T W E N T Y F I R S T E D I T I O N
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SERVICES & TREATMENT :
PROTEC TION & REMEDIAL TREATMENT
4.1
MORTARS & RENDERS
a soap and calcium stearate. It is calcium stearate that gives the mortar
water repelling properties.
Water repellents are often incorrectly called water proofers. Water
proofers would not allow either water droplets or water vapour to pass
through them, like a plastic mac with no ventilation, or’ shrink wrap’
resulting in a very sweaty building.
Bear in mind if you are excluding water from a wall, it cannot
succumb to the effects of water freezing.
We frequently specify tallow limewash for the last coat on new lime
render or harling as the effects of wind-driven rain are mitigated by the
tallow; when rain water hits the wall, it ‘beads’ like water off a duck’s back.
Again, overdosing with water repellents could be dangerous in
producing a hydrophobic mortar and markedly decreasing its strength,
and can also have a long term effect on the performance of any repair
work carried out on these materials in the future.
WATER RETAINERS
The principal water retainer used in mortars is methyl cellulose, based
on cellulose, one of the most common chemical compounds in organic
matter. Cellulose is a long chain of linked sugar molecules that gives
wood its remarkable strength as it is is the main component of plant
cell walls. Methyl cellulose particles are long sugar chain fibres which
have been finely divided and dried in a powder form. These form a gel
when mixed with water in a mortar. The water is retained within the
gel, slowing down evaporation and increasing drying time.
This effect is particularly useful in lime mortars for preventing
over rapid drying and consequent shrinkage cracks. A hydraulic lime
mortar will acquire strength slowly by avoiding desiccation. It is of
particular note that hydraulic lime mortars should be kept damp for at
least the first 72 hours after placing to ensure the hydraulic set forms. If
a mortar is allowed to dry out within this 72 hour period, rewetting will
not reinitiate the hydraulic set, and the work will have to be removed
and re applied. Water retainers are particularly useful on high suction
backgrounds or where protection of the new work is particularly
difficult to achieve.
In Mexico, cactus juice is used as a water retainer in mortars to
mitigate the effects of intense dry heat.
A WORD OF CAUTION
Although there is a place for the forms of admixtures discussed above,
and their appropriate use could have alleviated many of the failures that
have been investigated by us in the past, they need to be used in the
knowledge of their impact on the mortars in which they are included
and how their inclusion can affect the mixing, use and aftercare of
the mortars. Doing so should increase the success and thereby the
confidence of both specifiers and practitioners in the use of lime based
mortars and renders.
ROSAMOND (ROZ) ARTIS
MRICSDipBldgCons(RICS) IHBC is director of
the Scottish Lime Centre Trust
one of its primary course
tutors and the head of its building advisory service. A conservation-
accreditedsurveyor,RozisalsodirectorofDundeeHistoricEnvironment
Trust and a member of the Scottish Churches Trust grants committee.
She has written widely on the practical use of lime and other mortars.
Mature Lime Putty
Ready Mixed Lime Mortars
St.Astier And Ionic Natural Hydraulic Limes
Prompt Natural Cement
Limewash And Lime Paints
Breathable Paints And Finishes
Breathable Insulation Systems
Sands And Aggregates
Lightweight Aggregates
Friendly, Professional Advice And Back Up
Training Courses
Cornish Lime Company Ltd is part of the Ionic Group
Above parapet level and in extreme environments, masonry joints will often benefit
from pointing with a water-repellent mortar. (Photo: ©iStock.com/LindaMore)
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ANGLIA LIME COMPANY
Tel 01787 313974 Fax 01787 313944
Email
LIME PLASTERS, MORTARS AND RELATED PRODUCTS
: Since
1992 the Anglia Lime Company has been developing modern
and innovative lime-based products for repair, renovation,
conservation and new build. Suppliers of ready-mixed lime
mortars, renders, plasters, fibrechalk plaster and lime paints,
mature lime putty, St Astier natural hydraulic limes (NHL), laths,
woodwool boards, wool insulation and specialist tools.
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H J CHARD & SONS
1 Cole Road, Bristol BS2 0UG
Tel 01179 777681 Fax 0117 9719802
LIME PUTTY AND RELATED PRODUCTS
: H J Chard & Sons manufactures
for sale direct to the trade and retail users lime putty from best quality
Buxton non-hydraulic white quicklime. Lime putty is used in the
production of a wide range of sand-lime mortars, including hair mortars.
Other products available include pigments, tallow, linseed oil, PFA, HTI
powder and French hydraulic lime.
