul in Montreal.
    • CommentAuthorreefray
    • CommentTimeSep 15th 2010 edited
     
    <blockquote><cite>Posted By: Paul in Montreal

    Surely the fire rating is based on the thickness of the drywall, not the orientation.

    I've personally used both horizontal and vertical installation, depending on the walls. In some places, I had horizontal strapping (holding the insulation in place as discussed in other threads) and so I affixed the boards vertically (for an 8' high ceiling height and this gave me only 'factory edge' joints, rather than butt joints) but in other places I used horizontal - where I had ceiling heights greater than 8' and didn't want the hassle of having to handle larger (and heavier) sheets. In our new house, with 9' ceilings, they used boards that were 12' long and 54" wide so they could do the two horizontal sheet installation method.

    Paul in Montreal.</blockquote>

    The fire rating is based on the board thickness (and type of board) generally speaking. I assume that when the partitions are tested in the lab for a 60 min fire rating say the boards are fitted vertically therefore all partitions built afterwards to a 60min spec must have boards fitted vertically to comply.

    The trouble from a finishing perspective of fitting boards horizontaly is that you will end up with butt joints at 'low' level on the walls. Surely having only tapered joints vertically is a good thing?

    12'x54" boards! Imagine the fun carrying those babies through a house on this side of the Atlantic! If they are standard 1/2" board that would make them about 40kgs each. Recently we were on a job using 3m long 15mm thick soundbloc board- 46 kgs each and thousands of them- no craic at all...

    Ray
    • CommentAuthormarktime
    • CommentTimeSep 15th 2010
     
    Horizontal boards have a joint that is much easier to hide when dealing with an oblique light source. And as Paul points out, often much easier to work with. I don't skim so my taping has to be pefect.
  3.  
    this is the third time i have typed this so you better be gratefull. (deleted by mistake twice)

    right; its easier to fit vertical boards and quicker plus the boards are in roomish sizes 2400/2700/3000.
    you want the joints vertically as they are more broken this way, horizontal boards will mean continous joints and interjoining joints all over the wall bad for cracking and travelling cracks. also a joint is a concern for fire ratings as a joint is also a break in tha fire barrier so few and far between is best. ever seen an upper shop or commercial building ceiling with just the joints filled? this is for fire regs.

    now dabbing them; use a dedicated straight edge for tapping back (a long one) and dont tap one at a time tap loosely fit all the wall or a run of say 5 boards than tap this lot back together using the edge across two boards at once also this will keep you whole wall straighter together (hope that makes sense but you will see) if you do need string or pencil marks then do so or maybe get a plasterer in???? try for a skim finish where possible especially if its a residential property
  4.  
    PS over a stone wall such as yours the same fire rating will not be required
  5.  
    Posted By: reefray12'x54" boards! Imagine the fun carrying those babies through a house on this side of the Atlantic! If they are standard 1/2" board that would make them about 40kgs each. Recently we were on a job using 3m long 15mm thick soundbloc board- 46 kgs each and thousands of them- no craic at all..
    Don't forget the boards come in pairs too!

    Posted By: reefray
    The trouble from a finishing perspective of fitting boards horizontaly is that you will end up with butt joints at 'low' level on the walls. Surely having only tapered joints vertically is a good thing
    True, but if the boards are long enough you can avoid most of these butt joints - and it's easier to finish a horizontal tapered joint at chest height than a vertical one from floor to ceiling.

    As for dotting and dabbing, it's just easier to screw the boards to strapping that's already been levelled - then there's no problem with different thicknesses of adhesive, though I guess dot-n-dab maybe faster ... though the automatic screw guns that professional installers use are very very fast.

    Anyway, here's a couple of pictures. First one is the boards being brought in - the room is 39 feet long and 16 feet wide so 12' long boards are not a problem. The second is after the taping and jointing. The butt joints are pretty much invisible post-painting. You can see on the ceiling they are staggered by 4' to make up the 16' width.

    Paul in Montreal.
      dscf0334.jpg
      dscf0359.jpg
  6.  
    I am begining to get confused here. Just to confirm (cos I also have thick stone walls and need to internally insulated as discussed).....
    1. Are people agreeing that there should be NO air gap between the stone wall and the insulation / plasterboard? (I have been advised that an air gap / ventallation is important - thus dab / dot seems a sensible idea, and follows advise elsewhere on this site regarding increased moisture levels in old walls if inetrnally insulated)
    2. If so - is it OK to screw PIR / PUR insulation to a thick stone wall? Or is it better to use a fabric (sheeps wool etc?)
    3. Would dab / dot breech fire / building regs with stone walls behind?
    4. Is a VCL required?
    5. Is it worth skimming over the plasterboard if it can be tapped / filled - then painted?

    Sorry - but I am not clear on this at all. Many thanks

    RR
    • CommentAuthorevan
    • CommentTimeSep 16th 2010 edited
     
    Rose, it's complicated isn't it.

    1) A ventilated air gap is advised if the walls are susceptible to damp, especially if there is something rottable behind the plasterboard (i.e. timber).

    Remember that if they weren't susceptible before, adding the insulation makes them colder, and also non-permeable on the inside so that water may become trapped in the wall. Whether the outside is rendered and what with is a factor.

    Either way, if you avoid the timber, maybe it doesn't matter if the small gaps you'll have between a stone wall and the back of the board gets a bit damp / mouldy. So it's probably OK.

    2) Yes. I'd keep well clear of sheeps wool, I've seen it go badly wrong before.

    3) See above - you need a couple of mechanical fastenings per board as well. No big deal.

    4) a VCL is required unless you're making a breathable wall. If you are using polystyrene boards, it's not a breathable wall.

    5) Less work to just tape and fill, if it's done neatly.

    This is just opinion after going through the same wrangling myself. My walls seemed too uneven (and tapering) to apply the board method sensibly, and I am cheap, so I used wooden battens with glasswool, and didn't bother trying to make the outside wall airtight, so it will be mildly ventilated.

    Hope that helps :)
    • CommentAuthorDarylP
    • CommentTimeSep 16th 2010
     
    Roserambler,

    The last (similar to yours) job we did was a stone/rubble wall construction, drylined with Kingspan insulated p/b.
    The stone wall was left alone, but a metal furring system built about 50mm off the wall, floor to ceiling, tied back to the wall. The stone wall was uneven, so we could not use it to attach the p/b to directly. The Kingspan was screwed through to the metal C studs, as well as being sealed to the top and bottom rails.
    The joints between the p/b sheets, and around the edges where the boards met the wall and floor, were caulked, and then the whole lot was painted with two coats of board sealer, and a vinyl undercoat. This gave us the vapour impermeable layer required to stop condensation problems. The cavity between the back of the p/b and the stone was ventilated to the outside.

    I am not sure if this helps, but feel free to whisper me if you want any more info.

    Cheers:smile:
    • CommentAuthorRobinB
    • CommentTimeSep 16th 2010
     
    I'm also a bit confused. Does that air gap need ventilating and if so presumably to the outside? If to the inside it would still get condensation on the outer leaf wouldn't it? How would I ventilate to the outside without making holes right through the wall? If you were able to remove all rottable stuff e.g. replace timber battens with plastic would you still need an air gap or ventilation?
    thanks
    RobinB
    • CommentAuthorevan
    • CommentTimeSep 17th 2010
     
    Yes, you make holes right through the wall!

    As far as I can tell:

    1) No air gap: mould shouldn't grow but you now have a wall which is basically waterproof on one side and possibly both sides if it's rendered. It might fill up with water and disintegrate. Also it might leak through to the drylining.

    2) Unventilated air gap: mould might grow in it. Is it a concern to the occupants, providing the room is properly sealed? Not sure. Also no good way for moisture to get out if it gets in, but at least it shouldn't reach the room interior.

    3) Ventilated air gap: should eliminate moisture and mould problems but also removes the insulation value of the outside wall, and you have to make holes in the wall.

    How lucky do you feel?

    (PS anyone please correct any of the above if it looks wrong)
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