Hi Folks,
Thanks go to Brien for that wonderful quote "Too much sugar for a dime". It reminds me of many colorful sayings from when I grew up in Virginia.
After going through the first stages of wall beef-up on the Dissonati build (will have it's own thread soon) here's a discovery I thought I'd share. After careful cost analysis, it seems that the means of sealing up the stud bays of outer leaf walls with acoustic caulk is very expensive, even if you're properly using backing rod as Rod Gervais has suggested in his brilliant book.
Acoustic Caulking (w/ backing rod) - Pros:
1. Flexible for life of wall;
2. Density equal to original drywall if maintained at 1/2 thickness of original panel (Acoustic Caulk mass approx. twice that of drywall);
3. Allows for much easier installation of drywall in stud bays than having to pressure-fit and perfectly match bay dimensions (if as Rod explained you undercut your dimensions by 1/2", allowing a 1/4" on all sides);
4. Costs go down if you increase thickness of drywall (fewer seams to caulk per unit mass);
5. Prevents direct air leaks in beef-up attempts (this is of course its primary purpose).
Acoustic Caulking - Cons:
1. In no substantial way increases the mechanical stability of the assembly, except perhaps by the minimal increase of side pressure that the slightly compressed rod achieves (that's certainly not intended to be its job).
2. Costs (based on 24" OC bays, 2011 over-the-counter Big Box non-contractor prices):
A. 1/4" Backing Rod = approx. $2.50 per 21', one bay, one layer coverage
B. OCI 175 = approx. $7.50 per 29 oz. tube (4.41 tubes per gallon = $33.08/gallon), two bay, one layer coverage
C. Total of above costs = approx. $2.50 + $3.75= $6.25 per bay, per layer. This equates over or nearly the cost of drywall to cover the same surface area (for beefing-up stud bays), depending on drywall thickness used.
3. Product can be messy as it never cures (hopefully!)
In our situation, with a very minimal budget, it was decided to beef up our outer walls by recycling the original 1/2" drywall wherever it was previously installed. This meant that we had to beef up approx. 16 bays @ $3.75, as well as find an efficient way to repair prior screw holes (some of them quite enlarged by the removal process).
So I got to thinking (Bad brain! Down boy! :) ), what if one were able to inject drywall joint compound into the seams and holes instead of caulk, in other words, Gaulking (Gypsum + Caulking)?
Gaulking (w/ no backing rod) - Pros:
1. Cost:
A. Premixed Beadex General-Purpose Drywall Joint Compound = approx. $13.50 per 4.5 gallon bucket (well, 62 lbs. worth, bucket not listed in liquid volume gallons). Gaulking would require approximately twice the liquid volume per bay that regular caulking techniques would (if not using backing rod), so approx. 1 tube's worth (29 oz. per bay, per layer) = approx. 4.41 bays per gallon X 4.5 gallons = 19.85 bays (one layer) per bucket; therefore $13.50 / 19.85 = $0.68 per bay, per layer
B. The means to apply the Gaulk easily that would ensure full (at least 95% or over) filling of the seams, gaps and holes.
This required a bit of thought, but the solution I came up with that works wonderfully was an inexpensive bulk-loadable grease gun (one-handed pump style , with a simple nozzle using galvanized iron plumbing pipe and assorted fittings). Also required (as I soon discovered) was a means to lubricate the working mechanisms so that the drying drywall mud wouldn't jam them, and which wouldn't substantially negatively effect the strength of the mud. Vegetable oil seemed best, as it is a light oil, will disperse easily with water, is non-toxic, and will dry more quickly than other oils. It is also available in a spray can as a cooking aid for approx. $3.50 per can. The very slight amounts that mixed with the mud as it was sliding through the gun seemed to have not effected the mud strength after observing the mud two months after first application.
So, the cost the grease gun = $24, plus $7 worth of various plumbing pipe and fittings = $31, nearly 4.5 times the $7 cost of a cheap version of a 29 oz. caulking gun. In exchange for a much more messy loading procedure (using a small garden scoop to load the grease gun from the mud bucket) I got a tool that is capable of injecting the mud with up to 4,500 psi of force - more than enough to fill cracks and holes easily to at least 95% fill coverage. Total cost grease gun + veggie oil spray = $34.50
2. Density/mass of Drywall Joint compound is very nearly the same as drywall itself. If properly applied it may very well slightly excede drywall's mass, as most drywall I've ever cut into had some amount of "foaming" (small air bubbles inside), whereas dried mud is nearly bubble/void free.
3. Dried drywall mud has a little strength of its own - you can chip it with your finger nail, but this implies that it can withstand a few psi before it gives out or breaks. This means that it can provide a (very weak) glueing action to help secure it in the stud bays - Note: never depend on this entirely for mechanical securing of your beef-up layers! Use the methods Rod recommends: finish nails as edge binders, and final 1X cleating, potentially drywall screwing the perimeter if your screws can sink into something meaty such as solid wood, MDF or OSB as your first beef layer.
4. Drywall mud is relatively non-toxic, i.e. although it may be a little alkaline and hygroscopic (absorbs water) its carrier is water-based, and therefore has very few fumes. Cleans up with water very easily until cured.
And now to the Cons of Gaulking as a technique:
1. Drywall mud is guaranteed to crack if it is applied thickly, or if it is applied to a surface which has a different temperature & humidity expansion index. This is the primary reason behind using drywall joint tapes - they tend to provide a sort of "rip-stop" or "rebar effect" to the mud, and equalize stresses somewhat. The larger the gap trying to be filled, the larger the cracks become. After two months application, a 1/2" X 1/2" gap I filled by Gaulking had a 1/16" crack develop, then stabilize at that size, due to shrinkage when the water content had normalized. This implies that the size was reduced to 87.5% of its original application volume due to loss of water content. In other gaps, (1/4" or less) ther was either no visible cracking, or cracks less than 12% of the gap dimension. Is this cracking a big issue? Yes but only a substantial one for the final layer of the assembly - the last beef up layer, wherein we must try to maintain an air seal. Every layer that was Gaulked behind the last one (which would still have to be Acoustic Caulked w/ Backer Rod) would only have lost a very small percentage of its mass, especially related to the panel mass as a whole.
A. Volume of single-layer 1/2" drywall installed in stud bay of typical 8' wall w/ single top & bottom plate = 1/2" (Thick) X 22" (Width) X 92.75" (Height, only 1/4" gap required as the panel will rest on bottom plate) = 1020.25" ^3
B. Volume of single-layer Gaulk at three-sided 1/4" perimeter gap = 1/2" (Thick) X 1/4" (Wide) X 208" (Running Length = 22.5" (Top) + 0" (no bottom side required for stud wall beef-up) + 92.75" (Left side) + 92.75" (Right Side)) = 26" ^3
C. Volume lost after Gaulking due to drying (worst case) = 26" ^3 X 0.125 (shrinkage loss) = 3.25" ^3 (22.75" ^3 Gaulk volume after shrinkage)
D. Volume change due to Gaulk shrinkage = 3.25"^3 / 1020.25"^3 = 0.0032, or a 0.032% loss of mass by volume (for 24" bay beef-up)
2. Gaulking is messy. Yes, but it cleans up with water. Loading the gun, and cleaning the gun is the messy part. Because you are applying it in minimal amounts, it may be less messy than doing regular mudding & taping of drywall seams (by the way, I see no benefit to using Acoustical Caulk in between the seams of successive panels in a single wall assembly - only as a filler for the entire wall assemblies' perimeter edges)
Alright, here's the caveat: Gaulking as a technique (using an appropriate grease gun setup) may have special benefits, such as relatively easy forced-injection of a liquid mass into awkward locations, and for small hole repair i'd say its pretty good for this.
It does take a little longer than applying Acoustic Caulk and backer rod, due to cleaning and periodic lubing requirements of the grease gun. Its biggest benefit that I can see is in putting more layers than two into a beef-up assembly (I used it for our build beef up which required 4 layers - 3 layers of Gaulking, 1 layer of Acoustic Caulk and Backer Rod).
I would not necessarily recommend it for ceiling beef-ups, due to the increased shifting of the flooring due to Live Load (people walking around).
I'm also not going to use this for the inner structure in place of AC & Rod, as I feel the additional vibration of the inside isolation sources may cause accelerated problems of seals breaking down, but I would definately use it for small hole repair, if necessary.
So what do you folks think - Is this, in the immortal words of Brien "too much sugar for a dime"? Or is this a case of "spending a nickel to save a dollar"? I know that we couldn't have afforded our 3rd and 4th layer of beef up if I hadn't come up with this.
If anyone is interested in "action piccies" I'll try to upload them.
Bill
Wall Beef-up - Gaulking Saves Money or "Too Much Sugar..."
Originally posted at johnlsayers.com, topic 16160.
use less expensive latex 25 year caulk? the main goal of the caulk is to seal, not add mass... definitely buy or rent a powered caulk gun because you will have popeye forearms by the time you're done...
Hi Glenn,
Thanks for the response -
If sealing were its only function, then only sealing the last layer would be necessary-yes? Nothing would be gained by redundently sealing each layer unless mass replacement weren't at least part of Rod's intentions, do you think?
Also, less expensive 25 year caulk is still expensive proportionately, heck even regular latex caulk is expensive relative to Gaulking.
Bill
the reason for the double (or triple layers) of sealing is to avoid a break in the a single seal resulting in loss of performance. the mud approach can result in a loss of performance if it chips and leaves an opening - is it catastrophic? depends. maybe the mud approach with the spray on thermal insulation over it keeps things in place and enough of a layer to seal. but then that may be more expensive than the caulk...
Just so we're clear, the Gaulking method would be used for every "Seal" layer up to the last. The final layer I propose would be to go with Rod's suggested Backer Rod and Acoustic Caulk, as this would certailnly:
1. Maintain the mass (AC by itself = 2 X drywall mass, with BR = 1 X drywall mass)
2. Stay in place (as shown by lots of long term successful cases)
3. Compressed BR would mechanically hold the Gaulk in place, even if the Gaulk broke into small pieces. This hasn't happened by the way, the cracking I observed happened as a single parallel crack nearly in the center of the gap between drywall and studs.
Your idea has merit because of the tenacious stick and finished rigidity of the expanding polyurethane foam, at some small reduced cost to mass. Although possibly more expensive due to the spray can quantity costs, this might be a perfect solution for partial stud bays (end bays, usually) wherein the normal beef up technique would be difficult due to lack of space to swing a hammer. I have 4 of these areas in our build, so for these I will definately try your idea out in the following manner:
1. Pre-assemble the mass layers
2. Apply a thin bead of construction adhesive to what would have been the 1st layer into the bay.
3. Insert the laminated mass "chunk" and position for equal gap, press into place to bed the glue
4. Gaulk as a whole, 3 of the 4 layers deep, leaving the 4th layer's gap maybe just partially filled
5. Finish off with a shot of the polyfoam. This would seal the gap, and act as final assembly "glue" instead of having to also add the finishing cleats. For a small surface area such as this I think the polyfoam by itself would have sufficient strength.
Thanks for that idea Glenn!
Bill
"what if one were able to inject drywall joint compound into the seams and holes instead of caulk, in other words, Gaulking (Gypsum + Caulking)?"
:)
The issue you are dealing with is flexibility, continuity, mass, and a less rigid wall assembly. I appreciate your work and effort, but your attempt to override what is typically requested by the manufacturer is gonna be a challenge.
The holes you can mud but the corners, overall, need to be a break in the ability of the panel to vibrate, one to the other.
Injecting a hard substance like joint compound into the corners, assuming you have a device to do as such, makes a hard connection, at EVERY Layer.
This is something you do not want to do. You want to, at every step of the construction, remove every rigid connection you can. so the addition of a hard bridge like sheetrock mud...well, it should speak for it self.
If it doesn't...it is a hard connection, with minimal weight and serves no useful purpose or benefit to you.
Thanks for stopping by Brien,
<<Injecting a hard substance like joint compound into the corners, assuming you have a device to do as such, makes a hard connection, at EVERY Layer.>>
Yes, I've already built and used the device (the Gaulking gun mentioned above). Well I see your point, that this technique would couple every layer to each other somewhat (less so than using construction adhesive in a fully adhered lamination) but since the hard connection would be to the studs on the edges of the bay, do you think this would somehow raise the resonant frequency of each panel layer? Keeping in mind that I only propose doing this for the beef-up, not for the inner room (which will be a fully decoupled seperate stud wall). I guess what you're suggesting is that by decoupling the panels from the frames, some amount of benefit would be gained.
In the case of full wall panels, I would totally agree, for the same reason that I wouldn't try to glue the panels to the stud edges, as this would definately raise the resonant frequency of the entire assembly (just like fretting a guitar string makes for a higher frequency, even though it is one continuous string), but in this case of wall beef-up, we have seperate panels which have higher resonant frequencies already, wouldn't coupling in this manner potentially lower the resonant frequency by making the mass (of the entire assembly) more continuous?
<<If it doesn't...it is a hard connection, with minimal weight and serves no useful purpose or benefit to you.>>
The weight would be nearly the same as the drywall panels themselves (if they were precision cut to fit in the stud bays); the benefit as I mentioned above has been that we could afford to add mass (more layers) to the beef-up due to the cost savings.
Bill
Your goal is to have a wall that has a known frequency, this cannot be achieved with the coupling you are suggesting. And no matter how you do it, the mud is a rigid connection. Granted the last layer is the best overall place to install this, but even that can be by-passed.
The issue with a hard/rigid connection at any placement is that it is either a flanking path or an acoustic hole. In the case of making every piece of mass rigid you make a a wall assembly, like your exterior wall with added mass and sheetrock mud in the joints, that is so rigid that the street traffic will vibrate the wall...your goal is to develop a basically decoupled semi rigid wall assembly, unless you build a brick wall which is better overall than a beefed up sheetrock wall.
<<Your goal is to have a wall that has a known frequency, this cannot be achieved with the coupling you are suggesting.>>
Well, the end goal is to understand what I'm doing in general terms, so that even if I can't calculate to the nth degree or predict with 100% accuracy what the result will be, at least I'll be heading in the right direction with the build results- to improve the isolation of this space as much as possible with the least cost involved (sweat equity notwithstanding).
<<your goal is to develop a basically decoupled semi rigid wall assembly>>
Hmmm, alright, let's see if what I've learned so far is correct...
This is obviously a very complicated subject, and I'm only just beginning to understand some of the nuances, so I appreciate your patience with me on this-
1. It is my understanding that the outer leaf assembly (if it is to be both up to code and representing a single leaf in a true two leaf system) must have rigid, strong connections- particularly if these connections are load bearing walls, etc. Flanking paths necessarily, unavoidably occur here otherwise there isn't going to be enough strength to hold up the walls or the roof. If the Gaulking method increases the outer radiating surface area by coupling with the studs then it wouldn't be any worse flanking than masonry walls (which should suffer flanking noise the worst- right?). Besides, to avoid triple leaf effects as much as possible the beef-up needs to make direct contact with the outer sheathing of the building, which would definitely represent the greatest surface area of flanking- there's just no way around that.
Following Rod's original recommendation to the letter would still require using cleats, which have to be pressed up against the beef-up layers firmly enough to prevent any inadvertant triple leaf gapping, and to prevent the layers from simply falling out of the stud bays- this means they are rigidly coupled to the studs to some degree.
2. I believe it has been shown that once you've successfully decoupled the inner leaf the best way possible (within your budgetary constraints), adding decoupling to the outer leaf may actually make things worse, by allowing a greater amount of coupling at the MAM resonance- for example... you only add RC to one leaf of a two leaf system, otherwise you risk losing more TL in the low end.
In our case, we've decided to not to isolate the floor (we're already on a concrete garage slab) due to costs. We have decided to make our inner leaf using proper double wall construction (no structural members connecting the outer leaf wall to the inner), how much more decoupled could the two leaves be than that?
Bill
In a decoupled wall assembly the only coupled path will be the concrete slab which we have sufficient proof that this is not going to be, all things considered, a flanking path of any concern. Directly to code, the existing structure with the elimination of the interior sheathing (the sheetrock) may well reduce, depending on your placement in the world, the ability of this structure to withstand whatever elements of Nature that you may endure. That said, there are ways to overcome this and still satisfy code, x bracing with metal strapping, etc.1. It is my understanding that the outer leaf assembly (if it is to be both up to code and representing a single leaf in a true two leaf system) must have rigid, strong connections- particularly if these connections are load bearing walls, etc. Flanking paths necessarily, unavoidably occur here otherwise there isn't going to be enough strength to hold up the walls or the roof. If the Gaulking method increases the outer radiating surface area by coupling with the studs then it wouldn't be any worse flanking than masonry walls (which should suffer flanking noise the worst- right?). Besides, to avoid triple leaf effects as much as possible the beef-up needs to make direct contact with the outer sheathing of the building, which would definitely represent the greatest surface area of flanking- there's just no way around that.
This has nothing to do with this highly glorified threat, the 3 leaf. What you are doing is adding mass to an exterior wall, plain and simple. What you are doing is keeping the parts in place, it isn't the rigidity that is in question since we are talking about small pieces, 14 and 3 eights of an inch wide, that are all decoupled one from the other via the studs. [/quote]Following Rod's original recommendation to the letter would still require using cleats, which have to be pressed up against the beef-up layers firmly enough to prevent any inadvertant triple leaf gapping, and to prevent the layers from simply falling out of the stud bays- this means they are rigidly coupled to the studs to some degree.
You add RC to one side of a single frame. The single frame isn't a two leaf it is a single frame, the thing that makes it a decoupled two leaf, is the addition of the RC, other wise, it is either a double sided single framed assembly, or a single sided single framed assembly.2. I believe it has been shown that once you've successfully decoupled the inner leaf the best way possible (within your budgetary constraints), adding decoupling to the outer leaf may actually make things worse, by allowing a greater amount of coupling at the MAM resonance- for example... you only add RC to one leaf of a two leaf system, otherwise you risk losing more TL in the low end.
It would help if I had a picture or floor plan of what you are doing...believe me, I cannot remember everything that I comment on:)In our case, we've decided to not to isolate the floor (we're already on a concrete garage slab) due to costs. We have decided to make our inner leaf using proper double wall construction (no structural members connecting the outer leaf wall to the inner), how much more decoupled could the two leaves be than that? Bill