bumperette refinishing (for cheap and/or broke bastards)
03-10-2007, 06:16 AM
#1
Drifting
Thread Starter
bumperette refinishing (for cheap and/or broke bastards)
A few weeks ago, someone was grousing about needing their rear spoiler refinished but seemingly forgot they were driving one of the more expensive, exotic, and luxurious sports cars ever made. The wise thing to have done is to scour e-bay daily like I do and look out for deals. If I see a good part out there on e-bay I buy it whether I need it at the moment or not. I do this because with a 928, it's not a matter of it something will go bad, it's a matter of when. So anyway, I was able to score a set of ever so slightly used bumperettes for my '85 which would leave me with an extra set. I have a lot of painting materials around my garage so I decided I would experiment and try to come up with a good way to refinish the bumperettes. This method should work on spoilers as well.
The first thing that must be addressed is the poor choice in materials that Hans and Fritz chose when making these parts. They seem to be plastic, with a layer of rubbery material, and finally a very thin layer of textured black plastic on the surface. This outer layer is what usually fails and begins to crack and delaminate over time. I don't have any pics of these items prior to sanding, but most of you can go out and look at your own cars to know what I'm talking about. Aside from the cracking and peeling issues, the material is very difficult to sand and isn't receptive to refinishing. In the first set of pics, I will post most of the materials I'm using.
This is for repairing plastics. It's a flexible epoxy. This particular stuff is made by Evercoat. 3M also has it's own version.
This next pic shows some DuPont plastic cleaner. This is some vile stuff. I'm not sure if it's a solvent, or what it is, but I advise people to have plenty of fresh air when using it. It has some of the worst fumes of all the products I used in this project. Next to it is some 3M adhesion promoter for use with their line of plastic repair epoxies. I won't go into detail because I found in this application it seemed to hinder adhesion.
This pic shows some SEM guide coat, and SEM adhesion promoter. As I said, the adhesion promoters didn't seem to work so I won't go into detail. Guide Coat is used for blocking out a surface prior to painting. Cheapskates will try to cheat the system and substitute some cheap sprayable lacquer. While SEM guide coat is a lacquer, it has virtually no solids and is mostly made up of very fast reducer that dries almost instantly (2-3 seconds.)
This stuff is SEM texture coating. It is what I'll use to restore the grainy surface on the bumperettes.
You should use one of these to avoid lung cancer. Since it's not meant for vapors, you can still get brain damage when using this.
These are some of the best sanding blocks on the market. Much better then the fancy ones at Eastwood that cost over twice as much. If you ever attempt to do your own bodywork, these are one of the first things you should pick up.
3M adhesive backed sandpaper is pricey and runs about $40-$50 per role. Unless you have another bodywork project going on, don't spend the money. Get regular full sheets of sandpaper instead. For this job I used 80, 180, 320, and 400 grit paper at the various steps.
There are some other items I didn't post but should mention. They are:
Razor blades: I don't think I used them for this job but I've learned that you can never have too many razor blades in the garage. They always come in handy.
Body filler spreaders: The really cheap, pink, Bondo brand spreaders at the discount parts store are very good for this job. For other jobs I use a set of spring steel spreaders, but for this, the cheap plastic ones are just fine.
Lacquer thinner: use it to clean up the epoxy filler before it kicks.
Paper towels: 2-3 rolls
3M wetordry sanding sponge: Softer then the durablock sanding blocks and very effective on surfaces that have many contours. I used this more then any other block for the job. Available at Car Quest and your paint jobber.
Dupli-color flexible sanding primer: Not always available at the discount parts store, but can be found at car-quest. No self respecting jobber carries dupli-color, then again, no self-respecting person uses it on a 928, but when you're broke, or you're just cheap, chances are, you've got no shame in your game.
Dupli-color classic black lacquer: see comments above.
I call this the cheap method because I already had most of the materials needed for the job. I decided to do it when I was at Car Quest and saw they had a flexible lacquer based primer. The primer and paint were the only items I needed for the job and they cost about $15. The SEM guide coat was about $15 but you can substitute some of the black lacquer spray paint if you just mist it on. The plastic cleaner is also optional provided you thoroughly scrub the part with some strong dishwashing soap like Dawn Foam(which is a better degreaser then most automotive degreasers.) Adhesion promoters weren't needed. The epoxy bumper repair stuff and some bondo spreaders were about $20. The SEM texture spray was $12. The lacquer thinner cost about $3 for a quart (note: cheap and/or impoverished people will want to substitute mineral spirits for lacquer thinner which they shouldn't do because mineral spirits leaves a much heavier residue.) Anyway, on to the actual job.
The first thing that must be addressed is the poor choice in materials that Hans and Fritz chose when making these parts. They seem to be plastic, with a layer of rubbery material, and finally a very thin layer of textured black plastic on the surface. This outer layer is what usually fails and begins to crack and delaminate over time. I don't have any pics of these items prior to sanding, but most of you can go out and look at your own cars to know what I'm talking about. Aside from the cracking and peeling issues, the material is very difficult to sand and isn't receptive to refinishing. In the first set of pics, I will post most of the materials I'm using.
This is for repairing plastics. It's a flexible epoxy. This particular stuff is made by Evercoat. 3M also has it's own version.
This next pic shows some DuPont plastic cleaner. This is some vile stuff. I'm not sure if it's a solvent, or what it is, but I advise people to have plenty of fresh air when using it. It has some of the worst fumes of all the products I used in this project. Next to it is some 3M adhesion promoter for use with their line of plastic repair epoxies. I won't go into detail because I found in this application it seemed to hinder adhesion.
This pic shows some SEM guide coat, and SEM adhesion promoter. As I said, the adhesion promoters didn't seem to work so I won't go into detail. Guide Coat is used for blocking out a surface prior to painting. Cheapskates will try to cheat the system and substitute some cheap sprayable lacquer. While SEM guide coat is a lacquer, it has virtually no solids and is mostly made up of very fast reducer that dries almost instantly (2-3 seconds.)
This stuff is SEM texture coating. It is what I'll use to restore the grainy surface on the bumperettes.
You should use one of these to avoid lung cancer. Since it's not meant for vapors, you can still get brain damage when using this.
These are some of the best sanding blocks on the market. Much better then the fancy ones at Eastwood that cost over twice as much. If you ever attempt to do your own bodywork, these are one of the first things you should pick up.
3M adhesive backed sandpaper is pricey and runs about $40-$50 per role. Unless you have another bodywork project going on, don't spend the money. Get regular full sheets of sandpaper instead. For this job I used 80, 180, 320, and 400 grit paper at the various steps.
There are some other items I didn't post but should mention. They are:
Razor blades: I don't think I used them for this job but I've learned that you can never have too many razor blades in the garage. They always come in handy.
Body filler spreaders: The really cheap, pink, Bondo brand spreaders at the discount parts store are very good for this job. For other jobs I use a set of spring steel spreaders, but for this, the cheap plastic ones are just fine.
Lacquer thinner: use it to clean up the epoxy filler before it kicks.
Paper towels: 2-3 rolls
3M wetordry sanding sponge: Softer then the durablock sanding blocks and very effective on surfaces that have many contours. I used this more then any other block for the job. Available at Car Quest and your paint jobber.
Dupli-color flexible sanding primer: Not always available at the discount parts store, but can be found at car-quest. No self respecting jobber carries dupli-color, then again, no self-respecting person uses it on a 928, but when you're broke, or you're just cheap, chances are, you've got no shame in your game.
Dupli-color classic black lacquer: see comments above.
I call this the cheap method because I already had most of the materials needed for the job. I decided to do it when I was at Car Quest and saw they had a flexible lacquer based primer. The primer and paint were the only items I needed for the job and they cost about $15. The SEM guide coat was about $15 but you can substitute some of the black lacquer spray paint if you just mist it on. The plastic cleaner is also optional provided you thoroughly scrub the part with some strong dishwashing soap like Dawn Foam(which is a better degreaser then most automotive degreasers.) Adhesion promoters weren't needed. The epoxy bumper repair stuff and some bondo spreaders were about $20. The SEM texture spray was $12. The lacquer thinner cost about $3 for a quart (note: cheap and/or impoverished people will want to substitute mineral spirits for lacquer thinner which they shouldn't do because mineral spirits leaves a much heavier residue.) Anyway, on to the actual job.
03-10-2007, 07:02 AM
#2
Drifting
Thread Starter
I'm assuming you have removed the bumperettes from your car. Make sure the water has been turned back on and clean the parts thoroughly. Allow the parts to dry completely. Sand the parts until all of the delamination is gone and you are left with a surface that looks even and consistent. Use 80 grit on the sanding sponge for this. When you are done, sand it again. Cheap people cut corners because it's in their psyche to do so as part of their cheapness. Poor people are poor because they aren't thorough workers. When removing the layer of material, you can't cut corners or else you'll have adhesion issues. Once you have sanded a second time, clean the part again and dry thoroughly. It is imperative that the part be completely dry and free from contamination at this point.
Now I will explain in detail why I chose to experiment with the epoxy. As I said, the original material is crap and leaves a substrate that is not receptive to refinishing. Epoxy will stick to almost anything as long as the surface is clean and dry. This type of epoxy can be sanded down very thin and still be a stable substrate for paint adhesion. In addition, epoxy is highly effective at sealing out moisture which is important because the primer I will later use is loaded with talc solids. While this part won't rust, I don't want moisture to pass to the substrate and cause an adhesion problem down the road. To use the epoxy follow the instructions on the box. Once thoroughly mixed, apply it to the entire surface of the bumperette. It should look something like this.
[img]https://img84.imageshack.us/img84/2071/img0130ns0.jpg[img]
Although the epoxy claims to cure in about 15 minutes I had to reapply it a second time because I started sanding and it peeled off. When I reapplied it, I let it cure for over an hour before I started sanding and had no issues. To sand the epoxy filler, spray on the guide coat, and use some 80 grit on the sanding sponge. Only sand until the guide coat is gone. Once the guide coat is gone, apply another guide coat and switch to 180 grit paper with the sanding sponge. Again, sand ONLY until the guide coat is gone, then repeat again using 320 grit and the sponge. Once you finish with the 320 it should look like this.
As you can see, I sanded through the epoxy in some places which is not a big deal. Most of the surface is still covered with some of it and that's all that matters. Do not use any cleaners from this point from this point forward. Your major contaminant will be dust and compressed air will remove it just fine.
The next step is the flexible primer-surfacer. Normally, I think primer surfacers are **** and make a car more prone to chips. For some bizarre reason, when they have a flex additive, they seem to work much better. Spray on one wet coat. A "wet" coat means you apply enough material to make the surface wet but not produce runs. Some people like to spray it on, let it dry, spray on more, let it dry some more, and do this 3-4 times and then block it. I don't like that because that builds a thick film and you risk solvent pop later on. With good paint however, I always follow the manufacturers tech sheets. With this I spray on a wet coat, let it dry, apply guide coat, and block it with the sponge and 320 until the guide coat is gone. This will rub through in some areas. I repeat this process several times until I am satisfied and at least 90% of the surface has some primer left once the guide coat is gone. This first pic is of the bumperette with primer-surfacer.
This is what it looks like with guide coat. Hold the can about 18 inches away and only make one or two quick passes. That's all you need.
This is how it looks after 4 or 5 coats of primer-surfacer and being blocked out between each. You'll notice in some spots you can see the epoxy. That's not an issue since the texture coating will stick to it just fine.
Now I will explain in detail why I chose to experiment with the epoxy. As I said, the original material is crap and leaves a substrate that is not receptive to refinishing. Epoxy will stick to almost anything as long as the surface is clean and dry. This type of epoxy can be sanded down very thin and still be a stable substrate for paint adhesion. In addition, epoxy is highly effective at sealing out moisture which is important because the primer I will later use is loaded with talc solids. While this part won't rust, I don't want moisture to pass to the substrate and cause an adhesion problem down the road. To use the epoxy follow the instructions on the box. Once thoroughly mixed, apply it to the entire surface of the bumperette. It should look something like this.
[img]https://img84.imageshack.us/img84/2071/img0130ns0.jpg[img]
Although the epoxy claims to cure in about 15 minutes I had to reapply it a second time because I started sanding and it peeled off. When I reapplied it, I let it cure for over an hour before I started sanding and had no issues. To sand the epoxy filler, spray on the guide coat, and use some 80 grit on the sanding sponge. Only sand until the guide coat is gone. Once the guide coat is gone, apply another guide coat and switch to 180 grit paper with the sanding sponge. Again, sand ONLY until the guide coat is gone, then repeat again using 320 grit and the sponge. Once you finish with the 320 it should look like this.
As you can see, I sanded through the epoxy in some places which is not a big deal. Most of the surface is still covered with some of it and that's all that matters. Do not use any cleaners from this point from this point forward. Your major contaminant will be dust and compressed air will remove it just fine.
The next step is the flexible primer-surfacer. Normally, I think primer surfacers are **** and make a car more prone to chips. For some bizarre reason, when they have a flex additive, they seem to work much better. Spray on one wet coat. A "wet" coat means you apply enough material to make the surface wet but not produce runs. Some people like to spray it on, let it dry, spray on more, let it dry some more, and do this 3-4 times and then block it. I don't like that because that builds a thick film and you risk solvent pop later on. With good paint however, I always follow the manufacturers tech sheets. With this I spray on a wet coat, let it dry, apply guide coat, and block it with the sponge and 320 until the guide coat is gone. This will rub through in some areas. I repeat this process several times until I am satisfied and at least 90% of the surface has some primer left once the guide coat is gone. This first pic is of the bumperette with primer-surfacer.
This is what it looks like with guide coat. Hold the can about 18 inches away and only make one or two quick passes. That's all you need.
This is how it looks after 4 or 5 coats of primer-surfacer and being blocked out between each. You'll notice in some spots you can see the epoxy. That's not an issue since the texture coating will stick to it just fine.
03-10-2007, 07:30 AM
#3
Drifting
Thread Starter
The next step is to apply the texture coating. When you initially sanded the part, you removed the texture. That was fine because it allows you restore it to your own preference with the texture material. The texture material is very thick like the primer-surfacer. With both items you MUST shake them thoroughly. Imagine you're a young British nanny with a fussy American infant. That's how much you have to shake the stuff. It's best to apply the texture in two coats. You control the amount of texture by how close or how far you hold the can from the surface and how wet or dry you lay it on. What you're essentially doing is controlling orange peel. I put on the first coat and didn't like the consistency of it because it went on wet and heavy. That was not an issue since I figured the first coat was mainly for building material anyway. I let it flash for about 20 minutes and then I went and sanded the stuff with some 320 grit until it was smooth and consistent all over. This is the first coat of texture after having been sanded:
On the second coat I wanted the same fine texture as the part initially had. So I held the can about 18 inches back and laid on a dry-medium coat. It came out perfect but stupid me didn't think so at the time and decided to give it a very light sanding to make sure everything looked consistent. I shouldn't have done it, but I'm not using them anyway. The first pic is of the perfect texture. The second one shows my light sanding.
For the final application of color I used some black lacquer(2 coats.) It would probably look better with some satin finish clear.
As I said, on e-bay you can usually find bumperettes in almost-new condition on a regular basis. That makes this almost pointless. The perk of it is that you should be able to use this technique for the spoilers since they are made from similar stuff. If I were to do it on a spoiler which isn't readily available, I would use a catalyzed primer and a catalyzed single stage paint with a satin finish. I would consider skipping the texture coating as well.
On the second coat I wanted the same fine texture as the part initially had. So I held the can about 18 inches back and laid on a dry-medium coat. It came out perfect but stupid me didn't think so at the time and decided to give it a very light sanding to make sure everything looked consistent. I shouldn't have done it, but I'm not using them anyway. The first pic is of the perfect texture. The second one shows my light sanding.
For the final application of color I used some black lacquer(2 coats.) It would probably look better with some satin finish clear.
As I said, on e-bay you can usually find bumperettes in almost-new condition on a regular basis. That makes this almost pointless. The perk of it is that you should be able to use this technique for the spoilers since they are made from similar stuff. If I were to do it on a spoiler which isn't readily available, I would use a catalyzed primer and a catalyzed single stage paint with a satin finish. I would consider skipping the texture coating as well.
03-10-2007, 07:56 AM
#4
Bumbling Neophyte
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Sounds like you know what you're doing. How about some tips on repairing the scratches on my plastic bumper? They go right across the "porsche" lettering and really look bad. I have seen several products, but I have no experience and would like to see a step by step guide to doing it the right way!
Thanks
KK
Thanks
KK
03-10-2007, 08:25 AM
#5
RL Community Team
Rennlist Member
Rennlist Member
Wow! This is going in my bookmarks/favorites!
Why couldn't you post this 5 months ago when I was restoring my dad's 928?
I couldn't think of how to freshen up his spoiler, so I just sprayed it with black SEM color coat to give it a richer color but it hardly helped at all.
This should work well with the 944 hatch as well!
Why couldn't you post this 5 months ago when I was restoring my dad's 928?
I couldn't think of how to freshen up his spoiler, so I just sprayed it with black SEM color coat to give it a richer color but it hardly helped at all.This should work well with the 944 hatch as well!
