How to do a minor Rust Repair and Touch up.
Updated: Sep 27, 2020
Today Im going to be showing you how to do a some minor rust repairs and
and a spot blend, which can save you hundreds of dollars if not make you thousands. this is for all levels. BRAVE DIYERS, APPRENTICES to even qualified tradesmans.
I always start the job off with a wash using a PH neutral detergent, few squirts of diluted degreaser if it needs itand then after drying the vehicle off I wipe the panel im working on down with a solvent.. like wax and grease removeror thinners.
The wash breaks down and removes water soluble contaminates like mud, soft drinks, blood etc
and then the thinners wipe down just to loosen any oils and greases that havent been lifted off the surface from the wash.
The advantage of cleaning the vehicle and panel is that it this makes it much easier to work with also to see if theres any other damage you might've miss and for prepwise it
stops the sand papers and abrasives from clogging up and contaminates smearing all over the surface and bare metal.
Take some photos beforeshots at different angles so you can keep as a reference incase you forget what goes where.
Remove or loosen anything thats going to get in the way, also helps free any trapped contaminates like dirt or dust that could
land on your fresh paint later. For this vehicle you just pull away the rubber seals which exposes the screws to undo and the mould should drop.
Start with using using a hard block with 80 Grit sand paper, keeping the block flat at all times, do not use its edges or corners thinking its faster start to dig the damage out it will leave a missive dip and low spot in the panel
sand with the flat surface. use the 80 grit, once youve hit the rust and taken 70% of it out, move onto the 120 grit,again same technique however just a tiny bit bigger overlap sanding surface area then the previous 80 gritso your basically removing the 80 grit scratches out completely, then after the 80 grit scratches are gone with the 120 gritmove up in papers.
Using the 240 grit and removing the previous 120 grit scratches
each time the repair area is going to be a tiny bit bigger so always remember keep everything as small as possible.After 240 grit we're going to treat the steel with some phosphoric acid, I'll be using 3m Rust converter.
Dampen a clean scotch brite with the acid and wipe over rust and raw steel, make sure the surface is saturated with the acid.
Let it soak for a good 5-10 minutes occasionally re wetting it up wit the acid. dont let it dry on the surface.
after 10 minutes give it a good scrub where the corrosion is. Now with some clean towels,
what I do is wet 3 up and ring them out so that their moist, wipe the acid off with the 3 towels one after another and then with the 4th DRY one to make sure theres no moisture left.
Now the rust has been neutralised, and the raw steel is conditioned. Its ready for body filler/bog/bondo. At this stage remember to keep wearing gloves, try to work in a low humidity environmentment to prevent flash rusting and if someone comes along and tries to start a conversation with you, tell them to turn and face away from the panel
incase their giving you news and the full weather. One thing I cant is when blokes start coming over and start talking shit and then start putting
their grubby fingers all over the panel and conditioned steel..
Wax and grease remover will remove the oils and greases from finger tips however it doesnt remove the the salts and salt speeds up the rusting process !!
Anyways back to the car.
I'll be using 3m platinum body filler, a disposable paper mixing board With a steel applicator.
For the applicator, round off the sharp corners with some sand paper. makes the application and spreading much easier, you will understand how after you spread a few rows
of the filler. The sharp corners can mark the bog when you decide to do like a sharp corner drift while spreading it.
Mix the hardner and filler whatever the TDS recommends. during the winter times people tend to add extra hardener to speed up the process however sometimes it can come back and bite you in the ass. especially with white cars. this is called bleaching, when the peroxide from the hardener start coming through the hifill and basecoat and you see a red tone yellowish patch weeks later and customer brings back the car tripping out. So mix it according to TDS and be patient, go have a ciggerette or something.
Once its 85-90% dried I like to use a hard block with some 40 grit, this will give it a nice quick chop removing strands of the body filler, majority of what you dont need. kind of like grating cheese, bit moisty. Gets rid of the excess quick without making heaps of dust. After that Bog should be hard.
Starting at 80 grit, keeping the block flat and keeping the repair small chop down the body filler, move up to 120 grit, and then to 240 and then 320 and even 400
and 500 grit because this is going to be a wet on wet process.. meaning your not leaving the primer to dry overnight in order to block the next day, we're going to be using a acrylic pressure pack primer without as much build, so the repairs got to be done pretty good.
Always remember... the higher the grit you end with, the less porous the surface is going to be for the paint to sink into. For example, say you got a slab of polished concrete and you crack it in half, you pour a glass of water on the polish surface and on the other half you pour it on the rough face it split from. Rough ones going to soak it up faster. Same concept. This is known as sink backs, .. too fine and you might have adhesion and paint delamination issues... but better to go a bit finer and then a coat of adhesion promotor, depending on what you want to achieve, if I was priming it up to leave over night I would finish it with 320 and then the first coat of primer, it would be reduced with a extra 10-15% to make it thinner, allowing it to actually sink in and root itself into the foundation for extra adhesion.
Another way to prevent sink backs for WET on WET process is to throw 10-15% of your fastest hardener into the base coat. Add a few drops of accelerator in it if you have to wear a jumper Then just dust a few coats onto the repair section,
make sure their open coats, close coats might fry up if you dont have your timing down pat. After 15-20 minutes to cure you got a pretty good foundation to hold up the next coats.
so back to repair preperation...
While we/re on the topic of prime ups and the grade of sand papers to finish the repairs .. Heres a story for any APPRENTICES reading this. In the last decade Ive worked in 11 shops. At the production shops.. usually the panel beaters will send their repairs finised off with 180-240-320 for the painters to prepare for hifill, this is in Australia of course, Ive heard in other countries the painters do all the bog work not the beaters. so in Australia any lower then their either lazy, or just cant be fucked, or whatever the issue.. Painters usually have a sook and whinge sending it back to be feathered out in a finer grit .
How I see it, we all work together for the same boss. Its all about Team work for that same ONE VISION. Whoevers got that BEATERS VS PAINTERS mentality then Im not sure whats going on in their head, reminds me of primary school.
When the jobs come down in the afternoon for prime ups, give the repairs and the next meeting panels a good wipe down incase they could be blend panels if there is damage on the blend panels then repair that too because theres no feeling worse then painting over a damaged panel just to get a colour match, just cant squeeze dat trigger. So go over everything and see if they missed anything. If they missed a ding/dent or the bodylines arent straight then just finish the repair off. a skim coat of bog to finalise repair wont hurt. And if you dont know how to do it just do it anyway and you will know how to do it. End of the day your an apprentice, you will fuck up so just take the risk to learn... you get paid ragardless.
Its much faster then having a sook and shuffling cars back and forth to the beaters. The repair maybe doing their head in for days and their just over it so just take a deep breath and finish it off yourself. Youll upgrade your skillset which means = more money and more money means more tools. Be a team player.
Ok sorry got carried away reminiscing about the past. So the filler repair is done, and finished off at a higher grit then usual for us to carry out this wet on wet process... a coat of pressure pack acrylic primer ( a lot thinner then 2k hifill/primer ) hence why the repairs got to be spot on.. let that flash off and dry it with a heat gun then second coat.. let that dry flash off and throughly dry with a heat gun... now with some dry 800 grit sand paper just flatten out the 1k pressure pack primerthat way it gives you a nice flat foundation lay your paint down onto and also allowes better adhesion.
Mask everything up, make a softedge with some 3/4 inch tape... this is also known as backmask, flipmask... its crimping the edge of the sticky side back on itsself so your tape has a edge
folded in the sticky side leaving a little non sticky edge. this just allows the paint the land on that soft edge with creating a hard line when you peel the peice of tape off for a
smooth transition. good for like when you want to end the paint on a hard line for example if your doing a close door respray you will put it on the edge inside the joor jamb so you dont have a hardline of paint buildup ending at corner where it goes into the door jamb but a rather soft edge. hence soft edge ok so that first line on the turrets where Im going to end the blow in I put my soft edge there, quick tip... always face the gun and spray inwards, even on the second coat
rather then spraying outwards like a normal painter spray inwards, away from the edges, lines and where you plan the lose the fade. so your not creating a massive job with
overspray all over your edges.. you will understand once you do a couple.
second coat of colour, again over lapping the first coat in painting inwards. whilst its still wet... drop the pressure, hold the gun fruther back and do a drop coat.
This allows the metallics to fall nicely and melting into the wet surface. so the metallics are are uniform and sitting evenly, because this colours got some pretty coarse metallics in it.. the coarser the metallic and the hotter the weather then the more chances of getting whats known as ' MOTTLE ' thats another lesson for another day.. on a silver car or some thing.
So now you got the colour down and its tried.. lets go mix up the clear. we'll be using a 2k air dry clear with a 4:1 mixing ratio.
Give the panel a tac rag, especially in the area where you plan the end the blend next to plastic. tack rag to collect any dust and also metallics thats landed to far out
when you done the drop the coat, you dont want to clear over those mattalics will stand out like a diamond giving away the spot blend!.
First coat.. again spraying inwards, cover the colour/ basecoat... let it flash off for a good 5-10 minutes and then second coat a bit bigger then the first coat spraying inwards...
Now a lot of painters usually use a spot blend reducer.. all that is is a slow reducer with a % of acrylic clear which is shit, just empty 90% of the clear out of your gun..
and replace that 90% with some recycled gunwash thinners this will allow it to bite and grab into the outter sections thats finished with 2000/3000 grit. give it a shake, squirt pure clear out of the fluid tip so the gunwash thinners mix is pissing out of the gun
Flick it inwards at the edges where you ended the 2nd coat clear coat but dont go over the gloss unsanded section. you rather leave a dull edge and buff it later on , that way you got good adhesion and the clears thickness tapered down.if you finish the flick the thinners and clear mixture and go over the dull (2000-3000grit) into and over the gloss then it will leave halo ring which gives away the spot blend.
Practice makes perfect. theres a lot involved to do it right like timing, colour matching, prep, masking up.. if you get it the first time then go start a touch up business.