Pink stains on marine vinyl: what they are and how to avoid them

What it is

It is a biological stain. ASTM E1428, the standard used to test how well a plastic resists pink staining, uses a bacterium from the Streptomyces group as its test organism. Spradling, a marine vinyl maker, puts it this way in its warranty: the stain is a by-product of a microorganism that can reach the vinyl from the boat components around it, such as the seat foam.

PCI Magazine, a technical title for the coatings industry, describes how it works: the microorganism feeds on the plasticiser in the vinyl and gives off a soluble red dye that colours the material.

Why it won’t come out

Because the colour isn’t on the surface but in the material. Morbern, another marine vinyl maker, explains that the pigment from these organisms migrates to the vinyl surface and won’t wash out. Its disinfection guide adds that disinfectants help against bacteria but don’t remove stains.

So once the stain has appeared, the answer is usually new vinyl, and at that point what goes underneath matters more than the vinyl itself.

Where it comes from: what lies beneath

Spradling’s warranty makes the point through its conditions. To cover pink staining, it requires the vinyl to be fitted over new foam, not the foam from the old upholstery, and that foam to be certified.

Seams are the other weak spot. A specialist from Lonza, the biocide maker, told Marine Fabricator, the trade magazine for marine canvas and upholstery, that seams and foam padding hold moisture and become a breeding ground. Morbern suggests thermoforming the vinyl where possible to do away with stitched seams, which it says harbour mould and bacteria.

What the vinyl maker does

Marine vinyls carry treatments against microorganisms. Spradling says the topcoat on its Permablok3 range guards against surface growth of fungus, mould and mildew, which cause pink and black stains. Morbern says its Splash range is formulated to significantly reduce the effect of microorganisms.

Those treatments change with the law, too. Spradling announced that it had moved away from the biocide OBPA to comply with the EU Biocidal Products Regulation, 528/2012, and that the new formulation stands up better to mould and pink staining. These are each maker’s own claims; ASTM E1428 is what allows one vinyl to be compared with another.

The care that prevents it

Morbern asks for frequent cleaning with a mild detergent, which removes the organic matter and dirt that microbes feed on, followed by a rinse with water. It advises against abrasives, steel wool, citrus cleaners and solvents. Spradling excludes staining caused by cleaning products from its warranty.

The rest is letting the cushion dry. If water stays in the foam and the seams, so does the place where whatever stains the vinyl lives.

What to ask before retrimming

With these answered, the stain has fewer places to come back:

The vinyl

Is it treated against pink staining? Has it been tested?

The foam

Is it new, and does the vinyl maker approve it?

The seams

How many are there where it gets wet? Can they be avoided?

Drying

Does the cushion drain and breathe, or does the water stay inside?

Cleaning

What is it cleaned with, and which products does the warranty rule out?