J & J Sharpe is the longest established producer of lime products in Devon. The range of products available can be confusing to many people who are unfamiliar with these materials.

To help you decide on the best materials for your repairs and building work we have set out to describe the uses and terms for our products and to explain the differences between the two main types of lime.

Lime based products are the basis for most work on traditional buildings and these can be broken up into two categories Lime putty based (non-hydraulic lime) and Natural Hydraulic Lime (NHL) based

Non-Hydraulic Lime or Lime Putty

Quicklime is the raw material in the production of lime putty. This is added to water and a chemical reaction occurs which is termed as slaking. The resulting mixture is sieved and left to mature for at least 3 months. During this time the liquid slaked lime thickens to the consistency of toothpaste and is pure white in colour and is called lime putty.

Lime putty based products harden by absorbing carbon dioxide from the air to revert back to calcium carbonate (carbonation).

Mortar
Coarse sand is mixed with lime putty to produce a mortar suitable for rendering and pointing.

Fine Skim
This is a topcoat plaster, which is made with fine sand.

Lime Wash
Lime wash is made by diluting lime putty with water to create a wash. Adding suitable pigments produces many different colours.

Haired Lime Plaster
To achieve greater tensile strength in plaster hair (usually goat hair) is added to the mix. This is particularly important when plastering onto laths and is quite usual for any internal plastering onto a solid background.


Hydraulic Lime or Natural Hydraulic Lime (NHL)

Natural Hydraulic Lime (NHL) is made from limestone, quarried in France, Italy, and a small amount in England. The production of NHL differs from slaked lime. NHL is produced from limestone containing clay or other silica impurities. The limestone is burnt and then slaked, however a harder set is obtained because calcium silicates and aluminates form in the presence of water as well as calcium carbonate from carbonation. Therefore it can set under water hence the term hydraulic. NHL is graded by strength into three types 2, 3.5 and 5. These are termed, feebly hydraulic, moderately hydraulic and eminently hydraulic.

Since there are two types of natural lime that are suitable for repair of old buildings it has to be decided whether to use non-hydraulic lime or NHL. The more hydraulic a lime is the greater its strength but it is less permeable and flexible. Therefore the right balance for the job needs to be struck. For example slow setting non-hydraulic lime is good for internal plasterwork and for use on soft backgrounds such as cob, soft stone or friable material.

At the other end of the scale, rendering an exposed stone wall or chimney, then a stronger NHL would be beneficial 3.5 or if very exposed, for instance a granite church tower, then the strongest, NHL 5 would be used.

Hydrated Lime or ‘Bag Lime’
Hydrated lime can be bought at many builders’ merchants. This is non-hydraulic lime produced by slaking with a precise amount of water, driven off during the reaction to form a dry powder. It is inferior to lime putty and is often added to cement, also it is difficult to achieve a set. Hydrated lime is not as fine as lime putty and can carbonate in the bag. It is not suitable for use as a lime wash.

Metastar
This is a pozzalanic additive inert material made from crushed fired clay and comes in the form of a dry powder. The additive is mixed with lime putty based mortar in order to reach a faster initial set more akin to a hydraulic lime.

Daub
As well as lime mortars we also produce daub, which is a mixture of locally sourced clay, chopped straw and sand. This makes a good earth plaster and can be used straight onto lath, straw bale and cob.

Riven or Sawn Laths
These are used to make plaster and lath walls and ceilings. Sawn laths are cut by machine therefore these are straight and even, riven laths are split following the grain, by hand.

Cob blocks
Are very useful when repairing or rebuilding cob walls. These blocks are dense and weigh about the same as a concrete block. They are made by extruding cob mixture, (sub soil with a clay content and chopped straw) and drying.

Stainless Steel Fixings and Mesh
Some repairs to old buildings require stainless steel fixings helical ties and rib lath. We supply stainless screws, washers, threaded bar, nuts, bolts and mesh. Helical ties are driven into cob walls with the use of a special tool in a drill. Rib lath is sometimes needed in order to create a firm base to plaster onto.

Plastering Tools
We supply Harling Trowels, Steel Floats, Gauging Trowels and Hawks

Loading the mortar mill or (pan mixer) with lime putty and sand to produce mortar. The mill mixes a quater of a tonne at a time

Settling tank full of matured lime putty. This is now ready for mixing with sand to make mortar. Or diluted to make lime wash

Slaking tank (the metal tank with pipe coming from it) - settling tank is the wooden one. The slaking tank is the one in which the quick lime is added to water. When it has cooled the tap is opened to let the resulting mix run into the settling tank

Cement mixer full of runny mix (lime putty, sand and water) for scat coating

J & J Sharpe now supply cob bricks.
Unfired cob bricks are made from a mixture of clay and straw. They can be used for non-loadbearing walls or infill for timber frame constructions. They have a high density that gives them a high thermal mass and sound insulation. They are well suited for modern buildings as well as old. Cob bricks absorb odours and water vapour. Cob also has the property of keeping surfaces cool in summer and warm in winter.

Cob bricks can be bedded in a clay or lime mortar. An appropriate finish would be lime or clay plaster, lime rendered for external walls.

The bricks are manufactured in Devon, south west England. Cob bricks are excellent for historic building repairs as well as new build.

Product Data
· Height - 65 mm
· Length – 22O mm
· Width – 105 mm
Compressive strength 3.0 N/mn2
· Density – 1850 kg m3
· Weight – 3.07 kg
· Pallet weight (348 bricks) – 1.068 tonne
Price 40p per brick

How Our Products Are Supplied

Lime putty - products are supplied as ‘wet’

Hydraulic Lime - Supplied as a dry powder. For technical information click here

All our products are delivered throughout the UK and we arrange international delivery. However you may wish to collect products yourself. They can either be bought from Shiptons Builders Merchants, North Tawton, Devon or can be collected from our yard but please telephone to arrange orders.

We work on many types of old buildings and monuments and use a range of lime mortars, plasters, and lime washes. We have found that working with hydraulic lime is particularly useful during the winter months as it reaches an initial set faster than non-hydraulic lime.