Steve,stcstc wrote:ormand
what are the disadvantages of MDF, as backing. or otherwise
There are many disadvantages and Robo has pointed out some of them. Acidic as all hell, absorbs moisture like a sponge, can go mouldy, is quite heavy, is not easy to cut.
There are products that are lighter, easier to cut, have very little lignin/acid, some have no lignin/acid content, are not as absorbent and much less likely to grow mould and are still very inexpensive, yet there is an entire topic in a another part of the forum devoted to methods of cutting MDF.
IMO the best answer is "don't cut it, cut something that doesn't have the same disdavantages, but I know that will fall on deaf or stubborn ears.
There will also be the usual cries of "I've been using it for years and nothing bad has happened" and we all know that not all negative changes can be seen with the naked eye.
I know some people will propose that MDF is so much cheaper than foamboard, artcare foamboard or corflute, and that may have some validity in commercial framing, but certainly not in custom/bespoke framing. The very small extra cost can be passed on to the customer along with the extra benefits.
It beats me that some framers have moved with the times and bought machinery such as vee nailers, which cost so much more than a mitre box and a hand saw, to do the job faster and to a much higher standard, yet persist with using a product that has so many disadvantages. I just do not get it!