When Finlock concrete guttering fails

Finlock guttering is the term given to concrete gutters that were popular in buildings in the 1950s and 60s. Like many defects in concrete buildings of that era, the legacy of installing Finlock guttering has unearthed its own set of problems, both internal and external.

Concrete was used for guttering after the Second World War because metal was scarce. Unlike traditional guttering, which hangs off a building under the roof, Finlock guttering was built into the fabric of the building and kept in place by the weight of the roof. Because the concrete guttering is integral to the building, when problems occur they can be difficult and expensive to remedy.

Common problems with Finlock guttering

There can be severe maintenance problems relating to Finlock guttering:

  • Firstly, concrete is heavy and often permeable to water, especially if the concrete cracks.
  • Secondly, where the concrete gutters meet they were commonly made good with a mixture of bitumen and mortar. Over the years this can crack and split and moisture then seeps through the gap.
  • The third issue to look out for is when windows are replaced. Window companies don’t often realise that the guttering forms the window’s lintel and so don’t build in the support needed for the weight of concrete gutters.

A tell-tail sign that Finlock guttering is failing is the presence of condensation and damp patches at the junction of the top of the wall and the ceiling – both inside and outside the building.

Repair or remove Finlock guttering?

There are a number of options you can consider when you notice a damp patch:

  • The least expensive is to repair the guttering by painting the interior of the guttering with a thick bitumastic liner. The downside is that it doesn’t last very long and problems invariably recur.
  • Alternatively, the gutter can be lined with reinforced fibreglass felt which can also be taken up to the roof beneath the first few rows of tiles. This has slightly better longevity but still has a limited life.
  • It is sometimes possible to also install modern gutter systems but because the Finlock gutter is integral with the building a specialist firm is needed to maintain or repair them.
  • The final option is to remove the concrete guttering altogether. This is the most expensive option but worth considering because by cutting out the concrete blocks you are dealing with the root cause of the problem. With the final option, you will need to be mindful of your neighbours and consider the Party Wall Act. In semi-detached properties and terraced houses the concrete gutter is in effect a party structure and therefore you have a legal obligation to adhere to the Party Wall Act 1996. In this case you should seek advice from qualified building surveyors, such as McCarthy Partnership, who can assist and advice on how to tackle Finlock concrete guttering.

 

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