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BMW 3-Series and 4-Series Forum (F30 / F32) | F30POST > Technical Forums > Cosmetic Maintenance: Wash, Wax, Detailing, Repairs > DIY: An Enthusiasts Guide to Painting with Rattle Cans
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      09-16-2019, 09:59 AM   #1
B1ue52
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Following on from my other two guides:

1. Basic Detailing - https://f30.bimmerpost.com/forums/sh....php?t=1649367
2. Colour Sanding - https://f30.bimmerpost.com/forums/sh....php?t=1651370

I thought to complete the series I would provide a guide on how to spray paint your own parts at home... with rattle cans. I recently got a quote from a local body shop to have an M Performance front splitter prepped, painted and colour sanded and it came back at £230.00 GBP, or around £200.00 USD. That was just for gloss black everywhere with a clear coat over the top. Fair enough, but although I haven't done it for a while, I figured I could save myself at least £200.00 doing it myself. You can do the same. You don't have to be an expert in painting to paint something like a grill, a splitter or a diffuser, just follow these simple steps and you can knock out a paint job that would be more than satisfactory to pretty much everyone.

As I was doing it myself I decided against going full gloss black and went with spraying the canards EB11 to match the car, with the lower section of the splitter in gloss black. The part I am using has a nice return on the front lip that wraps around underneath the piece with a nice even join about half an inch underneath, so I decided not to spray the underside of the piece and leave it bare plastic. Why? Because for starters, the join being where it is gave me a really nice seam to mask to, secondly, nobody is ever going to see it, thirdly, when it inevitably gets scuffed and scraped, I can just sand back the bare plastic to a smooth finish and won't have to repaint. Lastly, it's a waste of paint.

I will be painting this with rattle cans from start to finish, including primer, base coat and clear coat. There are a number of places to get colour matched paints made up in aerosol form, but in the UK I prefer paints4u. The EB11 turned out to be a perfect colour match.

Required tools and materials:
1. Scotch Brite Pads in various grades (Burgundy, Green and Grey) – Available from Amazon or auto parts stores such as Halfords in the UK
2. Masking Tape
a. Standard width around 15mm – Suggest a low tack variant like Frog Tape
b. Wide width around 40mm – Any cheap stuff will do
c. Fine line tape around 5 to 8mm – I like Tamiya hobby tape for this
3. Plastic Primer (one large can)– Choose the colour depending on your base coat colour. If in doubt, go with grey
4. Base coat (two regular cans)
a. For the EB11 I just had it mixed by paints4u
b. For the black I used Fiat 601 black from the 1920s as it is a very "black" black and matches the black on BMW trim very well
5. Clear Coat (one large can) – Make sure you buy the correct clear coat for your base coat – paints4u sell kits of primer, base and clear together with free next day shipping for around £22.00
6. 2000 grit wet and dry paper
7. 800 grit sand paper or a sanding stick or steal your Mrs's nail file
8. IPA solution and/or panel wipes and/or paint prep solvent in a spray can
9. Knifing putty or body filler for plastic repairs
10. Spray can trigger
11. Mask – Preferably a charcoal filtered mask, but anything is better than nothing
12. Tack cloths

Contents

1. Preparation
a. De-flashing
b. Filling
c. De-greasing and keying
d. Masking
2. How to Paint
3. Shooting Primer
4. Knocking back
5. Guide Coat - Optional
6. Shooting Base Coat
7. Shooting Clear Coat
8. Colour/Wet Sanding

Section 1 – Preparation
Any good paint job relies on great preparation. The more effort you spend here, the better your final result will be.

1. De-Flashing – 20 mins
Any injection moulded part will have flashing and mould lines due to the processes required to form the part. Spending a few minutes on these areas makes the world of difference to the appearance of your piece when painted. You may find marks where the piece was attached to the mould or similar and also thin edges will likely have a sharp edge or even burr (flashing) attached to them. Using something like 800 grit paper or a sanding stick, or a flexible nail file, take the edges off the thin edges using a circular sanding motion at around a 45deg angle to the edge. Slightly round off any sharp points or corners to help the paint adhere to these edges. The piece I worked on needed some smoothing out on the trailing edge of the canards and there was also a seam line on the very front of the lip that I smoothed down entirely.
2. Filling – 30 to 60 mins
Search the piece all over for any irregularities such as pin holes or dips in the surface. For pin holes, just use some knifing putty to fill the holes, smooth back with a spatula type tool and feel free to sand immediately. For any larger dips or surface differences, use some body filler intended for use on plastics and sand back to smooth. Have a look at the piece from different angles and in different lights to spot defects and such. If your piece is screwed together, kinda like a sandwich, then you may have some dips on the surface from the fixing points underneath. These are very hard to spot on a bare matte finish. I missed them and they showed up once the clear was shot. Other than that, I was lucky and didn't have any pin holes or defects so no filling was required. It is up to you how far you take this process. The more time you spend on it and the more anal you are, the better the finish you will get.
3. De-greasing and keying – 10 mins
We can kill two birds with one stone here. Firstly, we want to ensure all releasing agents used by the moulding process are removed but also we want to key the surface ready to accept the primer coat. Keying the surface gives the paint something to adhere to.
Get a bucket of warm soapy water (washing up detergent) and a burgundy Scotch Brite pad. Soak the pad thoroughly and start "sanding" the piece. Ensure that all your sanding strokes go in the same direction down the length of the piece. However, if you need to remove any scratches, sand 90 degrees across the scratch until it is removed, then go over it again to match the "grain" to the rest of the sanding strokes. You don't need to go crazy here, just ensure the piece is very clean and has a good scuffed matte finish to it like in image 1, 2 and 3 below.
4. Masking – 0 to 30 mins
You may not need to mask at all. If you are painting all faces of your piece in the same colour, then you can skip this step. However, working to the example of the front splitter, mask off the bottom of the piece if you're not painting it. Use the fine line tape first to set your edge as this is more flexible and easy to lay down around curves and bends. Then back mask this with the standard width tape to secure it in place, overlapping it by about 50%. Now just fill in the bulk of the area with the fattest tape you bought. If you are planning on painting the canards a different colour, then don't mask them at this point.

Note: Do all tasks that involve sanding or creating dust, outside, or at least not in the room you are going to paint in!

Section 2 – How to Paint
These are general guidelines on how to paint with a spray can, or gun for that matter. The principal remains the same for primer and base coats and similar for clear coat.

1. Plan your attack. Sit and look at the piece and decide how you are going to paint it, then execute that plan. Spray larger areas first, then edges afterwards
2. Spray cans of any description don't work well, if at all when inverted, so orient your piece so you can hit the vast majority of it with the can upright and at 90 degrees to the piece
3. Always start spraying off the piece – This avoids splatters
4. Move across the piece in one motion – You will need to get a feel for how close to be and at what speed you move, this will differ with different cans or pressure setups
5. Finish spraying off the piece – Again to avoid splatters
6. Assuming your first pass was from left to right, start your next from right to left
7. Move back across the piece in one motion again, overlapping your last pass by around 50%
8. Finish spraying off the piece again
9. Repeat until the piece is covered
10. Use the same principal to cover any edges
11. Allow 15 mins between coats for primer and base coats and 30 mins between clear coats
12. For primer and base coats, your first coat should be a mist coat. It won't look pretty, it should just lay a mist of paint down on the surface. Then follow up with two wet coats
13. For a wet coat, you ideally want to be painting a wet edge against a wet edge, so work confidently and quickly. If you overspray an area too late that has started to dry, it will do something called Flash Off, which will give a misty appearance to the finish. Just overspray again with your next coat and all will be fine.
14. For wet coats avoid spraying from too far away as this will allow the paint to dry in mid air and will lay down in a gritty fashion. You need to get closer with a wet coat but not so close that the paint runs.
15. For Primer go with 2 coats, one mist, one wet
16. For Base coat go with 3 coats, one mist, two wet
17. For clear coat go with 3 coats, 3 wet, as thick as possible without causing runs

The important thing is to not shake the can around like you are jerking off. Lay down your passes in confident, smooth and deliberate strokes from one end of the piece to the other. The rest is just feel. You can always practice on a spare panel or even a sheet of cardboard etc first to get a feel for the can or gun.

Section 3 – Shooting Primer
Primer is extremely easy to lay down, especially if you use a spray can trigger. This is just a plastic trigger that attaches to your spray can and turns it in to a spray gun... kinda. They are well worth the investment at around £6.00 and turns someone like me who is good with a rattle can, in to a pro by comparison. It is never going to be as good as using a proper compressed HVLP airgun setup, but we don't all have access or budget for that equipment, so it's the next best option.

See image 4 below.

1. Start by ensuring your cans are at ambient room temperature. If the room you are spraying is cold, keep them in another room so they are nice and warm to allow the paint to mix well and spray well.
2. Shake the can for at least 3 mins. I actually set a timer on my phone as it is all too easy to give up too soon.
3. Attach your trigger to the can
4. Test spray to get a feel for the pressure and volume and to ensure the paint is coming out evenly
5. Blow out any sanding residue with an airline, Side Kick Air Blaster or a hair dryer
6. Wipe over thoroughly with your choice of paint prep. Either Panel wipes, IPA solution or spray solvent and dry thoroughly
7. Remove any dust particles with a tack cloth and avoid touching the piece with bare fingers
8. Follow the guidelines above for shooting the paint. Primer lays down really nicely so is a nice introduction to the process and will help you get a feel for it. It is also very forgiving and don't forget this is just primer, we will be sanding it back once dry so nothing to sweat about here
9. Once your mist coat is laid down, leave it 15 mins to dry
10. Knock the surface back with a grey scotch brite pad, just enough to take any graininess out. It doesn't take much at all to achieve this
11. Blow out any sanding residue with an airline, Side Kick Air Blaster or a hair dryer
12. Shoot your second coat, a wet coat this time. Get closer, move slower, ensure full coverage and paint to the guidelines above
13. Allow to dry for 30 mins before knocking back

Section 4 - Knocking Back
The principal of knocking, blocking or flatting back the primer is twofold. One, we want the primer to be as level as possible before the base coat goes down, and two we want to key the primer to give the base coat something to stick to.

1. Use your green scotch brite pad to flatten the surface using the same sanding techniques as described above. This will scratch the primer up somewhat so then go over it again with the grey pad to take out the scratches you just put in with the green pad.
2. Blow out the dust as before
3. Wipe over with panel wipe and remove any dust particles with a tack cloth

Section 5 – Guide Coat (Optional)
Use this section if either you or the piece you are painting requires it. It's a bit anal but it is good practice and I definitely recommend it on a larger surface or if you have done a lot of sanding and filling in the prep stages. You can buy specific cans of guide coat from an automotive store, but you can also just use a can of black spray paint, or any colour that will contrast with your primer colour.

1. Spray a medium to heavy mist coat all over the piece
2. Let it dry for 10 mins
3. Knock it back with 1500 or 2000 grit paper on a sanding block – You must use a sanding block so that you are sanding with a flat medium, otherwise you will sand inside any hollows or ride over any bumps which will defeat the purpose

By gently removing the guide coat you have just sprayed, it will show you if you have any high or low spots. If you take off areas of guide coat very quickly leaving the majority of guide coat elsewhere on the piece, then that is a high spot. If you remove the majority of guide coat from the piece, but some is left in areas, then those are low spots.

Sand and fill to smooth out these areas, spray another guide coat and repeat the process until you are happy that the guide coat is being removed in a uniform fashion.

Section 6 – Shooting Base Coat
By now you should have a good feel for the cans you are using and if you are using the same manufacturer for both primer and base coat, you know what to expect from the can. Again, ensure they are at room temperature and test spray to ensure your nozzles are not faulty or dirty. Base coat, especially metallics, lay down really nicely and it is genuinely quite hard to mess it up. Follow the guidelines above for painting techniques and spray 3 coats, 1 mist coat and 2 wet coats leaving 15 mins to dry between coats and shaking your cans between coats. Remove any dust particles once dry between each coat with a tack cloth.

See images 5, 6, 7, 8, 9 and 10 below.

If you are going to shoot a single colour all over the piece, go ahead and call it done. If you are doing two colours, follow this process:

1. Shoot the body colour on the canards as per the process above and don't worry about getting overspray on the rest of the piece
2. Leave to dry for 24 hours
3. Mask the canards up using the above masking process
4. Knock back the overspray on the rest of the piece using the grey scotch brite pad
5. Blow out dust and wipe down with panel wipe
6. Shoot your 3 coats of the black on the remainder of the piece – Gloss black is a bitch to shoot, so take it easy and don't expect things to look great until you shoot your second wet coat. Even then they probably won't look stella, just aim for a uniform finish with no hazing and then you can call it done. The clear coat will give you the glossy finish you are looking for

Section 7 – Shooting Clear Coat
I hate shooting clear coat. It's thick and not very forgiving and is the critical part of the process.

See images 12 and 13 below.

Before shooting your clear coat, leave your base coat to air dry for at least 2 hours, but not longer than 12 hours.

1. If you are shooting two colours, go ahead and remove your masking tape from the canards and ensure any tape residue is removed
2. Panel wipe
3. Tack cloth
4. Warm and shake cans
5. Take a deep breath
6. Shoot a wet coat right off the bat. A good clear coat should be as thick as possible without runs so you will need to get closer and move slower and pay very close attention to how the paint is laying down
7. Concentrate hard on spraying wet edge to wet edge
8. Don't get scared and spray from too far away, if the clear coat dries in the air it will settle like fine grit on your surface
9. If you do get runs, leave them alone and carry on with the process!!! We will fix them later when colour sanding – You will find that some runs will sort themselves out. Paint has a good ability to self-level…. Sometimes!
10. Leave 30 min between coats and get 3 good wet coats down without hazing

It's worth noting that some of the higher end spray cans spray a pattern similar to a HPLV gun. Rather than a conical shaped pattern that you get with a cheap rattle can, automotive paint suppliers use nozzles that spray a vertical pattern. This helps no end with laying down even coats, but as clear coat is so thick, it can some times hit the rim of the can and cause build up. If this happens, it will fire splatters at your piece so ensure you are wiping this clean every couple of passes.

Section 8 – Colour/Wet Sanding
So you've laid down your clear, all has gone pretty much to plan. You have an even finish, maybe the odd run, definitely some orange peel and possibly, if you're unlucky, a little hazing. With hazing you have two options…. 1. Shoot another full coat of clear or 2. Hope that the colour sanding and buffing process removes it. I shoot another coat personally.

Leave your piece to air dry for at least 72 hours in a warm room, preferably not too humid. If you have access to a paint shop oven, then get it baked. Some people like to leave things out in the sun to "cure", but you have no control over the temperature the piece is going to get and if its metal or painted black, it will get damn hot. Different paints react differently to sun drying so I am not going to recommend it even though I sometimes do it.

Once your paint is dry using the above guidelines, you can now colour/wet sand it to remove the orange peel and any runs and then buff it back for a nice glossy finish. You can follow my Colour Sanding Guide here for great results:
https://f30.bimmerpost.com/forums/sh....php?t=1651370

Once that process is complete, leave it for around another two weeks and then use my Detailing Guide to protect the piece:
https://f30.bimmerpost.com/forums/sh....php?t=1649367

Tips:
I've covered lots of them above but in short:
1. Sand outside, paint inside
2. Panel wipe, panel wipe, panel wipe
3. Plan your paint coat. If the first coat plan of attack isn't ideal, adjust for the next coat
4. Orient your piece so you have to invert the can as little as possible
5. Paint with confidence, like you mean it
6. Learn from every coat on how to do the next coat better
7. Be rigorous about timings, including shaking your cans and drying times
8. Don't paint when it's too hot and humid, or too cold and damp
9. If you're scared, do it anyway, just practice first. The worst thing that can happen is you have to sand the piece back a good way and start again. You can always take it to a body shop if you utterly fail and don't want to try again and all you have lost is time and the money for the materials, which isn't much compared to body shop prices
10. Don't skip the Colour Sanding Stage, a body shop would do it, so should you. This is what gives you the finish you are looking for
11. Wear a mask
12. Use fans to blow out overspray from the room, but don't let them kick up dust
13. If you can, build a make shift paint booth to protect your piece from dust whilst drying. Build it a couple of days before you paint so you don't kick a load of dust in to the air just before painting
14. Don't shake the can around when you're spraying. Smooth even strokes the length of the piece you are spraying. NOT like you are colouring in like a 5 year old
15. If you miss a bit, leave it for the next coat. If you absolutely have to touch something up, do it in a localised sweeping movement, not a point and shoot type motion, that's just asking for a run
16. In between coats and also once you're done, invert your cans and spray briefly to clean the nozzle out

Picture Reference:

1. Keyed and ready for primer
2. Keyed and ready for primer
3. Degreasing and keying
4. After two coats of primer
5. After shooting the EB11 base coat
6. After shooting the EB11 base coat
7. Canards masked and ready for the black base coat
8. Canards masked and ready for the black base coat
9. After shooting the Fiat 601 Black base coat
10. After shooting the Fiat 601 Black base coat
11. Unmasked and ready for Clear Coat
12. After 3 coats of Clear
13. After 3 coats of Clear
14. Curing in the late afternoon sun

Happy to answer any questions and obviously it goes without saying that you follow this guide at your own risk. Above all, have fun trying something you would otherwise pay money for. I am not suggesting it is possible to respray an entire car with rattle cans to a good finish, but it certainly is possible for anyone to achieve more than satisfactory results on accessory parts. You can use the same techniques to perform small repairs to body work. Just use your judgement as to whether you can keep the repair localised enough.

Enjoy
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      09-16-2019, 02:09 PM   #2
Jungatron
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A+ work. Thank you for taking the time to write this all up. These guides should help a lot of members. You did a great job!
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      09-16-2019, 05:32 PM   #3
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Excellent. Subscribed
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      09-17-2019, 03:26 AM   #4
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Fantastic guide, thanks for taking the time to post.
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      09-17-2019, 06:09 AM   #5
B1ue52
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Quote:
Originally Posted by Jungatron View Post
A+ work. Thank you for taking the time to write this all up. These guides should help a lot of members. You did a great job!
Thanks man, appreciate the feedback
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      09-17-2019, 06:10 AM   #6
B1ue52
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Quote:
Originally Posted by rjwojcik View Post
Fantastic guide, thanks for taking the time to post.
You're welcome. Just trying to help people do things for themselves they can often be scared of.... and hopefully save some money also
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      09-22-2019, 02:52 AM   #7
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Wow thats an incredible guide and will help so many, top work!
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      09-23-2019, 05:05 AM   #8
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Heres some pics with it on the car after a wet sand and 2 stage polish.

As you can see, the EB11 is a perfect colour match and the black has a mirror finish. It will get one final polish now it's on the car and Gtechniq C1 and EXO coating
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