External Lime Putty Renders

RJ2.09

Non-hydraulic lime putty based external renders produced from 6 month mature Chalk lime putty mixed with particular sands in proportions of 1:2 or 1:2.5. Lime putty renders are normally reserved for early buildings. (Seek Technical Advice). Natural hydraulic lime (RJ1.05) is more often used for external renders.

Environmental Considerations: 

Lime putty render is an environmentally sustainable product.

Usage/Purpose: 

For all coats of external render. Fibre reinforcement is added to basecoats at a rate equivalent to 2.5 kg/tonne (or 3.5 kg/tonne when applied to lath). Basecoats are applied maximum 10mm thick and top-coats normally c.8mm. Top coats are normally finished with a wood or sponge float, but can be thrown or sprayed on as roughcast or harling. It is often appropriate to site-gauge with a pozzolanic additive (RJ7.01). Lime putty renders must be finished with external grade casein or tallow limewash (RJ3.02/RJ3.03).

Colours: 

Mortar colour is determined by the sand or aggregate mixed with the putty. 

Shelf Life: 

Standard basecoat renders now contain fibres and sisal, as there is no issue associated with deterioration of reinforcement. Animal hair deteriorates rapidly in wet plaster and hair reinforced plasters must be used immediately, preferably adding the hair on site immediately before use. Lime putty renders stiffen during storage, but can be plasticised by thorough re-mixing normally without the addition of water. The render will begin to set if a pozzolan is added. Do not remix pozzolan gauged render.

Coverage: 

50m2 /tonne at 10mm thick and 62m2 /tonne at 8mm thick.

Availability: 

Heat-sealed bags (c.25kgs, 40/tonne). Bulk bags (c.1 tonne) Standard mixes are normally supplied ex Stock.

Health & Safety: 

Calcium hydroxide ca(oh)2 alkali (ph 13).

Cas no 1305-62-0.

Einecs no 215-137-3.

Danger:

H318 causes serious eye damage.

Warning:

H315 causes skin irritation.

H335 may cause respiratory irritation.

See health and safety data sheet RJ 5.02.

Technical Advice: 

TAN 7 Internal Plain Lime Plastering.
TAN 9 Hair/fibre reinforcement in basecoat plasters. 
TGN 5 Use of Haired Base-coat + Fine Finish Plaster.

Observations: 

It is very important that tradesmen with experience of the successful use of lime putty renders are employed, as they do not perform as hydraulic lime or cement based materials. Although there is a weak hydraulic reaction if a pozzolan is added, the primary setting mechanism is the reaction with atmospheric CO2 in the presence of moisture. This ‘carbonation’ is slow, and control of the drying and curing process by mist-spraying, ‘tending’ and protecting is crucial to success and long-term performance. Protections are essential. Do not use below a temperature of 5°C or above 25°C. Do not use if there is risk of frost.