The 'secret ingredient' that I use is the Vallejo Textures range. I picked up a couple of tubs of this stuff from Boyes in Scarborough a few months ago and I've used it ever since. The tubs are pretty big and only cost £6.25 each so they are much better value than the texture paints from GW.
This stuff is quite thick and is almost more like a putty than a paint so I tend to spread it on quite thickly and then just leave it for a couple of days to thoroughly dry.
Next with this one I added a resin base from the GW 40k basing set and then blended it in a bit. I also then started to add some gravel from the same set.
From this stage I'll now let it dry for at least 2 days, I have no idea if it actually takes this long but I do spread the stuff on very think so I like to make sure that it's had plenty of time.
Here are a few flying bases for my Necrons that Im still working on as well.
UPDATE : I checked the main base featured in this after 2 days and it was still slightly squidgy, it definitely could be painted at this stage but some of the gravel that I add was still a bit loose so I'll be leaving for another couple of days at least. The smaller bases that I didnt put so much of the paint on were all fairly dry and firm.