The Lime Mortar Myth That’s Costing Homeowners Thousands

Comments · 912

• TA

  @talkingconservation · 10 months ago (edited)

  I hope you do not mind a bit of technical clarification, because the chemistry and performance of different limes is quite specific, and some of the narrative here about hydrated lime versus hydraulic lime is not quite right.<br><br>Hydrated lime (often called non hydraulic lime or high calcium lime) is produced by burning relatively pure limestone, slaking it with water, then allowing it to dry as a powder or mature as a putty. It sets mainly by absorbing carbon dioxide from the air and turning back toward a calcium carbonate state. This gives a relatively flexible mortar that can accommodate small movements and manage moisture transfer through the wall. Its long term performance on historic masonry is very well documented in both lab work and many decades of field study.<br><br>Hydraulic limes contain natural clay minerals like silicates and aluminates. When burned and then mixed with water they undergo additional chemical reactions that cause them to set hydraulically inside the mix, as well as through later carbonation. This means they develop strength more quickly and become stiffer, and they move moisture through the masonry differently from non hydraulic lime.<br><br>That is why conservation practice makes a careful distinction between hydrated (non hydraulic) lime and hydraulic lime, and does not treat them as interchangeable binders. In an older solid wall, the choice of binder is critical to how moisture and salts move, and how the wall copes with thermal and structural movement over time.<br><br>It is also worth correcting the idea that adding a plasticiser to a cement mix is equivalent to adding one part hydrated lime to a cement mix. Plasticisers are usually surfactant type chemicals that change the flow, air content and workability of the mix. Hydrated lime changes the fundamental binder chemistry and microstructure, affects how the mortar bonds to the masonry units and how it carbonates over time, and has a very different track record in traditional construction. So a cement plus plasticiser mortar is not the same in behavior or compatibility as a cement plus hydrated lime mortar, and neither of these is the same as a pure or high lime mortar suitable for many historic walls.<br><br>None of this is about nostalgia. There is a large body of research and many decades of practical conservation work that support the use of appropriate lime mortars in older buildings. Getting those distinctions right is really important for anyone working on historic fabric.<br><br>If it helps we’ve done a whole playlist series on Lime Mortars where we start from the chemistry basics and go into the various types and their uses - hope that helps 👌

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• DU

  @Dugberty · 10 months ago

  I own a victorian red brick building with a red brick garden wall. EVerywhere that modern cement has been used to repoint the brickwork the faces have blown off. Modern cement based mortar is too hard for soft red bricks. It doesn&apos;t allow mositure to escape so the brick becomes sacrificial. I know people argue about it but I have seen it with my own eyes, so I&apos;m happy to say, if your bricks are old, say pre 1930&apos;s you shouldn&apos;t be using portland cement with them.

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• GA

  @garethjudd5840 · 10 months ago

  I&apos;ve specialised in pointing brick a natural stonework with Hydraulic Lime Mortar for the last 40 years. I have never had to return to re- do any previous contracts.

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• ML

  @mleys3248 · 10 months ago

  &quot;The builders are going their own way, as they usually do&quot; without any regards to their customers wishes. THAT is exactly why I have 0 confidence in builders.

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• DA

  @davidwarren9204 · 10 months ago

  I&apos;m in Australia. I&apos;ve seen so many old &quot;red common&quot; brick walls where the old lime pointing was replaced by cement, and the bricks have just disintegrated over a few years.

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• BJ

  @bjj7889 · 10 months ago

  Too many builders who think they know all there is to know about building will tell you to put a gage of cement in your pointing mix for a solid wall that was built with lime mortar hundreds of years ago

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• RO

  @rowanshole · 10 months ago

  Roger sneaking in a walk video to skillbuilder gets my applause!🎉

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• PA

  @pauls7363 · 10 months ago

  Great update on lime. I own a listed building with brick work from 1700 up to 1890 depending on the part of the building. Where previous builders have used modern concrete for repointing the bricks have cracked because there is no flexibility.

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• KR

  @Kray675 · 10 months ago

  I own some land in Italy with an 800 year old olive mill ruin made of stone. The lime mortar walls are still absolutely straight and strong as the stone they’re made from. <br>All the wood and iron has rotten and rusted but the lime mortar is still going strong.

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• AN

  @andymathieson2432 · 10 months ago (edited)

  My house was built in 1880 and was used as offices (by a house building company) until we converted it back to a home, starting 20 years ago. &nbsp;We had extensive damp in one lower ground floor room that showed at skirting board and ceiling levels. &nbsp;Once we had stripped off the gypsum plaster and raked out the cement pointing repairs the amount of water held in the walls was a real eye opener. It was locked in by the gypsum and escaped above and below that. &nbsp;It also caused wet rot on some joists. &nbsp;It took over 12 months with dehumidifiers to get back to a normal level of moisture. <br>I raked out and repointed the brickwork myself - mucky but satisfying. &nbsp;I wanted to match the mortar colour with the original lime but found that the original was quite different shades, with different grit, in various parts of the building. I guess that the Victorian builders used what they could get and it wasn’t consistent. &nbsp;Also, inside the room, under the original lime plaster, they obviously used reclaimed bricks of quite different colours, even sooty black. &nbsp;<br>We call it the Victorian building school of “that’ll do”.

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• CL

  @clivewilliams3661 · 10 months ago

  When brickwork with sand/portland cement mix was first used, the standard for expansion joints was incorporated and this standard has reduced over the years from 20m to 9m for common bricks. &nbsp;Prior to that lime was put into the mix which allowed miniscule hairline movement such that movement joints simply weren&apos;t necessary. &nbsp;I worked on a brick industrial building that was over 500ft (150m) long that didn&apos;t have a single brick expansion joint and it showed no sign whatsoever of distress even though it was 80 years old.<br><br>I had to have a garden wall partially rebuilt due to vehicle damage and insisted that the builder use hydrated lime to match the existing since the wall is 15m long with no expansion joints. &nbsp;The result now 4 years on is a perfect match such that the repair is simply not noticeable.

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• PA

  @parashorea · 8 months ago

  funny how modern buildings last about 25 years, but old ones last hundreds

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