Veeduber wrote:
...
Plaster Lath is strips of CLEAR Redwood (meaning it's not supposed to
have a knots) ROUGH SAWN 1/4" thick by 1-1/4" wide in lengths of six
AND eight feet.
... find the 20 (twenty!) best pieces
in 6 (SIX) foot lengths. Grain is going to run all over the place but
that wasn't what this test was about. Then go find a sheet of
Doorskin plywood OR a sheet of 1/8" Luan plywood ....
Finally, go find a TRUCK TIRE shop. You want a USED tube
...cut it into as many 3/4" wide stripes, as long as you can make
them.

....
Make 4 (Four) booms, 6 feet long by 1-1/4" square. Use them to make
2 (Two) Box-type beams, 6" deep by 1-1/2" wide by 72" long. (use some
scrap lumber to make some intercostals 3-1/2" long by 1-1/4" wide.)....


-R.S.Hoover


I built something like this several years ago as a "strong beam";
something to sit on the sidewalls of the house in the attic and secure
the ceiling beams of the living room that had been enlarged by knocking
down a ground floor wall I believe. I was unhappy with a crack in the
ceiling plaster, and decided to put a stop to it with a strong beam.
It was made from two 18 ft spruce two by fours (not aircraft quality,
needless to say) and enough ply to make a 4 X 12 box beam. I drilled
though it over each rafter and placed a threaded rod bolted to a saddle
cross bolted to each rafter.
Was that beam ever stiff! I couldn't detect the deflection when I stood
on the middle (not that I was trying very hard either)

Brian W
p.s. I liked the rubber spiral clamp idea!