>>> There are several areas that are sticky to the touch, notably on head and armrests, so presume this is as a result of contamination by natural head and body oils.
There are 3 levels of stickiness, one to the leather structure and the other to the leather finishes and it could be both.
Where contamination penetrated into the leather structure especially sweat that carries traces of urea and when ferments shift the protein fiber ionic negative (-ve) thus the beginning of the denaturing of the leather, in other words reverting to rawhide, that why the feel of stickiness same as rawhide when damp or wet. The other less severe situation that involves only the finishes of the leather especially the topcoat and the extreme cases will be both the leather structure and the topcoat.
In all three possibilities the normal procedure is to degrease and pH balance as a complete system with Degreaser-2.2 (pH 2.2) and Acidifier-2.0. This system removes penetrated body contamination and protonate the protein fiber at the same time. Ionic charging the protein fiber more ionic positive (+ve) to attract the other leather constituents like the tanning agents especially when stickiness is concern. This degreasing treatment that wicks out the foreign contamination will also return the leather to its original squeaky feel, a sticky or slimmy leather is not healthy just like a stale fish. Leather is protein as well so resembles the freshness of a healthy squeaky fish when feels or rubs with our hands. If the leather in such situation does not return to a squeaky feel it has gone over the threshold and thus becoming a rawhide instead.
When the stickiness is only surface, after degreasing and pH balancing the topcoat is partially removed by Eraser-4 and 2000grit sanding, thereafter a fresh topcoat of matching luster is applied with a crosslinking agent thus – MicroTop-54 (G, S or M) is crosslinked with Crosslinker-25.
Will need pictures to be more precise what is necessary to solve the sticky problems.
>>> There is no discolouration although the patches are slightly dull in comparison to other areas and the slight grain texture present elsewhere is much smoother.
Dullness could be soiling accumulation or non-compatible products used. It could be the wear out of the topcoat – will need pictures to be more precise.
>>> I have tried cleaning with mild dish soap and mild leather cleaner (Autoglym) with no effect.
Soap is never used on leather notice the scum that left behind that accumulated soiling on our wash basin and bath?
What is mild, mild acidic is good and mild alkaline is bad for the leather, always check the pH of the cleaning solution when applying on leather. Leather is as amphoteric material and is sensitive to pH especially above 7, the higher the worst effect to denature the leather reverting back to rawhide.
Check leather cleaner residue by applying onto a glass surface - a good cleaner will have less residue - can clean computer screen and spectacles as well with clarity.
>>> After much reading of the web I also tried rubbing corn flour on the affected patches and warming with a desk lamp for a couple of hours, then wiping away.
Depends on porosity of the pores when using corn flour or any powder to avoid clogging the pores.
Heat is never suitable for leather in any situation, it will dries up the original fatliquor (fat, oil and water) that leads to dryness and when flexed will develop cracks
>>> This made the leather much drier to the touch but much of the stickiness returned once I had fed with leather cream ( that said I would estimate the stickiness is a good 30% improved).
Remember that leathers were not originally treated with “creams” of any kind – only fatliquor. Feeding of any creams only make the situation worse to the chemistry integrity of the leather. Fatliquor is a ionic charge fat, oil and water that hydrogen bond by ionic attraction. Creams when stuff into the pores of leather retards the natural transpiration that prevents the leather breathability.
>>> What to try next?
Do not need to try, all non compatible aftermarket products is consider foreign contamination and need to be remove entirely from the leather structure with Degreaser-2.2 > Acidifier-2.0. The leather structure has to be tested for squeakiness to confirm the chemistry integrity of the leather. The leather constituents especially the fatliquor need replenished to prevent leather stiffness that leads to cracks when flexed.
>>> If the problem us due to body oil contamination is this just a question of repeat treatments,
The grain of the leather is tighter than the suede side, you may reverse to see the extend of body contamination migrating to the more porous side of the leather and best to degrease from the reverse side. Repeat treatment is necessary to bring consecutive contamination as it wick in each drying cycle.
>>> should I try a leather degreaser .
There are many leather degreasers in the market, the best choice are those that is waterbased, non-flammable and has a pH value below 3 to protonate the protein fiber at the same time.
Emulsified grease need to be remove as well, so a compatible rinse is vital for suspension follows with extraction.
>>> or could it be that the protective coating has been broken down - how can I tell ? Any suggestions welcome.
A picture is worth a thousand word, show us some pictures and we will help further.
Roger Koh
Leather Care Consultant
www.LeatherDoctor.com