Those who have seen the AK Interactive Enamel Weathering Techniques DVD would have seen how mud splashes were made with the AK Interactive Earth Effects and using an airbrush to "splash" the mud onto models.

Well, for modellers like me who lack an airbrush, I have come up with my method of the technique (or maybe someone uses this method as well, I don't claim being the inventor of this method): Since I own a DSLR, I own an air blower normally used to blow dust from lenses or the camera sensor. This works as a perfect alternative for an airbrush! So the basic process is to dip an old brush into the mud mixture and use the blower to splash the mix from the brush onto the model.

Here's an example of what I use. Note that these come on several sizes and the biggest ones will provide the greatest air pressure.

One thing to note: repetitively squeezing the air blower works as a great stress relief too!