Thursday, March 15, 2012
Vinyl Liner Mold - Black Bottom Stain
Vinyl Liner Mold
A discoloration of a vinyl liner can occur from mold/fungus that may grow under the liner. This has the appearance of a black stain on the vinyl liner inside the pool. It us usually round over a large area and is only seen on the bottom and side walls of a vinyl liner where the liner comes in contact with the bottom areas of the pool. This can occur on the bottoms of above ground pools as well.
It does not brush off and may lighten in appearance after “shocking” the pool or periods of high chlorine residual. Shocking and use of a copper based algaecide may kill the substance on the swimming side of the vinyl. Although the mold can be lightened from water chemistry there is no way to treat the source of it on the outside of the vinyl from within the pool. The mold can only be eradicated when the liner is removed and the ground is sprayed with a sodium hypochlorite solution of 5-10%. The chlorine solution can be applied with a pressure type garden sprayer. The solution must dry before re-installing the liner. There are specific fungus products available on the market as well.
Another indication that vinyl mold/fungus is causing the discoloration is that the welded doubled seams of the liners do not show any discoloration as they are too thick for the mold to grow through. The heat welding process also inhibits the mold/fungus from growing all the way through the seam.
This mold/fungus thrives in moist ground conditions. Areas with high water tables or areas that have experienced flooding can be prone to this occurring. Infected sand that is used for the base of the pool can also contain this mold/fungus. Water tables can change over time and with environmental conditions and cause mold/fungus to grow when there may not have been a problem before.
The plasticizers and lubricants used to make the liners are ingested as food for these micro-organisms and allow it to thrive. The consumption of the plasticizers which make vinyl pliable comprises the liner integrity. It is common to see this occur in one season.
The liner can be compromised as the pigment of the liner may be removed during the process of the mold growing through it. This reaction happens when the bond of the ink and the vinyl is weakened and the ink rubs off. Many liners are manufactured with a biocide/fungicide but it can be overpowered with heavy infection of the mold.
To avoid liner mold/fungus always be sure that the pool base is constructed with clean sand that is free of organic matter. Be sure the liner you purchase contains a biocide or fungicide.
Chlorine levels of 5ppm usually will “fade” the mold on the inside of the liner. Over time these areas may look bleached as if someone improperly added chemicals to the pool.
Polyethylene sheeting can be laid down to act as a barrier between the vinyl and the ground as the mold/fungus cannot penetrate the polyethylene. However, if water tables rise the sheeting can “float” with the liner and bundle up when the water level retreats. A ground sealant or other chemicals can be applied but may get diluted by ground water.