Sweetwater forums' fabulous thread about Terrain-Mats motivated me to try this method myself. Conducting a test run, I built a simple photography-mat without fancy structures.
Unique about these mats is, that they are built really quick. This one took me just about 1,5 hours, including the time for searching the materials (which I fortunately all had at hand...).
Base material is stretched canvas on a 70x70cm frame. The one I used was already painted, but just because it was a leftover of a painting session... Unpainted/unprimed canvas would have been better.
To give the mat a realistic strucure, I mixed brown acrylic paint, sand and coffeepowder. Coffeepowder was a tip from the internet. Well it works, but the mat smells like a Starbucks...
Acrilic sealant was added to the colour-paste. For the whole mat I needed less than a half tube.
The paste was spread over the canvas. It works as well if you directly mix the paste on the mat.
The paste was smoothed, using a palette-knife/ spoon/ fingers/ whatever you have at hand...
Next step already is the greening. I used several flocks and static grasses to produce an irregluar basis. The trick is to spread the flocking material over the mat at random and just press them into the wet acrilic paste. Since the grass will stick to the paste you neither need glue, nor need to wait for the surface to dry.
This "basecoat" was further worked on with some MiniNatur tufts, some Atenociti foliage and brown spray paint. At the end I highlighted some parts with Galeforce 9: Summer Flock.
Done in less than two hous. Last thing that's needed is some patience to let the Acrylics dry. Afterwards you can cut the mat off the frame to get a terrain that is more or less resilient, can be rolled up, needs little place and still looks as great as a regular terrain board.
I abandoned this option since I just wanted a surface to take some pictures on.
Hope you liked it. Credits have to be given to the guys over at Sweetwater. Having in mind how easy this was, the result is truly stunning.