Cracks in Drywall Bulkhead

[ajk1]

Description of the Issue:

In renovations carried out in the room of an existing building, a new ceiling bulkhead was constructed along the exterior wall. The bulkhead is framed with steel studs and clad side and soffit with drywall. The vertical depth of the bulkhead is about 2 feet, the length is about 70 feet, and the width of the bulkhead soffit is about 3 feet.

The construction was carried out about November of 2011. About February of 2013, several vertical cracks were observed in the vertical face of the bulkhead, and also in the soffit at the same location as in the vertical face.

The relative humidity in the heated / air conditioned room varies from about 25% in winter to about 60% in summer. The room is used for assembly purpposes for about an hour in the morning and an hour in the evening every day, and is empty the remainder of the time.

All the cracks occur where a re-entant corner is created in the vertical face of the bulkhead, by the old concrete beams that extend thru the vertical drywall.

The cracking is most probably caused by shrinkage of the drywall as the RH drops during the winter heating season, and the accompanying stress concentration caused by the penetration of the beam thru the vertical drywall. It is also possible that there is a drywall joint that has cracked open at these locations.

There would not be any structural settlement issue, because the building has been there for 50 years and has performed very well. There have been no structural changes. The 50 year old plaster walls in the building are uncracked and performing well.

Please see attached photos of cracks.

Questions:

1. What is the approximate expansion and contraction of drywall over the RH range that I oultined above?
2. How is that movement usually accounted for in the design?
3. Is it usual to put movement joints in drywall? If so, at what centres and how are they constructed?
4. What is the appropriate repair? Rout and patch and tape the cracks during the winter heating season when they are widest, or should movement joints also be installed at some appropriate centres?
4. There is also distress (looks like debonding of a corner piece) in the new drywall ceiling-to-new wall corner region (see photo). What is causing this? Is it a workmanship issue, or materials issue, or something else?

 

[wannabeSE]

1. Would the hygrometric coefficient of expansion help? The Gypsum Association has a nice publication with gyp board properties -

http://www.gypsum.org/wp/wp-content/uploads/2011/11/GA-235-10.pdf

2. I see architects specifying control joints. See

http://www.gypsum.org/technical-information/technical-topical-papers/#control

 

[XR250]

I would put control joints in. We had this problem in our house over a 50 ft. run and the DW contractor came back and added control joints. No more issue.
I do not know the recommended spacing, however. I would think every 25 ft. would be plenty.

 

[ajk1]

wannabeSE - wonderful to wake up in the morning to this great information that you sent. Often I get answers on this site that are not useful, but you have responded beautifully. Thanks very much. May I ask some follow up questions:

- do you know where I could see what a drywall control joint might look like, and its details?

- the hygrometric coefficient of expansion for drywall is given as
6.5 / 1,000,000 in./in./%RH for the 10% to 90% RH range. Does that mean for a RH change of 40% (i.e. from 60% to 20%), and a length of 70 feet (or 840"), the length change is 0.22"? Seems like a lot!

- the coefficient of thermal expansion is given as 9.3 / 1,000,000 in/in/deg. F. That is the same as steel! I am surprised. Or am I misinterpreting something?

- in the same room, a new stud and drywall wall that has been constructed directly in front of the exterior wall (at the same time as the ceiling bulkhead was constructed), seems to have pulled away from the original exterior masonry wall assembly, as can be seen from the gap that has opened at the window sills (see attached photo) and also to a lesser extent at the jambs. Would such a new steel stud/drywall wall behind an existing exterior masonry wall, normally be tied into the existing masonry wall to prevent separation, or would it not be tied in but a control joint with sealant installed where the gap has now developed?


ExcelEngineering - thanks for the very useful information about your actual experience. That is very reassuring.

 

[TDIengineer]

Is this a 2-story structure? What is on the floor above.

Just wondering how these interior partitions were detailed to accomodate vertical deflection of your floor system.

The picture of the cracking at the corner doesn't necessarily look like thermal expansion cracks to me. They look more like differential vertical movement type cracks.

If the partition is a metal stud with a slip track at the top, and then you hang a soffit, you need to make sure the 2-systems play nice together. Just something else to consider.

But back to you OP, 70' is very long with no expansion joint.

 

[ajk1]

TDIengineer - that is an excellent thought, and I was almost convinced until I looked again at the structural drawings. The corner cracking is adjacent to the exterior of the building (within about 2 feet) and along the exterior of the building the supporting columns are at 10'-6" centres. The slab thickness of the floor above is 8". The actial live load on the floor above would not exceed 50 psf, and likely much smaller as it has fixed seats. Creep deflection is not an issue because the building is almost 50 years old. So the deflection would be very very small. I suppose it could still be as you say, but I am a bit doubtful. I will give your comment further thought though. Thanks very much.

 

[ajk1]

In checking the stress in the drywall due to the change in humidity from 60% in summer to 20% in winter, I calculate the stress in the drywall bulkhead to be about 70 psi. This assumes that the shrinkage movement is restrained by the concrete beams that penetrate the drywall, and that the steel studs do not participate. Now can anyone tell me what the direct tensile strength of the drywall is, when loaded in the plane of the drywall, in a direction parallel to the long dimension of the drywall? I had thought I could get it from the link that wannabeSE sent me, but that data gives the flexural strength of the drywall as 110 psi (with bearing edges parallel to the length), and the MOR as 750 psi. Why are these 2 values so different? And what is the direct in-plane tensile strength parallel to the long direction?

 

[ajk1]

Is there an architectural site where I can post architectural questions, similar to this engineerign forum site?

 

[ajk1]

Do you think that if the cracks are routed out and plastered, on a day when the relative humidity is very low in the room (today would have been ideal, since it is currently minus 25 deg. C in Toronto), that this would work? In the summer, when humidity is much higher, it would go into compression and perhaps the drywall might buckle...but if that did not happen, it would be a relatively simple fix.

 

[a2mfk]

Can you post a typical detail?

Per your question about architectural sites like this, if it is this problem you are talking about, most architects are not going to be able to help much. No offense to them, but most do not expansion/contraction and the necessity of movement and control joints as well as structural/building engineers. You can try and post it in the Building Engineering forum, which is more in line with this topic and those related to building forensics.

 

[ajk1]

Is there any way to reinforce some drywall joints so they are not so likely to crack open again, where there is a re-enraant corner in the drywall that is created by the concrete beam that extends thru the drywall? I believe someone suggested that a fibreglass scrim can be used to reinforced the drywall joint. Does anyone know anything about that, anything more specific, and will a fibreglass scrim create a bulge in the drywall that would be noticeable? Is that what is usually done where joint strengthening is required?

 

[Ron]

ajk1...there are two common materials used for reinforcing drywall joints. The most commonly used is paper tape. Second is a fiberglass or plastic scrim tape. The cracks shown in your photo are not re-entrant corner cracks but are termination separations. I assume for the re-entrant corner condition, you are referring to a 45 deg crack eminating from a penetration that forces a 90 deg cut or opening in the drywall.

To reinforce a re-entrant corner condition, I would use the plastic or fiberglass scrim tape placed in several strips perpendicular to the crack, in addition to a strip along the crack. These should be feathered 8 to 10 inches on either side of the crack to prevent an obvious "lump" at the crack. Normal joint feathering is about 4 to 6 inches on either side of a joint, but the thicker the joint material, the greater the need for wider feathering before sanding.

Since there does not appear to be shearing along the separations in the photo, it appears that your shrinkage is biaxial with respect to the ceiling plane.

Your computed shrinkage of 0.22" over 70 feet is not out of reason.

 

[hope9010]

Ron - that information is very helpful indeed. Much appreciated.

I believe that I have not posted a photo of the re-entrant corner crack to which I am referring. The photo I had posted some time ago was of a different condition, at the end of the bulkhead, which is also an issue but not the issue that I had in mind this morning when I posted my question. I will find the appropriate photo and post it. My apologies.

The cracks that I am currently concerned about start at the re-entrant corners and extend vertically down from the re-entrant corner i.e. as you quite correctly surmised, the re-entrant corner was created by a penetration (in this case a concrete beam). Most probably this is a tearing apart of the drywall joint. My apologies for not posting the specific photo pertaining to the condition of the re-entrant corner. I will post the correct photo this weekend.

Do you think that remedial work should be covered by warranty, or would the contractor say that it is not his fault because there were no movement joints or isolation joints specified for the work, and no special joint reinforcement like fibreglass scrim specified? There were in fact no specs as far as I am aware. Bad.

Again, thank you very much for the help.

 

[hope9010]

..by the way, hope9010 and ajk1 are both me....just depends whether I am sending from home or from the office.

 

[a2mfk]

Agree with Ron's recommendations using fiberglass tape. I have had some pretty good success in home renovation repairs of drywall cracks using this method, one along the crack, and then "stitches" perpendicular. You have to use a little wider swatch of compound, but this is necessary sometimes to get a good feathered edge anyway. Funny thing I never considered was although fiberglass mesh adds tensile strength to the joint (positive), it also is more elastic than paper tape (negative), so you are more likely to get cracks (small ones hopefully).

http://www.finehomebuilding.com/too...e/paper-and-fiberglass-mesh-drywall-tape.aspx

I also see they are now selling it in a wider roll, which I wish I would have known about a couple of months ago.

http://www.homedepot.com/p/BOEN-6-i...glass-Mesh-Joint-Tape-FM-675-FM-675/203071694

However- from the picture, is the concrete beam that protrudes through the ceiling just painted, with drywall abutting it? Or is there a layer of gyp around it? I ask because where gyp meets a dissimilar material, this junction is a very common place for these types of separations to occur. If the surface was painted concrete and they tried to flush out the bulkhead with tape and compound, this was asking for trouble. See the attached sketch, with one possible alternative detail (I know, too late now). I am guessing at the actual construction.

From doing forensic investigations like this, it is my opinion that the gypsum board industry, architects, and builders need to collaborate a bit more when it comes to alternative joint details and installation methods. Often gypsum board is "asked to do things it wasn't meant to do". Lack of expansion joints are another issue, which likely contributed to this problem, at least on the right side of the picture.

Another big problem area in residential is the wall-ceiling joint, with separations caused by truss bottom chord movements which causes rotation movements at the joint. Tape with compound is really bad at accommodating movements.

 

[a2mfk]

FYI: good gypsum board article

 

[a2mfk]

another good article on gypsum board

 

[ajk1]

a2mfk - thanks for the info. I think that the second article on gypsum board that you sent is based on conditions that we do not have. Structural deflection is not an issue in my specific case because the cracking is occuring immediately adjacent to the exterior columns where there is virtually no floor deflection. There is no wood framing (it is all reinforced concrete. The building is 50 years old, so there is not foundation settlement. The relative humidity conditions they talk about in the paper are the opposite of what we have here in Toronto. In Toronto, the RH in buildings is very low in winter and relatively high in summer (unless the HVAC system is designed to introduce moisture in the winter and dehumidify in summer; generally they are not designed to do this). I have not read the whole paper yet. Thanks for bringing these papers to my attention.

http://www.homedepot.com/p/BOEN-6-in-x-75-ft-Self-...

I am not following your sketches. I assume that they are sections, but they do not seem to correspond to the condition that I am dealing with and I do not have a scanner here at home to make a sketch. But I understand your point, to keep the drywall unattached from the concrete beam.

I can come to no other conclusion than that the cracks (actually tearing open the taped joints where the concrete beams penetrate the drywall) is caused by the drop in RH from when the drywll was insatlled in the fall, till midwinter when RH is lowest and the drywall shortening the maximum. That and the reduction in cross section caused by the concrete beam penetration, and the stress concentration created by the notched corner out of the drywall where the beam goes thru.

Seems to me the solution is either to introduce control joints at the concrete beams or to reinforce the drywall joints with a fibreglas scrim.