No need for a lot (if any) pressure. Let the clay and lubricant do the work. You're just trying to remove the contaminants from the paint.

Just enough pressure to keep the bar on the surface. And knead the clay often. I've done many black cars. Never a problem.

 

^^^^This. Also never use it dry, make sure the area you are rubbing is completely wet (thats what she said) otherwise the clay will stick and it can be a pain to remove completely. You dont have to rub hard, just lightly over the surface and you will actually hear/feel the clay removing rail dust or whatever else is on your paint. You will know you are done when the clay glides extremely easy over the paint. After you claybar, be sure to put a good coat of wax on the paint as the clay will remove all wax.

 

SM Arnold Speedy Surface Prep Towel = Use this instead of clay! Works great, easy to use!
Speedy removal of bonded surface contaminants!

• <h2>Leaves surface as smooth as glass.</h2>
• <h2>Easy to use with less effort - saves time.</h2>
• <h2>Long lasting - use on up to 100 cars - saves money!</h2>

Web site/product info: http://www.smarnoldinc.com/VIDEOS.html
http://www.autodetailingsolutions.ne...l-ssp-589.html

You can buy this locally at a automotive paint store also.