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Yesterday I transported a frame a 4 hour round trip in the boot of my car to show a customer part of our packages for weddings, frame size 35x28 inches, double moulding frame, with double mount (3mm and 1.4mm thick respectively. 2mm float glass and 2.5 mm MDF backing board) It laid flat face up in the boot. When I got back to the workshop the backing board was bowed outwards from the back of the frame and mount and pictures had a visible gap between them albeit the board was still properly attached at the back of the frame.
Laid weight on reverse of frame overnight, all ok this morning and looks like it should again.
So my questions: with a frame this size, would it be advisable to brace the middle of the frame to prevent any bowing albeit not often a customer will transport a frame 4 hours by car I suppose? Would I be better using a heavier duty material as a backing board? or was it purely due to me laying the picture flat for transport? Thanks in advance. Ps We booked the wedding photography gig so it was worth it.
Maybe the board was too tight in the frame. 2.5 MDF is rigid enough, but it does absorb moisture and will 'grow' if it gets damp enough. If the ends have nowhere to go it will bow in the middle.
I suspect Prospero is right. With a picture that size, the MDF would want to be 3or 4mm smaller than the frame to allow for changes in humidity.
You also mention that there was a gap showing between the mounts - I would always use a combination of ATG tape (for instant grab) and PVA glue for permanent bond to glue the mounts together. Again, if the mountboard is too tight in the frame it may bow.
Years ago I backed pictures with the good old grey "framers" board. One day I thought it would be a good idea to get a portable gas heater for my workshop. In one frame the back bowed out about 4 inches in the middle.
One day I thought it would be a good idea to get a portable gas heater for my workshop. 