The Rough Cast-Armour Effect is suitable for military vehicles as it gives the effect of armoured steel.
The model or part of the model will need to be painted before the texturing process can be carried out. First, rub the area that you want to texture with a Scotchbrite pad. Then take an old brush, cut the bristles down to at least half the size, and load the brush with Humbrol Liquid Poly. Dab the area you wish to texture with the end of the brush.
Please note that this process softens the paint and can make it appear slightly lighter.
Also, make sure none of the bristles come out of the brush whilst doing this, if they do then remove them straight away or they will embed into the plastic. If the plastic starts to string then don't worry, just coat the area with a wash of liquid poly and this will remove the 'stringy' effect.