Finlock Gutters: Their Problems and The Solutions

Finlock Gutters: Their Problems and The Solutions

Thursday 25th July 2019
Enrico Hernandez BSc PGDipSurv MFPWS

Finlock gutters are a concrete guttering system commonly found in properties dated between 1950 and 1970. Mainly manufactured by a company called Royston, several different styles of Finlock gutters were introduced to the housing market and in recent times companies dedicated to their maintenance and replacement have sprung up across the country.

Why were Finlock gutters introduced?

It's said that the Finlock system was introduced to replace cast iron gutters, and with a shortage of steel at the time concrete was seen as a low cost and durable alternative. Moreover, with the increasing use of cavity constructed walls during this period, the Finlock system worked well in closing the top of cavity walls and could also serve a load bearing role for openings where window and doors had been placed.


Finlock concrete gutters are made up of two horizontal troughs which sit at the head of cavity walls. One trough is the visible gutter and the other trough spans the cavity (the gap between the walls) sitting on the internal wall.

Varying in length between 200mm and 250mm, Finlock blocks were sometimes connected to each other using steel reinforced rods and mortar. The joints were then sealed and troughs lined with a waterproof coating such as bitumen or lined with mineral felt.

Common problems associated with Finlock gutters

Despite being a great idea at the time, in recent years Finlock gutters have been a nightmare for many homeowners due to their short lifespan (of approximately 30 years) and subsequent failure. Having been exposed to many weather cycles and changing living conditions, the following failures are commonly reported by homeowners:

1. Lining failure

This Finlock gutter was leaking at the time of this photo. You can see the dark patch above the down pipe.

There are many reasons why the lining in Finlock gutters fail, but the main cause is related to the thermal expansion and contraction of the lining, which is the expansion and contraction of the lining in response to temperature changes. In this instance, some linings may separate at junctions or weak points and the heavy inflexible concrete troughs can crack at joints providing the perfect entry point for water.

When the lining fails in Finlock gutters, the damage can be extensive and should be addressed immediately. Left unrepaired, water in the gutter may enter weak points in the guttering ending up in the the cavity and causing costly damage to the wall ties, insulation, internal plaster or other wall finishes and damp - the source of the leak can also be extremely difficult to find! Externally, perished joints can also result in water running down the outer face of the brickwork, leaving a dark and unsightly stain.

2.Thermal/Cold Bridging

If you live in a property which has Finlock gutters and you've noticed a horizontal grey band on the perimeter walls at high level then this can be attributed to 'cold bridging'. Cold bridging occurs when a cold material comes into contact with a warmer material and causes the warmer material to cool down. In terms of Finlock gutters, this cold material is the concrete and the warmer material is the inner leaf of the masonry wall. The horizontal grey band is the result of condensation - warm moisture laden air settling on cool surfaces - and can lead to wallpaper peeling away at the top of the wall. On tiled walls, you may see that the tiles become slightly raised.

Whilst internal and external temperature conditions aren't too much of an issue in the summer, when it's cold in the winter and you decided to crank up the radiator, the temperature difference between the internal and external environments is greater, which will exacerbate the problem of cold bridging. In modern homes where there is a tendency to replace single glazed units with double glazing along with complex heating systems, internal room temperatures will also be higher.

3. Sagging and uneven gutters

As previously mentioned, Finlock gutters can act as lintels for window and door openings, however where they haven't been adequately filled or strengthened at the time of the installation due to and poor workmanship they can sag slightly. Sagging can also occur when windows are poorly replaced making them more difficult to open/close.

Finlock Gutter Solutions

There are generally two ways to resolve the problems associated with Finlock gutters and both options come down to how much the property owner is willing to spend.

Option 1: Complete Replacement

Complete replacement of Finlock gutters is the most costly option but removes the problems associated with this guttering system if carried out by experienced tradesmen. Typically, the removal process looks like the following:

1. Erect scaffolding/platform around the property to provide a safe working area in accordance with Health and Safety Executive guidelines.
2. Remove the bottom rows of roof tiles above the gutter to ensure they don't get damaged and determine whether the underlying felt is in good condition.
3. Remove failed linings from the existing gutters.
4. Remove faceplates from the Finlock gutter (this varies depending on your gutter profile).
5. Cut away the gutter using a diamond-tipped angle grinder so that a flush and level base is achieved. How far this is cut back is dependent on the tile overhang of your roof. Note: Some Finlock gutters and down pipes may contain asbestos so it is important that this is identified before any removal works take place.
6. Fix pressured timber faceplate to the face of the concrete.
7. Fix PVC/Aluminium soffit and fascia to the timber faceplate.
8. Fixing new guttering connecting it to your neighbour's guttering system where applicable ensuring it runs on the same line as your neighbour's gutters. It is advised to discuss this with your neighbours well in advance.
9. Install an eaves protector.
10. Replace the roof tiles.
11. Dismantle scaffolding/platform and clean the surrounding premises.

Depending on the size of your property, this work can be carried out in a couple of hours and shouldn't cause too much disruption to your neighbours.

Option 2: Repair and Relining

If this level of work seems too daunting for you or if you are quoted absurd amounts then depending on the extent of the damage it may be more feasible for you to repair and reline the gutter with a waterproof material as a short term solution. Such repairs may involve the following:

1. Remove the bottom rows of roof tilesand remove the first batten.
2. Cut back deteriorated felt and fix a new layer beneath it by replacing the batten.
3. Strip the gutter of any existing lining down to a sound working base and dry it thoroughly (always difficult in the British weather!).
4. Apply the new lining, for example a single layer of EPDM or rubberised bitumen with a foil liner.
5. Replace the roof tiles.
6. Test the system.

Again, this is a short term solution and should be viewed as such because some of the lining systems available may not be a good quality and their performance is very much dependent on the quality of the workmanship at the time of installation. It's one of the reasons why most companies will only offer a 10 year warranty for lining systems.

As you can see, there are a lot of problems associated with Finlock gutters so it's important that any issues are corrected as soon as possible. Therefore, if you are buying a property which contains a Finlock gutter system, make sure your surveyor takes a good look at it to identify any possible issues. Alternatively, if you haven't yet found a surveyor then get in touch with us today to find out more about our Detailed Building Surveys.

This article was written by Enrico Hernandez BSc PGDipSurv MFPWS. Enrico is currently on the RICS APC Building Surveying Pathway and is a member of the Faculty of Party Wall Surveyors.

If you have any Building Surveying enquiries then please call us at our Pinner office on 0208 426 1448. We cover all of Pinner, Harrow, Stanmore, Northwood, Central London and the surrounding areas.