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Thanks 'Gloop' is just a rough mix of PVA, sand, and paint (acrylic or emulsion) made into a paste.If you want a 'stiffer' mix, add more sand; if you want a runnier consistency to work with, add more paint and or PVA (the paint:PVA proportion is roughly 50:50 - the amount of aggregate is the main variable to consistency).You can store it forever in an airtight jar or tub. It costs pennies / cents to make up.You can use any old water based paint you need to get rid of or aren't otherwise aren’t going to use.Add railway grit or similar, or use 'sharp sand' if you want added textures - with small rocky bits in your basing or terrain. You can embed larger pieces of rock while the mix is wet. They will stick fast in the ground mix once dry.Paint it on with an old brush. In small quantities (on a miniature's base) it sets hard within a couple of hours. The PVA plasticises the end product, so it's very very durable.Easy to overpaint whatever colour you like, although if you're careful with your choice of paint you can actually make it up in the right base colour...And yes, while it's wet you can sprinkle sand on the surface if you prefer a sandier finish...
Depending on how much trouble you want to go to, you could look at some other texture materials than sand.Crushed vermiculite, for example, has a much lower density than silica sand, so it stays in suspension longer — i.e. you don't have to stir the paint every five minutes. Graded sawdust is another option, though because it is absorbent it will retard the curing time of the paint to an extent.
The celing paint is basically paint + PVA