Clogged Cast Iron Drain Pipe: 7 Ways to Easily Fix It

If you live in a home built before 1975-1980, there’s a good chance your drain pipes are cast iron. And while iron is a tough material that can last as long as 100 years, it needs to be treated correctly and maintained.

This is because cast iron is prone to rust and corrosion, which, if not addressed promptly, can lead to cracks that require extensive and costly repairs.

These days we’ve abandoned the use of cast iron in place of copper or plastic drain pipes, but if your home does have a clogged cast iron drain pipe, we’re going to show you how you can easily fix it without causing damage to the pipe. 

Why is your cast iron drain pipe clogged?

While cast iron is undoubtedly one of the toughest materials, it requires some care and maintenance to stay in good working order. When neglected for long periods, it’s liable to start breaking and corroding.

1. Textured surface

Cast iron is prone to clogging because of its rough interior texture, which provides a perfect surface for bacteria and debris to cling onto and start growing. 

As the iron ages and corrodes, the ‘pits’ in the edge deepen, creating a vicious cycle of more pitting that leads to more clogging.

2. ‘Low-flow’ toilets

Many modern homes have been upgraded with special ‘low flow’ toilets and water fixtures to save money on water.

This means that even though the toilet bowl might look clear, insufficient water is being used to push the waste the entire way through the sewer pipe.

As a result, that waste gets additional time to sit in the pipe, cling to its edges, and build up a blockage over time.

3. ‘Bellies’ have formed in the pipe

Cast iron is very inflexible, which means undue movement, whether from aggressive drain cleaning or disturbance of the soil surrounding the pipe, can lead to compromised seal joint of the development of ‘bellies.’

‘Bellies’ are where a force has caused the iron to flex at a joint, creating a belly or dip that can reduce the amount of space water/debris flow through the pipe. 

This issue is not solved by cleaning and usually requires an entirely new section of pipe to be inserted in the place of the bellied pipe.

How to fix a clogged cast iron drain pipe

When fixing the drain pipe, it’s vital to unclog your drain so that it won’t damage the sewer pipe and cause further problems down the line.

There are a few things to be mindful of as we begin the process of cleaning a cast iron drainpipe:

  • Some drain cleaning processes used to unclog a cast iron drain pipe are aggressive. If there is significant rust or corrosion, the cleaning process may further compromise the cast iron pipe and cause more problems. 
  • Cast iron pipes will always eventually need to be replaced. We have methods to replace compromised pipe sections with PVC pipe sections using reinforced PVC couplings. So you may need to upgrade your pipe system soon if their wear is significant.
  • Be very selective about the kind of chemicals you use. It’s recommended when using a drain cleaner to use something specifically formulated to work with cast iron pipes, as it will further the corrosion and result in an expensive call to a plumber.

1. Employ good practices

While this may seem like more of a preventative measure, it’s also something you should employ immediately to assist in the cleaning process and ensure the problem doesn’t just immediately return.

The first good practice you should be doing is to avoid pouring cooking oil or grease down the drain while it’s still hot. This will cool mid-way down the pipe and then dry onto the wall of the pipe. 

This will not come loose again with just hot water and will require a more aggressive cleaning method that often harms the pipe. So you should instead just let the grease cool beforehand and scrape it into the trash.

Another huge factor in drain blockages is hair. The volume of hair that just two people with long hair can produce can be pretty shocking.

Try to make a habit of combing your hair before showering to remove the already loose hair from the night’s sleep, so it doesn’t come out mid-shower and go down the drain.

You should also only put items down the drain which are easily dissolved. Avoid putting feminine care products down the drain unless they explicitly state they are acceptable for flushing. Likewise, you should only use toilet paper that can easily be dissolved.

Now employing these practices themselves will go a long way to preventing blockages in the future. You will still have to deal with pipe buildup because even just running pure water down the drain will eventually result in mineral deposits that need to be addressed.

So once you have these good practices, you can look at other more immediate methods to address a clogged pipe.

2. Use a drain cleaner

A good drain cleaner is usually people’s first port of call when unblocking a pipe. However, the process is not as simple as cleaning a PVC pipe, where you can find the most effective cleaner on the shelf and chuck it down the pipe.

Cast iron sewer pipes are susceptible to damage from overly aggressive cleaners, so you should only use a cleaner that will work with cast iron .

Most plumbers will recommend avoiding a drain cleaner altogether. Still, in the absence of a feasible alternative method, something like liquid-plumr does a good job of breaking up clogs without harming the pipe.

3. Cable cleaning/drain snake

Cable cleaning is one of the most popular methods of cleaning a pipe. It involves funneling a cable (also called a drain snake) down the pipe, which is then spun on a drill to break up the clog and help with descaling the pipe.

Running some hot water down the pipe beforehand is recommended, which can help soften the blockage and give you a better shot at unclogging the pipe.

After you have cleaned the pipe using the cable, you can use something like BioClean to help safely protect the inside of the pipe seeing as you’ve just exposed fresh iron.

4. Use a hydrojet

Hydro jetting is another very popular method for unclogging a pipe as it doesn’t use chemicals. It just utilizes a high-pressure stream of water that shoots out at a whopping 4000psi by using a special nozzle that slices through the dirt, debris, and grime that’s present.

Hydro jetting can be one of the more expensive cleaning methods, so be sure to find a reputable cleaner before paying for their service. But because it’s such a clean and natural method, we think it’s worth it.

5. Picote cleaning

Picote is one of the most recommended methods for cleaning a clogged drain because it simply uses high-powered air, spins a small chain in a cyclone fashion, and then physically breaks up the blockage.

The genius of this method is that it stays centralized within the pipe and is set to the plumbing pipe’s diameter. This means the chain doesn’t destroy the edges of the pipe and only clears out the ‘space.’ Which makes it one of the least destructive methods around.

Sound great, right? Well, it’s unfortunately also the most expensive cleaning method, which may cost you as many as several thousands of dollars depending on where you live. 

6. Sodium hydroxide

Sodium hydroxide is a substance found in most common drain cleaners. It’s a relatively aggressive and toxic chemical drain cleaner that is strong enough to dissolve hair, making it great at dealing with deep-down blockages primarily comprised of hair.

The main issue with this method is that it can also be corrosive to the lining of the pipe – so it should only be used in an emergency as a one-off unblocked instead of any other reasonable method.

But one thing that makes this a compelling choice is that it’s one of the cheapest methods available.

7. Cut out a section of pipe

This very extreme method should only be used when the blocking is sitting in a unusually hard-to-reach place. This can commonly be in areas such as along a garden where a stretch of horizontal iron sewer pipes causes the water to ‘pool’ at a particular spot.

Between gravity allowing items to deposit themselves there as was mineral build up over time, this can easily turn into a complete blockage.

The cabling and hydro jet methods can reach far down a drain, so you should explore those methods first.

But providing all other methods have been exhausted, you can dig up some of the ground and remove a small section of the pipe. Even if you haven’t got it exactly over the blocking by creating a new entry point much closer to the blockage, you can employ one of the other methods mentioned here, such as the hydro jet or picote cleaning methods.

Now you are situated much closer to the location of the blockage. You stand a much better chance of being able to reach the backup.

The patch of pipe you have removed will need to be repatched by welding a new piece of cast iron onto it.

This is a troublesome method, but assuming all other methods have failed, it can work well as a last resort.

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