Drywall Finish at corner of wall and ceiling

[corleyd]

I can not tell from my reading and the many great pictures posted and drawn -- how do you approach the drywall finishing step (the tape and mud) regarding the corners where the walls and ceilings meet? you have the 1/4" gap filled with acoustic caulk -- do you just paint over the caulk? OR do you mud/tape that? Wouldn't that just crack with the movement of the walls and ceiling?

Thanks,
Dennis

[knightfly]

That kind of depends on the level of finish you want in the room - there are a few ways to do it. One is, you use fiberglas mesh tape and mud/tape as usual, keeping buildup at a minimum in the corner. You will lose a little bit of isolation that way, but won't need other mouldings.

There are some newer inside corner beads that use are semi-pre-formed, and use a rubber connection between the two halves of the bead - these can give a bit better isolation between surfaces.

Yet another way is to do a "fake out" - you can put actual molding up on the wall, but not touching the ceiling - if you leave about 1/8" gap (between the top of the molding and the ceiling) when fastening the molding to the WALL ONLY, it gives the joint a finished look with no physical contact. In that case your caulking is responsible for all sealing.

USG also make a vinyl part, shown in figure 81 on this page of their Sound Control Manual -

http://www.usg.com/design_solutions/2_3_12e_details.asp

Here's a good example of the flex-bead install method - you would of course still do the acosutic caulk thing first -

http://www.trim-tex.com/installation/4325install.htm

If you really want to get deep on this, you can order a book from Amazon, called Drywall, by Myron Ferguson. It's not heavy on sound proof construction, but very thorough on all other aspects. The book is about $15 if I remember correctly.

Hope that helped... Steve

[JoeMilner]

And if you're in a real hurry and can't wait for Amazon, I bought that book at Home Depot.
So it's OK to use mesh tape for sound walls?

[rod gervais]

Joe,

Yes it's perfectly OK to tape sound wall/ceilings, walls/walls.

In fact - it's taken into consideration when they establish the STC ratings for these assemblies.

Although it's possible (as Steve noted) to lose some isolation in theory - it is such a small amount as to be almost non-existent.

Rod

[corleyd]

Steve,
That section of the USG manual implies (to me) that using the P-1 Vinyl trim is within 1-2 STC pts of caulk. Is that how you read it?

....

Tests by USG Research have shown that the base trim on the partition will not suffice for sealing. The performance of an STC-45 partition cailked on top and sides and with aluminum base trim was found to be STC 35. In a similar test but with caulking all the way around the partition with aluminum base trim, the performance was STC 45.USG P-1 Vinyl Trim (Figure 81), used to seal the perimeters, can be expected to perform within one or two STC points of beads of USG Acoustical Sealant.

?? Dennis

[knightfly]

Joe, I actually got my copy of the book at HD, should have mentioned that but figured Amazon was more world-wide for our worldly members' benefit -

On the seal thing - Yeah, that's the way I took it too - haven't seen the beast in the flesh, but personally I wouldn't trust a seal whose sealing properties relied on "bend resistance" over a long time period - their material may be able to support long-term deflection without "taking a set", but I would feel kind of squeamish trusting it without further proof of long-term performance.

That's why we don't use ordinary caulk for sound joints in the first place.

Maybe Rod has used this stuff and can enlighten us... Steve

[JoeMilner]

Hi Steve & Rod
I knew that mud & tape was a must, but it seemed that the mesh stuff wasn't as good a barrier as the "solid" paper tape, being a mesh and all. Of course, once you put the mud on maybe it doesn't matter.....? God knows the mesh is LOTS easier to work with
And on the Home Depot/ Amazon topic, of course living in LA I was only thinking of myself and the micro-world that is Hollywood

[knightfly]

Hi Joe - yeah, doing this for a while you can get several "wake-up calls" - like, in Indonesia drywall is super spendy but bricks are like a penny apiece, in England drywall is roughly 5 TIMES what it costs here, etc...

Actually, for corner joints that are already "floppy caulked", mud and tape are more for aesthetics IMO - the caulk is your sound barrier. The mud/tape will add strength and make it look better, at a possible slight loss in performance due to coupling between intersecting walls/ceilings.

In my more grandiose delusions of time availability, I've thought of contacting Mr. Ferguson re a possible added chapter to his next book with more coverage on sound isolation - yeah, right... Steve

[rod gervais]

Why do you all buy books? I just download mine directly form the USG site - print em out and put em in a loose leaf binder with chapter tags.

As far as the vinyl trim goes - i don't use it. Taint nothing like caulk to assure no air passage - and i have a real hard time giving up even 2db in sound reduction when that added 2db is so inexpensive in comparison when you take into account everything else you've done up till that point.

The vinyl trim was really manufactured to use in places where you had dissimilar materials and were looking for structural relief along with sound isolation. Very difficult to do a finished product when you need movement and no cracking.

So instead of caulking (flat taping is no good if there is any flex in structure) and placing some sort of movable trim over the joint - they developed this P-1 vinyl trim. Friction fit over the sheet - no tape required.

Not bad - but not prefered when taping is required or to be provided.

Rod

[knightfly]

Hey Rod - that was my impression of the "plastic fantastic joint" idea also - as far as buying books, once in a while there is one that's worth the $$ - I have all the USG stuff bookmarked, most downloaded in PDF, and there are still times when it doesn't illustrate things as clearly as it could. The one I referenced has better/more pictures and better explanations than most of the USG literature, especially if someone hasn't grown up in the trades.

Some of our members have so little experience with tools/building that I (almost) literally have to explain what a hammer is - others have more experience than I do in some areas (present company for example) but I try to present things at the level necessary for the particular individual to benefit from. I find that the USG info, while an invaluable resource, is sort of like "preaching to the choir", in that if you've not already "been there done that", sometimes you won't get there without further help.

I remember one poster from France who wanted to build a booth and incorporate a slot resonator to smooth modes and disrupt parallel walls - I spent several pages just explaining basic framing, down to realizing that he didn't know which way studs were placed on sill plates - so there are times when being able to "regress" to what I knew when I was 10 and helping my Dad build our second house really comes in handy. Like, for example, learning that if you're going to miss the nail with the hammer, it's better to wait til you have it "started" and your fingers are elsewhere ... Steve

[rod gervais]

Steve,

I understand completely.

I'll never forget working with my dad - and when it came to trim - he would not let me take my fingers away until the nail was ready to set - he said my fingers were made to protect his wood from hammer marks.

Needless to say - i had pretty sore fingers before i learned how to nail properly.

I suppose I'll have to take a look at the book at HD and see what the hubbub is bub..............

Rod

[AndrewMc]

In my walls I only mudded the final layer. Used the mesh tape in all layers embedded in caulk. A lot of caulk was used in the walls.

The final layer seams was mudded. Each layer was mudded to the layer below and then screwed thru into the studs (but with fewer screws on the 2nd / 3rd layer).

Sound proofing is more than I could have ever dreamed of.

[knightfly]

Andrew, do you mean more WORK or more isolation Steve