Boot floor preparation for paint
The boot floor was in excellent condition considering that most 190SL's I have viewed have water penetration past the rubber weather strip. Eventually rusting away the channel where the weather strip bonds to with rust settling in the lower parts of the wheel wells and boot floor. Preparing the floor to accept its first coats of paint was easy. What was not easy was treating the inner wings up to the 'B' posts as my rear wings had not been removed. The entire floor and rear wings were acid washed with POR15 Metal Ready in a plastic spray bottle. This allowed the acid to be sprayed deep into the inner wings. Several costs were applied including to all joints on the boot floor with a hard brush and 3m Scotch Brite pad until all signs of surface rust were removed. The acid was continually sprayed with water from a plastic spray bottle to keep the acid from drying and to reactivate it. After soaking in acid for 20 minutes the floor was thoroughly washed down with warm water and immediately dried before any rust formed.
Notice in the photo of the boot floor the original factory grey/tan primer PPG's DAR 4065 "Sandalwood." In fact this colour can be found on the seat base frames, behind the dash and probably under the colour coated body. The factory did not colour code the floors and had they been aware of rust would have probably provided greater protection to the undercarriage of these cars. In fact the frame box sections were never painted nor were coated with rust preventative material. That is why these cars rust from the inside out.
The dry floor was then sanded with 3m Scotch brite pad and cleaned with panel wipe and degreaser. I used a Devilbiss GTI gravity feed gun with a 1.4mm tip to spray the floors with three coats of PPG DP40 epoxy primer. This should provide sufficient coats to seal the metal over which was sprayed 3M smooth anti chip coating, Grey part number: 08886. I like this product as it is smooth and overpaintable and sharing the same, robust anti-chip benefits of the textured product, 3M™ Smooth Coating dries rapidly to an excellent finish. Applied using the pressure adjustable air-fed 3M Pressure Pot Stonechip Applicator gun gives the best results.
The joints were seam sealed with Wurth Polyurethane adhesive and sealing compound. Product 0890 100 2 Grey using a hand application gun. A further coat of PPG DP40 epoxy primer will follow three coats of PPG Semi-Gloss black DB167 or RAL7167 (DB164 or DB167 Tiefdunkelgrau Matt) in the inner boot floor and the undercarriage side will be painted PPG's DAR 4065 "Sandalwood".
Incidentally any one planning on replacing the rear wings and or the rear panel should pay particular attention to how these parts were joined at the Mercedes-Benz factory to the boot floor. The outer sides of the boot floor had a felt strip between the lip of this panel and the rear wings. The felt should be removed and replaced with a modern sealer after de-rusting as it acts as a wick soaking up water and rusting these two sections. Ensure that the outer floor is not welded to the rear wings at this section otherwise the rear wings will distort with stress marks at the meeting points. The lip on the rear of the boot floor should be spot welded to the rear panel. The factory's welding equipment and workers were remarkable as there was very little distortion or dimples on the outside of the rear panel. Once spot welded any dimples should be finished with lead even though this area will be behind the rear bumper centre section. All joints should be sealed after epoxy priming.
