John Sayers' Recording Studio Design Forum Archive

Here is a slightly enhanced version showing a possible rough design cross-section of the duct area... (I also posted this under the other thread, but I kinda wanna keep a record of things about my project all in one place, so I put it here too)

Other notes:
- Ceiling joist spacing is 24 OC where duct precludes placing a joist; this is more than enough since the joists are back-to-back 400S165 20 guage structural (thus it's an 'I' shaped member, which will help tremendously with it's self support (in combo with the recommended web and flange supports); the combined web is also as thick as a single 14 gauge joist)
- Note that to maintain a roughly 16 OC for the rest of the ceiling joists, AND to get a 24 OC spacing around the duct, some of the ceiling joists will be pretty off-center in relation to the floor joists; there was really no way to keep a 24 OC ceiling joist spacing, due to the spacing of the floor joists, so I decided on 16 OC (roughly, as best as possible).
- Between-joist blocking is planned over cross-bracing since there would be little room to do that once the outer-leaf sheetrock is placed, and it can't be done before the sheetrock; the solid blocking can't be 100 percent solid because of the notches required to clear the ceiling joists, so it will likely be either doubled 2-by-8's or perhaps sandwiched multi-layer plywood (angle metal might be used at notches); the solid blocking will be done BEFORE adding sheetrock, as there would be significantly too little depth if added afterward.
- Ceiling joists will be blocked on the bottom flanges, but cannot be blocked at upper flanges since the floor joists will be in the way; there is relatively little chance of torsional movement or web crippling since the joists are back-to-back and flanges will be supported at ends and at least every quarter of span; additionally, a steel straping could be setup as a 'guy wire' in some places (screwed to the bottom steel straping or adjacent joist bottom flange); moreover, there seems there will be no real top force to initiate twisting (unlike a floor joist), but a force pulling down from the bottom flange -- AND, they are only 4 inches high, but with 2 back-to-back members joined together, they will be 3.25 inches wide (thus, I ask you: how much twisting force will there be?... it's not at all like, say a 2x10, which only has a 1.5 inch flange, yet is 9.25 inches tall!).

thanx,
K

Kenni,
funny i just came inside to get a break from the humidity we are having. Nothing like Boston but we are not used to it here.

Sounds like good news on the black mastic.
A couple of reaons why it has come off, held on for so long and why you dont have moisture for the most part.

The moisture through the wall was probably minimal or the down spouts were re-routed during the time the coating was applied and they solved the majority of the problem. (I know you did some more work on the down spouts and that will definately help.)

If you had heat in the basement it will pull moisture into the room. If its been chilled or basement temperature all this time it wasn't sucking the moisture inward. Once you heat the room it will tend to pull moisture from cold to hot.

And as far as the other materials directly against them it had nothing to do with it. I think it probably was minor when they fixed it and you have had small amounts of moisture for 25+ years. You just happened to be the lucky one to open the wall and notice it.

One more thing (for now): assuming I didn't really 'need' the MRB layer, would it hurt if it were there anyway

An once of prevention is worth a pound a pound of cure

Another stickling point I have (I'm sure there will be many more during the course of the project) is what to do about the spaces between the subfloor planking (of the above floor)...

[SEE PIC:
it's a view looking straight up at the bottom of the floor from the basement below]

I will be adding the sheetrock between the joists soon, and need to know what -- if anything -- I should fill those spaces with.
I don't have a plywood subfloor; it's solid wood planks (1x8's).

Thus, since it's solid wood, it must be allowed to expand and contract with moisture content when it needs to; so anything that goes there should be flexible.

Can't really see using acoustic caulking on every gap (that would be a BIG untertaking)...

Been fleeting with the idea of perhaps using a construction adhesive.
PL Premium is a polyrurethane adhesive and should be sufficiently flexible (?), but I've heard that it could bubble up (?) some and might need support while curing.
Something like PL 400 might also be flexible enough (and it's cheaper too), but I am not sure.

This type of subfloor doesn't seem to be mentioned in Rod's book...
Anyone have any ideas or similar experiences?

The ONLY thing I could find on a search was a statement from Steve:
"... Probably a better way is to use drywall joint compound; if the subfloor is older, plank type construction it will probably have gaps. If so, these should be filled with joint compound and smoothed with a taping knife before adding the wallboard inserts. ..."

I am concerned about the flexibility of joint compound allowing cross-grain expansion of the wood planks; perhaps there is a more elastic type of this stuff? I know that the PL 400 subfloor construction adhesive is pretty runny (as in fact I was even trying to use it in the joist 'sister act' and found that it just dripped off the face of the joist when it was vertical -- much more so than the Titebond II left to set for 2 minutes (one would not think this would be true, but it is)); this adhesive may be also flexible enough to allow plank expansion (?).

Now, there is red oak 3/4 t&g flooring above the subfloor...
As I understand, there are voids on the bottom of the oak strips, and therefore also air gaps between the oak floor and the subfloor, no? (surely these cannot be addressed and have to be lived with).

thanx,
K

[Note the the spaces between the joist sisters is for illustration clarity; there are NO spaces between the sisters -- they are glued and screwed tightly together; the spaces between the planks show heavy a kraft paper beneath the hardwood flooring]

why do you think construction adhesive or drywall joint compound would be easier than using caulk? it seems like it would be the same amount of work either way.

caulk and backing rod are designed to be flexible and able to expand and contract with the joint. it seems like just the ticket ...

Dan Fitzpatrick wrote:why do you think construction adhesive or drywall joint compound would be easier than using caulk? it seems like it would be the same amount of work either way.

caulk and backing rod are designed to be flexible and able to expand and contract with the joint. it seems like just the ticket ...

Hi Dan:

Steve had recommended the joist compound in a post to someone about a year ago or so (I myself would not have thought of using that -- but of course, I don't know anything about this situation...)...

I seem to be under the impression that acoustic caulking is a more expensive route, but YEAH, the backing rod does seem to be quite straight forward....
Since these gaps won't be like the gaps in the corners of walls and ceilings, where the layers of sheetrock intersect, I didn't think that the acoustic sealant was required, and something more firm or denser (yet flexible) might be an option (based on ease of application, etc.)...

Also, the edges of the between-joist sheetrock pieces have been recommended to be attached with a construction adhesive (only along the edges, and not in the middles)...
IF construction adhesive were to be used between the planks, it would have to be smoothed flat and allowed to cure before attaching the sheetrock (?).

Another issue with using adhesive is that it can provide holding power to help eliminate squeaks and such in the above floor (especially in the plank gaps that run over the joists). In other words, it can make the floor more quiet -- I don't know if the caulking can accomplish that...
(I realize that this is not the main reason for filling the gaps, but there ARE some areas of the floor where a little bit of quieting could be an added benefit for the above rooms).

thanx,
K

On second thought, something that you could spread with a taping knife, like the drywall mud, WOULD be a lot easier than caulking. the construciton adhesive might work too. Not thinking very straight this morning i guess. sorry

IF your floor squeaks, it's because things are moving and rubbing together. This needs to be fixed first - if you have access to the underside, one way that works is to squeeze construction adhesive into the gap between joist and subfloor, then either use short screws diagonally up thru joist and into subfloor (immediately after using the adhesive) - another way is to use these

http://www.worksavers.com/squeek.html

As long as the cracks between floor boards are filled with NON-porous material it's not real important what that material is (although drywall mud is higher mass than caulk by a little bit) - even if the mud contracts slightly, and would otherwise maybe drop out, the layers of drywall below it won't allow that and any shrinkage wouldn't cause gaps large enough to cause any problems.

So what it comes down to is which is easier and cheaper and quicker, as long as it's NOT porous... Steve

(Oh, one other benefit of using mud with a wide taping knife - if your subfloor boards are CUPPED at all, the wide knife will allow you to get a flat plane so you don't create air gaps between the first drywall layer and the cupped boards...

knightfly wrote: IF your floor squeaks, it's because things are moving and rubbing together. This needs to be fixed first - if you have access to the underside, one way that works is to squeeze construction adhesive into the gap between joist and subfloor, then either use short screws diagonally up thru joist and into subfloor (immediately after using the adhesive)

There are no real 'squeaks' in the floor per se, that is, there's not much at all that sounds metallic -- like a nail rubbing... just these kinda tiny 'cricks', that are not very loud at all.
It's not like you'd walk over the floor and notice it if you weren't looking for it.
Not really a problem, but I figured since I'm under there I might be able to prevent some from occuring later (as well as to see if these ones went away)

(as an aside, I wonder if I should add long strips of plywood, say 1/4" or 3/8", in all the between joist spaces and glue and screw it all together, monolith-like... hmmm)

Exactly! I was planning on using construction adhesive at all joints between the subfloor and the joists... and -- since the spaces between the planks run above the joists -- some of the adhesive will go there as well...
SO... I was thinking, why not run the bead between the full spaces of the planks too (since I'm there with the gun in hand)?
Perhaps smoothing it over with a knife...

knightfly wrote: As long as the cracks between floor boards are filled with NON-porous material it's not real important what that material is (although drywall mud is higher mass than caulk by a little bit) - even if the mud contracts slightly, and would otherwise maybe drop out, the layers of drywall below it won't allow that and any shrinkage wouldn't cause gaps large enough to cause any problems.

I wouldn't be worried about it falling down...
What I would be worried about is that any small gaps between the mud and the wood might set up a scenario where the floor might experience an INCREASE in the amount of clicks and squeaks occuring...
Anything loose in a floor could potentially make some sort of annoying noise... or even worse, vibrate with low frequency sound...
So something that will stick to the wood and have a small amount of resilience -- to allow for movements based on moisture content, temp, and live loads -- could be a good thing (even if it is a bit lighter in weight).

knightfly wrote: So what it comes down to is which is easier and cheaper and quicker, as long as it's NOT porous... Steve

Certainly cheaper is a big factor... and quicker to me IS cheaper (since I would have a higher opportunity cost)...

Gonna run a couple tests on some products... it may just end up being a combo of things... (actually it WILL be a combo, since I do need to use construction adhesive in some places anyway)...

knightfly wrote: (Oh, one other benefit of using mud with a wide taping knife - if your subfloor boards are CUPPED at all, the wide knife will allow you to get a flat plane so you don't create air gaps between the first drywall layer and the cupped boards...

No cupping at all that I've noticed... planks are nice and flat.. although there are a couple irregs due to some small infrequent knotholes...

What sounds almost most attractive about the mud is that I can grab a bunch of it on a knife and spread it right on and smooth it at the same time... certainly seems it would be faster....
If I use something in a tube, I would need to go over it to flatten the fills with a knife...

I will keep yuz posted on how my 'tests' go, and what I end up doing...
til then I'm open to any additional ideas....
thanx,
K

Updates on tests for filling between the plank spaces:

Tried both the PL 400 and the PL Premium Polyurethane construction adhesives.
Both are VERY difficult to get a fillet that easily sticks in the spaces, and complete filling is almost as difficult -- although the polyurethane was much better at it (yet needed to be worked with a knife to get it near flat).

The PL 400 dried pretty rubbery, while the polyurethane was much stiffer (yet was still resilient).
The polyurethane seemed clearly much stronger, although when cutting into the inside of the fill, it looked a bit like really really heavy bread.

Both stuck to the surface of the wood, but when attempting to tear off the polyurethane, it actually took a few mils of the wood surface with it (although not nearly as much wood as, say, if you were attempting to separate a wood glue bond, like TiteBond II).

I then tried another material.....

Below are some pics of tests I ran with this product called " Elastomeric Custom Patch", made by Custom Building Products
( www.custombuildingproducts.com ... but it's not on their website).
Found it at the local HD.
The label says it's permanently flexible, and can be used on wood, drywall, concrete, etc...

I took a piece of 2x4 and screwed 2 pieces of strapping on top, leaving a space between them (replicating the larger of the spaces between the subfloor planks).
The space was about 1/2 inch.

The pics with the 'smooth' white colored filler, are those where the 'pure' filler was used.
The pics with the tannish color and texture, are those where I had mixed the pure filler with coarse sawdust/shavings in a 4:3 to 2:1 ratio (heavy on the sawdust).

As you can see, the pure filler sunk a bit, and then cracked in the middle, presumably due to irregular drying....
The mixed filler/sawdust faired much better, although you can see it clearly separated from the edge of the plank.

I did all the tests with the construction adhesives and filler in an inverted horizontal fashion -- that is, in the same position that I would have to fill the plank spaces in 'real life'....
NONE of the joints were stressed, bent, etc.... i.e., any changes in the joints or material were NOT due to mechanical movement; they were allowed to dry in the same position and environment as the real planks.

Observations:

The mixed elastomeric filler/sawdust stayed together better, but still separated from the wood... (the tests are still not 100 percent cured, but I don't expect them to get better of course... I will add more info if they get worse).
Obviously, the mix would be alot cheaper than the pure filler, so that's a plus....

The polyurethane filled way better than the PL 400, but is more costly; I haven't done any calculations yet, but this could get expensive in a hurry...
As far as the 'bread' apperance, I'm not sure that I would call this material porous, since there were no holes through it.
Neither of the construction adhesives filled the spaces easily at all, so there would be an increase in time spent during this process...

*** I have not reached any decision on what to use just yet....
In fact, I am not even 100 percent sure I should fill them anyway (after all, there will still remain the depressions on the bottom side of the oak flooring strips, which cannot be filled -- unless I tear up the floor, and that's NOT going to happen).
I'm almost sure the drywall mud will crack if the 'elastomeric' filler did, but that's my next up.
Maybe I should look to having to use fiberglass tape over all the spaces?
This is getting frustrating.
***

thanx,
K

First of all, K, I'm really impressed with the work you've done on these tests and your effort in documenting everything!! You just earned 500 points! (Of course, the "points don't matter," ala "Whose Line Is It Anyway?")...

So, I think I understand your challenge: you have gaps that are compromising your outer leaf ceiling that are detrimental for two reasons: first is the fact that it is not air tight, and the second is the lack of mass in those gaps.

Perhaps it would be better if you didn't even try to fill the gaps, and instead, just focused on beefing up the area, which would (if it is done properly) be air tight and would hopefully consist of enough mass that the "imperfect mass" above it would not have to be counted... ...Kind of like a third leaf compromise, except that the third leaf is firmly attached to the middle leaf (and, thus, isn't really a leaf at all).

Since weight is surely an issue, then Green Glue would be a wise choice. That would allow you to use two layers of drywall as beef-up material, yet have it perform as well as or better than four layers.

You could apply your first layer directly against the gappy planks, seal the edges with backing rod and acoustic sealant, and then apply a second layer with Green Glue in between.

As far as the gaps between the sistered joists is concerned, perhaps backing rod (or two or more backing rods twisted together) can be used with a liberal application of acoustic sealant. Or, if you can afford to lose an inch or so of headroom below the joists, then you could use the same "two layers of drywall strips with Green Glue in between" strategy attached to the joists, with a bead of acoustic sealant along the bottoms of the joists before the first layer of drywall beef is applied.

And, perahaps this would be a scenario worthy of Mass Loaded Vinyl (MLV) -- something that we routinely disregard (rightfully so) in most situations, but that may be quite fitting in this one.

Finally, let's not forget that you've got that tongue-and-groove uppermost layer, which is heavy and consistent and probably pretty air tight. I would surely suffocate in a box constructed of that tongue-and-groove stuff, whereas I would survive in a box constructed of that gappy plank stuff... In other words, maybe this problem isn't as big as it seems.

--Keith

sharward wrote: First of all, K, I'm really impressed with the work you've done on these tests and your effort in documenting everything!! You just earned 500 points! (Of course, the "points don't matter," ala "Whose Line Is It Anyway?")...

LoL. 500 points is better than 250 points!

sharward wrote: So, I think I understand your challenge: you have gaps that are compromising your outer leaf ceiling that are detrimental for two reasons: first is the fact that it is not air tight, and the second is the lack of mass in those gaps.

Well, actually, I think that I should be able to achieve the airtight aspect.
It's more the fact that there WILL be 'pockets' --- and that is EVEN if I fill between the subfloor planks, as the undersides of the oak finish floor strips have those typical small hollows in them.

sharward wrote: Perhaps it would be better if you didn't even try to fill the gaps, and instead, just focused on beefing up the area, which would (if it is done properly) be air tight and would hopefully consist of enough mass that the "imperfect mass" above it would not have to be counted...

Yes, in fact I did propose that (ignoring the gaps) in a prior post -- I think... It's an idea that has alot of merit... (if everything is taken into consideration)

sharward wrote: ...Kind of like a third leaf compromise, except that the third leaf is firmly attached to the middle leaf (and, thus, isn't really a leaf at all).

Indeed, it wouldn't be a 'real' true leaf....
(This reminds me of that diagram of the double-leaf wall where layers of sheetrock from the faces of both leaves, are moved to the middle of the wall (ya kno, the famous one where a loss of STC is 20 points occurs); THAT isn't really third leaf either, because the sheetrock is still attached to respective inner and outer leaves, and it seems that a big factor in that case would be that there is a major decrease in the TRUE dead airspace between the leaves, and that there is a direct connection from the exposed faces of the leaves to those moved layers of sheetrock...
I sure wish that tests were run which compare TRUE 3-leaf (and higher) construction to the double-leaf construction... I can imagine that the effects would not be quite as dramatic... anyway, I digress...)

sharward wrote: Since weight is surely an issue, then Green Glue would be a wise choice. That would allow you to use two layers of drywall as beef-up material, yet have it perform as well as or better than four layers.

Weight IS an issue, but is somewhat less of an issue since the inner leaf will be NOT be supported by the above floor, and rather will be supported by the inner-leaf walls on separate ceiling joists...
So, having 3 layers of sheetrock supported by the above floor would not be as bad as if I was supporting 4 layers TOTAL (of both inner and outer leaves)....
One of the reasons I sistered the joists was to allow me more of an option for adding weight to the outer ceiling leaf.

Green Glue, however, remains a option.....

sharward wrote: You could apply your first layer directly against the gappy planks, seal the edges with backing rod and acoustic sealant, and then apply a second layer with Green Glue in between.

Yes, that would sound like the way to do it, I agree...

sharward wrote: As far as the gaps between the sistered joists is concerned, perhaps backing rod (or two or more backing rods twisted together) can be used with a liberal application of acoustic sealant. Or, if you can afford to lose an inch or so of headroom below the joists, then you could use the same "two layers of drywall strips with Green Glue in between" strategy attached to the joists, with a bead of acoustic sealant along the bottoms of the joists before the first layer of drywall beef is applied.

Perhaps I caused confusion by my diagram in a previous post...
There are NO gaps between the sistered joists -- I just drew it that way so that it was apparent that the joists were sistered...
The joists are thoroughly and tightly glued and screwed together (screwed from both sides no less at 8" OC)....

sharward wrote: And, perahaps this would be a scenario worthy of Mass Loaded Vinyl (MLV) -- something that we routinely disregard (rightfully so) in most situations, but that may be quite fitting in this one.

I would rather pursue acoustic lead (1/32 "), as I already have some (free), and I believe I can get more....
But, with the 3 layers, and maybe even the Green Glue, I feel I should be pretty safe... I hope...

sharward wrote: Finally, let's not forget that you've got that tongue-and-groove uppermost layer, which is heavy and consistent and probably pretty air tight. I would surely suffocate in a box constructed of that tongue-and-groove stuff, whereas I would survive in a box constructed of that gappy plank stuff... In other words, maybe this problem isn't as big as it seems.

YES. I'm thinking this 'problem' is not all that much of a problem...
The problem of filling the gaps between the subfloor planks IS a problem --- if one considers attempting to make the fills solid and crack-free, AND not being a potential source of floor noise in the future (I mean creaks and cricks)...
As far as a source of noise, I would think that the polyurethane construction adhesive has next to no potential to cause noise, and in fact might reduce the risk of such noise...

sharward wrote: --Keith

thanx for the good ideas,,,, I really need help (sometimes?)
K

PS: Pic: consider the dark stripe down the middle between the joists to be the 'glue line' ; the glue line is of course much narrower in reality -- there is NO gap between the joist sisters worthy of filling...

Cool. Always glad to be of assistance.

Maybe Steve can chime in on the "how big of a problem is this really?" question at some point.

And I agree with you that most of the "third leaf" problem is related to the fact that the gap width is compromised by the middle leaf. Most of the "three leaves are bad" illustrations demonstrate that using the same amount of materials in the same amount of space, two leaves are much better than three.

Anyway, to be clear, we're not talking about a three-leaf situation here... So I'll stop talking about it so as to not create any (more) confusion.

--Keith

sharward wrote: Maybe Steve can chime in on the "how big of a problem is this really?" question at some point.

God, that would be great.... Steve would probably offer the best opinion on this...
But as I'm tending to think now, there is probably no 'evidence' based on trials as to what exactly the effects of leaving the gaps there would be -- and conversely, what the benefit of filling them might be (... in lieu of evidence, there is always the possibility that it could be WORSE by filling them, no?... remember, we want to base our construction and design on what has been tested -- as best as we can -- and if it isn't tested, it's all presumption (educated or not)).
So, I'm hoping that there is evidence, or at least testimonials from people who have filled and not filled plank gaps...

sharward wrote: And I agree with you that most of the "third leaf" problem is related to the fact that the gap width is compromised by the middle leaf. Most of the "three leaves are bad" illustrations demonstrate that using the same amount of materials in the same amount of space, two leaves are much better than three.

Yeah, those famous 'leaf' diagrams leave me in want of more direct (i.e., controlled) comparisons between 2-leaf systems and added leaf systems...
All GOOD medical and scientific studies have a high level of control; if you are looking to find the effects of a single specific change or intervention (in this case, the addition of another leaf), you CAN'T allow other factors to change at the same time (in this case, bridging the leaves, changing amounts of mass in other leaves, etc.) -- otherwise you CANNOT reliably predict what the effect of that SINGLE change will be.
... If you try to get a paper published that doesn't follow research standards, the scientific journals will laugh you off the stage, or worse yet, simply ignore you.


.... NOW (with all that said, here I go and postulate....)
What do you think of the addition of strips of plywood in the coffers between the joists?
There may be a couple of benefits to doing this...
First, it would create a smooth surface for mounting the sheetrock...
Second, it would physically 'tie' the subfloor together in those spaces (strengthen, stiffen floor?)...

Of course (as I'm learning), ANYTHING added to the floor system has the potential to create noise...
So, while strength may be added, it seems possible that there may also be cricks created as well...
(A good example of this is the use of tongue and groove underlayment: it sounds like, as opposed to planks or butt-edge sheets, that this would reduce noises (keep the sheets from moving), but it seems in reality the wood in the tongue and groove joints actually often rubs against each other and creates cricks and creaks of their own!)...

Furthermore, it may be difficult to get the strips the perfect shape to fit the coffers, as the joist spacing can (and does) vary a bit through the spans...
Therefore, there would inevitably have to be a (deliberate) gap between the plywood and edge of joist (then again, this could be a good place for the construction adhesive....).
As far as the construction adhesive is concerned, I can't ever see it -- with it's resilence -- to be a source of crick and creak floor noise...

So, there it is...
I throw out the question of using say 3/8" or 1/2" plywood strips to tie it all together...
The pic below doesn't really show the correct positioning of the strips ( they would be better to terminate in the middle of a plank), and they should also probably be as long as possible (full 8' or 10' (marine ply)strips), in order to 'tie' things together as best as possible.... glued and screwed, as usual...

I don't think I'd bother with the plywood, or OSB (a little cheaper usually), in your case. It's less dense than drywall so you won't get as much benefit.

sharward wrote:I don't think I'd bother with the plywood, or OSB (a little cheaper usually), in your case. It's less dense than drywall so you won't get as much benefit.

It could be a bit less dense, but the real reason to use it is not so much for the density, but for creating a flat(ter) and smooth(er) surface for putting the sheetrock against, and for 'tying' the planks together for rigidity (screws would sandwich the plank layers and the plywood together)... just a thought..


As for weight, actually a 5/8" thick sheet of marine plywood is about 1.94 pounds / square foot (and baltic birch -- dare I say -- is 2.2 lbs/sq.ft)...
Isn't the type X gypsum like 2.3 or less for the equivalent thickness?

Of course, I most probably would not use 5/8" plywood, but something like maybe even 1/4" thick (or 3/8")...
At eight foot lengths, that should tie alot of the planks together...
I wonder if I'm somehow wrong in the thinking that this could stiffen things up a bit...

The planks DO have enough irregularites that I could picture them 'stressing' the drywall in some areas... and maybe cracking/breaking them if an individual plank flexes (without the others flexing) or if there is enough live-load deflection in the floor...
I do know that the drywall is not screwed to the subfloor, although it should be as tightly against it as possible, no?
Then again, there IS 3/4" t&g red oak on the other side of those planks (which might help prevent that)...

Alas, you point out very well that the plywood would be significantly more expensive than drywall.... so in any case, it could be considered somewhat of a luxury....

thanx,
K