Ok, I have prime and blocked the car out 3 times or more and guide coated it, it looks strate. But I know after I paint it I will see small waves. How do I get them out? What is your trick? Or what am I doing wrong. I have painted about 10 cars, so this next one I would like to figure this part of the prep work out.
Thanks Pat

Guidecoat

dust a light spray of dark color on the primer, then use a long board sander in a cross pattern, the lows will remain dark and high spots will sand really fast.... when it all comes off even you know its FLAT.

What kind of long board do you use? Thank's for the reply.
Pat

it can be anything long enough to do the job that wont flex too much.

Eastwood (http://www.eastwoodco.com) has a good variety as examples, even big paint stir sticks wrapped in sandpaper can work well...

you want something that will flex to follow the body curves, but be stiff enough NOT to 'flow' with the waves in the surface. Big 12+" boards are good for hoods and such, where small blokcs are better on smaller flats. Many people use whatever they can find that fits body contours to make them as perfect as they can be. Pieces of pipe, scraps of wood cut to shape, etc....

Great topic on block sanders!!
http://www.chevelles.com/cgi-bin/forum/ultimatebb.cgi?ubb=get_topic;f=3;t=008196

What grit of paper are you using? Too fine of a cut will do NOTHING. Too course will leave you with problems.

The first go arounds, 180-220, DRY, is the ideal grit. It CUTS the surface level but doesnt leave behind too course of a scratch.
Once you feel that you have it prime it again then sand it with 400-500 grit wet.

I have to agree with sevt 180 and 220 dry are the only way to block primer surfacer for straightness. I usually use a long board or a paint stick. The longer the board or stick the straighter the panel. I even use a paint stick for the wet sanding 400 or 600. Keep doing with a guide coat and you wil eliminate the waves. Try using a dark color primer on your last priming this will also help show any imperfections. Blocking is the key to a straight car you know you blocked enough when you your fingers are as smooth as the car, just kidding, and happy sanding.

Kenny
Black 70

I wrapped a metal yard stick with sandpaper and a friend and I had at the big flat areas

Thanks for the info, It wil help alot.
Now to get to work. I will let you know what happens on this one.
Thanks
Pat

I'm having the same problem. When I use a guide coat, it pretty much comes off evenly, leaving me to believe that the panel is straight. But with my left hand over a paper towel, I can feel a hint of a wave (If I use my right hand or don't use a towel, it feels flat). This is driving me nuts. I can't tell if I really feel something or not or if I should trust the guide coat.

Saw in some other posts, folks suggest misting on some water or wax remover and using the reflection to identify waves. I guess you could look at the reflection of your overhead fluorescent tubes to see if they reflect straight or wavy. Anyone use this technique?

Originally posted by JohnC:
Saw in some other posts, folks suggest misting on some water or wax remover and using the reflection to identify waves. I guess you could look at the reflection of your overhead fluorescent tubes to see if they reflect straight or wavy. Anyone use this technique? Well, kind of. After I wetsand, I get the whole panel wet with water and look against a high contrast background (like dark night outside a lighted garage). This gives one a pretty good idea on how the bodywork is coming out.