How do you guys get paint chipping to look right on diecast heavy haulers?

The grey dandruff thing ussually comes down to the silver being too bright and applied too randomly. Real chips happen where the paint gets hit, so door edges, corners, around the fifth wheel plate, the front of the trailer deck where machines drag over it. Pick your spots, keep them small, and once the silver is down, go back over it with a wash of brown or dark grey so the chips sit down in the surface instead of floating on top. That alone kills most of the dandruff look.

For the layered rust-through effect, it's not really washes, it's building up colours underneath before the topcoat ever goes on. On my last heavy hauler I painted the cab, then sponged on patches of dark brown, then a lighter rust orange on top of that, let it all dry, and only then shot the final colour over everything. Then you chip through the top coat with a damp sponge or a cocktail stick and each chip reveals orange, then brown, then primer or metal depending how deep you go. Hair spray chipping does the same job and gives you more control than salt, worth trying since salt fought you on the thicker paint. Sponge chipping with a torn piece of foam works well on the trailer deck too because it gives those irregular clusters instead of scattered dots. On the chrome, don't hit it with matte varnish straight off the can, it almost always goes foggy. Two things work. Rubbing the chrome gently with fine sanding sponge or even an old cloth with a bit of toothpaste knocks the mirror shine down to a tired satin, then a very thin dark wash in the recesses makes it look like the plating is going. Or strip the chrome entirely with bleach and paint it silver, then weather it like any other part. A spare tyre on a working truck is usually scuffed, dull and sometimes missing chunks of rim anyway, so a painted spare often looks more honest than a dulled chrome one. One more thing on the deck, streaks matter more than chips down there. Machinery leaves rust stains and fluid leaks that run backwards, so a few vertical streaks from bolt heads and tie down points will sell it faster than a hundred chips.

The trick that finally cracked chipping for me was a box of cheap oil pastels from the art shop. I colour the actual edge of each chip with a rust orange pastel and smudge it in with a fingertip, so the damage has a soft wear ring around it instead of a hard silver dot. Went back and redid the whole front axle area of my Volvo that way and it changed everything.

On the spare rim I went with the strip and paint route, did it with oven cleaner in a ziplock bag outside, came off clean in ten minutes. Only warning, do it somewhere with airflow because the fumes are nasty.

Back before hairspray was even a thing in this hobby we did chips with a fresh no.11 blade. Nick the paint at an edge, then turn the blade flat and flick little flakes loose. Crude, but you control exactly how deep it goes, and it works on thick coats where salt gives up. Practice the flicking motion on that scrap piece first, it takes a light touch or you gouge straight to plastic. Also get some reference photos before you touch the back of the cab. I shot rolls of film at farm machinery shows in the 90s and the surprise was how much working wear is oily dirt film rather than rust. A grimy dark wash behind the cab and round the fifth wheel reads as worked hard faster than a hundred chips.

Still finding my feet here so excuse me if this is a daft question. I mostly do 1:35 military stuff, halftracks and the like, and I got decent results chipping by working on a small patch at a time while holding the model under a strong lamp. The side lighting shows you straight away when a chip looks like a sticker versus when it actually sits in the panel. Might help with the cab edges.

Also wondering, if you layer the brown and orange underneath then shoot the topcoat over it, how do you handle decals? Mine always ended up sitting proud so chipping around them looked wrong, and I never worked out wether you chip thru the decal itself or leave a clean halo round it.

One thing that helped my last lowboy was getting the sequence right: seal everythign under a matte coat before you start the streaking, because the vertical fluid stains feather out far more cleanly on a sealed surface than on bare paint, where they tend to bite unevenly and leave hard edges. I also worked out the hard way that the deck on a real lowboy is usually timber over steel, so the wear is concentrated on plank edges and around the raise-lower ramps rather than spread evenly across the surface.

Another small detail on the spare, it gets manhandled whenever it is swapped out, so scuffing just the areas a hand would actually grip sells the wear better than dulling the whole rim.