Occasionally we get questions from customers whose boat upholstery mysteriously turns up with unsightly vibrant pink, purple, blue, or sometimes even gray splotches once they remove their boat cover after a period of dormancy. Commonly, people assume that the "stain" is a color transfer between materials of the boat cover and vinyl cushion, however this is not the case and the issue is actually known as "pinking" in the boating industry. In reality, the culprit actually exists in the vinyl of the seat cushion itself. In this article, we will be taking a deep dive to advise on what pinking is, how to prevent it, and the good news about it.
The science and history behind it
There are actually two types of pinking; chemical pinking and bacterial pinking. The chemical version is more rare and has to do with the formulation found in certain vinyl cushion material. Bacterial pinking is much more common. The difference in appearance is that bacterial pinking is more splotchy and chemical pinking is more of a smear.
The bacterial version of pinking- or pink staining- is actually caused by a specific, common bacteria known as "streptoverticillium reticulum". This bacteria can be present in any body of fresh water (not salt water), such as lakes and rivers, and can also be found in fresh rain water or even water from your home faucet. It thrives in environments that are dark, humid and hot which seems to perfectly describe how it feels under a boat cover in a boat when conditions are right. The bacteria, coming from water, usually gets in though the stitching or other holes on the exterior of the cushions and tends to reside between the top layer of foam and underside of the vinyl. Albeit an aesthetic nuisance, luckily this bacteria is NOT HARMFUL!
The main food source for this bacteria is the plasticizer present in the formulation of vinyl commonly found in boat seat covers. Plasticizer is what makes the vinyl more flexible. Interestingly enough, various regulations implemented throughout time within the industry have made this issue more prevalent within the last 30 years or so. All of these regulations, of course, have been implemented for health and safety reasons - such as, for instance, restrictions on the use of arsenic as an antimicrobial agent, which is a known carcinogen. Terrible for human contact, but happened to do a great job at prohibiting bacteria growth. An unintended consequence to these rightful restrictions is that it seems to have made an impact on being able to combat the occurrence of the bacteria on vinyl. Furthermore, due to these restrictions and manufacturers attempting to create a formulation that is both compliant yet functional, we started to see chemical pinking turn up. Many high end manufacturers of outdoor vinyl have made revisions to their formulation, but no viable solution, so far, has been able to completely eliminate the era of pinking. Vinyl manufacturers also try alternatives that do not use plasticizers, such as TPO (thermoplastic olefin), but they do not seem to fit the bill in one way or another. Perhaps, in time, a perfect vinyl formulation will be developed but until then we will have to find a way to make due.
Is there a way to prevent this?
Cleanliness is key. Aside from the bacteria feeding on the formulation of the vinyl itself, it also feeds on ingredients that may be present in your sunscreen, Para-Animobenzoic Acid (PABA). So it is best to use sunscreens that do not contain this and it is important to not let your cushions remain fully soaked in water for too long. Even the most abrasive household cleaners will generally not work against present pinking and may compromise your material further. It is best practice to thoroughly clean your exterior vinyl cushions after each boating excursion with a damp clean cloth, ensuring that everything is wiped down but not soaking wet and let air dry before applying your boat cover.
Choose the right vinyl. If you are in the market for re-upholstering your cushions, you may want to investigate those who warranty against bacterial pinking, such as the "best-in-industry" five-year limited product warranty and a three-year warranty against bacterial pinking with Sunbrella® Horizon® engineered synthetic leather (ESL). There are other manufacturers out there who do a great job, but just make sure you do your research in selecting one that is easy to clean and repels water as much as possible.
The good news - out of sight, out of mind (for now)
The good news is, if this is a new development on your boat, the discoloration tends to visually DISAPPEAR on its own while out in the sun for the first few years. Just remove the cover and allow your cushions to adequately absorb sunlight. Give it some time and you will be able to enjoy your boating excursion without the discoloration visually present.
The ugly news
Once the bacteria has found its way into your cushions, it is quite difficult to eradicate. The sun will make it disappear for a while but eventually it will start to get worse and to point that the discoloration will not go away in the sunlight and the cushions start to become brittle and crack.
Definitely avoid applying a boat cover while your seats are wet. Try your best to keep the interior of your boat clean and dry when not in use. Avoid using sunscreen with PABA in it. Since the sight of it goes away once it's out in the sun and it isn't harmful, maybe it is something you are willing to live with for a short amount of time, however plans should be made to have your cushions replaced in the future.
The ultimate solution would be reupholstering to start fresh. Once replaced, the best practice to keep the bacteria away would require you to follow the preventive guidelines thereafter.
At Custom Covers L.H.C. we take measures and precautions to help mitigate the risk of pinking by installing ventilation on towing covers where necessary and using top quality Marine Grade Sunbrella which is water repellent, yet breathable. However, this does not completely eliminate the risk of pinking without proper care and use.