THE PAINTINGS ARE STURDY.
The frames are made of 15x45mm oak strips glued toghether with 34x34 mm pine strips. The back is either 6mm MDF board or pine veneer.
The paintings are made with an approximate 5 mm thick layer af filler, the ordinary construction type, used for smoothing walls etc.
The colour or the material will not change in foreseeable time. If the surface is damaged it will easily be repaired by sanding off the damaged part.
Below you can see the whole process.