I have been messing about with Concrete Mountains and Hills since around 1988/89 when I first discovered the method as used by the guys in the Florida Railway Society. In particular I got to know Bob Kelly well, he of garden Texture Buildings fame. The secret that I have found over the years is to get a good thick mix onto the mountains, then it does not matter if any sheeting rots as you have a good thick layer on the mesh. Also important is to have as good a stable foundation of wood as you can, too much flexibility and the cement can crack. We had a large section of Mountain drop in to a Swiss Sea for just this reason. The rebuilt bit has cracked a bit but not fallen into the Sea yet! The other thing that we do is to mix in some external quality PVA, Wicks do big drums of the stuff for a reasonable price, this strengthens the mix but I think helps a bit with flexibility. Our mix of choice is:-
2 parts sharp sand
2 parts building sand
1 prat cement
a couple of mugs of PVA
1/4 cup of Wicks Black Cement Dye
a sprays worth of washing up liquid, don't use the wife's best fairy liquid, get a bottle of the cheep stuff for your own use
Water to taste.
Get this to a nice pliable mixture, the sort of stuff that you would use to lay bricks with. Not too sloppy and trowel on with a putty knife. You can add strata as you go, a large brush with water and a spray bottle also help. If you mix too much, you can water it down to get it to last but try to mix around a Wicks Builders Buckets worth at a time.
Finally to get a good start on your material and to repair cracks holes etc, we now use Wicks posting Cement. This can be sprinkled dry to wet sheets and will go off in an hour or so to give you a good hard base to work on. For repairs just dampen a sheet of material and sprinkle the post crete on in good doses, it does work and set very hard but is a bit expensive for the whole job of a full large mountain. You can colour this with a slop of the Wicks Black Concrete Dye.
For Brown colour use 'Sulphate of Iron' from a Garden Centre. This is used to feed Azelias etc and is good stuff giving you a nice brown effect. I put this on by spraying the mountain with water then applying dry from an old Flour Sifter. It will go green as it gets wet then a nice Brown later. Use with care and caution, the warning on the packet tells about staining paths. You have been warned.
Good luck with your montains, some of my other posts have mentioned my techiiques and have a few pictures of my efforts. Look at the Ruschbahn on here and on the net.
http://ftp.uktrainsim.com/viewtopic.php?f=115&t=94179 < Link To http://ftp.uktrainsim.com....php?f=115&t=94179
The first picture on this link shows the large mountains and the height involved, those mountains are some 14 feet above ground level at the back of he lake.
JonD