Caulk Failure!

I still need to start a construction thread but already I’ve got my first goof up. I have hung lots and lots of drywall over the years and after a piece was cut to fit it was pretty much just slapped up and screwed into place. Not much thought was ever given to the cut edges before hanging it. If anything a quick tap on the panel or hand run down the edge. I am at the beef-up stage of my build and have been blissfully continuing on in my ways. Knowing that the edges will be caulked, I have at least made a little extra effort cleaning them of drywall dust, although apparently not sufficiently. Sure enough, a wall cavity I filled a week ago is showing signs of adhesion/joint failure in a couple areas! I’ve attached a couple pics including one with the caulk removed, exposing the backer rod. I have since tried different things to clean the edges including vacuuming, wiping them down with a rag or tack cloth and just knocking on the panel several times to shake the dust off. After doing any of those I am able to lightly run a finger over the edge and still get some dusting. My space has old carpet installed which will be ripped out after most of my construction is done. I’ve left it down to protect the concrete underneath which will be my finished floor. What seems to be working is running the edges of drywall back and forth on the carpet until dust no longer comes off on the carpet. The caulk I’m using is USG Sheetrock Brand and the drywall is Gold Bond Fireshield from National Gypsum. I’ve never noticed or paid much attention myself but are some brands of drywall more prone to dusting than others? How is everyone prepping the edges? Thanks, Chris

From the looks of the pictures you are using the wrong type of caulk. The proper acoustic sealant should remain tacky even after years... looks like you used standard latex caulking. You will have to carve it all out and replace it with the correct stuff. Sorry for the bad news... :( Dave.

It is acoustical caulk. I should have been more specific but it's Sheetrock Brand Acoustical Sealant.

I dunno about failure boss. Separation is my guess. Typically construction backer rod is at or below grade level in whatever application it is used. The pics look like the backer rod is far above the face of the rock level. Essentially, the rock, wood and backer rod get first crack at moving. The caulk just tries to keep up and isn't able to if I see it the way I think I am seeing it. Just my thoughts,

Hi Chris – I’m not really sure I can be of any assistance here at all as, being from the UK. I’ve never heard of USG Sheetrock caulk, or Gold Bond Fireshield. :shock: However Gypsum seems to be globally recognised up here, and more importantly is ‘plastered’ (no pun intended) all over the back of any plasterboard sheet I’ve ever seen, including the ones I’m currently installing. :wink: Looking at your pics, if that’s 3/8 backer rod you’ve applied, could it be that the gap you’ve left is a little too large? It’s difficult to establish how wide that gap is in your second pic, but it does look at least the same width as your backer rod, if not slightly larger, and the rod should really be a snug/compressed fit. (You need to be almost wedging it in place with a blunt scraper!) - I think! Really dumb question, but were any of your materials damp during installation? Have they been subjected to any moisture of any kind just after, or since? I’m sure not, it’s just a dumb question as I said.

How is everyone prepping the edges?

Well, clearly, I can’t speak for other builders, but for what it’s worth, I’m not prepping at all, other than a light ‘surform’ to even things out, and I end up with a perfect clean plaster finish – no porous property, and definitely no dust. (Other than what gets wiped all over my jeans of course.) :roll: The caulk I’ve used has hardened to a dense rubber like consistency, with a definite spring – but no cracks. Is it possible that the two materials are not compatible? Or is that crack in your first pic appearing because the cut in the left hand board (exactly where the crack is) isn’t straight enough? Shrinkage etc? As I said Chris, I really don’t know buddy, just trying to offer some constructive ideas to your problem ‘cos I know how frustrating these things can be. :roll: Hope this helps a bit and good luck with your project, Regards, Lou. 8)

Thanks for taking a look guys! It is hard to tell in the pics but I do have the backer rod installed well below the plane of the drywall all the way to the back of the joint, as illustrated in Rod's book and on this site. I have been trying to keep most of my joints with a 1/4" gap or "reveal" although the joists/studs are not perfectly straight in some areas making for a wider joint. I'll attach a couple pics that hopefully will clarify better. I've always run my surform plane along the edge but quit doing so cause of the dust and particles it created. I've just been using my razor knife to square up the edges which seems a little better. I also quit using the screen splining tool to push the backer into the joint cause it tends to scrape the drywall edges creating a similar situation regarding contamination. I'm really leaning towards the culprit being improper surface preparation as in "Surface must be clean, dry and dust-free" printed on any type of adhesive/sealant. I did contact USG and they agreed. I asked them about any compatibility issues with other brands of drywall/gypsum and they said any problems with bond failure, loss of adhesion etc. are when the surface is not clean enough or has a film on it. I think I might try a different brand of drywall just to see though. Like I eluded to it's my own bone-headed fault for not paying closer attention. I have to wonder though if folks are keeping an eye on this. How many compromised caulk joints are out there hidden behind walls or under cleats, ledger boards, battens etc.....? Chris

Make sure the backer rod is stuffed in well, then blow out the corner with compressed air before caulking... that should do the trick. Dave.

That's a good idea and the thought did cross my mind. I might have to "bite the bullet" and finally buy that compressor I've been wanting. Chris

It is only this one small area correct? Gouge it out, recaulk it and move on. If you have any more of these kinds of joints...paint the raw wood first, then caulk it.

It's a good project if you have to buy a new tool to get the job done! 8) Dave.

Amen! (He-He!) :D :D Hope you sort it buddy, Regards, Lou. 8)

i've had this same thing happen, here and there, but i haven't worried too much about it. i just add some more caulk into the crack, seems to fix the problem. you should wait a few days if you can between layers and inspect for this if you can. if you can't wait, then you should just rely on the redundancy of multiple layers to take care of you. unless you have an awful lot of this, it is unlikely to have two failures right on top of each other. finally, i think this is related to not having enough caulk in the joint. i always try to run my finger into the joint to push the caulk in ... also this pushes it against the rough edges of the board giving a better seal. of course with your nice 1/4 inch gaps this isn't realistic. but i would overfill a bit anyway and try to push the caulk in as much as you can. also the caulk will stick good to the paper which will help keep the seal closed, so if you have a littel caulk over flow onto the paper that is all good.

Hey guys if I can add a little to this thread. Caulking, glazing and joint installation with any elastomeric compound you have a rule of thumb that applies. Not that in the field it is a perfect situation every time but to understand the material and how it is supposed to function will help. Shrinkage will occur in almost any material ( ie; wood, sheet rock mud)that is wet or damp when installed. The acoustic caulks range of solid content can be 50-100%. What this means is if the material is 50% solids that when it is in its cured/dry state, 50% of your application has dehyrated or left the compound during its curing process. And most materials will tell you maximun thickness and maximm width to install. Because there is an elongation property of the material. It can only stretch so far until something gives.....the Bond line or the material iself.... In most cases and mine too. The wood itself was damp during construction. It shrunk ever so slightly that something had to give. I had to recaulk a few joints just for that reason. And I did cut a few out that were slight and the larger ones I just recaulked between the gap. Rule of thumb is half the depth of the width for proper elongation to happen. I tried an illustration but it was hard to draw and explain. But here is a way to understand elongation better. Take a piece of rubber that is 1" by 1/2" and stretch it. Now take a piece of rubber 1" by 1" and try and stretch that. Then you can understand that the depth is important to the width for movement and shrinkage Now having said all that .....if your materials..wood, sheetrock are all dryed in you can caulk as deep as you like as long as you have non to little movement. Peace Tom

What a crackin' post Tom! :D Very many thanks, and I hope that helps you too Chris of course. :wink: Regards, Lou. 8)

Thanks for the insight guys! It is much appreciated! I hope I’m not being too obsessive about it but it’s just a little disheartening when your carefully prepared joints start splitting on you. Especially after reading all the warnings about sound leakage through even the smallest of breaches. Dan, I think you are right in that I have a couple spots that might be under filled. I remember reading something from Brian Ravnaas from GG about the importance of not skimping on caulk, and here I am guilty! Like you mentioned, I was noticing a better seal when I let the caulk overflow onto the paper rather than neatly to the edge. I wish I could say all my joints were right at 1/4" but I know there are probably plenty of areas that widen out to as much as 1/2" or so. It is a cruel reality that the best implement for tooling caulk is a finger! I finally bought a couple pairs of those big yellow gloves to cut down on the raw fingers. Tom, Thanks for the enlightenment and your analogy makes perfect sense. Also, using that rule of thumb, 5/8" drywall minus 3/8" backer rod which is compressed slightly in a 1/4" wide joint, puts us right around that 1/8" depth. Eureka! I still think surface prep is at least as important but now I’m seeing the finer details and "the rest of the story". Time to get caulking. Thanks again fellas! Chris

Chris, You are so right. surface prep is very important for proper adhesion. And thats why I said in the field its never a pefect world. width, depth and proper cleaning What happens on larger joints such as your 1/2" wide one. The material probably shrunk on you because some of these caulks are not designed to go that thick/wide. I went for 100% on my build and ended up with about 97%. No ill effect My old studio had leaks that actually sounded like little speakers Peace Tom