So to start of, you need to identify the size of dent. If its a large size you may need it pulled first or tapped out from behind if possible. The idea is that if you remove the dent as much as possible, the less work you will have to do later. The best way to hammer out mild dents is to use a flat headed hammer, and a flat headed solid object behind. Usually this is done with whats known as a dolly:
Place the flat side of the dolly to one side of the panel, and hammer it from the other side....the idea being that the panel is almost returned to its original shape.
The next stage is to choose a suitable filler. Now most of the fillers on the market these days will not adhere to un galvenized metal. I.e. the coating of the metal has a coat to protect it from rust, if this is removed then the metal will show a different colour, slightly darker. You need to make sure that when purchasing the filler, that it will adhere to ungalvenized metal as you will most likely brake through to the ungalvenized metal when fixing a dent. These fillers are mostly 2pac, i.e. they have a base product and a hardener. A decent filler can be pruchased from halfords for £6.45 i believe, that should be enough to do an rea about the size of your hand.
Before applying the filler it is important that you prepare the panel back to bare metal, to do this i recommend using 180grit paper. You only need to go back to bare metal on the area that will have filler, but, bare in mind you maye need to skim slightly over the dent afterwards to blend it smooth. Remove all the impurities like dust, then you can apply the filler.
Mix the filler up on a clean surface, and use goggles and gloves as it does like to flick about. Mix it with 10% hardener, and now you can smoothly apply it to the dents. Me personally i like to do this in two stages for accuracy. In the below case i applied it just over the dents with the purpose of rubbing it back to the dents like so:
Then, once hardened over 10mins, i now apply a second coat going much further:
Again, once dry you can begin to rub it, i suggest using a dust maska nd goggles, rubbing it down with 180 grit paper on a block afterwards. you need to make sure that all the edges are rubbed back smooth, and use you hand flat on the panel to assess whether the filler is firstly flat, and that it isnt fipping too low or too high. If need be add more layers to get it perfectly flat. The below exapmle just needs a little more rubbing to remove the edges.
If you plan to use aerosol primer, and therefor very thin, you may wish to finish the filler off in first 320 grade paper, then 500 as the primer is so thin it wont cover the scratches. However if a 2k laquer is going to be used then you can leave it in 180 grit paper.
Now you are nearly ready for priming. Firstly though, the paint needs to be feather out using 320 by hand, or 180, then 320 on a da.
if its all a bit daunting atm, dont worry, cos in a post to this topic ill demonstrate it on my own car.
but bascially, there mustn't be any large steps up in the paint. i.e. you paintwork is made up of several layers, and there needs to be at least 5mm gap between the layers.
Now you can prime the panel up. Here comes the first of the spraying stages. Using a compressor and an airgun...doesnt have to be the best for priming.
First you need to mask of the area around where you want to prime, now you only need to cover the filler, bare metal, and the feathered paint edges. Also however we dont want any harsh masking lines where the primer has gone right up to the edge of the masking tape, so i suggest masking a wide area, but only spraying over exactly what you need, as you can see on this bumper below:
Nexa autocolour HS+ Primer filler. It is avaible with hardener from any unipart.
I will be applying it with my nice gun:
setting it at 2bar pressure. Applying 3 coats, first coat, just over the primer, second to cover the bare metal and 3rd to cover the feathered edges.
Depending on the colour of your car you will need to tint the primer. So if its a dark coloured car, dark primer etc etc. The autocolour stuff is catagorised by SG, so SG01 is white, SG05 is mid grey and SG07 is dark grey, if you need to inform the provider. You also need to add hardener to the product.
If being airdried you need to leave the applied primer for at least half a day, then you can begin to rub it.
I suggest rubbing it with 320s, the 500 grade paper. And finally 1000 grade paper. You need to make sure with your hand flat on the panel that the primer is smooth and flat. Before you begin rubbing it you can apply some black aerosol as a guide coat, so when there is non left after rubbing it, then its ready to paint.
Around the rest of the panel, you need to grey scotch it using scotch brite:
https://weldingsupply.securesites.com/cgi-b...1:UNDEF:OR:7447
the idea is that the panel is no longer shiney, and therefore ready to accept laquer/basecoat.
the last stage is to mask off the panel and to blow it all off so that no dust is present. Then finally you can use some panel whipe to degrease the panel. Now you are ready to apply your basecoat. The basecoat i am using is a waterbase product made by ici. It can be purchased ready mixed. As it is waterbase it obviosly goes off like water does, so blowing the trigger of the gun half on will just produce air, allowing the panel to get drier quickly. For metallics, you jsut blow the area you have repaired, no the whole panel.
Waterbase also takes the form of 3 coats, The first coat is a light dusting, the second slightly heavier, and the third is a smooth even drop caot applied by turning the pressure down and flickig the gun away at each edge of the primer. At this point, once its dried of between the coats you may wish to shine a torch on the panel to check the primered area has been covered. If not, apply another final coat.
Now using a clean tack rag:
Whipe any excess dry paint from off the panel.
Now clean the gun with a waterbase cleaner if you are using waterbase paint.
Now you can apply the panel with laquer. By far the best laquer is the most expensive 2k laquer, but it is up to you how much you apply.
The laquer is made up of base product, hardener and 10% thinners.
The best way i find, is to apply a very light dust coat, then apply a smooth top coat. The pressure needs to be quite high and you need to pull the gun about a foot away from the panel. So you will need to cover the whole car to do this. Work from the bottom up in smooth motions over the panel. Resist the urge to flick the gun, and try to keep it smooth.
The 2k laquer will need to be cleaned out of the gun using thinners, i just spray it through.
the laquer will need to be left for at least a day to dry.
Thats basically it, but i will post exactly each stage as i do it on my car tommorow so you can see how it is done.
Hope this helps, i appreciate that some people may do it differently, but this is how i have been demonstrated how to do it by the manafacturers of the products.
If you dont understand how to use a pray gun, i wouldnt attempt this, but you can save yourself some money by doing the stages upto and including primer.