Examine the worn or faded spots on the urethane surface to decide if the condition has sufficient integrity (see Repair Compound and Mechanical Repair (Sub-patch) for renovation. Also, any imperfections you see at this stage will be amplified after the pigmentation. These can be removed with a light sanding using 3000 grit finishing paper and follow with a tack cloth and final cleaning.
The urethane pigmentation used for automobile upholstery is classified as a semi-solid permeable membrane, is a thermosetting polymer (with elastomers) it remains flexible while retaining its tensile strength, to enable it to expand and contract, following the temperature fluctuations (elasticity) of the substrate. The urethane although very resilient to abrasion wear from entering and exiting the vehicle, by using additives it still maintains its physical properties like flexibility, tactile hand and its patina
A urethanes fibre structure will stretch in all directions with no particular grain or stress pattern. The urethane surface coating will not withstand multi-directional stress, however, and when it’s flexed or stretched continuously in the same place the surface coating develops minute cracks. So any pigmentation, fillers or adhesives used must be able to maintain this flexibility, without compromising its structural integrity
Urethane Surface Cracks
As the leather hide loses moisture, it begins to shrink and stiffen. This leaves a minuscule gap (delamination) between the leather hide and the pigmented (colour) urethane coating on top of it. The urethane coating is no longer supported by the hide; without proper support, it starts to crack.
Colour change - if you are applying a pigmentation to change the colour of the finished leather; surface preparation (removal of existing pigmentation (colour) is the most important step.
Unlike lacquer-base preparations, which close the urethane micropores, water-based products allow hydration (transpiration and evaporation of moisture) via the micropores. This enables hydration of the finished leather, maintaining its soft and supple patina after you have renovated the pigmentation.
To bring about the best renovation results, it is essential to prepare the leather before application. It will be necessary to remove most of the original pigmented urethane finish without creating thin spots or sanding all the way through the top coat. By correctly preparing the surface and breaking down the original pigmentation, your newly applied pigment will look like an OEM applied a translucent finish.
Swissvax Leather Healer is an easy-to-apply leather pigment (dye) comprising a high number of superfine pigments combining best results with a minimum thickness pigment application so that the look and feel of the leather are not affected as it is the case with many other leather dyes. The Swissvax dye is easily applied with a small sponge and sets automatically and permanently.
The leather fine and natural structure, as well as its typical original feel, are perfectly preserved. 46 Standard Colours are available or you can also send a small leather sample and they will match your interiors leather colour.
Swisswax Leather Glaze- (finished leather top coating) new leather remains new for many years thanks to the colourless protective layer provided by Leather Glaze which drastically reduces any signs of wear. Leather driver’s seat, the smooth leather steering wheel and the smooth leather shift knob are places where the leather undergoes the most noticeable wear - even on new cars. That's why every leather interior should regularly be protected with Leather Glaze for keeping it in mint "factory" condition - an inexpensive measure and little time invested for the best interior maintenance
A few days before commencing the actual leather renovation, clean the finished leather surfaces. As a cleaning solution, I use a formula that is used by one of the major tanneries to clean their leather. Mix a solution of 3% detergents that contains a surfactant (P21S Total Auto Wash) 10% isopropyl alcohol (IPA) and the balance distilled water. And then apply Leather Master Soft Touch (formally Vital) this is not a conditioner per se; it softens the finished leather and makes it easier to remove the seat covers.
Like all detailing task’s the correct surface preparation prior to the application of the pigmentation (colour) will ensure that it adheres correctly, and has both durability and aesthetics. Use a safe degreaser to ensure any oil and grease free surface (Leather Masters™ Leather Degreaser) this aerosol product is ideal for cleaning as it dissolves the oils and transforms them into a powder that is more absorbent than the leather. This powder is what is wiped off, cleaning and degreasing the leather. Allow the white powder to dry fully. If the powder is drying to a yellow colour, it means that there are still a lot of oils in the leather.
And then use a safe solvent cleaner (Leather Magic DT-152 or Leather Master Color Prep & Cleaner) this chemical is formulated from several types of alcohol and milder based solvents and is used primarily to prepare the surface of leather for repair or pigmentation application. It will remove all dressings, protectants, waxes and oils from the surface, but more importantly, it will strip off the topmost layer of the finish, which cleans the surface so that it is receptive to the application of repair and colourant materials. This also creates a permanent bonding of the materials to the leather.
The solvent should be sprayed lightly over the surface, and then by using a medium soft upholstery brush will ensure any ingrained soiling is effectively removed prior to application and to ensure proper product adhesion. Using a cotton terry cloth towel, immediately wipe dry. This will thoroughly remove any foreign matter found on the surface of the leather; mild solvents also work as an excellent degreaser. After letting the solvent dry off for a few hours the area should be lightly sanded over, this will remove any cracks in the surface coating.
Use painter’s tape and/or masking paper around anything that doesn’t require pigmentation applied
To ensure adhesion lightly sand areas to be re-coloured by using an abrasive (Scotchbrite 7447 - Maroon pad, General Purpose Hand - 320-400 grit) You’ll need to break down approximately 25µ (1 mil) of the surface, this is important to the new leather dye can ‘key’ into the finished leather and look natural. Be consistent in how far you remove the pigmentation, it is not necessary to completely remove the pigmentation that is sitting on the leather surface. Remove dust with a tack rag or damp micro fibre towel.
[: in the US pigmentation is called dye (although it’s a very different process for the application of a colourant]
Swisswax Leather Healer
An easy to apply pigment (colour) that sets automatically and permanently, without leaving a heavy layer of pigments as often encountered with other leather tinting leaving the typical original feel of leather perfectly preserved
Certain areas of your vehicles leather interior like seats, upholstery, side mouldings and steering wheels inevitably start to show signs of wear, even if well taken care of, that spoil its overall impression. Often these imperfections are not serious and are simply the colour that has worn off or light scratches on the leather surface which can be removed and will disappear with the right application technique and our leather dye.
Swissvax Leather Healer is an easy-to-apply leather dye comprising a high number of superfine pigments combining best results with a minimum thickness of the dye application so that the look and feel of the leather are not affected as it is the case with many other leather dyes.
The Swissvax dye is easily applied and sets automatically and permanently. The leather fine and natural structure, as well as its typical original feel, are perfectly preserved. Available in 45 standard colours; provide a small leather sample and Swisswax will perfectly match the colour to your interiors leather.
Spray a mist of water on the surface and then dab a terry weave towel or a small sponge into the pigmentation and gently rub it in, use small circular motions. Apply over one small section at a time overlapping the circles.
Swisswax Leather Glaze (Colorless)
Use after the renovation of finished leather’s pigmentation, this clear top-coat has a dramatic impact on leather, reducing signs of wear. The colourless, clear protective layer provides a matte finish and protects finished leather, keeping it looking 'as new'. It's a must-have product particularly in areas which get the most use, such as steering wheels, leather seats and gear stick knobs.
Leather Upholstery Abrasion (Rub) Resistance Testing
The abrasion resistance of finished leathers thin urethane covering is designed to contend with clothing abrasion from exiting and entering the vehicle. Wear from abrasion is a complex phenomenon and the information Taber Industries provides at Abrasion Testing: Taber Industries-Material Test & Measurement is meant to give you an introductory understanding of the common wear processes and their underlying causes. Having this practical knowledge will help to address the cost of failures caused by wear and abrasion.
Dirt is the real enemy of leather, acts as an abrasive every time you sit down or change your position while driving. Abrasion wear is due to hard particles or hard protuberances forced against and moving along a solid surface. These hard particles might be commercial abrasives like silicon carbide and aluminium oxide, or naturally occurring contaminants like dust particles and sand [crystalline silica (quartz)]. If the abrasive particles are allowed to roll, rolling abrasion or three-body abrasion occurs.
This can lead to catastrophic wear, which is a rapidly occurring or accelerating surface damage, deterioration, or change of shape caused by wear to such a degree that the service life of a part is appreciably shortened or its function is destroyed.
ASTM D7255 Standard Test Method
Abrasion Resistance of Leather (Rotary Platform, Double-Head Method) this test method covers the determination of the abrasion resistance of leather using the rotary platform, the double-head tester (RPDH).