Hello all,

I will be painting the bay on my Derby whilst the engine is out. I have no idea on painting but I want to do it myself and learn in the process!

Not looking for a pro job, I want it to look presentable and anything will be an improvement on what it is now. I'd like some pointers on what I can do to get the best results.

Questions:

Surface rust: Do i treat it with rust remover or do I take it back to bare metal?

What grade of sandpaper do I use to key it for primer?

Which primer? High build/epoxy etc? (As you can tell, I have zero knowledge!)

Sanding back, again, wet & dry?

Top coat

Thanks in advance.

Clean the bay down with a spirit degreaser to make sure no oil grease etc is left.rub down the rust with 180-80 grit paper depending on how bad.a sander might be useful depending on condition.once all or most of the rust is gone u could treat it with something like qrust.then fill with body filler if need bethen smooth off with 240-320 grit.from there ul need to coat any bare metal with something like acid etch primer.then fill the scratches with a high build.i use u-pol.as for the rest 400 wet and dry and a green or red scotch brite will key the surface enough for the paint to stick.depending on the finish paint you are using u might want to prime the whole bay.

U may want to flat the bay back after priming to get out any imperfections before u top coat. What paint r u using? 2pack gloss base and clear (solvent or water based)

I did this just at the weekend (on a front panel, but the theory is the same)

1. Clean the bay - petrol is a great degreaser.Be careful though, if your bay is anything like mine was there will be endless amounts of wax/sealer in every crevice and once you start, you have to see it through.I found a flat ended butter knife the best tool for this
2. Attack any rust with a wire wheel on a drill or 120 grit paper to get most of the loose rust off. If the metal has bubbled, you may need to sand it smooth again as it can raise up and sit proud of the surrounding metal.
3. Treat any areas where there is or was rust with something like Kurust - leave to dry then give it a going over with 400 grit paper to key it
4. Fill any pits left behind with body filler, sand smooth using 400-600 paper and repeat as necessary (use a coarser grade to start with if you've really piled it on! But never skip more than a single grade)
5. Now this stage seems to be forgotten, using a knifing putty (a thinner, often cellulose based filler) go back over the 2 part filler used before. 2 part filler often leaves small pits but the 1 part knifing putty fills these in. Use it very thinly or else it will never dry. Very rarely have I seen this product mentioned when this topic comes up. It saves so much time as you're not constantly trying to sand the 2 part filler smooth. When dry, smooth with 400-600
6. Now you need to feather the old paint in around the areas of rust you've not got looking smooth. Working from the coarse grade from step 2, work through up to 600 removing the scratches left from the previous grade. Work outwards from the filled area blending at the paint edge. You don't want a visible boundary between bare metal and paint. In fact, you really want to see a blend from paint to original primer to bare metal. Make sure you remove all the scratches left behind from all earlier stage. Yes high build will fill some of the shallower ones but it's always worth putting the effort in now as if you find the high build doesn't fill the scratches, you'll need to go back and sand them out before re-priming. Use sanding blocks where possible (I often use small pieces of wood or whatever I can find) and only use fingers where you have too. Filling and sanding really does take practice and you won't see the minor imperfections until your first coat of primer is on
7. Scotch brite the rest of the paintwork or alternatively use 400-600 grit paper with plenty of water. Clean up
8. Once everything is smooth de-grease again using panel wipe/pre-paint. Use nothing else as it will leave a residue behind. Use a tack cloth to remove any dust once the panel wipe is dry (it's very volatile, so doesn't take long)
9. Take a step back, make sure you've done everything, and then attack it with primer. If you have bare metal, you'll need to use acid etch on those areas. This comes in 1 or 2K or even as part of a high build. This is what I used. If you are using etch and high build separately, you'll need to scotch brite or use 400/600 grit between etch and build primer, cleaning, degreasing and tack clothing each time to remove grease/dust. If like me you use an etch/build combo then you only need give it 2-3 coats leaving 5-10 minutes between coats. Beware, most 1K paints are up to 90% solvents and propellants so you need to use a few coats but don't go too thick, instead build up in thin coats. Your first coat shouldn't cover up what was beneath. You ideally want to prime the whole bay, even if it's going to be the same colour. Watch for overspray 'blobs' and remove these with 600 grit paper when dry
10. Once happy, use 400/600 grit paper wet on anything you've primed. You will no doubt see imperfections at this stage. They show up worse with primer than with top coat so it's your decision whether to go back and repeat the filling and smoothing process on any parts you're not happy with or go ahead with top coat.
11. Once ready for top coat, remove all dust, degrease and use a tack cloth and go with your top coat. Again, 1k (so cellulose or similar) is the usual choice but again, it goes on thin so 3-5 thin coats is what you'll need. Otherwise, 2K is an option. There are lots of safety concerns with 2k, but I have used it with a good respirator mask (air fed should be what I use) and not died yet. However, this is not what I advise. It does however give a great gloss finish from the can, goes on much thicker and dries much harder. It is your choice, but do your research. 2K does however stick like shit to a blanket and takes a lot longer to dry than 1k so dust contamination is more of a problem for 2k. Either way if you get runs or a non-gloss finish don't panic. As long as you have enough paint on you should be fine
12. Once you have the top coat on, leave it for at least a week to harden off, ideally with some heat/in the sun (once touch dry as you don't want dust falling in it, though this can be remedies as described below)
13. Now the hard work begins. If you have runs, use a small sanding block, 1000 grit wet/dry paper and a spray bottle and sand it out. A block is essential here. I know this sounds mental, but if you work from 1000-2000 grit, you will achieve a gloss finish eventually, especially if you give it a very good polish and wax after. Some would say to start at 600 grit on runs but that can be a little harsh and cause paint damage. Bes to start with the least abrasive option and then work down if you have to. If the finish is not glossy and is 'rough' to the touch, again, use 1200 grit paper and work your way to 2000. Keep the paper wet throughout and change it as it gets clogged and discard. A build up of paint may become hard and scratch your new paint.
14. If you can, use a 'soft' cutting compound (like G3) and a damp rag to cut the paint back after the 2000 grit along with a lot of graft. A machine polisher would be best, but that's hard in the bay. Give it a polish and a final wax.
15. Stand back and wait for the ends of your fingers to grow back!

Beware, to do this properly takes a lot of time and dedication. Despite the paint contamination issues I had with my previous attempt at painting, my prep was second to none, but took months of evenings and weekends to achieve. On the other hand I did a much more 'daily' job on a coupe boot lid and front panel in two days over the weekend. It all depends on what you want from the job.