Whilst Tony gets his coat, the black layer is recycled rubber crumb, bound together with a tight bonding resin. It is for drainage and sand retention. Helps to prevent bunker drains clogging with silt washed off the face of the bunker.
Were these black layers installed at Stoneham?
I believe so.
If this is the case, I am not impressed. I was in one bunker that the sand kept sliding down the face so I couldn't get a stance. In the end I just had to hit while sliding down the face and I left an exposed black face. Is there special sand that is meant to be used with these liners?
There isn't a 'specific' sand that should be used but the sand should be selected based on the use of the liner and the steepness of the faces and has found to be one of the limiting factors of these types of liners. Generally you can't go quite as steep with them as you may be able to do on an unlined or turf lined bunker or even some of the other liners on the market. Despite this so far though the rubber liners do seem to be preferred in the UK due to their other properties. The liner company will specify a maximum angle to build to but during construction this could easily be missed and exceeded if not careful. If this happens and then the maintenance isn't keen eyed enough to top-up/compact the faces then the problem you encountered can happen quite easily.
Wentworth installed the same liner on the West course and from experience of the previous bunkers (which didn't have a liner but were quite steep faced in places due to their depth) having issues with holding sand on some of the faces they asked for a specific sand mix from their supplier. They mixed some equestrian sand which compacts more easily into the 'standard' bunker mix (from that particular quarry/supplier) to ensure it held on the faces better. They were also careful with the angles of the faces during construction. You may remember though that during the first BMW tournament there following the renovation there were a few plugged lies in the faces of the bunkers as the sand was so fresh and hadn't had time to naturally weather and compact for long enough so it was still abit soft. This happened to Brendan Grace (I think it was him anyway...) who realised that he could dig his foot into the sand deep enough to uncover the liner and then complain to the referee that he was slipping on the liner and was granted a free drop..... not ideal. I don't think it has been an issue at all since though as the sand naturally compacts over time on the faces and as far as I am aware they are very happy with the sand/liner combination.
Personally I'm still not completely convinced by any of the liners I've seen. They all seem to have a downside and it's still quite hard to tell which of them will really last the distance and pass the test of time. Saying that I wouldn't be adverse to installing most of them given different situations and what the client is looking to achieve. I think the biggest benefit is where the site is stony and the liner prevents rocks/stones migrating up into the sand. Chalk downland courses for instance may be able to save alot of time, effort and money spent on replacing sand and cleaning out material which has come up through the sand over time.