of the inner form lining 3 a and surrounds the ceiling form lining 2 a the t shaped vertical support 6 is rigidly connected to the ceiling table 2 i e to the main beam 2 c in the area of the part that corresponds to the upper line 6 a of the t by means of two bolts b 1 b 2 the bolts b 1 b 2 have angled handles see fig4 and project through bores in the vertical support 6 and the main beam 2 c the bolt b 2 additionally also projects through an elongated hole 14 of the guide 7 several holes 15 are formed below one another in the vertically extending part of the vertical support 6 the lowermost hole is used as a first hinge point gp 1 a bolt b 3 extends in this hole and also projects through a hole in the bottom locking bar 4 d the bottom locking bar 4 d and thereby the overall ceiling joist base 4 and outer board 5 are disposed on the vertical support 6 such that they can be rotated about the hinge point gp 1 the bottom locking bar 4 d has numerous further holes 16 that are disposed next to each other one hole of the bottom locking bar 4 d is used as a second hinge point gp 2 a bolt b 4 projects through this hole and additionally also projects through a hole of the guide 7 the guide 7 is thereby disposed to be rotatable about the bottom locking bar 4 d on the second hinge point gp 2 further holes 17 are formed on top of each other in the guide 7 the inner board 3 is rigidly connected.