Get ready to experiment!
I tried painting some spare floor panels in order to get the drips. I had some success but if you get the formula just a little wrong you end with a mess that requires a lot of sanding, more primering and a possible loss of detail. So I decided to create the drips by hand and where I wanted them. See the Virginia Mustang Blog for their paint results.
I started with a product Jeff recommended for wheel well and other sealer use, called Spectrum. Check the library as Jeff has an article on that use.
It's sold by Second Skin Audio for use as a sound deadener. The Spectrum product is sold as a spray on product called either "Spray on Deadener".
"Sludge" is the same thing as the "Spray on Deadener", but includes a bottle of a thickener. You want Sludge.
The thickener just raises the viscosity from a light pancake batter to cold butter or anywhere in between by adding more or less of the thickener. The thickener does not reduce dry time so it is not a catalyst. It's more like adding flour to a recipe.
Check pictures of SJ car bottoms (like Richard's) to get a sense of the pattern of drips. Print out the pics of sections you want to emulate.
The factory drips are a result of the body being moved over a row of paint jets, pointed up, as the body moves over them. The application is heavy enough to cause drips. The body immediately moves over a bank of heating elements. I'll leave the type of heating elements out of this discussion.
The heating of the still dripping paint caused some small drips to instantly harden. Some drips were larger and stayed intact that way. Others exploded due to "solvent popping" and looked like a post eruption volcano. Some exploded so much they ended up looking like moon craters with just a ring left over.
Basically there are three drip types. Small dot drips, large drips and exploding drips.
A fourth drip is not really a drip but a crater.
To prepare, experiment with the spectrum and a few drops of thickener. Use either a hypodermic without the needle or a pet medicine hypo. The later is used to feet cats and dogs specific amounts of medicine and has hole on the end well suited to this task.
I use one hypo for adding thickener and another to dispense the sludge.
Using a rotisserie, flip the car upside down.
Small drips are just that. Experiment with viscosity in a small container and just lightly apply to a rib with the hypo. Since this stuff is water soluble you can quickly remove it. I used a spare floor section for the experimentation phase.
Larger drips are usually just more thickener and more product.
Exploding drips require a timer. Make a large drip, let it dry some amount of time, poke the middle and let it sit. It should look "exploded".
The craters are done using a circular item like a ball point pen middle section (where they are screwed together) or a hole punch. Dip the open end into the sludge and apply to the floor. This might either be straight down or using a rocking motion.
Some drips make take more than one application.
After you have enough drips I take the base of each drip apply a little 2k primer to where the drip attaches to the floor so as to smooth out the transition.
Finally I apply as many coats of 2k primer to the floor to even it all out.
This requires a lot of experimentation to get the results you find satisfactory. If don't have a lot of patience this may not be for you.
As a final note, sludge can be mixed and placed into plastic baker's bags for the rear trunk areas that used to have the tar-type sealers. You can use tools on sludge to move it around or to create patterns like stacked dimes.
Included are pics of various experiments and final application (yellow glove).
