Research into Cast Iron Radiator Gaskets

Cast Iron Radiators Ltd have been assembling and restoring traditional cast iron radiators for approaching 15 years. We regularly get asked about what Gaskets we are using and how these effect the different types of traditional radiator castings we use. We wanted to share some research performed by our technical team in association with foundries and scientific advisers.

There are several different types of gaskets available in the UK including paper gaskets, silicon gaskets, steel reinforced gaskets, EPDM60 gaskets (the same material used to make tap washers) and other types - all have different strengths and weaknesses or work better with different products depending upon the Ferrite micro-structure of the casting.

In association with spectroscopy test, we have been working with foundries to perfect the casting of difference cast iron radiator sections. However, the main reason cast iron radiators develop issues with their gaskets is because of a poorly maintained ph level of the system.

The water in cast iron radiators should be maintained at a constant ph level of 7.5-8.5. A system inhibitor should be used when your cast iron radiators are installed and this may need to be topped up every 2 to 3 years depending upon the number of Cast iron radiators you have. System inhibitors can easily be applied and are available locally from local suppliers. We do sell system inhibitor cans if needed.

System inhibitors serve two purposes -

Firstly they help to maintain the ph level of a heating system to the optimum ph7.5 - ph8.5 or a slightly alkaline level.

Secondly - system inhibitors reduce the amount of dissolved oxygen in the water in your heating system.

The reason why system inhibitors are important is that over several years, if left untreated, cast iron radiators will start to oxidise a little from within. At Cast Iron Radiators Ltd we x-ray random sections to ensure that our castings have a universal wall thickness that will resist oxidation from within for several decades - probably 100 years or more. However, this oxidation changes the ph level of the water in your system.

To be more scientific for a second - electrons in the iron are consumed by hydrogen ions in the water in combination with dissolved oxygen:

(H2O) and dissolved oxygen or O2(aq). 4e- + 4H+(aq) + O2(aq) --> 2H2O(l)

Basically, this drives up the ph to a much more alkaline level. This increased alkalinity attacks most gaskets that are on the market. It will dissolve silicon, EPDM60 or other reinforced gaskets.

cast iron radiators gasketsOur technical department have been able to prove this by assembling a cast iron radiator using a variety of gaskets available in the market including EPDM60, silicon, steel reinforced silicon and other gaskets available in the market place and advertised in the UK as being for cast iron radiators - we assembled this cast iron radiator and added water without any inhibitor. 18 months later every gasket was under attack by the increased alkalinity of the water as you can see by the picture on the right. This cast iron radiator is available for inspection at our factory in North Yorkshire if you want to discuss this or any other technical issues through.

The only gasket material that can cope with such changes in ph - is traditional gasket paper or what the gasket industry now call 'non asbestos fibrous material' or NAF Gaskets, as these are able to resist alkalinity. Indeed whilst restoring cast iron radiators over the last 15 years, we have regularly seen cast iron radiators that are over 80 years old, with original paper gaskets that are in the same condition as the day they were assembled.

There is always a 'however' of course and it is - to our knowledge the only cast iron radiators available in the UK where the casting tolerance and engineering standards are high enough to use a gasket material as simple as paper - are Sovereign Cast Iron Radiators. Sovereign Cast Iron Radiators are cast in a European foundry, have a 25 year guarantee and are quite simply the best cast iron radiators available in the UK.


1) There is no difference which Gaskets are used in Cast Iron Radiators if your system is correctly installed and properly maintained - including the addition of a system inhibitor. If you are being advised that there are major differences between compounds used in gaskets - this is either because you are being sold an inferior casting or you are talking to someone who simply does not understand the science.
2) In heating systems where maintenance can not be guaranteed - i.e. the system is not serviced every few years and where the ph level is not monitored - select Sovereign Cast Iron Radiators because the casting tolerance and engineering standards allow the use of paper gaskets which are less susceptible to changes in the alkalinity of the water within a system. This is why they have the longest guarantee period in the UK.

If you have any questions about system maintenance, gaskets or your heating system - call the experts, call Cast Iron Radiators ltd and ask to talk to one of our technical team.

We have taken a leadership role in perfecting cast iron radiators in Europe for the last 10 years. Call us now on 01723 321 000.