The floor was definitely concrete. I spent a weekend lying on it working under my Morris 1000 !
Concrete! Luxury, sheer luxury!
As a smallish child, probably some time in the late 50s, my dad took me to the BRM place in Bourne, and the main workshop had an earth floor, and the windows were too dirty to see through, they didn't look as if they'd ever been cleaned. A friend of dad's knew some of the BRM management, and that Mr Stanley seemed like a really nice man...
I was there again around 1970, with David Jackson, fitting new Specialised Mouldings bodies to I think, P160s, and it was still hardened earth, black but hard almost like concrete, windows still filthy. Their cars looked well-made, but they didn't seem to be quite symmetrical, a top shell fitted to one new car had to be tweaked with slightly elongated fastenings to fit a second one parked alongside it. I went to a few race shops in those days, McLaren in Colnbrook were the best, and BRM definitely the worst. The Tyrrell woodshed looks quite sanitary in comparison.