Cleaning sails
Saving Sails and Canvas from Mildew
It can be a rust stain caused by a loop of chain that spent the winter lying on a sail. Perhaps a bird crawled under the sail cover and built a nest, pooping on the sail for weeks. Laminate sails present a particularly vexing problem, since mildew likes the adhesive that bond the layers, resulting in stain that is sealed between waterproof layers. Some of these just look bad (rust stains), but others can slowly weaken a sail (mildew in the laminate adhesive). But in all cases, overly aggressive cleaning can make things even worse, weakening the sail more than the mildew ever would.
Stains can be removed in three general ways. They can be physically removed, dissolved, or bleached (made invisible). Each requires different chemistry and a different mindset, so it helps to understand the stain.
Most stains are linked to moisture. Good ventilation prevents condensation, and consider taking sails home for the off-season. Canvas should be water repellent treated. This is the single most effective way to combat lichen mildew on both the cover and the sail under it.
Physical removal requires that the bond be broken. In the case of mildew and algae, this requires that the organism be killed and for some time to pass. Borax, oxygen bleach (sodium percarbonate or sodium perborate), chlorine bleach (sodium hypochlorite), and quaternary amines (benzalkonium chloride and others) are all effective if given a soaking period. The required dose is not very high, so more is not better. Sunlight works on mildew, though very similar looking black algae are not killed by UV (unless the mildew truly grew in the dark, consider that it might actually be algae).
Surfactants - including both organic soaps and detergents, and inorganics such as trisodium phosphate (TSP), baking sodas, and borax - help by breaking static bonds and emulsifying grease. Again, soaking time helps, followed gentle agitation, or more effective and less damaging, little light work with a brush with the sail laid out on a non-abrasive surface. But remember that stains that are between laminate layers or deep in a seam will not be helped by scrubbing.
Dissolving works best on rust, corrosion, and metals stains. The trick is to reduce the pH far enough to dissolve the metal oxide without damaging the cloth. Nylon is vulnerable to strong acids, literally dissolving before your eyes in battery acid, so nothing with a pH of less than 3 should be used. Polyester and other fabrics are less vulnerable, but we like to keep the pH above 3 because nylon thread can always sneak in.
It is always better to soak for longer rather than to use stronger chemicals, since the cloth is not affected by long soaking times at a safe pH, but the stain will slowly vanish. Some products contain chelating agents (EDTA and its relatives) to help dissolve and suspend metal at less acidic pH. The pH values for common cleaning acids such as hydrochloric acid (sold as muriatic acid), oxalic acid (Ospho), acetic acid (vinegar), and lactic acid (CLR brand) can vary by concentration, so if you are going to use an acid cleaner, you may have to dilute it further. Here are the pH levels of common acids used for cleaning (note that the acid concentrations indicated by percentages can vary by product):
Hydrochloric acid (3% acid), diluted with water 20:1, very low pH
Oxalic acid (100% acid), diluted with water 20:1, pH 2-3
Acetic acid (vinegar, about 4-6% acid), used undiluted or diluted with water 10:1, pH 3.3-2.4
Lactic (CLR brand acid is about 15%), diluted with water 10:1 to 20:1, pH 3.5-3.0
For specifics on ways to control and clean mold and mildew, including product reviews and evaluations, purchase The Mildew-Free Boat, Volume One: Cleaning and Protecting Fabrics and Plastics from Practical Sailor.
It can be a rust stain caused by a loop of chain that spent the winter lying on a sail. Perhaps a bird crawled under the sail cover and built a nest, pooping on the sail for weeks. Laminate sails present a particularly vexing problem, since mildew likes the adhesive that bond the layers, resulting in stain that is sealed between waterproof layers. Some of these just look bad (rust stains), but others can slowly weaken a sail (mildew in the laminate adhesive). But in all cases, overly aggressive cleaning can make things even worse, weakening the sail more than the mildew ever would.
Stains can be removed in three general ways. They can be physically removed, dissolved, or bleached (made invisible). Each requires different chemistry and a different mindset, so it helps to understand the stain.
Most stains are linked to moisture. Good ventilation prevents condensation, and consider taking sails home for the off-season. Canvas should be water repellent treated. This is the single most effective way to combat lichen mildew on both the cover and the sail under it.
Physical removal requires that the bond be broken. In the case of mildew and algae, this requires that the organism be killed and for some time to pass. Borax, oxygen bleach (sodium percarbonate or sodium perborate), chlorine bleach (sodium hypochlorite), and quaternary amines (benzalkonium chloride and others) are all effective if given a soaking period. The required dose is not very high, so more is not better. Sunlight works on mildew, though very similar looking black algae are not killed by UV (unless the mildew truly grew in the dark, consider that it might actually be algae).
Surfactants - including both organic soaps and detergents, and inorganics such as trisodium phosphate (TSP), baking sodas, and borax - help by breaking static bonds and emulsifying grease. Again, soaking time helps, followed gentle agitation, or more effective and less damaging, little light work with a brush with the sail laid out on a non-abrasive surface. But remember that stains that are between laminate layers or deep in a seam will not be helped by scrubbing.
Dissolving works best on rust, corrosion, and metals stains. The trick is to reduce the pH far enough to dissolve the metal oxide without damaging the cloth. Nylon is vulnerable to strong acids, literally dissolving before your eyes in battery acid, so nothing with a pH of less than 3 should be used. Polyester and other fabrics are less vulnerable, but we like to keep the pH above 3 because nylon thread can always sneak in.
It is always better to soak for longer rather than to use stronger chemicals, since the cloth is not affected by long soaking times at a safe pH, but the stain will slowly vanish. Some products contain chelating agents (EDTA and its relatives) to help dissolve and suspend metal at less acidic pH. The pH values for common cleaning acids such as hydrochloric acid (sold as muriatic acid), oxalic acid (Ospho), acetic acid (vinegar), and lactic acid (CLR brand) can vary by concentration, so if you are going to use an acid cleaner, you may have to dilute it further. Here are the pH levels of common acids used for cleaning (note that the acid concentrations indicated by percentages can vary by product):
Hydrochloric acid (3% acid), diluted with water 20:1, very low pH
Oxalic acid (100% acid), diluted with water 20:1, pH 2-3
Acetic acid (vinegar, about 4-6% acid), used undiluted or diluted with water 10:1, pH 3.3-2.4
Lactic (CLR brand acid is about 15%), diluted with water 10:1 to 20:1, pH 3.5-3.0
For specifics on ways to control and clean mold and mildew, including product reviews and evaluations, purchase The Mildew-Free Boat, Volume One: Cleaning and Protecting Fabrics and Plastics from Practical Sailor.
Note, article reproduced from Practical Sailor magazine.
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