Application - Fat Lime Mortar Application

Preparing the Mortar

Do not add water - a premixed mortar when purchased may appear too dry. It must be ‘knocked-up’ (the process of chopping, beating and turning) which will release the water already present in the mix. Water should only be added CAUTIOUSLY if the mortar is still too dry AFTER ‘knocking-up’. For small quantities, an ordinary drum mixer will be sufficient, if you are going to mix large quantities then a mortar mill is recommended (Tŷ-Mawr has several types to hire/ purchase see www.lime.org.uk).Keep the mortar stiff - mortar for pointing should be kept stiff and dry in order to compress it into the joint without smearing. Take care not to get mortar on the face of the brick/stonework. Mortar for laying/bedding work needs to be a little wetter but should still be kept as stiff as possible to avoid excessive shrinkage. The mortar needs to be just wet enough to be workable.

Pointing

Preparing the Surface

• Loose existing mortar must be raked out and dust removed, usually to a depth equal to twice the width of the joint. Sound mortars should be left.
• Assess the moisture content of the background – for dry substrates, dampen all stones/bricks and adjoining surfaces by spraying with water or immersing in water, otherwise they will ‘suck’ the moisture out of the mortar before it sets, causing it to turn to dust. However, if the wall is already wet, do not add more water, in fact it may be necessary to encourage it to dry out first.

Application

• Do not overwork mortar - pointing mortar should, initially, be pressed into the joint without any attempt to ‘finish it’.
• Large holes should be packed with gallets/pinnings - small pieces of stone or bricks, as large volumes of mortar will shrink.
• Bring out mortar joints in layers of up to 10 - 15mm thick to allow carbonation, using a pointing or finger trowel from a small plastic hawk.
• Leave each coat until it is hard i.e. set, but not dried out - the mortar should be ‘too hard to dent with a knuckle yet soft enough to mark with a thumbnail’.
• It should be left to ‘stiffen up’ for up to 24 hours (depending on the speed of drying). Only then can it be worked over to compress it (to overcome shrinkage) and to produce the required finish.
• Brush when firm with a churn brush, to achieve desired finish.
• We do not advise the use of pump-action mortar guns.