Ashlar joints

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.)

Application
Laying sawn six sided blocks or rubbing bricks: Butter a full bed of mortar on to beds and perpendicular ends and firmly press into place to slightly more than the desired bed thickness. Lay the 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 of normal coarse stuff on to 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 100mm 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
See Pointing with NHL (re-pointing ashlar joints)