> I can't see how, or even any reason why the white wash would be
> done at any other time but in situ.
> So can anyone think why or how the interior of the chamber
> could have been white washed before construction. By "before
> construction" I mean at any time before the last block was
> installed in each chamber. Thus preventing further access.
The "how" isn't really that tough. Recall that, according to Petrie's description, the uber-complex formed by the King's Chamber and Relieving Chamber ("RC") assembly is really a unitary complex that essentially "floats" within the east and west "Great Walls" the latter forming a sort of vault around that complex. In other words, the east and west walls that you see when you're in one of the RCs is not at all attached to the RC but rather (according to Petrie) is separated from the RC by something like 3+ inches. As such, it's quite possible that a given RC level might have been completed before the east and west walls were constructed upward to enclose it afterward. This sequence would allow adequate human access through either the east or west openings in the RC for someone to apply plaster before the east and west walls were then completed.
Getting back to the "why", I would say it seems there was an attempt to give the blocks a sort of hermetic seal. It obviously wasn't cosmetic but rather functional. And I doubt it was to make it a perfect seal since there were a good 3" between each RC and the east and west walls, but perhaps the builders needed to control exactly how much of a "leak" there was from RC to RC.