Can you give me an idea of the best way to do butt joins in cornice?

Cornice can stay in position and look good for a long time if a few simple tips are followed.

  • When buttering up the back of the cornice in the corner mitres ensure there is plenty of compound behind the joint so when it is pushed together the compound will bond across the back of the mitre. This substantially strengthens the joint and in most cases saving filling it with no more gaps in 12 months’ time at the end of the defects period.
  • As for the butt join in the cornice, always try to place the join in an inconspicuous place and not in the very centre of the room.
  • When cutting the cornice, make the cut diagonal rather than 90 degrees to the face as this gives extra surface area to bond the cornice cement, once again providing a stronger joint and better fit.

An extract from the Australian Standard AS/NZS 2589, as follows:-

Cornices shall be securely bonded at the wall/ceiling junction with a modified plaster-based adhesive except for painted surfaces which require scoring or abrading, or both, to provide an adequate key for the plaster adhesive prior to the application of the plaster adhesive and cornice.

Cornices shall be accurately butt-jointed with ornamentation matched as required on long runs, and with all angles matched and mitred.

Where walls are to receive a cement render and setting plaster finish, cornices shall be installed after the cement render has been applied and before the walls have been set.


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