Gyproc joints - best practice

Whats the best way of jointing Gyproc sheets for multilayer studio plasterboarding- I'm assuming Joint cement: http://www.british-gypsum.com/products/ ... ement.aspx And Acoustic Mastic in the corners with Backer rod?

The normal recommended method here is to leave a slight gap between the drywall sheets, insert backer rod in the gap, then caulk over that. That gives you two independent flexible seals, and also keeps the surface density constant across the entire wall. - Stuart -

Clarification here please. Is the ? of the OP regarding jointing of sheets on a given layer, i.e. using joint adhesive on the edges of boards as they butt against each other, or are we talking about between layers? If joining panels on a given layer I was always led to assume taping and mudding - especially if the panels have tapered edges. I'm not sure I'd trust Joint adhesive on drywall, and would go with taping and mudding. Between layers, apart from green glue or a similar product, I wouldn't use anything. Corners with backing rod and acoustic sealant or silicon as you mentioned.

I was always led to assume taping and mudding

Tape and mud does not create a flexible joint: it is rigid, and therefore can crack, thus destroying the seal on that layer. Even a tiny crack will do that. Backer rod and flexible caulk remove this issue, creating two seals for each layer of drywall, and BOTH seals are flexible. So if there is any movement in the drywall after it is finished, the backer rod plus flexible caulk approach will not lose the overall seal. - Stuart -

Stuart, again many thanks for your response but just to clarify, after jointing using this method, do you use Calk to fill in the tapered edges of the Gyproc or having used the calk,do you then use cement? I'm assuming the latter as if the cement does crack with movement of the boards, then the joint itself will keep its integrity due to the calk and backer rod?

On the final layer of drywall you might need to tape and mud for aesthetics, yes, and that would go over the backer rod and caulk. I was talking more about underlying layers, which only need backer rod and caulk, not tape and mud. - Stuart -

So on the intermediate layers (Base layer#1 and mid layer #2) you just use acoustic calk over backer rod to fill in the tapered joints?

Yes. I choose not to use mud and tape on my final layer, even. But that is just my choice and does not mean it is any kind of "rule" :)

Brien, What do you do with your seams to make them look finished?

Ok, let me clarify. I didn't tape/mud the vertical joints, the horizontal joints, yes I did. but in the corners I used the caulk and basically troweled the caulk down flush with a putty knife to include the top of wall/ceiling joints :).

That sounds good. I am definitely going to do that.

So Stuart (or anyone) as I understand this you recommend leaving a gap between every gyprock sheet on a surface (not between layers) above, below and to the sides. How big should that gap be and what thickness backer rod? Should it be closed cell or open cell? Is it best practise to put up the gyprock first and then squeeze in the backer rod in between the panels - or stick up the backer rod first on the edge of a panel with spray adhesive and butt up the next panel hard against it so it compresses a little. Or is this uneccessary in that the caulk will fully seal any gaps around the rod anyway? Its these kind of details that might be a bit vague on looking through builds on this amazing forum. Should these gaps should be accounted for in the stud spacing? Forgive me for my ignorance but is there any way of building standard 2x4 stud walls without having to cut the 600mm insulation batts? Gyprock comes in widths of 1200mm here in UK but I seem to remember when I built my first studio over 10 years ago that the standard was a bit more like 1210mm. Anyway I might be tripping about that - it has been a long time. If the centres are 600mm apart (which seems very common on this forum) that makes the the batts 50mm oversized which is bit too much to be crammed in there. Or is there simply no way round this - the insulation has to be cut??

tardishead, Get some books, read the threads...these things you ask are answered by the product makers, and those giants that we all quote here. No one here speaks with his on words we recall someone that has come before us. Buy the books, start your own thread, clarify your thinking.

How big should that gap be and what thickness backer rod?...

You might find these threads helpful: viewtopic.php?p=28924 viewtopic.php?p=20003 - Stuart -

Many thanks, these were very helpful links along with the replies here. However, in the interests of clarity and for the avoidance of doubt, I have some further questions. :) I am aiming to have a dual layer plasterboard construction over Resilient bar and stud wall. For my base layer, I will use 19mm gyproc plank and the outer layer will be 15mm Soundbloc gyproc with GG in-between. Q1) Where does backer rod get installed on the base layer - perimeter and/or in between planks? Q2) Should the plank have a tapered or square edge? My instinct is to order square to minimise caulking? My studio construction is now entering the exciting stage - see here for the photo blog including the latest pictures..... http://www.flickr.com/photos/99314602@N ... 681739957/

Soundman2020 wrote:

I was always led to assume taping and mudding

Tape and mud does not create a flexible joint: it is rigid, and therefore can crack, thus destroying the seal on that layer. Even a tiny crack will do that. Backer rod and flexible caulk remove this issue, creating two seals for each layer of drywall, and BOTH seals are flexible. So if there is any movement in the drywall after it is finished, the backer rod plus flexible caulk approach will not lose the overall seal. - Stuart -

Stuart, With all due respect I have to disagree with this. Properly taped drywall joints are extremely stable - they do not crack....... this due to the covering for the joint used in the base coat. If cracking (which would allow the passage of air) was really an issue it would not be suitable for fire wall construction - where not only is the flame an issue - but the passage of hot gasses through the fire barrier. And this is true with even a single layer of drywall. Now - with a double layer of drywall all of the joints are supposed to be lapped when the 2nd drywall layer is applied. That means that in addition to the joint compound and tape covering the initial joint - you have the solid body of the 2nd sheet. There really is no reason for joints in the body of the wall need to be left open for backer rod and caulk. Rod

I'm not sure if my two questions were answered in that last post. Rod, are you advocating butt jointing the 19mm base layer boards and then the same for the top layer with mud and taping, no backer rod, no caulking?

Paul881 wrote:

I'm not sure if my two questions were answered in that last post. Rod, are you advocating butt jointing the 19mm base layer boards and then the same for the top layer with mud and taping, no backer rod, no caulking?

Yup....... that would be correct. The wall/floor, wall/wall & wall/ceiling points need backer rod and caulk - but not the joints in the field.. Rod

Wow, this is fabulous news and will save us hours of hassle :yahoo: Muchos Gracias!!!! 19mm planking on order; should be here the weekend!

Paul881 wrote:

Wow, this is fabulous news and will save us hours of hassle :yahoo: Muchos Gracias!!!! 19mm planking on order; should be here the weekend!

All of this of course assumes that you will be lapping all joints with subsequent layers......... if you stack the joints all bets are off....... Rod

Rod, fully noted and understood - they will be lapped; no coincident joints between layers :D Many thanks!