I embarrassingly stand corrected over this gap between edge of floor and base of wall business.
Earlier this evening, I remembered (prompted by Jon) that Piazzi Smyth measured the distances between the floor joints along the south, north and east sides of the King’s Chamber’s floor.*
South side east wall to west wall total distance = 412.6”
North side east wall to west wall total distance = 412.5”
Joints along east side total 206.3” to 206.4”
Petrie gives the base length of the Chamber as N. 412.78” and S. as 412.53”
The base width of the Chamber as E. 206.43” and W. as 412.53”
I now think that I can safely say that the Chamber’s flooring fitted tight to the surrounding walls – and was thus watertight (except for the doorway, of course).
Robin (MJT) with sincere apologies for wasting folks’ time.
*Life and Work at the Great Pyramid. Vol.2. Pages 103-104. 1867.