How to Descale Cast Iron Pipes: A Complete DIY Guide

Understanding Cast Iron Pipes and Why They Need Descaling

Cast iron pipes have been commonly used in plumbing systems for over a hundred years. While durable, they have a tendency to corrode internally over time. This corrosion leads to buildup on the interior walls of the pipe, which needs to be removed through a process called descaling.

What Causes Corrosion and Buildup in Cast Iron Pipes?

There are a few key factors that contribute to corrosion and buildup in cast iron pipes:

• Water chemistry - Minerals like calcium and magnesium in hard water interact with the iron in the pipes, leading to corrosion.
• Age - Older cast iron pipes are more prone to corrosion issues.
• Fluctuating water pressures - Changes in water pressure put stress on pipe walls and can cause pitting.
• High water velocity - Fast moving water wears down the protective coating inside pipes.

This corrosion causes rust, scale, and lime deposits to form on the inside of pipes over time. The buildup accumulates and eventually constricts water flow through the plumbing system.

Signs Your Cast Iron Pipes Need Descaling

Here are some common signs that indicate your cast iron pipes need descaling:

• Reduced water pressure - Buildup in pipes blocks water flow, reducing available pressure.
• Discolored water - Rust and scale cause yellow, brown or red stained water.
• Strange noises - Hissing, clanging or banging sounds can come from blocked pipes.
• Lower hot water volume - Heat exchanges less efficiently through scaled pipes.
• Higher water bills - Flow is reduced, so water runs longer to accomplish tasks.
• Pipe leaks - Corrosion and pitting can lead to cracks and pinhole leaks in pipes.

If you notice any of these issues, it’s very likely your cast iron pipes need descaling. When scale accumulates to more than just a thin coating, it’s time to take action.

Descaling Options for Cast Iron Pipes

There are a few different options available for descaling cast iron pipes, each with their pros and cons.

Chemical Descaling

Chemical descaling products contain acids that react with the buildup in pipes and dissolve the scale. Products can be in liquid, powder or gel form. They are poured or pumped into the plumbing system and left to work for several hours before flushing the pipes with water.

Chemical descaler pros:

• Effective at dissolving mineral deposits and corrosion.
• Relatively affordable and easy to find.
• No need to take pipes apart.

Chemical descaler cons:

• Harsh acids can damage pipes if not used properly.
• Often requires repeat treatments.
• Does not address pitting or cracks in pipes.
• Disposal of flushed descaling solutions may be restricted.

Power Descaling

Power descaling uses an electronic signal to induce a physical vibration inside pipes, essentially shaking the scale loose. The loosened scale then rinses away with water flow. Devices can connect to outdoor hose bibs or indoor plumbing.

Power descaler pros:

• Non-chemical and non-invasive method.
• Effective for regular descaling maintenance.
• Environmentally friendly.

Power descaler cons:

• May not remove heavy or mature scale buildup.
• Only reaches scale on interior pipe walls.
• Does not address corrosion or pitting of pipes.

Mechanical Descaling

Mechanical descaling uses physical force to scrub away scale and corrosion inside pipes. Polyurethane foam pigs and nylon pipe brushes can be pushed through the line with water pressure. High pressure jet nozzles can also be snaked through pipes and blasted at problem areas.

Mechanical descaling pros:

• Directly scrubs away scale and corrosion deposits.
• Powerful water jets can clean entire pipe wall surface.
• Pigs and brushes reach bends and joints.

Mechanical descaling cons:

• Unable to thoroughly descale entire system.
• Only reaches sections of pipe the tools can fit through.
• Possible damage to pipes if tools get stuck.
• Labor intensive.

Step-by-Step Guide to DIY Chemical Descaling

Chemical descaling is a common DIY method for cleaning light to moderate scale out of cast iron pipes. Follow these steps for the process:

Assemble Necessary Materials

You will need:

• Chemical descaling product - Consider strength needed based on pipe condition and age.
• Pump or funnel - For pouring descaler into plumbing system.
• Hoses - To connect pump or direct descaling solution.
• Plugs - For sealing off any openings not being descaled.
• Protective equipment - Gloves, goggles, apron as recommended by product.

Disconnect and Prep Plumbing

Take the plumbing being descaled out of service:

• Turn off water supply and open highest and lowest faucets.
• Disconnect water heater and appliances like dishwashers and washing machines.
• Remove aerators and shower heads.
• Plug drains and openings not being descaled.

Fill Plumbing with Descaling Solution

Using pump or funnel, fill entire plumbing system with descaling product diluted to proper concentration per product instructions. All pipes and fixtures should fill with solution.

Allow Solution to Work

Let descaling solution soak and react with scale for recommended time, usually 3-6 hours. Periodically operate valves and fixtures to circulate and agitate solution.

Flush Descaling Solution

After soaking, reattach water supply and turn on. Flush pipes thoroughly, running water at full flow for 10-15 minutes to rinse away dissolved scale and residual descaler. Flush toilets 3-4 times.

Inspect and Resume Use

Check for improved water pressure and flow. Reinstall aerators, shower heads, water heater and appliances. Monitor for any leaks. System can now resume normal use.

When to Call a Professional for Descaling

While DIY descaling is possible in some cases, there are times when the job is best left to professionals:

• Extensive corrosion and complete pipe blockages - May require pipe replacement.
• Cast iron drainage pipes - Special equipment needed.
• Presence of lead components - Avoid chemical descalers leaching lead.
• Limited isolation points - Hard to take whole system out of service.
• No improvement after descaling - Indicates larger issues.

Plumbing professionals have specialized tools and the know-how to fully descale cast iron systems and identify any underlying issues. Get help for severe buildup, repeat scaling and signs of pipe deterioration.

Maintain Cast Iron Pipes and Prevent Rapid Rescaling

To maintain cast iron pipes and avoid rapid rescaling after descaling, keep these maintenance tips in mind:

• Install corrosion inhibitors - Chemicals that minimize corrosion.
• Consider pipe lining - Epoxy coatings prevent future scale adhesion.
• Remove points of turbulence - Smooth out elbows and transitions.
• Manage water pressure - Use pressure reducing valves.
• Filter hard water - Water softeners and filtration minimize mineral ions.
• Descale regularly - Don’t allow heavy buildup again.

With periodic descaling and preventative maintenance, cast iron pipes can have a long service life. Stopping corrosion and buildup before it escalates saves plumbing headaches down the road.

FAQs

What causes scaling and corrosion in cast iron pipes?

Mineral deposits from hard water, fluctuating water pressures, high water velocity, and general age of the pipes all contribute to corrosion and interior scaling in cast iron pipes over time.

How can I tell if my pipes need to be descaled?

Signs like reduced water pressure and flow, rusty colored water, strange noises from pipes, issues with hot water volume, and higher water bills can indicate cast iron pipes need descaling.

Is chemical descaling safe for DIY projects?

Chemical descaling products contain harsh acids and should be handled with care, but are relatively safe for DIY use if directions are properly followed. Protective equipment is recommended.

Will I have to descale my pipes frequently?

How often descaling is needed depends on factors like water hardness and pipe age, but for older cast iron pipes every 2-5 years is fairly typical to maintain flow and prevent major buildup.

When should I call a professional instead of DIY descaling?

For extensive corrosion, blocked drainage pipes, lead plumbing components, limited isolation points, or lack of improvement after DIY descaling, it's best to call a professional plumber for the job.