Block Sanding 101 Part 2: Saving The Line and High Spot/Low Spot Identificaition

 Any bodyman will tell you that destroying a bodyline is one way to get on the shit list.  Even when you have to move fast and get cars moving, it's best to take the time and tape off and maintain the body line.  It may take a minute or two but as you practice, the faster and more creative you will get.

Now, after taping off the line. Begin sanding in an "X" pattern.  Up & down sanding is a big no-no due to the fact that the grit of the sand paper is parallel and primer build up will occur.  Why is it a big deal?  Simple, Primer build up will compress into tiny or large clumps and this in turn will scratch deep lines into your primed surface in turn requiring yourself to sand deeper to rid of the line.  the "X" pattern will reduce the chance of clumps greatly and increase productivity.  Always check sandpaper periodically for clumps and wipe off with a scuff pad if necessary.

While sanding with the appropriate block/stick/etc., be wary of dark spots and burns.  Follow these guidelines:

a)  High Spot:  This occurs when the surface/substrate is to high as oppose to the surrounding areas.  When sanding, filler and/or metal will reveal it self.  Body work will need to be performed to even the surface.  Always ask shop foreman/boss for advice if needed.
b) Low Spot:  This is the appearance of a dark spot, (darker if using guide coat), in the location where sanding.  When a large area of filler is applied, this is not that uncommon.  Continue sanding a little longer and if there is no improvement, stop sanding!  This is an immediate indicator that a low spot  is present and body work is to be performed.  Filler will need to be added.
c)  Pin holes/Solvent Pop:  This can happen if the primer isn't mixed correctly or to heavy of coats are used.  This can also happen if body filler was still wet or already had pin holes before primer application.  If holes are minor, spot putty can be used.  if holes are deep, body filler is STRONGLY ENCOURAGED AND A LIGHT COAT OF PRIMER WILL ALSO NEED TO BE APPLIED.
d)Trash:  Most trash that lands on primer can be flattened or sanded away.  If it doesn't go away, sand down to substrate or filler and reapply primer.
e)  Bare metal:  Metal conditioner or etching primer is  required.  Some urethane/epoxy primers can be used of small spots.

Well, that's it for now.  Till next  time.

A low spot was identified near the body line.  Body filler needs to be applied and re-primed

Each Straight tape outlines either the top or bottom of a body line.  Tape is also used to protect surrounding areas

         

To be continued.