He was non-sleaze (the man in the white suit), this one if I have this right (no reason I should on past experience) aired a concern that grouting Silbury would use watery agents to facilitate pumping the goo to where it was needed and when draining down through the layers that agent and even air I think could damage material at the core that is sensitive and v.important (again if I understand it) as it is a natural landscape from c3000 BC (perhaps the only one we have) that is perfectly preserved beneath the mound. (Tangent coming up) so. as I think Nigel suggested, we need to dig into Marlborough Mound as a matter of urgency to find out if it is Neolithic or Norman to see if a floor is preserved under that too.
I shall shut up now as I don't know what I am on about...
VBB