Part of Historic Environment Scotland

Mortars, Plasters and Renders 1

Dates: 06/11/18
Days of the week: Thursday, Friday
Total hours: 56.5
Taught hours: 27.5
On-site instruction: 12.5
Off-site instruction: 12


Discover the wide range of raw materials used both in the past and today to make mortars, plasters and renders for traditional Scottish structures.

Classification of raw materials and their impact on the physical properties of mortars is the core focus of this module. You will also examine the relevant British Standards for lime binders and aggregates, and why it’s best not to rely wholly on these in the specification of mortars.

Find out how mortar preparation is affected by water content and mixing time as well as by additives. The technical suitability of proprietary ‘restoration mortars’ and ready mixed materials will be discussed – as will the philosophical implications of their use.

This module has a significant practical element, letting you gain first-hand knowledge of how different mortars, plaster and renders should be worked. You will also try out methods of mortar analysis such as acid digestion, X-ray diffraction and petrographic analysis.

Entry requirements

Individual modules are open to anyone with an interest in the subject matter. Applicants for the Advanced Professional Diploma should have a relevant degree or professional experience.

Classes, lectures and presentations

  • Mortars – Origins and Scottish Traditions 1
  • Mortars – Origins and Scottish Traditions 2
  • Plasters, Renders and Harling – Origins and Traditions
  • Production of Historic Mortars
  • Mortar Analysis
  • Mortar Analysis Lab Work 1 (Microscopy)
  • Mortar Analysis Lab Work 2 (Chemical and Mineralogical)

Potential site visits

  • Scottish Lime Centre and Charlestown kilns
  • City Heritage Trust sites
  • Conservation Area Regeneration Scheme sites
  • Townscape Heritage Initiative sites
  • Historic Environment Scotland estate schemes


Origins of the material and Scottish traditions

  • Historic background and traditional practice
  • Sources of materials
  • Geological and mineralogical characteristics of limes – e.g. porosity, permeability
  • Types of limes – e.g. hydraulic, non-hydraulic, magnesian, pozzolanic
  • Ordinary Portland Cement and other cements
  • Other cementing binders such as gypsum, clays and earth

Production of mortars

  • Cold and hot lime manufacturing processes – quarrying, slaking, mixing, curing
  • ‘The lime cycle’
  • Gauging with additives – e.g. pigments, polymers, cement
  • Aggregates – e.g. sharp or soft sand, and size, colour
  • Pigments
  • Quicklime – coarse stuff and fine stuff
  • Pure lime putty
  • Traditional hot and cold mixes
  • Workability
  • Safe working practices

Mortar analysis

  • Simple hand lens examination
  • Microscopic analysis
  • Chemical disaggregation tests (acid solution)
  • Sieving aggregate residue for particle size
  • Enhanced lab tests – e.g. sectioning, scanning electron microscopy, X-ray diffraction
  • Physical and mechanical testing for durability and performance to determine binder type, colour
  • Mix proportions
  • Comparative examinations of archived samples

Plaster composition

  • Plaster mixes – limes, gypsum, clay and cements
  • Selection of aggregates, pigments, reinforcements – affecting texture, colour, workability, strength and so on
  • Role of substrates – e.g. plastering on the hard, timber laths or armatures for cornices and projections

Render composition

  • Constituent materials for external lime, cement or clay-based coatings, including lime harling, floated flat or cast/dashed finishes, limewash
  • Advantages and disadvantages of cement-based coatings
  • Selection of aggregates, pigments, reinforcements – affecting texture, colour, workability, strength and so on