This document discusses different types of plasters used in building construction, including lime plasters and cement plasters. Lime plasters were widely used historically but have limited use today, though they have favorable properties like high workability. Cement plasters are now more commonly used for exterior applications due to their strength and durability when exposed to moisture. The document provides details on recommended mix proportions and application methods for different plaster types.

1. PLASTERING AND DRY LINING
Building Construction III
Spring 2012
Dr.Hikmat Hammad
Lecture 3

2. Lime plasters
• This type of plaster was widely used before the
Portland cement was available with reasonable
prices.
• Today the use is very limited as the basic plaster
element.
• However, due to its favorable properties it can
be used as a finishing coat over cement based
plasters.
• The minimum proportion of lime plasters is 1
volume lime to 3 volume sand for undercoat and
sufficient amount of water to give plasticity for
application.

3. • For finishing coat lime is applied neat with
water only.
• When the plaster of lime and sand dries
out it shrinks and fine cracks appear on
the surface.
• To prevent cracking natural or synthetic
fibers are used.

4. • Lime plaster hardens slowly. The outer
surface which is in contact with air
hardens first and delays the hardening of
deeper layers.
• Final attained strength is low and can
easily be damaged by knocks
• Durability is low and in time it becomes
powdery due to humidity
• Lime does not have resistance against
water and in direct contact it gets soft.

5. • Lime used in the plaster mortar should be
slaked completely any unslaked lime
particles on the wall surface may get in
contact with moisture and get slaked
causing damage to the plastering
• However lime plasters have high
workability which increases the
productivity
• It has the ability of absorbing humidity in
the air giving better comfort to the
occupants.

6. Cement Plasters (Rendering, Stucco)
• Portland Cement or other types of cements are used as
binder in plaster mortars to increase the strength and
durability of the plasters in moist environments.
• Since the exterior of buildings are subject to rain and
snow cement plasters (renders) are the main type of
exterior plasters.
• Cement hardens best in moist conditions so at the
locations of high condensation cement plasters give best
results.
• The strength of the mortar depends on the cement
content.
• Generally a mix proportion of 1 volume cement to 4 or 5
volume of sand is used.
• To improve the workability of the mixture 1 volume lime
or plasticiser can also be added.

7. • Cement plasters carry the desirable and
undesirable properties of cements. Namely:
– Cement plasters are hard, strong and durable
– They are not effected from direct contact of water and
freezing effect of weather unless no cracks are
formed.
– They are resistant to fire and fungus attack
– Cement shrinks during drying. Therefore too rapid
drying of cement plasters should be avoided to
prevent development of hair cracks on the surface.
– Undercoat should be completely dry before the
application of the successive coats.

8. • It is not recommended to trowel excessively to obtain
smooth surfaces since this creates high water content
layer at the surface. The rapid evaporation of water from
the surface cause irregular surface cracks known as
“crazing”.

9. • The following points to be considered in
the application of the cement plasters:
1. Internal plasters shall be 15 mm. unless
shown otherwise on the drawings and mixed
in the proportion of 1 part cement, 1 part
lime and 6 parts of sand by volume. If the
thickness of plaster exceeds 20mm, then a
two coat operation shall be carried out, the
first coat being finished with a uniform rough
scratch surface to provide a good bond for
the finishing coat. The plaster shall be
finished with a steel float unless specified
otherwise.

10. • As an alternative to the mix in above a mix of 1 part
cement to 4 parts of sand with plasticiser may be used.
The use of plasticiser in the mix shall be strictly in
accordance with manufacturer’s instructions.
• External plaster shall be 15mm thick applied in one coat
unless specified otherwise and mixed in the proportion of
1 part cement to 4 parts of sand by volume. In conditions
of high temperatures, external plastering shall not be
carried out without protecting the surface from direct
sunlight and wind to the satisfaction of the S.O. the
plaster shall be finished with a steel float unless
specified otherwise.

11. St. Astier natural hydraulic lime