Bendable materials for an arched top cornice board

arch-top-shaped-bottom0001.jpgimgp1809.jpgimgp1810.jpgWhen a shaped dust cover is required for a cornice board there are several alternatives.  We could use bendable plywood (wiggle board) which is about 1/4″ thick and not suitable for today’s application.  Another choice might be FirmaFlex, a bendable fibre board which can be ordered in six foot lengths and edge joined for longer pieces.  If you are building your own cornice and cost of materials is not a big issue this could be a good choice but for the average workroom it would be a little too pricy.  Next you could buy dimensional lumber such as a 1″ x 4″ board and cut hundreds of slots (kerfs) across the width of the board until it can be bent to the shape you want.  Once again for the average workroom time is money so the time involved would rule this out.  My choice of material for today is Homasote, a recycled newspaper material.   They put the old newspapers in a huge vat, add water or other liquids and stir until the mixture becomes a mess of sludge.   Then the sludge has most of the liquid removed, it is poured onto a flat surface and highly compressed to get the remaining liquids out.  The finished product is cut into 4′ x 8′ sheets that are 1/2″ thick and similar to plywood although the cost is about twice as much.  Homasote is easy to cut with a circular saw but very, very dusty so it is best to use a dust mask while cutting.  For our arched top cornice we need 3 1/2″ returns so we cut strips of homasote 3″ wide.  Since the cornice board will have a finished width of 111″ and the homasote comes in 96″ long sheets we will need to cut two strips and join them end to end with aluminum or steel edge joiners (sometimes called ‘dog ears’ because of their shape).  Once the ends are joined we cut the strip about six inches longer than needed, stand it up on one edge, and lay the cutout plywood on top of the other edge.  Then we start the process of stapling and bending, stapling and bending with the staples about three inches apart all along the top edge of the cornice.  With a little extra beyond each end we can now cut down through the homasote at an angle to match where the curved top meets the straight top of the returns.  You can either staple through the top board (homasote) into the top of the return board or staple through the top of the return board into the edge of the top board.  The first way seems to be the most simple.

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