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Howto : Bumper Corner Repair
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27-01-2011 4:18pm#1
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This is the car as it came to me, bumper scuff encompassing the upper and lower bumper, and across a vertical body line which will need to be restored before painting.
First thing I do in this situation is to sand using 120 paper, and a flat sanding block. If you sand by hand, or machine (Unless you know what you're doing), you'll cause divets to be gouged into the bodywork. They might be so slight that you can't see them or feel them - or even when you apply basecoat - but once the lacquer goes on, you'll spot them a mile away.
What I'm trying to achieve first here is to deburr the edges of the gouges in the plastic, but also to keep the shape of the existing bumper, so using the block, I sand only the vertical edge of the bumper first. Here's the result :
Next up is to use the same paper and block, and sand the burred edges off the rest of the scratches keeping the block flat and smooth. You need to be careful where you're sanding, as the 120 paper can easily damage the original untarnished paint and cause more work for yourself. Here's that done.
Next up is some filler. Remember, we've only deburred the edges of the gouged channels, so we need to fill them up now. On the Onion Board (Like an A4 pad with thick paper you can tear the sheets off each time and have a new mixing surface to work with - loads of layers, hence the name Onion) I have Ed China's recipe for filler, a golf ball of filler to a pea of hardener. Cause it's a cold day today, I have a slightly larger amount of hardener. Here's it premixed :
And here's it mixed. You can clearly see there's no streaks of pink or grey which means it's properly mixed. It has to be applied quickly, as it starts to go tough after a few minutes.0 -
When applying the filler, you need to put on the correct amount to the damage. Only experience will tell you how much, too little and you'll always have an echo/impression of where the damage was when you finish painting. Too much, and you'll be sanding it forever and creating work for yourself. Here, I've selectively applied filler to the scuffs themselves. While I was waiting for the filler to go off, I also masked around the area I was painting. This is vital, as you don't want overspray hitting the areas you're not painting. Because I'm using a very accurate HVLP Turbine setup to spray the paint/lacquer, I don't have much overspray so I only need to mask a small area - if you're using a compressor and guns you'll have to mask a much larger area due to the amount of overspray.
Once the filler had hardened enough, I sanded it back with 180 paper and a block, but this obviously left a rough surface. I switched to 400 and a block, and sanded it smoother with that - again, being careful to sand the vertical flat area, and the curved sections of the bumper separately to keep the body curve intact. I was left with this :
Now the surface was prepared, I could apply primer. Course, I forgot to take a photo of that, but I applied the primer in very light coats, just dusting it on - in between drying it out with my heatgun. Once I'd built up enough primer and was certain it was dry, I got a small bucket of soapy water (The soap acts as a lubricant), and some 800 wet and dry paper. You sand this by hand using plenty of water, and you'll feel the primer become smooth under your hand. Pay particular attention to the edges of the primer where it meets the undamaged bumper, you'll need to sand this so smoothly that it almost appears transparent - this is called feathering the edges. You should be aiming at the end to run your hand across the primer and not feel any lumps, or steps in it, and you shouldn't be able to feel the change between primer and undamaged bumper paint.
A tip for this is if you're right handed, use your left to feel the surface, and vice-versa. Your brain gets more tactile feedback from the hand you don't use often.
Wipe off all the soapy water, and dry everything with a heat gun. The next step is to decide how much you actually need to paint and lacquer. In this example, I've decided to apply the carbon black metallic basecoat as far as the curve edge, and then blend the lacquer half way underneath the headlight.
At this point, you need two things, some scotchpads (Like a pot scourer in the kitchen, available from any motor factors) and this chemical called Antisil.
The anti sil is a surface degreaser, but it also removes any silicone from the surface. Silicone is in sprays like back to black, and even if you're sure there's none there, there probably is and it has to be removed. I pour a little into the scotchpad, and scour the surface of where I'm going to be painting. This removes the silicone which will prevent our waterbased basecoat from adhering, removes road tar, removes other contaminants, but the scotchpad also puts light scratches into the undamaged lacquer allowing our new lacquer to get a grip. I do this as far as the middle of the headlight. Get a clean rag, and wipe off the antisil. Then get your heatgun and dry the damp residue - this will turn white and chalky, and you need to wipe that off too. Make sure to use compressed air in the gaps between the bumper and headlight, bumper and wing, towing eye, headlamp washer and fog light in case there's any other liquids in there that might spit out when spraying paint on to the panel.
Once you're happy with that, make sure your masking tape is still secure, and begin to spray your basecoat. I'm going to assume you know how to use your spraying equipment, but it's vital that you always filter your basecoat and lacquer using a paint strainer such as the one below - for water based paint, it's a 125 micron mesh which removes any lumpy bits or contaminents.
Build up the base coat in very light dusty layers again, just like the primer, using the heat gun to evaporate the water and dry each layer. The paint will go on glossy, and as you dry it, it will turn matt. You need to be very cautious with the heatgun, if you use too much heat, you will burn the paint and it won't grip properly. Bodyshops don't use heatguns - they use compressed air blowing over the panels instead to spirit the water away, but this is a faster solution if you know what you're doing. After you've built up a few layers, and brought the paint to the area where you previously decided you would (In our case, the edge of the curve to the front of the car), it should look like this :0 -
While the basecoat is sitting on the bumper, I usually mix lacquer at this point. As said before, I assume you know how to use your spraying equipment and have a second gun for the clear coat with a thicker needle as it's a thicker liquid. Lacquer is made up of 3 solutions, hardener, lacquer and reducer/thinner. The stuff I use is extremely expensive but dries in about 18 minutes under infrared lamps - so to anyone I've told I've a minimum price and shag off haggling - this is why, this stuff ain't cheap :pac:
First is Hardener :
Second with the blurrycam iphone is the lacquer, roughly about double the amount of hardener (We mix it 2:1 Lacquer to Hardener), and finally drop in about 5% of thinner/reducer. The hardener will make the lacquer even thicker than it normally is, and we use the reducer to give it more liquidity, and allow it to sit more smoothly on the finished panel.
Stir this up well, it'll go crystal clear, and then using a fresh strainer, pour it into your lacquer gun. Set that up the way you feel is best for your equipment (Fan size, lacquer amount) and do a test sprayout on a scrap piece of cardboard to ensure you're getting a consistent finish first before hitting the bodywork.
Apply the lacquer in long even strokes, keeping the gun perpendicular to the surface. Don't be tempted to spray in an arc, you have to have the gun 90 degrees to the panel at all times. Spray from one side to the other, bring the gun up and allow the next line of spray to overlap the last by about 50%. You need to really know what you're doing here - too much lacquer, and it'll run off and look horrible causing you work flatting and polishing later - runs are usually recoverable, but too little lacquer and it'll look cloudy. Make sure your air supply has enough pressure - too little and you'll get an orangepeel texture, and make sure your lacquer is thinned enough or that'll cause orangepeel too.
Lacquer to the area you've chosen (In our example, midway under the headlight). Course, you've a horrible edge now where the new lacquer meets the old, and that has to be taken care of. There are many lacquer blending techniques you can use, depending on the shape of the panel you're painting including painting up as far as a crease/swage line and polishing the line smooth later, but for this example, we're going to do something different.
Very very quickly, empty the lacquer gun, and flush it with some standard thinners. Then pour in a capful of this stuff - fadeout - using one last clean strainer to sieve it. Fadeout is a very strong thinner which for want of a better word melts the old lacquer so the new can fade into it. Spray that starting from the opposite end of the repair, about 3 inches away, and apply a good dusting until you see it begin to blend. This is a fast process, don't spend too long at it, or you'll cause runs by thinning the new lacquer too much.
Here's what it looks like masked up. I have it drying under a shortwave infrared lamp at this point, which I move around the repair, ensuring all the fresh paint has been baked thoroughly. The finish on this example I'm glad to say is like glass direct from the gun, and will not need polishing or flatting.
Here's the final article demasked, and the end of the drying process.
At this point, the lacquer is dry enough to touch, and if you were very anal about the finish, dry enough to polish. The car can now be driven and even if it rains, the paint can cope with it, but washing it needs to be left for a day or two.
Hope that helps anyone thinking of doing it themselves, and if anyone has any questions, I'm happy to answer them.0 -
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Any chance you could put up the names (brand or industry terms) of the lacquer components so I dont look like a complete newb when shopping for these?
Is there a lacquer product that achieves say 90% of the gloss without the need for the hardener and thinner blending? What nozzle size is good for spraying lacquer?
Thanks for the guide btw!0 -
Matt Simis wrote: »Any chance you could put up the names (brand or industry terms) of the lacquer components so I dont look like a complete newb when shopping for these?
I use HB Body lacquers, they do a few different types, but if you don't have an short wave infrared lamp, there's no point in spending the extra money on the stuff which dries quickly and still has the high gloss. TBH, if you're doing a few small jobs at home, you're better off talking to a local body shop, or a smaller motor factors who might sell you the chemicals in a smaller quantity - the kits you buy from the motor factors are (By the time you add them together) 8.5 litres!
Most Motor Factors who sell paint are generally friendly when giving advice about what to use - I've seen a few talking to enthusiastic newbies, and they do really give good advice.Matt Simis wrote: »Is there a lacquer product that achieves say 90% of the gloss without the need for the hardener and thinner blending? What nozzle size is good for spraying lacquer?
If you're talking about spraying without hardener, or reducer, you'll need a 1k (1 pack) lacquer. U-Pol do a 1k lacquer but bear in mind it won't be as tough as a 2k lacquer when applied.
If you're spraying lacquer using a turbine, probably a needle size of 1.3mm, if it's a compressor, 1.5mm minimum.Matt Simis wrote: »Thanks for the guide btw!
No problem, glad people are enjoying it! 0 -
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First thing I would always do is try to polish up the faded paintwork and restore the original colour. Red as you know is a nightmare for this. If that works, you can normally get away with the original colour if you blend it into the original paint correctly.
Failing that, it gets interesting. Next step would be for me to take out my paint sample cards/swatches, put the kettle on in the car and make a coffee while going through the 170 odd thousand paint cards to find one which matches. If that lucks out, then I'll mix the original paint, and then darken/lighten it manually. Problem with that is that water based paint dries a different colour to the freshly mixed stuff in the paint pot, so you need to keep applying a sample to the area on the car, dry it, and repeat until you get it right. I had to do it on an old Mini recenly when the colour code was completely different to what had been sprayed by the owner himself on the car. Took a good 2 hours to get the colour right, and was pretty frustrating.
Some bodyshops now use a spectrometer. If I had a few thousand to throw away, I'd love to buy one. It's like a bluetooth camera that snaps photos of the paint at high magnification from 6/7 angles, and sends the data back to the laptop and it'll give you the mix immediately. Life would be a lot easier with that
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