Finlock Concrete Gutters – Relining and Sealing

Unlike modern plastic gutter profiles Finlock concrete systems are so heavy that they suffer from frequent downward movement, especially over window frames that are unable to support the weight of the blocks.

You may notice this yourself if you have a look at any Finlock system, it is a well known and recognized issue. Window fitters dread replacing window frames underneath these heavy blocks for fear of disturbing them.

With all this movement, it doesn’t take long for small cracks to appear and for leaks to begin. The design of these gutters is flawed and they really need to be re sealed or re-lined on the inside.

Three Options to Repair Concrete Guttering

There are only three ways to repair concrete guttering leaks – sealing, lining or complete removal and replacement with a traditional gutter system.

1) Sealing

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This option is best suited to DIY as it requires no specialist tools and is also commonly used by handymen and general roofing contractors.

Here is what you need to do:

  • Remove all debris from gutter and allow to dry
  • Wire brush inside of gutter to remove any existing flaky sealant
  • Fill any gaps inside gutter with fast setting cement
  • Coat inside of gutter with an acrylic roof sealant – see right of page
  • Apply a thick coat of sealant or two average coats
  • AVOID cheap alternatives such as Bitumen as they have a shorter life expectancy

This method is by far the cheapest and if done correctly should last 6-10 years, after which it will need to be repeated. This work can be completed by DIY or handyman but please note that you may need to remove the first course of roof tiles so access to the gutter can be achieved.

You can buy the sealant from Amazon.

2) Gutter Liners

Another popular method is to secure a liner to the inside of the concrete gutter. There are three types of gutter liner available – rubber, aluminium and torch on felt (similar to what is used on flat roofs such as garages).

This type of work needs to carried out by specialist roofing contractors and extra care must be taken when lining the gutter. If your property is a semi detached or in a terrace and your gutter is shared with a neighbour then please be advised, it is best to have all neighbouring concrete gutters lined at the same time. If neighbouring gutters are not lined a seal will need to be created on the boundary and this is a common weak spot in the system and known to cause leaks.

The life expectancy of torch on felt is over 15 years and for both the aluminium and rubber liners it’s in excess of 20 years, assuming the work has been done to a high standard.

3) Removal of Concrete Gutters

It is possible to completely remove the concrete gutter blocks and replace them with a more attractive and leak resistant alternative such as Upvc or aluminium.

Although this may seem a drastic step, it is worth considering especially if your property is detached. The work usually involves cutting the blocks and then securing a timber or plastic fascia board to which the new traditional guttering can be secured to.

If the property is semi detached or terrace then it would be best to replace all the blocks but if that is not acceptable to the neighbours then the blocks can be capped off at the end, see photo.

Photo courtesy of TLG Guttering (opens in new window)

Why Concrete Gutters Leak

The design of concrete Finlock guttering is flawed. Concrete itself is heavy and water permeable. They were initially used during the second world war as other materials such as metal were sparsely available. Concrete guttering was never designed or used because of any advantage – They are for many people a nightmare aspect of their home.

The main problems of these gutters are outlined below:

  • 1) Heavy concrete will suffer frequent movement and cracking of the joints
  • 2) Sealant used on the inside of the gutter is also subject to cracking caused by movement
  • 3) The guttering is often only a few inches from the ceiling – a leak can cause considerable damage
  • 4) Finding the specific location of a leak is sometimes impossible – leading to expensive repairs
  • 5) Unlike normal gutters repairs need to be carried out by specialist guttering companies