Poly Tank Repair FAQs

Plastics are probably one of the greatest innovations of the twentieth century. Our houses are full of it. Our jobs depend upon it. It is likely that you are reading this on a device that is made of at least 75 percent plastic right now. Plastics are so prolific that they even have become a problem in and of themselves. Waste plastic litters our streets, our woodlands, and even the waters of our oceans. This occurs because, as durable as plastic can be, it still breaks down, bends, cracks, and becomes no longer useful in its present form for its current function.

Thankfully, there are several methods created to repair minimal damage in plastic (poly) tanks. Most of these involve an innovation called a poly tank weld. Some of these welds require a heat source to “patch” damaged areas in plastic tanks while others are able to be molded in with a chemical reaction between two materials. See below for Frequently Asked Questions about how to repair a poly water tank.

What is the best way to repair a crack in your poly tank?

Plastic or poly tank welds are one of the most common ways of repairing cracks in the world of poly tank repair. Metal welds usually involve extreme heat and special torches to fuse pieces together. Poly tank welds are not melted pieces of plastic used to join the two sides of cracks back together. Instead, they are hand-mixed epoxies that use a chemical reaction to fuse plastic together like a moldable glue. These two chemicals heat up upon contact and the more you knead them together, the hotter, and more pliable they become.

Some thermoplastics (such as polyethylene and polypropylene) require their own special thermoplastic welders. For these, you need heating elements that can reach between 500-600 degrees Fahrenheit.

How do you prepare a poly tank for poly tank repair?

The easiest way is to purchase a poly tank repair kit. If it does not include a cleaner for the plastic area, you will also need to buy either an acetone or a lacquer thinner. It is possible to use soap and water, but they are not ideal for cleaning plastic in preparation for poly tank repair. It is crucial that, when cleaning the damaged area, you DO NOT use any alcohol or other types of cleaner that leaves a petroleum-based residue behind after cleaning.

First, empty your tank entirely. If it contained something other than water, be sure to wash it out. Allow it time to dry completely. You may want to work on the crack area to smooth out any rough areas, but do not let the crack get too wide. Once the cracked plastic is dry and ready for repair, apply the acetone or lacquer cleaner to the damaged area. Give it several minutes to dry in a safe, clean space.

Is poly tank welding water resistant?

Yes. Poly tanks are often used for holding liquids such as water, fuel, oil, or other chemicals. Most poly tank weldings are resistant to being dissolved by any of the above liquids. There are specialty poly tank welds for poly tank repair on tanks that are submerged in water or gasoline.

Is poly tank welding resistant to heat?

Yes, although it depends on what kind of welding you use. Many poly tank welds, once dried and cured will withstand a consistent heat of up to 500 degrees and flashes of up to 600-degree heat. This is important to know if you keep your tank in a kitchen or shop where they might accidentally get too close to a heat source or catch fire in an accident.

Most of these poly tank welds take 4-6 hours to set and up to 24 hours to cure. There are quicker alternatives though that set in minutes and cure in just a few hours. These faster alternatives tend to have about two-thirds of the resistance of standard poly tank welds so they will be less resistant to heat, cold, force, etc.

Are poly tank welds resistant to cold?

Yes. Poly tank welds can withstand cold temperatures down to -67 degrees Fahrenheit. As mentioned above, if you choose to use a faster curing weld, it may not withstand quite as much extreme cold as a standard poly tank weld.

Can I use poly tank repair kits to work on my car?

You should NOT use a poly tank weld on an exhaust manifold or catalytic converter.

You should NOT use a poly tank weld to make repairs on a combustion chamber.

For areas that do not get above 450 degrees Fahrenheit, it is safe to use poly tank welds. If you are not sure whether the damaged piece of plastic you are hoping to repair stays below 450 degrees Fahrenheit, check with your local mechanic or plastic tank expert.

Are poly tank welds from poly tank repair kits toxic?

Unless labeled otherwise, they are not. However, you should not ingest poly tank welds.

Will poly tank welds conduct electricity?

No. Poly tank welds are insulators and will not conduct electricity.

Does poly tank welding work with all types of plastics?

Yes, but not all welds work with all types of plastics. Thermoplastics such as Polyethylene plastics and Polypropylene plastics each have their own particular kinds of welds and may require a heating element to work correctly. If your plastic is too thin, it may not be recommended that you attempt to repair it.

How do you finish up a poly tank repair?

Once you have waited the recommended time for the poly tank weld to set and cure, you can get several grades of sandpaper – starting at 60-grit and working your way through 360-grit sandpaper to help smooth out the area of the weld. If you are working with a thermoplastic (polyethylene or polypropylene), there is a trick to getting the shine back on the plastic. If you hold a small yellow open flame from a propane torch near the area, you may be able to return the glossy sheen to your tank. When the area is finally set, cured, dried, cooled, and ready for work, you may choose to paint the outside of the tank. Do not use paint on the inside of the tank, especially if you use the tank for holding drinking or irrigation water as it may cause the contents to become toxic. It is also not recommended for tanks holding fuel or any other chemicals because it may alter the chemical contents in ways that are dangerous or cause the contents to become unusable.

When should you replace rather than repair a poly water tank?

As you make a decision about whether to repair your tank or replace it, consider the following questions.

Is the type of plastic your tank is made of repairable by a poly tank weld? Some plastic tanks are made of special plastic that may not have welds of the same type. For instance, many tanks made for drinking water tanks are made with a special Ultraviolet Light resistant plastic to keep the water they hold from becoming toxic when exposed to many hours of sunlight. If your weld is not made of the same type of plastic, your water may become toxic because of the weld’s own exposure to sunlight over time.

• Is the thickness of plastic in the damaged part of your tank thick enough to hold a poly tank weld? If the plastic you hope to repair is too thin, it may be more cost effective to just replace the tank as a whole.
• Consider the shape of your tank. Is it a rectangle-shaped tank? Is it a round tank? Remember that straight-sided tanks have more pressure on the center of each side, so if your crack is there you might be better off replacing the tank.
• Where is the crack located on your tank? Can you maneuver yourself or the tank well enough to get to the cracked area without any trouble?
• Here is the big question: How long is the crack in your tank? If the crack in your tank is between 1 and 6 inches, a poly tank repair kit should be able to repair it without any problem. If the crack is longer than 6 inches, it is probably too extensive to repair with a poly tank weld, and you should consider replacing the tank. If the crack is more than a half-inch wide (which often corresponds with longer cracks), you should also probably consider replacing, rather than repairing, the tank.

How to repair a poly water tank:

1. After preparing your plastic tank for repair (see above) by cleaning it thoroughly, you need to cut a piece of the weld out that is long and wide enough to cover the crack.
2. Put the weld material into the crack and insert the “rod” or the second element of the weld.
3. Once the weld-forming reaction begins, you will need to ensure that the tank does not move for several hours. Weaker, quick-setting welds require 4-6 hours to cure, and stronger standard welds take about 24 hours before they can be safely handled without damaging the tank again and potentially losing the weld.
4. Sand the weld area with gradually finer degrees of sandpaper to smooth out the area.
5. Paint over the OUTSIDE of the tank only with a quality plastic-adhering paint to make it look brand new.

If you have any questions regarding poly tank repair, do not hesitate to ask your local poly tank experts for help. If you are unable to repair your tank and are looking to replace it, don’t forget to recycle your old tank.