Why service gaps are so common
Plumbers, electricians, heating engineers and broadband installers all drill through walls, and making good afterwards is often an afterthought. In an older Brent house that has had a new boiler, a new kitchen and a few generations of cabling, there may be a dozen such holes, many hidden behind units or boxing.
Materials that work
- Cement-based mortar or filler for gaps in brick and block walls
- Coarse stainless steel or copper wool packed tightly into the gap, then sealed over
- Galvanised or stainless metal mesh with holes no larger than 6mm
- Metal cover plates or pipe collars fixed around the pipe
- Purpose-made rodent-resistant sealants used over a solid backing
Materials that do not work on their own
Expanding foam, flexible silicone, caulk, wood and plastic trims are all soft enough for a determined rat to gnaw through, and mice will work at them too. They can be part of a finish, but the barrier itself needs to be something harder. Why gaps grow explains what gnawing does to a soft seal.
Specific pipes and services
Waste and overflow pipes
The most common route. Pack the annular gap around the pipe with metal wool, finish with mortar outside and a collar or sealant inside. Leave the pipe itself free to move slightly so it does not crack.
Cables
Cable bundles leave irregular gaps. Pack around them rather than squeezing the cables, and do not use anything that could damage the insulation.
Gas pipes and boiler flues
Do not pack gaps around a gas pipe or boiler flue yourself. Gas pipes passing through walls should be sleeved, and any work on gas pipework or flues must be done by a Gas Safe registered engineer. Point out the gap and let them make it good.
Inside as well as outside
Seal both ends of a service run where you can. A gap sealed outside but open inside still lets rodents already in the wall or floor void into the room. Behind kitchen units is the usual place this is missed — see stopping mice behind kitchen units.
Order and timing
Proofing works after the rodents have gone, not before — before or after treatment explains why. If you are unsure which gaps are being used, read how to find the holes in use.
Having it done for you
Sealing pipe and cable gaps is exactly what our rodent proofing service covers: £180 for up to one hour of small-hole work. Book rodent proofing — larger structural work is one for a builder.
