In regions with hard water, every drain carries dissolved calcium and magnesium, and where the water evaporates or sits, some of it comes out of solution as a hard, pale crust. On hot water lines and water heaters it is a familiar problem. In drain lines it is less talked about and just as real: kitchen and laundry drains, condensate lines, floor drains with little flow and any line that carries hot water develop a mineral scale that narrows the bore, roughens the wall and catches everything that passes. On a sewer camera it looks unlike rust and unlike grease, and the distinction decides how it is removed.
Quick answer: mineral scale shows on camera as a white, cream or grey crust on the pipe wall, hard-edged and often layered, heaviest at the water line and around fittings, in a pipe that may be plastic or copper rather than iron. Rust scale is orange-brown and only on iron; grease is smooth, waxy and pale; mineral scale is hard, crystalline and pale. It is removed by descaling with a chain or cutting head, or by acid treatment in some lines, and it returns unless the water is softened.
What it looks like
A crust rather than a coating. The surface is rough and crystalline, sometimes in rings that mark successive water levels, and it is pale: white in a plastic pipe, off-white or grey where it has taken on sediment. It is thickest where water sat and evaporated: at the water line in a trap or a flat run, around the edges of fittings, at the outlet of a water heater drain or a dishwasher line. In a plastic pipe, which cannot rust, any hard pale deposit is mineral. In an iron pipe, mineral scale sits on top of rust scale and the two are hard to separate. The tuberculation guide covers the rust kind.
Scale, rust or grease?
Colour and hardness. Rust is orange to black and only on iron or steel. Grease is pale but smooth and soft, and it coats the top of the pipe more than the bottom. Mineral scale is pale, hard, rough and heaviest at the water line. A cable passing through grease leaves a smooth channel; through mineral scale it leaves a rough one with crust still on the walls. A camera that sees a pale deposit in a PVC or ABS line is looking at minerals or grease, and the texture tells which. The grease guide covers the other pale deposit.
Where it forms
Kitchen lines carrying hot dishwasher water. Laundry lines. Condensate drains from air handlers and high-efficiency furnaces, which carry mineral-laden water constantly. Water heater drain and relief lines. Floor drains and trap arms where water sits and evaporates. Urinal lines in commercial buildings, which develop a particular hard scale from urine salts. Any flat run where water pools. The common factor is evaporation or long contact, and the bed usually begins where the flow slows. Inspecting a condensate drain covers the most scale-prone small line.
How it is removed
Mechanically, with a chain cutter, a carbide descaling head or a brush on a cable machine, which knocks the crust off the wall; jetting alone often polishes it rather than removing it. Chemically, with acid-based descalers in lines that can tolerate them, which dissolve the minerals; this is common for urinal lines and condensate lines and inappropriate for some materials. In either case the camera goes in afterward to confirm the wall is clear, and the operator should expect to see a rougher wall than before, because scale that has been growing for years etches plastic and pits iron. Chain cutters and descaling covers the mechanical method.
Why it returns
Because the water is still hard. Descaling restores the bore for a period that depends on water hardness, flow and temperature, and the scale re-forms. A water softener is the only measure that addresses the cause, and in a hard water region it is the first recommendation after a descaling job. For a condensate line, a neutraliser cartridge or a periodic flush helps. The camera’s record of how much scale formed over how many years is the data that justifies the softener.
Inspecting a scaled line
Use a 17 or 18 mm head, because the bore is smaller than the pipe size and scale lips at fittings stop a larger head. Dim the LEDs; a white crust glares. Note the distance where the scale starts, which is usually where hot water enters or where the flow slows, and where it is thickest. Record the material underneath if visible. A line that a 17 mm head cannot enter is a line whose bore has closed below that, and that is the finding. The 17 mm camera guide covers the equipment.
What to record
The distance where scale begins and where it is thickest, an estimate of how much of the bore it has closed, the pipe material underneath where visible, and any fitting lip the head could not pass. A still of the thickest section gives the descaling contractor a target and the customer a reason to consider softening.
Common questions
Can mineral scale block a drain?
Yes, slowly. It narrows the bore until a normal load of hair or paper stops at a lip.
Will drain cleaner remove it?
Alkaline drain cleaners do not. Acid descalers can, where the pipe material allows. Mechanical descaling works on everything.
Does scale form in PVC?
Yes. Minerals deposit on any surface where hard water sits or evaporates.
Related guides
See preventing scale buildup in cast iron drains, camera inspection of a kitchen sink line, and the best sewer cameras for 1.5 in pipe.