Ash, it's not "solvents" as such, after all water is a solvent, but certain products in particular. Hence why I said check the ingredients, the ones I mentioned are a no-no on bitumen backed tiles.
Drying the carpet off and then bonneting with any decent product will no doubt make your pads look a bit dirty.... whether it would make the carpet look any different is another matter. in the past it has worked for me, but also has not... you don't know unless you give it a go! I always bonnet carpet tiles after HWE, and make sure the price accounts for it because it does add a considerable amount of time on to the job.
Your dilution of 1:20 is strong enough! Did you apply it hot? Your agitation sounds very good - I find a stiffer polyprop brush a lot better on carpet tiles though, for lifting the pile if nothing else (although if it's too flattened like your job seems, you can do nothing for it)
The oxidiser may well have helped, it's perfectly suited to polyprop of any style/colour
See if you can borrow an RX-20 off someone local, you might find it gets a bit better job done than the wand on some of these jobs. I presume you could just go back and haveanother crack at this whenever you want? Next time, try powerburst with an oxidiser mixed in to it, same procedure as before and if you can borrow an RX put that over it.
As Simon says, don't beat yourself up. When faced with carpet tiles as knackered as those ones look you will never make them look anything like what we as carpet cleaners would call nice.. .you can just hope to get the biggest before/after difference possible, which is quite often the solution to a client's problem in the commercial sector.
Just a case of trial and error and keep adjusting things until you find a way that works for you
