Apply a layer of Vaseline/petroleum jelly to your face. Don't forget about your eyebrows/hairline unless you fancy ripping your hairs out ;)
Cut your plaster roll/modroc into strips of about 5cm in height and 2/3cm wide. Dip a strip into water and wring the excess off between your fingers and apply diagonally on the bridge of your nose. Repeat so that you have an 'X' on your schnozzle.
Cover the entire area of your face, paying attention to the edges as these are the weakest areas. Wait about 10 mins and repeat. Aim for about 4 layers to give the mask strength.
An hour after your final layer should give the mask enough time to stabilise (though it won't harden completely in this time, this is ok). Exercise your brow, nose and mouth muscles to get the mask moving then finally gently prise from your face with your fingers. Once fully dry, cut to shape/tidy up.
Apply a layer of air drying clay to the mask using a little water to act as adhesive/smooth out/limit any obvious cracks. This would be the time to emphasise any key areas you wish.
Depending on the thickness of clay used, drying time varies- my layer of around 2mm took a day and a half roughly.
Mix up some PVA and water (equal parts works) and 'paint' on some toilet paper to seal the mask and create a nice crinkled effect.
Flip over and glue (superglue/silicone glue/PVA whatever) on a wooden rod of about 10cm in length- I chose one rectangular in shape as the flat edge bonded easier. Wait to dry.
Brush on a PVA/water/toilet paper layer to the entire underside of the mask/rod to complete the foundation then paint :)