Cracks in drywall seams of dome ceiling

[Edly]

Cracks in drywall seams of dome ceiling

Our dome was built in the '80s from a Monterey Domes kit. There are many cracks in the seams between the ceiling's pieces of drywall. They open and close with the expansion and contraction of the dome and the change of seasons. These cracks, while just visual, seem to me to be a shame, given that the ceiling of the dome is one of the things that makes it the amazing visual thing that it is.

We are renovating the dome this summer. Currently, the second floor goes only halfway across the dome. The renovations will complete the second floor such that it runs the full width of the dome. We are also adding some walls to the new second floor, two of which will go all the way up to the dome's ceiling, others of which will only go partway up, creating a partial third-floor.

We are trying to decide what, if anything, to do about the cracks in the drywall seams, especially since, with the new second floor, we will be that much closer to the ceiling, so it would seem that any cracks will be all the more apparent. 

We have two options (that we know of): 

1. Patch the cracks, such as they are now, with caulk, or some other flexing substance.

2. Mount molding/ribbing on all the seams to cover the cracks (to the tune of about $9,000), and don't worry about the cracks, because they'll be hidden. I've seen this in one dome, and it looked great. 

A structural engineer who came over and looked at the place said that it could well be that the additional rigidity from the new full-width second floor, in conjunction with the new walls, might be sufficient to hold the dome more rigid such that the cracks, if well-patched with caulk, won't open up again. But he's not sure. So obviously, if the expert is not sure, then I, a layman, don't know. I'm writing to see if anyone has any experience and knowledge about this.

So in summary, here are some questions:

1. Does anyone know if the full second floor and new walls will indeed add sufficient rigidity such that cracks, if well-patched, will not return?

2. Is there anything better than conventional flexible silicone caulk for patching the cracks?

3. Any opinions about the molding idea (other than it's really a whole lot of money)?

4. Other ideas?

$9K to put up the molding is a whole lot of money, and if we didn't need to do it, we would love not to. (On the other hand, if the cracks are likely to reappear, it would be great to get all the work done at once, and not have yet another construction disruption in the future!) What do people think?

Thank you any and all for reading, and any and all for any responses whatsoever. Much appreciated.

[Paul From Geo-Dome]

OK let me try and help...

I think the most likely cause of the cracking might be because there isn't any scrim cloth over the joints. Any join in a boarded and plastered ceiling always has a net like scrim material along all the board joins before plastering. If this hasn't been done then I'm not surprised there are cracks showing. How big are the cracks?

In my experience caulking doesn't work, the cracks always show up again.

I've seen the moulding idea and it works well and does look great, the quote you have seems high though, how big is your dome?

I don't  think that the rigidity of the dome will increase with the addition of the full width second floor and wouldn't expect this to have any effect on the cracks.

The moulding idea seems the best I think, you could use a very flat thin strip for this and it would still work but may be cheaper, I would make up some pent and hex blocks for the vertices so you don't have to be perfect with the moulding and it would add interest.

I'll let you know if I think of a better solution.

All the best,

                  Paul (from geo-dome)

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[Blair Wolfram]

Hello Monterey Domeowner;

$9000.00 to miter batten strips over the sheetrock cracks, for materials and labor including a skilled custom finish carpenter. If you have a 5/8 dome, that's $50+ per batten.

The additional second floor framing will in no way reduce expansion and contraction between the panels.

The only flexible material that has a chance to reduce cracking between panels is white silicone caulk, but not so much.
To drywall a strut dome correctly from the beginning, you would cover each triangle opening with 3/4" plywood, screwing each piece every 5" on all sides into every strut. Then screw the sheetrock to the plywood.

Blair

http://www.domeincorporated.com

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[Edly]

Thanks to both of your for your responses.

I'm not a builder, so am not sure about "scrim cloth." I do believe the joints are indeed "taped and mudded" (I believe that's the right lingo). I'm not there now, but would guess that the cracks are all well under 1/2" wide, which may not sound like much (to me, anyway), but is plenty to be visible from the first floor. They may even be narrower than 1/2". They're mostly jagged, not straight.

Our dome is 40' diameter.