Can external cables cause damp? And how to stop it!

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If given the opportunity, water will find its way into your property. This process is known as penetrating damp and in most cases, it is due to building defects, such as damaged brickwork, old pointing, or damage to external coatings, such as renders and pebble dash.

Water can also enter your property because of shoddy workmanship. Damp can easily penetrate holes created by external cables. This is actually very common; the hole and cable, provide the perfect conditions for water to penetrate your property.

can external cables cause damp

This could include cables for things like:

  • Tv aerials
  • Phone and internet cables

Cables coming from outside provide the perfect entry point for damp. Firstly, they often run down the wall. This means that water will collect on them and run down the cable until they enter the property.

Secondly, there is a manmade defect in the building. This is a hole drilled for the cable.

Usually defects are due to damage or wear and tear. However, a hole is a hole, it does not matter if this has developed over time, or if it is a hole created with a drill. It will still allow water into the outer skin of the property.

Finally, in properties with a cavity wall, the cable enables moisture to pass from one side of the cavity to the other.

This process is known as bridging, it is usually caused by materials lodged in the cavity. This could include building materials and debris. In the case of cables, they act as a very efficient bridge, allowing moisture to easily pass from one side to the other.

Identifying damp caused by external cables

Spotting damp caused by external cables is quite easy. Just like other cases of penetrating damp, it will usually be visible as a damp patch. However, in some cases, it may not be as obvious right away. For example, when smaller amounts of moisture enter, it may not be as clear initially.

Homeowners will often notice the problem due to other internal issues, such as flaking paint and the formation of black mould.

The location of damp will usually make it obvious the cable is causing the issue. This is because the damp issues are isolated to the area where the cable enters.

Next you can look outside to discover why the water is getting in. There are a few common reasons this might be happening:

  1. The cable is running down the wall and straight into the hole. Generally, this is not best practice, instead the cable should run down and past the hole. This would usually be a few cm lower than the hole, then it would be looped back up to enter the property.

    The reason the cable is looped below, is to let the water run down below the hole and drip off, instead of running straight into the hole.

  2. The hole has not been correctly sealed. Obviously, if the hole is just left exposed to the elements and not sealed this is inviting problems. However, it is surprisingly common for these types of hole to be left exposed.

How to stop damp coming through external cable holes

At this point, we have explained the main reasons water gets in. So now all we need to do is fix the issues.

Your first option is to reposition the cable. To do this you will need a small amount of slack on the cable. If there is even a few cm of slack you should be able to bring the last section of cable below the hole.

The only times you may have an issue with this, is if there is no slack. If there is no extra cable available, then you will not be able to reposition it to solve the problem this way.

You could also have an issue with thicker cables that do not have as much give in them. This could make it more difficult or even impossible to bend.

Where there is additional cable, you will need to use some exterior cable clips to create a curve in the wire that loops below the hole.

If this is not an option, you may be able to contact the company who installed the cable. This is probably only an option for recent installations. However, if this is the case you should ring them and tell them of the problem.

Most honest companies will rectify the issue, especially when it is clear they have caused it. After all, nobody wants bad reviews.

The next thing you should do, is make sure the hole is properly sealed. This can be achieved with a good silicone sealer. You can pick a tube of silicone and a mastic gun at most DIY stores or online from places like Amazon.

A good example of an effective silicone and mastic gun can be seen below:

As you can see, sealing the hole with silicone will only cost you around £10 – £15 and it will offer a completely waterproof barrier. This will mean that water can no longer penetrate.

Fixing damage caused by damp from external cables

Unless you have left the issue for a long period of time, it is unlikely that there is any significant damage. If this is the case, you will just need to dry out the area and remove any mould created by the damp.

To remove mould, you can use a good black mould remover. Our top choice for this is Cilit Bang black mould remover. This can be picked up at most DIY stores and supermarkets. Plus, you can also see it on Amazon by clicking here .

To dry the area, simply allow good airflow and temperature. This will allow the damp patch to dry over time. This can take a few weeks or even months in more serious cases. Ideally, you should wait till the area is completely dry before you touch it up with a lick of paint.


So, in conclusion, can external cables cause damp? As we have shown in this article the answer is yes. It is actually a very common problem.

The good news is it is also an easy issue to fix. Most people will be able to resolve this in a short amount of time, with some basic tools and a small amount of DIY knowledge.

For those who are not confident doing small jobs around the house, a local handyman could fix this issue for you in less than an hour. Also, don’t forget to check with the company who installed the cable. You may find they will come and resolve the issue for free.