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With Chris Curwen & Expert Auto Painter - Dave Gage (Car Cosmetics)

July 31st, 2007 - Issue 14

In this issue:

• We continue on the topic of Bodywork Repair and talk about making sure all surfaces are flat and cleaning sanded surfaces before undercoat applications.

So let us continue on the topic of bodywork repair and firstly cover: Getting it Flat.

Since you have the panels straight and aligned properly, do you feel ready to begin painting?

That will depend on a number of factors:

* Do you see any other minor dents or blemishes present on any of the panels?
* Do the doors have vertical lines in them? (This is all the more important if another door came into contact with your door panel)
* Finally, is the overall texture of the vehicle a little rough?

If you answered yes to any of these questions, then this means that you have some more work ahead of you before you can start spraying paint.

Take out that sandpaper again and a sanding block and carry on working until all those imperfections are taken care of.

Sanding using a Long Board

Any vehicle with a long wheel base will bridge the high and low spots of a road surface; resulting in a more comfortable and smoother ride for the occupants.

The same philosophy applies when you opt to use a long sanding board above a short sanding block.

The key to achieving the straightest and flattest possible surface upon which to apply paint is to use a long sanding board or block with progressively finer sandpaper.

After you sand using relatively coarse 80- or 100-grit sandpaper by hand, then use an air file sanding machine with 200- to 320-grit sandpaper.

It's important to remember here that when sanding a panel that curves in one direction from top to bottom say but is straight from front to back, sanding is mostly performed in the straight direction.

By using a long board across the crown you would tend to flatten the curve, this isn't the desirable result you want to achieve.

Simply move the file up and down on the panel, but still in the general direction that the panel is running.

In addition, by using a long board/air file will also give you a better indication of high and low spots than a smaller sanding block.

As we visualized earlier, the longer board will span the high spots and bring them down to the same level as the low spots, where the smaller sanding block will simply ride over the wavy panel.

Although sanding blocks are available commercially in various shapes and sizes, you will often need to improvise to find a block suitable for the particular area that you are sanding.

Thin layers of glazing filler can be used to fill any slightly low spots or to fill pinholes in the body filler.

The glazing filler can be sanded with 400-grit or finer sandpaper to smooth the panel to your satisfaction.

To finish, a normal-sized sanding block can then be used to touch up the edges of the filled area.

Try to understand, that you can never sand too much. What may look great in raw body filler will quickly show any pinholes or other blemishes when you apply a coat of primer.

Sanding Body Filler Repairs

OK...let's keep the ball rolling here. No matter what type of surface you intend to paint over, whether it be body filler or an existing paint finish, some sanding is going to be needed.

Remember that any remaining blemishes or imperfections on the surface will be magnified after you add coats of paint.

The top layers of body filler are sanded primarily using 80- to 150-grit sandpaper. This will flatten out the rough spots and get the surface on its way to being smooth and even. Next use 240-grit sandpaper to make the finish even smoother and flatter.

Due to the irregular pressure of your hand, you must always sand using either a sanding board or block. Using your hand alone will tend to make the panel wavy as more pressure will be applied by your fingers and less in the area in between them.

However, every few minutes stop and feel the surface with your hand to get an idea of how much progress you are making. If you can feel any irregularities, you can be sure they will be seen more prominently once you paint over them so keep on sanding.

Don't stop until the entire area is faultlessly smooth and flat; it needs to blend perfectly with the surrounding surfaces.

You can see body filler repairs being professionally sanded down in 'How to Paint a Car - The System' - Part 1.

For the best results, operate the sanding board and block in all directions rather than just moving them back and forth. Even rotate the board or block to make the operation easier.

This sanding technique, as confirmed by Pro Auto Repairer Mike Gage in 'How to Paint a Car - The System' Part 1, simply ensures that the surface is sanded smooth and free of grooves, valleys or patterns.

After you have flattened the area using 240-grit sandpaper to remove all of the high spots and other surface imperfections; use 320-grit sandpaper to remove any left over sanding scratches and minor imperfections.

So far you've been shaping the body filler to get it flat and to blend in with the other surface areas around it. By moving onto finer sandpaper grades, you are now striving to get the texture as smooth as possible.

You can get most of the finish sanding done quickly and uniformly using a DA sander. You should practice first however using an old spare panel if you aren't familiar using a small DA sander.

Even though DA sanders may not appear to be moving that fast, they will still remove large amounts of filler material very quickly.

Once you are satisfied with your filler repair, use 320-grit sandpaper to develop a well defined visual perimeter around the entire repair area.

The rings around the repair area in some circumstances may expose a band of bare metal approximately one inch wide maybe, then bands of roughly equal width exposing the primer, sealer and paint.

Your objective here is to develop a smooth wall between the top surface of the body filler area and the top surface of existing good paint.

This will allow fresh applications of undercoat material and the final coats of color in thickness that is equal to the rest of the paint finish.

This will give you the best blend, color tint and texture identical to encircling paint finishes. This process is referred to as 'feathering in'.

Finally this week, let us cover:

Cleaning Sanded Surfaces Prior to Undercoat Application

After you've completed sanding or scuffing of the surface being repaired, make sure you take your time to clean it thoroughly to remove all surface debris.

Most painters use an air hose to blow away the layers of dust left behind from sanding. Then they use wax and grease remover to thoroughly clean the surface down with. Again, it is very important that you only use a wax and grease remover that is deemed part of the paint system you will be using.

Simply dampen a clean cloth with wax and grease remover and use it to thoroughly wipe off all body surfaces in the area to be painted. To enhance the cleaning ability of wax and grease remover, follow the damp cleaning cloth with a clean, dry other cloth.

To find out how wax and grease remover displaces all surface contaminants, please refer to the 'How to Paint a Car - The Written Guide'.

To ensure you are left with a super clean and dry surface, you may wish to go over the finish with an aerosol glass cleaner after using wax and grease remover. This will help to disperse and evaporate moisture as well as to pick up missed spots of wax or dirt residue.

Finally, wipe the vehicle down again in the paint booth just before you start spraying on paint products using a tack cloth.

These specially made cloths are designed to pick up and retain very small specks of lint, dust and other particles. Simply take the tack cloth out of the package, open it fully and let it air out before use.

You will need to go over every square inch of body surface that will be exposed to paint product application to be certain that all traces of lint are removed.

Don't forget to refer to product instructions to determine how many times you can use them effectively. Once tack cloths are saturated with lint, debris and residue, they will no longer pick up new debris.


That's all we have for you this week. Thank you very much for reading. We both hope this issue has been of valued interest to you.

Next week we'll cover Applying Primer.

Happy Painting!

Chris Curwen & Dave Gage
www.LearnAutoPainting.com