As copper pipes age, tiny through-holes often show up in them. These are a sign of pitting corrosion. But age alone is not the main reason they appear, as we will see below.
Unfortunately, a pinhole leak in copper pipe is often found only after a stain or mold shows up. Plumbers tend to have many different explanations for these leaks. This article sticks to a few of the most common ones, and then covers what to do about the hole, the pipe and the wet wall.
What a Pinhole Leak Looks Like
A pinhole leak is a small leak by volume, but it often causes real problems for a household. On the pipe itself it is a puncture so small you may not see it until you dry the surface and watch it bead up again.
A puncture like this usually lets out only a little water and does not bother the homeowner much at first. Even so, a small leak still helps mold grow and starts building materials rotting. Besides pinholes in the body of the copper tube, a leak can also come from a mechanical joint, for example because of a defective fitting.
Copper pipes are most often damaged at bends. Cracks there are a common problem in copper lines.
General Causes of Copper Pipe Corrosion
The most common causes are the chemistry of the water and water that moves too fast.
Water chemistry
The chemistry of the water, its pH, minerals and the disinfectant left in it, affects how fast copper corrodes from the inside.
High pressure and water velocity
In houses where the pressure is too high, pipes leak because the water moves faster. High water velocity erodes the inner surface of the pipes more, especially in elbows, tees and other fittings that change the water's direction. For this reason, a pressure-reducing valve is recommended where the system runs at high pressure, so household pressure stays within the normal residential range.
Signs of a Leak in Walls and Ceilings
A pinhole inside a wall shows up like any hidden leak: a stain or bubbling paint along the pipe run, a ceiling stain under a bathroom, or a musty smell. On exposed copper under sinks and in the garage, look for blue-green spots and crusty deposits.
Mold can be dangerous to health, so it should be removed right away and the leaking pipe fixed. When the growth goes beyond a small patch, read about how mold remediation is done.
Clamp, Spot Repair or Repipe
When you find a pinhole in a pipe, put the panic aside and work out how best to deal with it. The safe option is to call a plumber to fix the leak. It is another matter if you cannot get a plumber right away.
Working on a hot water line or a pipe under pressure calls for extra care. Never touch systems that carry flammable or hazardous liquids or gases yourself. If something is unclear, leave the repair to professionals.
Repair clamp
This is the cheapest way and can be done by a person with any level of skill. You only need to shut off the water, pick a clamp of the right diameter, put in a sealing rubber gasket and tighten the bolts firmly. A clamp can be used when:
- The line carries cold water. Hot lines are a harder case.
- The pinhole is small. The damage has a small diameter.
- Corrosion is showing on the surface but no water is seeping through it yet.
It is important to understand that a clamp is not a cure, only a way to hold the situation for a while. In the next few years the leaking pipe will have to be replaced anyway.
Temporary stopgaps
For a small puncture in copper, an epoxy patch helps, but only until a proper repair.
Shut off the water, wash the pipe around the leak with soap and wipe it dry. Sand the copper around the hole with fine sandpaper. Mix the epoxy per its instructions and lightly coat the copper around the hole. Wait until it starts to set to a putty consistency, shape a piece of the right size and press it hard onto the leak. Let it cure fully, as long as the product's instructions say. A patch like this can hold for a long time, but it is still not recommended to skip a professional repair later.
Fittings and soldering
For a lasting spot repair, a plumber cuts out the damaged piece and joins in a new one with soldered, press or push-fit fittings.
Repipe or repair
For a long time people thought copper pipes were forever. It is now clear that this is not so. PEX polyethylene pipe is replacing copper. It is easier to install and is practically not subject to corrosion. A little-known side of PEX, though, is that rodents like to chew it.
A clamp or a patch buys time. If pinholes keep coming back in the same run, the repairs only postpone the moment when the leaking pipe has to be replaced, and a whole-house repipe becomes the choice to weigh.
Finding the Next One
Since pinhole leaks are usually found late, the next one is worth looking for before it shows up as a stain. A few checks:
- Pressure. Where pressure is high, a pressure-reducing valve takes load off elbows and tees.
- The meter. The EPA WaterSense leak-check guide says to read the water meter before and after a 2-hour period with no water use; any change suggests a leak.
- Exposed pipe. Look over pipe under sinks, in the garage and near the water heater for blue-green spots, dents and damp spots at bends and fittings.
Drying the Wall After the Fix
Fixing the pipe is half the job. Even after visible water is gone, moisture stays inside building materials and can turn a remodel into ruins within a week. Mold, rotting wood and peeling finishes are typical results of drying done wrong or too late. This is the work covered under water damage restoration services.
Water gets into joints, under baseboards, into the pores of concrete and drywall and into wood fibers. Capillary action lifts moisture well above the waterline. Even if a surface looks dry, it can be wet inside.
Natural ventilation dries only the top layers. To pull moisture out of the full depth, forced drying is needed: active evaporation with forced removal of the humid air. The general steps:
- Measure moisture. Before work starts, measure the humidity of the air and of the materials with contact moisture meters and hygrometers.
- Remove wet finishes. Peeling plaster, paint and wallpaper come off. Small mold growth is scraped with a stiff brush or putty knife, wearing gloves and a respirator.
- Dry with dehumidifiers and air movers. Keep the room closed so the dehumidifier pulls the moisture out of the air and the materials.
- Check as you go. Measure the materials regularly. The target is a meter reading, not a date.
An ordinary space heater does not work for this. It lacks the power, gives no forced ventilation and heats unevenly, which creates a greenhouse: hot but humid, which is ideal for mold. If a damp smell stays after drying, it is a sign of either moisture left deep in the material or mold that is still growing.
Done right, forced drying takes days instead of the weeks or months of natural drying. If furniture and belongings have to come out of the room while the wall is open, read about contents pack-out and storage. For a bigger flood below grade, see what to do first when a basement floods.
More articles on leaks and mold are on our water damage news page. You can also read who we are and how we work, see what San Diego homeowners say, or go back to the restoration company home page.