Very basic question I have a round base for my figure (1/16th figure and horse) I would like to cover the top of the base with either dirt or grass to give the model some life. How do I do that on a plastic base. Do I just spread white glue/water mixture then sprinkle dirt? Any help appreciated.

You have hit the nail on the head. A thinned mixture of white glue and water is the way to go. Or if you want to add a lttle texture to your base, try a layer of plaster to get that rough ground texture and then you can add dirt to it. It will stick in the plaster very well.

You might want to consider replacing the plastic base with a wooden one, even and inexpensive round plaque from Michael's or AC Moore, with a stain, will look better than plastic. The wood will have move bite for you groundwork, as well, bit it "dirt" (I prefer a variety of Woodland scenic products) or plaster/Celluclay as ground to be covered with "dirt".

Try some Celluclay. It is basically just premixed paper mache' Add some white glue and water and whip it on your base. I swear by it.

I've never used plastic as a base and when I consider it one thing comes to mind.
Will white glue stick and stay on plastic?? I'd make some attempt at roughening up the suface to give the glue something to 'bite' Use a piece of sandpaper to give just a bit of texture to the area you are covering. Or a rotary tool would work too. Not to much just enough to give a roughness to it.

Take some white glue and add water to it. This should be a mixture at about 50/50. Add dry sand to it. This should be the finest sand you could get your hands on....white sand they use in birdcages, or yellow desert sand like they use in playgrounds.

Add as much sand to the mixture until it's almost dry. Then add Tamiya acrylics to reach the desired colour. After colouring it, you can spread it out on your base. Wait until it has completely dried (2 days or so) before you do anything else with it (making foot / track prints etc. should be done BEFORE it's completely dry offcourse).

After it has dried it is as hard as rock and you could weather it, put grass on it etc.

Hope this helps.

Keenan make's a good point here, especially if your using a plastic base. You want to use the CELLUCLAY or SCULPTAMOLD. This will permanently bond to the plastic and act as your ground-base. You can paint and weather the celly or sculpta with earthtone colors and then apply some fine ballast from WOODLAND SCENICS as your sand. Use SCENIC CEMENT for your adhesive. Without the celluclay or sculptamold as a ground-base your ground work will eventually loosen and flake off over time. I've seen some pretty nice vignette base's made from common plastic peanut butter jar lid's, instant coffee lid's, etc. etc. They work well with a bit of imagination & paint. ............The sculptamold just needs to be mixed by itself and applied. You can even add your earthtone paint while your mixing it.

- ralph

You might wanna be careful when using this.......... It warped my base and ruined the many hours of work! I find that plaster of paris would be a better medium for laying on your groundwork.

I keep hanging to the harmless white glue.... With a bit of care it won't come loose after all.

2c only

Celluclay works fine for ground work on plastic or wood.....it wasn't the Celluclay that warped the plaque...it was putting something with water in it on bare wood......would have happened no matter what you used.
You will want to roughen up the surface a bit as has been mentioned though...I use an X-acto knife and make a cross hatching of fairly deep cuts to give it something to grab on to.

For a cheap but convincing base, try a small picture frame made from wood. The cheapest you can find. They come in oval shapes as well. IKEA have sets with 3 of these for about $2.
What I do is stick a layer of polystyrene foam (the bottom of those disposable meat trays) on top of the glass to fill up the area level to the frame. Then build your ground up with small cutting of the same meat tray. Brush over with white glue and add your sand, small stones and basically and small dirt pieces you find available... even cat litter (unused!). then brush over with white glue again. Use some bristles of an old paint brush for long gras is places or a little static grass around stones etc. etc. etc. lastly fit your figures and make sure they will not be floating when fixing afterwards. Take away figures for painting.
Let dry for at least 24 hours. I would then spray everything black. Picture frame as well. Then tape off the sides and even a little of the the frame front for a nice effect , then paint the stones, grass etc. When finished lift off the tape and replace figures. Hopefully this helps a little!