Totally agree with not using the whole bag
I just use old 4Lt icecream containers and put a few cupfuls of the render in and then mix to the consistancy i need by slowly adding water (and oxide or paint if its the last layers) Because all of my snakes will be 8ft when adults i use 4+ layers. for smaller snakes you could do a few less, but why risk them crumbling under load, the render is cheap enough to add an extra layer for strength and wont add too much weight to a finished enclosure. i use a couple of thin layers first to get coverage then the layers get a little thicker but I dont do a lot of fine detail
Hey Jax,
if you want to build up a thick layer, there is ways you can do it without lots of thin layers.
I use a spatter coat before applying the first layer.
To do this, apply pva to the background, the once it's almost dry, mix cement + sand (tiler's sand) + water + pva (optional) to make a really runny watery mix, use a large paint brush to dip it into the mix, them flick the mix onto the background, keep the mixture well mixed, or the sand will sink to the bottom of the tub. The idea us to get blobs of sand stuck randomly over the surface, you don't aim to coat the entire surface. The small blobs adhere better to the background and dry leaving a rough surface with raised blobs all over it. Once It's dry, coat with acrylic render as usual (i use a sponge to spread it) the spatter coat means the first coat of render will be as thick as the spatter coat, plus 2-3mm on top of that.
If you want a really thick base, use river sand to do the spatter coat, your first layer of render would leave you with probably 6-8mm total coat thickness.
Doing the spatter coat is messy, but works well, particularly if coating large vertical, or upside down surfaces.
You might then just need to touch up any exposed edges before a final finishing coat.