Q: I’m a plumber, why should I be bothered about cement?

A: When you think about it, there are a number of jobs that involve passing a pipe or vent through an external wall. Repairing or installing non-condensing tumble dryers, boiler vents, waste pipes, and water pipes will all break through to the exterior and it’s important to finish the job with a weather-tight seal that keeps heat in and the elements (plus unwanted pests) out.

Q: What exactly is cement?

A: Cement is a powder and is the bonding element in any mix. When mixed with water, the setting and curing process hardens the mix and bonds it together.

Cement mixed with sand, coarse aggregate (stone), and water makes concrete. Without the coarse aggregate, (i.e. a cement and sand mixture) it makes mortar, which is typically used to bond brickwork and blockwork in walls, as well as in renders.

Q: Can’t I just use polyurethane foam?

A: It’s certainly an option and for some, polyurethane foam may be the most convenient choice. However, it’s a short term solution. It can be difficult to get a neat finish with foam and, once hardened, must be painted or sealed to ensure it doesn’t degrade due to sunlight exposure. There’s also a health and safety consideration – foam sealants are harmful if they come into direct contact with the skin, as well as extremely difficult to remove from the hands.

Mortar provides a much more durable solution. Products such as Tarmac Blue Circle Quality Assured Mortar will result in reduced maintenance of the finished job over many years and make it much easier to leave a neat and  professional finish.

Q: What about mixing on-site?

A: One of the secrets to a fuss-free application is to choose a ready to use mortar, which is pre-mixed and just requires clean water. This helps guarantee the correct mix of cement, hydrated lime, and sand, which can be vital because getting this wrong can result in decreased strength, increased permeability, and reduced durability of the hardened mortar.  

Q: How do I apply it?

A: By following a simple process, it’s incredibly easy for plumbers to leave a professional finish.

Firstly, carefully prepare the hole by squaring the edges using a hammer and chisel. Be careful not to damage the pipe of course, then remove any leftover dirt or debris by brushing around the pipe.

Start by adding a small amount of water to the mortar, adding in more if required  the recommended amount of water will be labelled on the bag. It’s important to use just enough to make it workable as more moisture means a weaker mortar.

Use a margin trowel to apply mortar around the pipe’s perimeter while, if necessary, making sure to work the mixture into the gap to fill any voids behind the surface.

Q: What else do I need to know?

Mortars must be kept moist while they gain sufficient strength, as is the case with all cement-based products. If the mortar is left to ‘dry out’, shrinkage will occur and will cause gaps around the pipe and cracks in the mortar. To ensure the mortar cures and hardens correctly, it should be covered with a damp cloth or polythene sheeting.

Care should also be taken when using mortar in hot and cold weather. Mortar should not be mixed below 3°C while the temperature is falling, or below 1°C while rising nor should mortar be laid on frozen surfaces.

Equally, it is important to make sure the mix water does not evaporate during hot weather. This requires dampening of the surrounding masonry units prior to application, and the mortar should be covered with a damp cloth or polythene sheeting as it cures and hardens.

Q: What if I don’t have room on the van for it?

A: We understand that larger bags of cement (for instance, a 25kg bag) can be impractical to store in the back of the van. However mortar mix in smaller 10kg or 5kg re-sealable plastic tubs are available, allowing plumbers to use a small amount of product before re-sealing the tub. This can help to reduce wastage, not to mention potential spillage.

It also means that the product can be easily carried in one hand, reducing risks of accidents by making it easier to transport up ladders or through confined spaces, such as passageways.