Ashlar Joints using NHL2 Ashlar bedding and pointing mortar
St Astier Natural Hydraulic Limes (NHL)
Traditional ashlar jointing and bedding mortars were made with lime and crushed chalk, usually with a small amount of crushed stone or sand added for bulk. This was mixed on a marble slab with just enough linseed oil to grease the tools, it was made up into a consistency similar to stiff glazing putty, wrapped in oiled cloths and stored until required.
Material. Supplied in dry powder form in 20 Litre plastic buckets with re-usable airtight lids.
Ready for site mixing with clean drinking water and linseed oil (optional).
Background. Generally, natural stone (Ashlar blocks) or rubbing bricks, for building, or existing masonry for re-pointing. The background should be clean and free from loose or friable material, well washed to remove dust. Dampen high suction units. (Do not dampen very low suction materials such as granite)
Laying sawn six sided blocks or rubbing bricks.
Butter on to beds and perpendicular ends a full bed of mortar, firmly pressed into place to slightly more than the desired bed thickness and lay next block firmly in place to line and level by tapping firmly and repeatedly. Excess mortar will squeeze out. Leave excess in place for several hours.
Laying single faced masonry units.
Lay a ribbon of ashlar mortar (approximately 25mm in width on the leading edge of the ashlar faced unit and a bed or normal coarse stuff to bed the irregular meeting faces. Tap down the stone to line and level, excess ashlar mortar will squeeze out. Leave excess in place for several hours.
Mixing. The materials are firstly mixed dry to fully combine all the ingredients and just sufficient water is added to make the material into a dough like consistency, a good double handful size lump of the mortar has a thimble full of boiled linseed oil added and kneaded into the mix until it leaves the hands clean and is fully plastic. (Disposable or rubber gloves are usually worn for this process). The mortar should be used within 24 hours, if being stored for more than an hour it should be wrapped in polythene to keep it moist.
Because it is feebly hydraulic the mortar sets slowly but positively and on final set and full carbonation resembles hard chalk, matching exactly traditional ashlar jointing.
Consumption: 1,000 linear metres of bed joints, at 2mm thick, and 100 mm on bed requires 200 litres of mortar. Re-pointing 1,000 linear metres of 2mm thick joints at a depth of 10mm: 20 litres of mortar are required.
Re-pointing: Pointing with Natural Hydraulic Lime (re-pointing ashlar joints)
For further Guidance, contact your St Astier Distributor.
Copyright © 2016 CESA, Chaux et Enduits de St Astier