window frames

["Marc Anderson" <khaskoo@zzzzzzzzzzzzz>]

The first hurdle to overcome is going to be the outward thrust taken up by
the two outside vertical supports of the window, generated by the weight of
the arch pieces above. If you have a continuous horizontal header just above
the window opening, then it may be possible to drill out the centers of
these segments and install a full length rod of all-thread after assembly.

Tighten this down with metal plates and nuts at each end of the window
assembly and this will counter the thrust that would otherwise destroy the
freestanding piece. I would also suggest attaching metal support rods from a
high point of 8' onto the outer segment frame and running this diagonally
(45 degrees) back to the rear of the structure and into an anchor point in
the ground. I am assuming this stone frame will be rather fragile as a
freestanding item. I don't think you are going to achieve the elegance you
want by adding additional stone buttressing or concrete block filled with
rebar and concrete.. You may also consider running a continuos metal strap
around the outside perimeter to maintain stability. You would need an
acetylene torch to warm the strap as you go to get good compliance.

I would drill the strap and tapcon it to the stone as you go round.  Strap
might be 3/16" X 1-1/2".

One last suggestion that I find is useful in laying used stone is to slice
grooves into the segments that will be receiving mortar. I use a 12" diamond
blade to score pieces @ 1" strokes apart, 3/8" deep. This provides excellent
bonding surface that otherwise will work loose normally in a short time. The
freestanding form will be taking a wind load, so every little bit helps.

Good Luck,
Marc