Guide: Iron Rainwater System

With care and attention, there is no reason cast iron rainwater systems can't last just as long as they previously have. As always, prevention is better than cure and establishing a regular maintenance routine will provide the most effective way of ensuring longevity.

Whilst every effort has been made to make this guide as informative and detailed as possible for owners of cast iron rainwater goods this is not a definitive resource.

This guide aims to provide a description of the material, a best practice maintenance and care plan and signs to look for which may indicate deterioration. 

If you are uncertain about anything concerning your cast ironwork, it is advised to get in touch with Dorothea Restorations first, who are happy to discuss best practise and a potential plan of action for ironwork in need of specialised care.



Grey cast iron was most commonly found in 18th and 19th-century architectural ornamentation rainwater goods. With a higher carbon content than wrought iron, cast iron is harder and more crystalline in composition. Cast iron is made by re-melting pig iron in a furnace, skimming of the slag and pouring it into a mould to cool.

Whilst cast iron is hard and strong in compression, it is also brittle. Where wrought ironwork would bend out of shape cast ironwork will break as a result of mechanical stresses.


Identifying Cast Iron


Since cast iron is formed by pouring its molten form into a mould, usually made of two halves, identification of cast iron is most easily done by finding a mould line. Cast objects are generally of larger sections than those produced in wrought iron by a blacksmith.

Since a mould can be used multiple times for particular casting designs, cast ironwork tends to have identical elements with little or no variation and designs tend to have repeating sections.

Furthermore, cast iron can often be identified by the fixing methods used. Flanges, lap joints, mortise and tenon along with concealed bolts are common methods of joining castings together.

Castings may also have a manufacturer's name cast into them, which with a little research may aid identification but also start to build the historical context. 


Rainwater Systems Through History

Over the years, rainwater goods have been made from a variety of materials; lead, zinc, copper and cast iron. The first documented gutter installation dates back to 1241 when the Tower of London had a gutter fitted to protect its newly white-washed walls. 

In the 16th century, lead was most popular – arguably due to the increased availability of recycled lead due to the dissolution and destruction of monasteries. The use of lead, a malleable material, allowed scope for ornamentation.

Until the late 1700s, the high production cost of rainwater systems meant the goods were predominantly reserved for high-status individuals and their residences. With the industrial revolution and a much improved more economical manufacturing process for cast iron, lead rainwater goods were superseded by cast iron alternatives. The affordability of the systems resulted in them becoming widespread in the UK.

Cast iron’s versatility allowed for the development of particularly ornate patterns and designs contributing to the external character of the property. Decorative cresting, barley twists, highly ornate hopper heads and motifs embossed into goods became commonplace. The level of embellishment varied dependent on the type of house with simpler rainwater systems being used on smaller buildings.


Care and Maintenance


With care and attention, there is no reason cast iron water goods can’t last as long as they have already. As always, prevention is better than cure and establishing a regular maintenance routine will provide the most effective way of ensuring the longevity of your rainwater goods. A good maintenance routine should involve bi-annual inspections of all rainwater fittings, particularly after autumn and again in spring.

Gutters and hoppers should be cleaned out regularly to remove vegetation leaves and debris and drains at the base of downpipes. Excess water can encourage plant growth, further impeding your rainwater system.
Snow should be cleared from parapets and gutters to prevent moisture from seeping through and fittings are best checked for leaks and systems for overflow in heavy rain where issues are most likely to be spotted.

Leaf guards can be fitted to gutters and wire balloons placed at the top of downpipes to help reduce blockages occurring. Though these should also be checked regularly for blockages.

Very small bits of corrosion can be removed using a chisel or bronze wire brush and sandpaper before repainting. Take care not to damage the ironwork and don’t use mechanical tools.


Painting Rainwater Systems


Rainwater systems should be painted periodically when it becomes apparent that the surface finish is deteriorating, taking particular care to paint difficult access areas (e.g. the back of downpipes) as these are particularly susceptible to corrosion.

The best approach should really be decided on an individual case basis. Historical significance, your budget and performance requirements will of course vary. Larger scale projects, bare metal restoration and serious corrosion should only be undertaken by a professional.

Minor patch repairs can normally be undertaken by the owner but it is essential to follow some basic procedures to ensure the paintwork doesn’t fail.


  • Ensure the surface is clean and free from dirt, grease and corrosion
  • Ensure the paint you intend to use is compatible with the existing paintwork. If uncertain seek advice before undertaking any work.
  • Existing sound paint should be roughened with sandpaper to help paint adhesion
  • Any small holes should be filled prior to painting to prevent water from seeping in and getting trapped.
  • Wait for optimum weather conditions - cold weather can hinder the paint curing process and a breeze can result in debris sticking to your newly painted surface 


Types of Deterioration, Decay and Corrosion


Cast iron is a strong and durable material. However, if the paintwork which acts as a protective layer is neglected, the cast iron is likely to suffer and fail over time.

Cast iron corrodes and damages in different ways than wrought iron. As a brittle material, it can only accommodate a small degree of pressure or movement before failure. As mentioned previously, where wrought ironwork will bend cast ironwork will fracture or shatter. 

Typically, cast iron is likely to fail due to rusting occurring when the metal is exposed to air and moisture. Cast iron is at its most susceptible to rusting when exposed to high humidity or where the detailing of a casting forms areas likely to hold water.

Structurally, imperfections may exist in a cast iron component due to the production processes. Air pockets uneven cooling and interrupted pouring into moulds all lead to mechanically weak spots more likely to fracture or fail.


Contributing Factors to Deterioration


Factors that can contribute to cast iron water system failure include:


  • General Neglect. The difficulty of access often leads to rainwater systems being overlooked
  • Vegetation growth can cause blockages in gullies, drains, downpipes and gutters eventually leading to flooding and potentially rising dampness.  
  • Mechanical Damage, gutters are particularly susceptible to edge damage if objects are placed against them.
  • When particular components such as drainpipes or gutters misalign they are no longer effective. Usually caused by fixings or collars for the drainpipes have become loose or missing.
  • Bad workmanship or poor repairs can cause ongoing problems
  • Previous section replacements with the wrong size components can often lead to leaks and overflows.
  • Fractures caused by trapped water that freezes within pipes
  • Infrequent or badly undertaken paintwork, particularly to the backs of downpipes and hoppers.
  • Badly sealed and/or leaky joints are prone to further corrosion, freezing and deterioration.



Signs of Rainwater Systems in Need of Intervention


Both external and internal warning signs on a building can indicate potential problems:

  • Excess algae or plant growth
  • Erosion to mortar joints  and masonry work
  • Staining of walls behind rainwater goods
  • Render, brickwork or masonry saturated with water leading to failure
  • Rot to any external joinery
  • Excessive water build up in drains
  • Mouldy and damp walls and ceilings
  • Decay and rot of wooden skirting boards and/or timber wall panels
  • Dry rot occurring in hidden structural timbers 


Typical Repair and Replacement Techniques


The majority of repair works should be carried out by qualified and experienced professionals using traditional materials and techniques. It is always preferred to retain as much as possible of the original fabric and only components completely beyond repair should be replaced.
Cast iron can be particularly difficult, though not impossible, to repair and it is advised to seek specialist advice in such circumstances. You can find more detail on typical restoration techniques here.
It is not recommended to weld cast iron gutters due to the thickness of the cast material. The sudden input of heat can cause thermal shock to the cast iron and create more cracks and problems.  In some cases, items can be welded by using a process of pre and post-heating of the iron but this is best done under controlled conditions in a workshop environment.
Plate repairs on the inside of gutters can be used bedded on epoxy fillers, these are a good alternative to replacements although you will always see the repair.
Where restoration is not possible, replacement sections of rainwater goods should always be on a like-for-like basis. Replacement sections ought to match the original both in dimension and appearance.
Matching castings can be obtained from particular foundries that hold certain patterns. Where this is not possible, what remains of the system can be used as a reference for a new pattern to be made.
Fixings also need to be chosen with care to avoid potential galvanic corrosion and existing fixings such as gutter brackets should be reused where ever possible. You should not use stainless steel when joining your gutter sections together unless they are isolated from the iron.
Where downpipes are being replaced, care should be taken for them to be fixed away from the wall. Both to facilitate painting in the future and to allow condensation to evaporate. 

Click below for guides on other architectural metalwork features: