- 1 How to repair a big bumper scratch
- 1.1 Materials
- 1.2 Prep
- 1.3 Painting
- 1.4 Finish
How to repair a big bumper scratch
Someone very kindly reversed into my car while trying to park, rather than leaving a note they just did a runner leaving me with a £3-400 repair to get the bumper off, re-sprayed and put back on.
I figured I had nothing to lose by having a go at fixing it myself before I'd have to pay out anyway, and so this is what I did.
I don't have any fancy rotary sanders or professional spray gear, so I did the best I could with what was available, and it turns out it's perfectly possible to do a reasonable job even if
- you've not done this before
- you don't have pro kit
Obviously it's not going to be as good as a professional job that you'd get if you paid the £400, but it is very rewarding and without close inspection the paint job isn't noticeable.
Get yourself over to http://www.paints4u.com and order up the following:
- adhesion promoter aerosol
- primer aerosol suitable for priming bumpers
- custom colour aerosol (they'll match on Lotus paint codes)
- lacquer aerosol
- plastikote gun grip attachment for aerosols - this makes a huge difference !
- bumper filler
- a bunch of wet & dry paper at different grades (150 up to 2000)
- some rubbing compound
- automotive grade masking tape
- tub of warm water with washing up liquid and a rag
- tack rag
It's all about the prep work !
It doesn't matter how good you are with the final coat of paint, if the prep work isn't done right, it's not going to look good. Remember this as you're working through the job below; 95% prep, 5% paint.
Cut out the paint
As you can see from the original picture, the damaged area was pretty large with cracked and delaminated paint extending for 30-40cm, to remove all of this paint I took a scalpel and cut around the damaged area, then picked off the chunks of paint.
Do this until you're sure you've removed sufficient paint such that what was left is still securely bonded to the bumper itself.
Sanding part 1
Next up, tape around the area you're going to be working on, and get to work sanding down to get a smooth edge on the paint edges. Since I didn't have any fancy rotary kit this was done by hand. I used 150 grit to do the heavy work.
You should end up with a surface that's smooth to run your finger over, no hard edges where the old paint stops.
Once you're happy that you've sanded enough (see Prep above), wash the area down with the soapy rag - you want to remove all the sanding dust/wax/polish/dead flies/grease/whatever from the area, once it's dried off, go over the area with the degreaser.
Once the area is dry from the washing you just did, mix up some of the bumper filler and apply it to the area you've just sanded down. Ideally you want to build it back up so that the line of the bumper is slightly proud of how it was originally
I didn't quite put enough filled in one or two places, it's quite difficult to see what the surface contour looks like when it's all matte white, I learnt afterwards that you can spray a very light (one quick pass) coating of a contrasting colour to help with this.
Sanding part 2
Once the filler is properly dry, you need to sand it down. What you end up with here is going to be the contour of your finished bumper, so make sure that you're happy with it - you want to get rid of any bumps or edges, and end up with a smooth transition from the original paint to the filler and back again.
wash down with the soapy water again.
How to use a spray can
- Shake the thing for at least as long as it says on the tin - really - if it says shake for 10 mins, then get a clock, note the time, start shaking and don't stop until the clock says 10mins has passed, not until you think "it's probably been 10mins by now", or until your arm is tired, or until you get bored.
- Use a plastikote spray handle, they clip on to the top of the can and provide you with a handle with a trigger to use - this makes it much easier to move the can in a consistent fashion.
- when you're finished with the can, clean the nozzle by inverting the can and spraying until the paint stops coming out.
How to paint from a can
- Get a large square of cardboard, and cut a circle out from the middle (about 30cm should be fine).
- You're going to hold this between the can and the car to catch the splatters which happen when you start and stop spraying:
- if you are spraying left-to-right, then you'd start spraying onto the carboard to the left of the hole
- In one smooth motion:
- move the can to the right so that you're spraying through the hole now onto the target area
- move the cardboard mask and car to the right in unison, keep spraying through the hold onto the target area
- once you're at the end of your run stop moving the cardboard, but continue moving the can to the right so that you end up spraying onto the cardboard to the right of the hole
- stop spraying
Practice a few times using the method above, it takes a bit of getting used to but doing it this way will catch all of the splatters and lumps that occur when you start and stop spraying from a can.
When spraying, many light coats are better than one heavy coat !: Put a light coat down, and wait for it to flash dry before putting the next coat down.
Once the area is fully dry, run over it quickly with a tack rag to remove any bits of dust that might have settled on your newly primed work.
If you're happy that it's clean as a whistle, put down a coat or two of the adhesion promotor.
One that's dry, put down 3 or 4 coats of primer and leave to dry.
You may want to do a test on whether a dark or light primer results in better colour match with your paint - I sprayed over some black and white glossy paper for this.
wet sand the primer down using 400 grit until you have a smooth finish
Clean the area with the soapy rag.
Once the area is fully dry, put down a couple more coats of primer.
wet sand the primer down again using 800 grit, until you have a very smooth finish.
Clean the area with the soapy rag, and once it's dry go over it again with the tack rag.
Put down 3-4 layers of paint, use the cardboard technique outlined above to avoid any splatters. Take your time, and remember that many thin layers are better than 1 thick layer.
Leave a good 10mins in between each layer for the paint to flash off - you don't want it to dry completely but you do want most of the solvent to evaporate.
Right, you're going to leave it to dry for a day now.
Don't sand the colour coat !
Again, run over with a tack rag to pick up any dust that's settled while you were leaving it to dry.
Now put down 5-6 layers of lacquer on top of the paint, use the same technique as you did spraying the paint on, leaving it to flash dry for 5-10mins between coats.
Once this is done, leave it to dry for a day.
Don't worry about any orange peel effect that you see on the paint at the moment, it's the compound effect of many layers, we're going to sort that now.
Using 600 grit, wet sand the lacquer down - you'll see a mottled effect where you've hit the high spots of the orange peel but not taken them all the way down, keep going and use a damp rag to wipe every now and then until you get a dull uniform sheen across the area.
Clean the area and run the tack rag over it.
Put another 2 coats of lacquer down, and leave to dry for a couple of days
wet sand (using washing up liquid) with 1500+ grit paper to finally kill off any new or remaining orange peel. Same as the last round - look for the mottled effect to tell you where the imperfections are and sand until it's gone.
Clean up the area with a damp rag.
Get a clean rag and use the rubbing compound to finish off the lacquer, take your time and get it right.
Leave the whole lot to dry for a couple of weeks - don't wash and wax your car during this time - the wax will seal in any solvent left and then the paint will never dry properly.
Does it really take 2 weeks for it to dry ? Maybe, maybe not, but do you want to ruin the hours of hard work you've put in so far ? Leave it alone !
Once you've left it to dry properly, you might want to t-cut in the areas where you're blending the new paint with the old paintwork, then give you car a good deep polish, and cover with a high quality wax, buff up and admire your handiwork !