vanster

My front bumper has not had a good life and now it's on my short list of things to do. It needs not only painting, the cover has enough waves in it that will contest a roller coaster ride.
I have an airless gun and lots of body shop tools (scary stuff).
My thinking is to take the bumper off and put it on horses, sand, fill, color coat and clear coat.
Or sucumbe to taking it to a body shop. How many have done this themselves? Any secrets or tips? I looked on past post but could not find one specific to this.
Do I have to replace bumper shocks? Seem to be a topic from time to time.

Vanster
'80 5sp

Mrmerlin

look through here for front bumper pictures if your lights dont look like these then you need new front bumper shocks.
https://rennlist.com/forums/928-foru...h-project.html

For the first part of your question, if you plan on repainting the front bumper, you should have the old coatings removed first,
do this with walnut media blasting.

simply sanding down and filling the cracks will just about guarantee that they will come out in the new paint in a few weeks of the cover being exposed to the sun BTDT

vanster

Merlin
Good tip regarding media blasting. The extended shocks in the picture are the newer replacements?

van

Mrmerlin

yes the new used parts are the longer ones its easy to tell before taking off the front PU cover if the bumper shocks are damaged,
or post a picture and we can see it

James Bailey

getting rid of waves is somewhat difficult and trying to sand it when not supported by the car makes it even harder.....it just keeps moving....

Podguy

Merlin has it right. Walnut shells is the way to go. Chemical removers will warp the plastic even more and will leave behind scrap marks as the plastic softens with the chemical.

Failure to remove the old paint will just make a mess. Once the old paint is removed you will probably find some tears. Urethane Supply Company makes a plastic welding rod - the one that is universal with fibers - that can be used with a simple soldering iron to repair the cracks. The rod can also be used to weld in support to remove some of the ripples. Scrap from another crashed bumper can be used.

SEM makes a plastic primer and there is a plastic sealer in a spray can that is available at most body supply shops. The SEM primer is flexible and easy to sand to get a nice finish.

Since you are probably using a two part system with base coat and clear the base can be applied over the SEM plastic primer but the clear coat should have a flex agent added. The flex agent will not prevent you from color sanding and polishing out the the clear coat.

vanster

Thanks
This appears to be a very interesting project. I was under the impression that
3M makes a flexible filler as well.
1) remove bumper
2) Media blast with walnut shells
3) Fill in any cracks or splits
4) 3M filler ?
5) Prime with SEM flexible primer spray can)?
6) Guide coat ?
7) Block sand
8) Color coat 4 coats?
9) Clear coat (2 coats)

I will document with photos as I go as well as cost accounting.

vanster

Forgot
Inspect shocks and replace if needed
Then on to Pebble Beach

G Man

If you are going through the trouble of removing the bumper cover, why not search for a replacement that isn't warped?

Mrmerlin

I would figure you only need 2 to 3 coats of base and 3 coats of clear

Podguy

Three coats of clear is over kill. I assume you are going to color sand and polish. In the case of the plastic bumper less is more. The thicker the paint the more likelihood of cracking. It is very important to use a flex agent in the clear coat.

The welding rod from Urethane Supply Company will fix the cracks and tears. A soldering iron can be used with the rod.

http://www.urethanesupply.com/catalo...gory=FiberFlex

The T2000 flex filler works well for filling in pits the primer will not fill. Even two small tubes will last a long time. The filler feathers out well.

http://www.urethanesupply.com/catalo...prettyPhoto/3/

Here is a primer - I have not used it as it is new.

http://www.urethanesupply.com/catalo...esion%20Primer

Here is the SEM primer I use

http://semproducts.com/Catalog.asp?prod=138

One note of caution - sanding plastic is counter intuitive. As you sand high places the plastic will expand and the high spots will just get higher as the plastic gets thinner. Machine sanding can be a problem is it is too agressive. The walnut shells should leave a rough surface that will help with the adhesion. If there is a high spot you are better off sanding the under side to relieve the tension.

When you are putting on the beading do not use staples that will rust. A little 3M trim glue helps

http://www.shop3m.com/60455029946.html

Good luck

vanster

Thanks Dan
These are great tips and they make sense. My guess is that if I dropped my car off at the local body shop
they would never take as much care to do it correctly.

M. Requin

Well that made a light bulb go off! Thanks for the tip!!

Podguy

The local Porsche body shop here strips all parts before painting. I think they have learned to start with clean parts to avoid paint reactions. I am not sure how many shops do this but here it is pretty standard. Modern materials are tons better than what was available when the 928 was built.