Bricklaying & Repointing

Conflicting information with repointing (lime mix or not)

Anonymous user 28/02/2024 - 4.04 PM

Hey everyone, this is my first question. This website seems like the best platform to get a professional opinion. I have a 1920's property with a slate damp proof course and cavity wall. Internally, it has penetrating damp a few corners. An independent damp surveyor has made a few recommendations. The first being to remove defective render externally and repoint at low level - 1 meter high all the way round. This is because the render is right down to the floor. The state of the current mortar at this level is breaking away and easy way for water to come in - seen better days! The damp surveyor has said to repoint with a lime mix (4 sand, 1 cement and 1 lime). But the brickwork contractor has said to stay away from lime because, upon inspection, the property has been built without lime. The contractor has said repointing with lime could cause problems because once any water meets the existing/original cement mortar 20mm in, it has no where to go apart from into the bricks. It could essentially trap the moisture in and blow the bricks. The damp surveyor said suggested a lime mix to ensure the building is more breathable and flexible with movements. The brickwork contractor is saying this is not needed and we should stick with cement. Both of those recommendations seem right to me. But what option is best?! What issues could it cause longer term with retaining moisture, if we add lime given the house is built with cement mortar? After this phase, we'll look at the damp spots via the cavity wall, remove debris and re-do the internal walls. Would appreciate your view & help. Thanks in advance.