SILL REPAIR & PAINT

1

Our 2003 Chrysler PT Cruiser had a sizable rust hole, with surrounding paint blisters indicating further corrosion. First, it was important to establish why the panel had rusted.

2

We probed the suspect areas. A screwdriver passed through the bubbled paint and it was clear that the panel was rusting from the inside out.

3

Both the welding and paintwork required were made more complicated by the suspicious bubbling paint extending into the rear door shut.

4

As replacement sill panels are unavailable in the UK, we had a section cut from a scrap car. This included both the outer and inner sill.

5

The spot welds (see inset) were drilled out with a suitable drillbit (see Step 10) to separate the outer sill from the inner. The top section was sliced with a cutting disc.

6

Our replacement panel bore some light surface rust, which could be removed with a wire brush prior to receiving a coat of rust converter.

7

We then removed any plastic liners, or trim, that might get in the way, or be damaged. This section was secured by a screw and several plastic friction clips.

8

Plastic and fabric wheelarch guards can trap mud and moisture, promoting corrosion. The affected area must be cleaned, or repaired, where necessary.

9

We assessed the point at which we needed to cut out the rust and ensured that we could weld to unaffected metal, by scribing reference marks on the car.

10

As with the repair panel, we used the special drillbit on the original spot welds that secured the bottom of the inner sill to the outer (see Step 5).

11

After removing any flammable material inside the sill, such as the sound-deadening material that had caused our rust, we relocated any wiring that was present.

12

The outer sill here had corroded severely, so we checked that the rust had not spread to neighbouring panels, such as the inner sill, which would have required further repairs.

13

Surprisingly, the inner sill on our car was in excellent condition. Light surface rust was removed with a rotary wire brush and…

14

…coated with anti-rust converter. Try to avoid areas that will be welded, because you risk compromising weld strength if the metal is contaminated.

15

The amount of metal removed showed how far the corrosion had extended, even though the inner sill was unaffected. Ideally, we should have replaced the entire section but…

16

…because the scrap donor car had suffered frontal crash damage, the full length panel was unavailable, hence the gap (circled) on the far left, below the front passenger door.

17

With the panel clamped in place, we made minor adjustments to both the panel and car body to ensure an accurate fit.

18

An edge setter/joggler tool created a step into which the edges of the new panel would locate. This reduces the risk of distortion and the body filler needed.

19

Before the panel was clamped in place accurately, we coated all bare metal with a weld-through etch primer to reduce the chance of corrosion striking again.

20

Once we were certain that the panel was positioned accurately, we disconnected the battery and started welding. Weld in short bursts only, leaving time for the metal to cool, to avoid distortion.

21

As the area had been spot-welded originally, the panel’s shape made seam-welding difficult – the bottom edge of the outer sill was plug-welded.

22

Next, using a sheet of Zintec steel, we measured and cut a suitable section to cover the remaining hole. Once again, weld in short bursts only, to avoid distortion (see Step 20).

23

The plate was fitted before the sill section had been welded fully. We secured it with a welding clamp, although several mole grips will usually suffice.

24

Due to the MOT regulations regarding welding repairs (see page 64), we elected to seam-weld this homemade panel into place, including its bottom edge, to ensure maximum strength.

25

If your welds stand proud (like ours, not helped by us using 0.8mm diameter wire on this thin metal, instead of 0.6mm), use a grinding disc to flatten their tops and…

26

…finish off with a flap disc, which is less aggressive. Note that grinding also risks distorting surrounding metal, and flying sparks can burn upholstery and mark glass.

27

We removed any paint and potential contamination (such as oil or polish/ wax) with an orbital sander and 400-grit sandpaper from a decent quality brand, such as Mirka and Starcke.

28

We mixed the body filler on an onion board, available from bodyshop suppliers for about £8. Seam-seal any joints, where moisture might enter the sill.

29

You should not need much body filler, although several light layers are preferable to a single heavy one. Wear protective gloves.

30

During sanding, you may encounter high-spots, which will require tapping-down and the area refilled. Wear a mask to protect your lungs from filler dust.

31

Use 80- or 100-grit sandpaper for initial shaping. Modern abrasives do not need water, especially as filler and primer absorbs moisture, which will cause the paint to micro-blister.

32

Pictured is the result after sanding two light coats of filler. There was a slight variation in the lower sill to door gap that could be tapped down and refilled but...

33

…we decided to paint the whole sill panel end-to-end. Using 400-grit sandpaper on our sander, we prepped the whole panel lightly.

34

Some areas could not be reached by the sander, so the filler had to be shaped by hand. We started with 40-grit, progressing to 100-grit, then 400-grit.

35

Small indents in the filler can be repaired without remixing a new batch. Instead, an air-drying cellulose stopper can be applied with a finger and sanded with 400-grit.

36

The whole sill does not need filler priming, only the work area. Paper masking rolls are surprisingly inexpensive from a bodyshop, as is good-quality masking tape.

37

We wiped the sill down with a panel wipe solvent, then coated any bare metal with air-drying acid etch primer to optimise adhesion and corrosion protection. Wear a suitable mask.

38

Working in a well-ventilated area, we applied the thick filler primer, including just beyond the repair. The spray gun required a larger diameter nozzle (1.5-1.8mm).

39

Note how the filler primer ‘feathers’ into the wheelarch and does not form a step at the masked line. Apply a dust of black aerosol paint, which acts as a guide coat so that…

40

… when you sand it down with 400-grit, it guides your eyes to the imperfections. The aim is to remove all of the black paint, leaving a smooth and even surface.

41

Hand-sanding with a block and 400-grit will be needed in areas that cannot be accessed by the orbital sander. Should you rub through the primer, another coat may be required.

46 We masked up the car comprehensively. Note how far up the masking goes on the wheelarch; your intention should not be to paint up to the tape (see Step 43).

48 If the rubbing-down process reveals any bare metal, coat it with an acid etch primer – a small aerosol is ideal for this purpose. Wear a suitable mask.

47 After ensuring that all paint had been dulled by Scotch-brite, we applied a panel-wipe solution with clean kitchen roll to remove any lingering grease and dust.

45 A different approach was used for the front door jamb. The masking tape was folded back on itself ‘back-taped’ along the panel edge, avoiding a defined edge.

44 As it was easier to paint the whole door jamb, the area was masked up to the door seal and the original paint rubbed down with a grey Scotch-brite pad.

42 When you are satisfied that the primer coat is smooth and uniform, tricky corners can be prepared with an abrasive Scotch-brite pad.

43 Where you cannot mask up to an edge, work beyond the repair. Using your Scotch-brite pad, dull the surrounding paintwork to provide a suitable key.

51 Apply 2-3 coats of colour base-coat, allowing sufficient drying time to avoid the risk of the paint sagging. Do not paint up to the taped line on a flat panel.

49 Any paint shop should mix colour basecoat for you; most types are waterbased. We bought a quarter-of-a-litre, then stirred and filtered it into a measuring cup.

50 Our base coat needed thinning by 50%. We used slightly better quality thinners than plain gun-wash. The pictured quantity is sufficient for the whole job.

52 When dry, base coat takes on a matt appearance, while clear lacquer creates the sheen. We recommend using a non-isocyanate lacquer.

59 The final result was a vast improvement. We will follow this up by rustproofing, including cavity wax injection, and checks that our welding has not burnt away any underseal

53 Lacquer is thinner than base-coat, so it is easier to create sags and runs. Apply 2-3 coats, allowing sufficient time for the paint to ‘flash-off’ between applications.

58 We replaced any trim that was removed, including the wheelarch liners. Many manufacturers recommend that fresh paint is not waxed for several months.

54 Allow the paint to dry for several hours, before removing the masking paper. Leave the car for several days, before commencing any final finishing touches.

55 While we had not intended to create a definite edge, by painting up to the masking tape on the wheelarch, a line of new paint was obvious.

56 This was blended into the surrounding paint, by rubbing the area down with 2000-grit wet-and-dry, used wet, avoiding excessive hand-pressure.

57 A rubbing compound paste, followed by polish, was used to finish the task. This also removes any dulled finishes, created by the Scotch Brite pads.