Around mid-day on Saturday 19th July 1958 ex LBSCR C2X number 32450 passes through Redhill station on the through roads with short freight working including what appears to be loaded limestone hoppers from the nearby quarry although it could be sand from Holmethorpe but they appear too highly loaded (and therefore overloaded), for this.
The Redhill sand was very fine and used for glass making and some went to Warrington in the 1970/80s. I have heard that if it was covered it became explosive which is why the hoppers were open-top. The need for 35mph wasn't only because the train was unfitted, but the ensuing dust storm was considerable if we exceeded that speed. The following trains never had adhesion problems. Rugby men would work it from Willesden/Brent taking over from the southern men with their class 33 or 73.

This would explain why the wagons in this photo are unsheeted even if they are carrying sand, but it doesn't address the issue of the weight of it in such a wagon.