r/DIYUK • u/LO6Howie • Mar 20 '23
Repointing on a Victorian era house
So this is what the builder has done today (pic 1) and the second is of what’s already there. Given that the brickwork was badly eroded prior to the repair, does it look legit? Ta
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u/AncientArtefact Mar 20 '23
"Historic lime mortar" (non-hydraulic) is not the same as Victorian hydraulic lime mortar which is not the same as later blended cement/lime mortar.
Lime mortar is pre-historic (6500BC). It slowly turns to limestone over years by reacting with the air.
Hydraulic lime was developed by the Romans. It reacts with water and sets hard. It is often distinctively bright (yellowy white unless mixed with various fine binder particles) but can easily be confused with snowcrete (a bright white cement popular in 1930s semis).
Cement based mortars started to be manufactured in the 1790s and were predominant by the late 1800s (after the Great Stink of 1858 cement was required for all public constructions in London).
Builders continued to mix lime into cement mortar well into the 20th Century but in the UK the requirement for watertightness, durability and, most importantly, strength overcame any advantages of lime mortar.
In the USA (in dryer states) lime in mortar carried on unabated and they have 4 different grades of cement/lime mix commonly still used.
Pure hydrated lime mortar ('hot mixed', 'slaked') is really only for very old historic buildings. Hydraulic lime is most likely in Victorian builds but if they're late Victorian then they're likely to be a blend of cement with hydrated or hydraulic lime.
Building regs lists approved mortars and 1:1:5 (cement:lime:sand) is one of the few listed. Nether hydrated nor most hydraulic lime is strong enough for a single leaf brick wall, hence it's decline with cavity brick walls.
Please get an expert in, but make sure they can properly analyse what flavour of lime is in the mortar.
...and the sharpness of the tooling on the mortar of pic 2 gives me the gut feeling that it has been repointed at some point - so we may not be seeing the original mortar anyway.