Lime Plaster vs Conventional Plaster


What's the best plaster to use?

What's the best course for you?


The following information may help you choose to use either a conventional plaster or lime plaster:


Conventional Plaster defined

Backing coat: sand & cement, or gypsum based such as 'Hardwall' or 'Browning'

Skim Finish Coat: gypsum based, Multi-Finish or Thistle Board Finish.


Lime Plaster defined

Backing Coat: Lime mixed with sand 

Skim Finish Coat: Lime mixed with sand (slightly stronger mix, finer sand)




Conventional plaster is:

  • available throughout the UK
  • 
specifically manufactured for purpose
  • 
provides consistent setting times - ensuring reliability for commercial building
  • not always the best solution for older properties





Lime Plaster
 is

  • not widely available (lime putty and hydraulic are generally available through specialist suppliers)

  • is the most suitable material for older properties allowing walls to breathe
  • 
can be used to achieve a special finish such as polished plastering, venetian and Tadelakt
  • one of the oldest building materials, being used in construction since Roman times 
  • used less since the advent of cement but now seeing a resurgence



A rough guide to which plaster to use



Consider using Conventional plaster if:


  • working on a modern house (Early to Mid 1900 onwards) and 
the walls are built with sand & cement or timber & plasterboard





Consider using lime if:


  • working on an older property built with lime mortar

  • there are damp or condensation problems (the alkaline properties of lime are naturally bacteria repellant)
  • you want something different (experiment with added pigments to give a rich depth of colour)




Lime Plaster is classified as either:


Hydraulic or Non-Hydraulic


The main difference
Hydraulic lime will set when wet, whereas non-hydraulic will not set when kept moist.

A non-hydraulic lime in exposed conditions externally (without the presence of an additive such as pozzolans) may not withstand the elements as well as a hydraulic lime. Both types of lime harden through a process of carbonation however the hydraulic lime also has a chemical set as a result of impurities present within and so hardens more. But the harder it is the less flexible, so a balance is sometimes needed.


Non-Hydraulic lime - available as a lime putty (flexible and able to withstand the most movement) or hydrated lime (white powder) from builders merchants. 


Hydraulic lime is available in bags in different strengths (NHL2, NHL3.5, NHL5). The stronger it is the less flexible.