How to Treat Rust on Cast Iron Gutters and Pipes

If you are living in an older building, it is likely that your guttering system is made from a metal like cast iron. This means that, as is the case with all metals, your gutter will be susceptible to rusting over time as the moisture and oxygen from the air reacts with the iron. Although this oxidation process is irreversible, and your gutter might look like something you find during a zombie apocalypse, there is a good possibility that it will not be necessary to go through the trouble and expenditure of getting it fully replaced with a new one.

Below is a step by step guide on how you can remove rust from cast iron gutters with a rust converter.

Can my rusted iron gutter be repaired?

It is first important to assess the condition of your guttering system to understand if repairing is the best option.

When iron reacts with oxygen and moisture, which happens very easily every day, it is essentially being eaten away by the corrosion process. The longer you leave this untreated, the more likely it is that sections of your gutters will be corroded completely, leaving nothing but holes in their place – not ideal for catching and transporting rain water. Before you restore rusted cast iron, you should repair rust holes in gutters.

Smaller holes can be managed by applying a roof and gutter sealant, or by using a metal patch made from the same material as your gutter (iron in this case). It is very important not to use a metal that is different to that of your gutter, as this will cause a galvanic reaction between the different compounds and can result in the rapid corrosion of the patch or your gutter. A larger hole can be filled by using a glass fibre filler, however, if your guttering is in poor condition with multiple holes, it is recommended to get it replaced altogether with a new one to prevent bigger problems in the future.

Step 1: Dismantle the cast iron guttering

If this is a DIY job, you are going to want to be very careful with this first step. Cast iron guttering is heavy and can be very difficult to remove, especially if sections have been rusted into place. Ensure your ladder is set up stably against your house, and take huge precautions when lifting the gutter, as a fall from that height can cause serious injury.

The best way to take down your metal guttering would be by dismantling it section by section, and climbing safely back down the ladder with it in a very controlled manner. Try not to drop it directly to the ground, as cast iron can shatter and small fragments can fly off. You also need to remove the downpipe offsets, which connect the gutter to the downpipes, and prepare to rid them of any rust.

Step 2: Remove any loose flakes of rust and paint

To begin the process of treating rust on the cast iron guttering, it is important to first get rid of any loose flakes of rust and paint, or any high spots of rust. This will remove any voids created behind the raised surfaces, allowing the rust converter solution to reach the key areas of contact. You can scrape these flakes and high spots of rust off by using steel wool, sandpaper, or a wire brush.

It is important to note that hard rust should not be removed from the surface at this stage, as the rust converter requires rust present to react with and convert into a corrosion resistant surface against oxygen and moisture.

Step 3: Ensure the surface is free from oil, grease, and salt

Rust converters are unable to penetrate oily and greasy surfaces, so for the best results, you should make sure to clean your iron guttering.. This can be done by using a suitable detergent, or sugar soap solution, and cleaning the surface with a soft, dry cloth before treatment. Salts, or any other contaminants that may interfere with the reaction of the rust converter on the rusted surface, will require your gutters to be rinsed thoroughly with clean water.

Once dried, the rusted surface can then be worked on.

Step 4: Initial test area of the rust converter

An initial test of the rust converter on a small surface area of your cast iron guttering is recommended to ensure the compatibility of Neutrarust 661® with the rust surface being treated, and the top paints to be used for over coating. The next steps can be followed for this initial test area.

Step 5: Application of Neutrarust 661® to restore rusted cast iron

When using Neutrarust 661®​ Rust Converter & Primer​, the surface temperature at application should be between 5°c and 40°c. Stir the solution well before use, and transfer the required amount of rust converter into a non-metallic container, ready for application. Try not to take out more than you need for the job, as unused rust converter must not be poured back into the original container. This can contaminate the fresh product, degrading it.

Being water based, the Neutrarust 661®​ Rust Converter can be applied in many ways, including by using a brush, a roller, or by spraying the solution on with airless spray equipment. Brush the solution well into deeply pitted areas to ensure that all areas of corrosion are properly covered.

Step 6: Allow the rust converter to dry

After the rust converter solution has been applied thoroughly to the rusted cast iron gutter, it can then be left to dry and react with the rust. This drying process can take between 20 and 45 minutes, depending on the temperature and humidity. Your gutters should be protected from rain whilst it is drying.

During this period, you will notice the solution transitioning from an off-white colour, to a light blue, and then to black when the conversion has taken place. It is recommended to gently keep brushing for a few minutes during the light blue phase, and then leave it alone to finish drying.

Whilst the rust converter is applied to the cast iron gutter rust, it will produce a chemical reaction that reacts with the rust to produce a black inert surface. The black coating creates a barrier between the metal surface and the air and moisture, which helps prevent further corrosion taking place.

Step 7: Recommended two coats of the rust converter solution,

depending on the surface condition. It is recommended to re-apply another coat or two of Neutrarust 661®​ Rust Converter over the surface, to ensure complete conversion and sealed coverage. The additional coats cannot not be applied within an hour of the previous coat being dry to the touch however.

Step 8: Paint over the primed surface, if desired

The chemical barrier created from the rust converter can then be followed up with a top coat. This can have your gutters looking brand new again, whilst also providing an extra layer of protection against corrosion. It is recommended to use a quality paint if you are wanting to paint rusted cast iron gutters, as this will extend the life expectancy of the substrate from adverse weather, including rain and direct sunlight that gutters face regularly.

How to care and maintain cast iron gutters

Although plastic gutters are more popular than metal ones nowadays, there is no reason for you to automatically replace your cast iron guttering for this reason alone. With the right care and attention, you can prolong the life of your metal gutters and stop them from rusting again. A regular maintenance routine can bring longevity to your rainwater protection system.

Twice a year inspections of all rainwater fittings can be included in a good maintenance routine. An inspection after autumn is highly recommended, as this is when fallen leaves can cause huge drainage problems in gutters. Clean out gutters and hoppers regularly from leaf blockages and other obstructions.

The periodic painting of your cast iron guttering system, when it appears that the surface finish is deteriorating, will help reduce the likelihood of oxidation occurring again. Cast iron is a strong and durable material, however, neglecting the protective layer of paintwork will cause the metal to suffer over time. A buildup of moisture in your gutters is an invitation for rust to eat away at the iron. If you do find your cast iron gutters rusting again, you can always use the Neutrarust 661®​ Rust Converter & Primer again to convert that rust into a non-reactive inert surface. Our rust converter was developed over 40 years ago, and is still recognised globally as the best rust converter for almost any rusted metal project. Tested and approved by the MOD and NATO, and extremely easy to use, you can safely restore rusted cast iron gutters with a brand you can trust.