When should I use lime mortar?

20 February 2022

Hello, I’ve got some questions about lime mortar. I’ll soon be working on a barn conversion in Norfolk made of soft red brick and I’ve never used lime before; we’ve always used white cement. From what I’ve read, I should use natural hydraulic lime to repoint, to build the extension and on the plinth walls using reclaimed soft red bricks.

So, my questions are:
Can you use lime mortar below dpc (damp-proof course) on new builds?
I’ll use a lime render internally to level out old walls where necessary, but do I need to use lime mortar on new internal blockwork, or should I just use a cement mix?
Should I use lime mortar on roof work to match brickwork or just go for white cement?

Sorry if any of that is unclear.

2 Answers

  1. Anamika Talwaria says:

    Hello Jason,

    Thank you for your question. I’ve posed this to our experts and hope to have an answer for you soon.

    Anamika Talwaria, Build It Features Editor

  2. Alan Tierney says:

    Hi Jason,

    You are right to be planning to use lime mortar rather than cement for your soft red bricks. Natural hydraulic lime can be very strong (sometimes as strong as cement) so I would avoid using it in most situations. It also makes a mortar which is less easy to use.

    You should use a lime putty mortar or even better hot-mixed lime mortar. The advantage of lime putty mortar is that you can buy it mixed and ready for use. Hot-mixed mortar needs to be mixed on site and has some greater health and safety implications. However it produces a much more workable mortar, which we are now finding to have significantly better functional performance. Find out more here: https://www.historicenvironment.scot/archives-and-research/publications/publication/?publicationid=d49812ea-b515-4b33-a96c-a59500a5ef36

    Yes, lime mortar can be used below dpc – here I would use natural hydraulic lime.

    I would advise you to use a lime render / plaster internally throughout. The appearance, feel and influence on the internal environment is very different. Using lime on all internal surfaces will give you a consistent and beneficial finish.

    If you are using old clay tiles on the roof, you should use lime mortar. Otherwise it is mostly an aesthetic consideration. If the two materials will be seen alongside each other, matching them will give a more coherent appearance.

    Kind regards,
    Alan Tierney (Build It Historic Buildings Expert)

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