Most times I post a model with a cast texture applied I'm asked how I did it.
So to save time in the future I thought I'd write a short(ish) tutorial.
Stage One - Light Texture
Firstly you need a model. :D
Mask off any areas that you don't want to be surfaced.
I use Maskol as Mr Surfacer doesn't stick to it too easily.
You will need to remove and reapply the mask between the different stages, to prevent the sponge and surfacer from building up too much over the masked parts.
(I know, I know, this was photoshopped in after the fact :P )
These are the main ingredients. Mr Surfacer 1200, and 500, plus one sponge.
It is a fairly simple technique. load up the sponge "tip" with surfacer and repeatedly dab it against the models surface.
Only do a small area at a time If you try to do too large an area the coat will dry and wont react the right way.
Split the model into quarters (front/back left/right that sort of thing)
First the surfacer will develop small humps, then it will start to string a little.
Don't worry this will melt back into the wet surfacer.
The main point of this is to make the surface coat dry out and start to grip the sponge.
Small parts of sponge will tear from the main body and stick to the surface, this will create the pits that give it that open cast look, and also the raised areas that will be applied in a later stage.
Leave it to dry overnight. Important! It might look dry on the surface, but if you try to sand it too soon it will just tear and clump up.
Better to leave it a little longer than do it too soon and ruin it.
Once its dry.
Cut the Layer back so it is very thin, otherwise it will overpower the later stages.
Then sand first with a mid grade sandpaper (I use wet and dry 280 grade paper)
Then move on to a fine grade (400), the point of this is to remove the small pieces of sponge just leaving behind their impressions.
Then remove the mask.
I normally stop at this stage for things like arms and legs as they don't really need the heavy texture applied to the body.
Stage Two - Medium Texture
re-apply your mask.
This next stage is to add some slightly heavier pits to specific areas.
The goal is not to re coat the model at this stage but to either emphasise earlier pits or re-apply to areas sanded clean.
Using the sponge from the previous stage causes larger clumps to gather on the surface, due to the sponge already being coated in surfacer.
As with stage one sand back and remove your mask.
Stage Three - Heavy Texture
This stage will add the "scabs" seen on the surface of WWII era tanks particularly Shermans and other sandcast Allied tanks.
I use a thickened bottle of Mr Surfacer 500 for this.
You can either use an old bottle or thicken it with acrylic resin, talc, or calcium carbonate.
Again mask off areas you want to keep..
The thicker surfacer will dry faster and differently to the neat stuff, leaving behind large clumps due to it drying quickly and pulling more sponge off as you go.
One final sand and its finished :D
Obviously you can alter this to taste, stopping at whatever stage you like.
Unfortunately the camera doesn't pick up on all the subtle pits and marks until its painted, and the effect will always look better in real life than in pictures.