Whats with these lines in the ceiling?

May 15, 2011 8:25 AM

How was this ceiling constructed? And what are these "lines" running in it for?

Picture here: http://i.imgur.com/DWpQJ.jpg

Found in a hotel. It either has plaster or some other material over the whole thing with a popcorn texture. There are dips/lines running in it the whole way across. They're about 1/2-3/4" deep. The question my friends and I want answered is: is there any reason for these lines, or are they just decorative? Is that where the support structure is and there is some necessity for the dip in the plaster (or whatever it is)?

posted by ish__ to grab bag (6 answers total)

precast concrete ceiling/floor assembly. the "lines" are the joints between the panels.
posted by katocolon at 8:32 AM on May 15, 2011

katocolon is correct.
posted by Thorzdad at 8:52 AM on May 15, 2011

Is there any reason they don't fill in the joints for a smooth surface? Or just someone said "this looks good" ?
posted by ish__ at 9:19 AM on May 15, 2011 [1 favorite]

The joint is both aesthetic and functional. Concrete expands and contracts. It is usually installed in slabs with expansion joints between them. This allows them to move a little without cracking. Sometimes the concrete is strengthened by "prestressing" it by sealing slightly stretched rebar (metal reinforcing rods) inside the slab. They could have probably filled in the joints, but then they'd run the risk that at least some of them would crack over time. Better just to make them a feature instead of a bug.
posted by Benny Andajetz at 9:32 AM on May 15, 2011

Additionally, filling the joint would add quite a bit of time to the job - they would have to fill the joint with some sort of plaster or cement, wait for it to dry and then come in and spray the texture. This method eliminates that first step.
posted by davey_darling at 7:59 PM on May 15, 2011

The precast panels are also not perfectly coplanar/flush (since they are cast/cured independently), so the reveal allows that misalignment to be concealed without a ton of work to feather out the transition.
posted by misterbrandt at 8:31 PM on May 15, 2011