Finish plaster, what exactly is it?
'Finish' as its known in the trade is the top and final coating for a wall or ceiling, the one you apply your paint or wallpaper to. Usually pink in colour it should be finished to a high standard without bumps, ripples, scratches or otherwise unsightly defects (within reason, its not supposed to be a nasa laboratory)
The main finish plasters in use today consist of gypsum. A rock, found in the ground.
Thats it, just rock, maybe a few additives to slightly change its behaviour as its setting to suit different backgrounds but essentially its the same stuff.
So, you take your gypsum, you crush it and you heat it.
The heating process removes any moisture in the rock so that the end product is a pinkish, fine powder, the stuff you find in the bag.
There is a chemical formula and process formula but no plasterer on gods earth has ever had to refer to it while skimming a wall so we'll leave that alone..
what happens is this...
You take your fine powder, and add it to water. This makes it spreadable.
It also starts it along its process to revert back to its origional state..rock.
You spread it on your wall and it starts to set quite quickly.
It sets because the water is a) is being sucked into the substrate, b) evaporating into the room and c) causing a chemical reaction with the gypsum so it reverses the manufacturing process and gives off heat.
Not a lot but if you feel the bottom of a bucket of mixed plaster after an hour you'll feel it.
The end result is what was once a lump of rock in the ground is now a flat smooth rock about 3mm thick which is bonded to your surface.
so thats it.
plaster is rock. Gypsum to be precise.
