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Mortar being used on bricks

How to avoid crumbling mortar in housebuilding

Mike Plaster
Wednesday 17th April, 2019

At the end of 2018, there were media reports of several new build homes suffering from crumbling mortar between the bricks. This is a great concern, and something that highlights the need for a better understanding about what it takes to create a long-lasting and top quality mortar.

So, what are the causes of crumbling mortar? And how can you avoid it? Here we share our answers to the top 7 questions house builders are currently asking about mortar…

1. What can affect the quality of a mortar mix?
Using unsuitable aggregates, adopting incorrect mixing procedures and adding too much water to the mix can all lead to inconsistent quality in mortar. Clearly these factors are a concern if you’re mixing mortar on site, but it’s also worth bearing in mind if you’re sourcing factory made mortar. The best way to ensure your mortar is consistently high quality is by using quality assured ready-made mortars that are produced to BS EN regulations and used using the official guidance.

2. How important is sand in a mortar mix?
Not all sands produce a good quality mortar. A reputable manufacturer will lab test many different sands to find the best locally available sands to go with the cement and Admixture that have been chosen.

3. What impact does an Admixture have on a mortar mix?
Admixture in mortar helps to aerate the mix, give it its workability and durability properties and reduce the amount of water going in – all essential factors to ensure the mortar is long-lasting and doesn’t dry crumbly.

4. Why choose a factory produced mortar?
Whilst your construction workers may have years of experience in mixing mortars on site; human error in quantities and different views on how best to mix can lead to a low quality finish. Good mortar plants, like the one we run at Marshalls, use a computerised process control unit which stores all the approved and tested designs and stores all the approved and tested designs. This means that the quantity of each raw material is incredibly and consistently accurate so that every mortar mix is the same high quality, every time.

5. How long can you use a ready to use mortar on site?
A factory made, ready to use mortar contains a chemical retarding agent which delays the cement set for a period of time. In the case of Marshalls factory made mortars, that is typically 2 days or more. It’s important to mention that whilst the chemical delays the hardening whilst it is in the plastic tub, once it is laid on a dry brick or block, the cement set begins as normal.

6. How is the quality of factory made mortar checked before it’s delivered to site?
At Marshalls we do a manual cone test on the mortar before it leaves the depot, and again when it arrives on site. This checks the workability and durability of the mortar so we can give customers confidence in the product. But over and above that, a good quality mortar supplier needs to be doing regular spot checks of products in a lab, where the individual sands used for different mixes can be checked, as well as the strength of different mortars for different areas of a building.

Premier Mortars is part of the Marshalls family, and through them you can source a range of ready to use mortars, that exceed the British Standard. You can find out more about this in the Ready to Use Mortar section of our website.

If you’ve found this article useful, the video below contains all this information and more, so please feel free to share with colleagues and your teams.

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