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T W E N T Y T H I R D E D I T I O N
SERV I CES & TREATMENT :
PROTEC T I ON & REMED I AL TREATMENT
4.1
arrangement of tubes inside the nozzle while
later types use a bladed or ported ‘stator’ to
induce the same effect. Generally, swirling
vortex abrasive systems are best suited to the
removal of brittle soiling and light coatings,
such as carbon sulphation (gypsum crust),
lime efflorescence, limewash and cement
based masonry paints. These systems have
largely displaced conventional air abrasive
equipment in the conservation field.
Dry ice pellets: the system ‘dices’ the pellets down
in size and they are reduced further when passed
through a mesh filter behind the nozzle.
Carborundum block and water applied to a ‘rubbing’
brick
MASONRY CLEANING
Practical Solutions - Professional, Technical Expertise & Project Support
Restorative Techniques is an innovative supplier and
manufacturer of surface cleaning systems and restoration
products, with a high level of technical expertise, based on
professional knowledge and significant, long experience in the
field.
The company is far more than simply a supplier. It provides
technical support, training, CPDs and consultancy services to
practitioners, architects and specifiers, involved with demanding
conservation and restoration contracts, to help attain successful
project results.
Being experts in the use of safe and effective cleaning and
coating removal techniques, the company can be engaged to
test and produce on-site trials, reports and aid decision making in
specification and implementation.
Those using, or specifying the Restorative Techniques range of
equipment and products, are supported with full technical
expertise, from members within its team.
Purchasers of machinery are supported and provided with
periodical, free update training, to ensure their operators are kept
informed of changes in regulations, best practice and to assist
them in continuing to sensitively achieve, the appropriate and
desired standards.
www.restorativetechniques.co.ukT: 0044 (0) 1454 417831
info@restorativetechniques.co.uk®
RIBA rps no. 27199
Safe & cost effective removal of soiling and staining
from historic masonry
Sponge jet
The equipment and operation is again similar
to the conventional air abrasive vessel-and-
hose construction but it is modified to meter
small pieces of colour-coded polyurethane
sponge impregnated with various types of
abrasive media. The sponge is directed dry to
the substrate and the spent media collected
for recycling. The used sponge is fed through
a vibratory sieve to remove particles of
contaminant and paint. Apart from supporting
the abrasive media, the sponge is designed to
temporarily encapsulate the cleaning residue.
The sponge can normally be recycled several
times and indeed this is necessary for the
process to be economically viable. The difficulty
is therefore if the spent abrasive cannot be both
contained effectively and kept dry.
Dry ice blasting
Carbon dioxide gas is frozen to approximately
-60⁰C and formed into pellets. The pellets
are metered and ‘diced’ from the bottom
of a chamber and driven by compressed air
through an insulated hose to the outlet.
Nozzles of varying types can be fitted to
direct the CO₂ pellets to the substrate. On
impact, the pellets turn instantly from solid
to gas. The energy released by the expansion
combined with the chill imparted into the
target area acts to separate the soiling/coating
from the substrate. The technique is most
effective at removing soiling or coatings
from smooth substrates and is not effective
for coarse-textured surfaces or for removing
absorbed residue.
Since the CO₂ turns to gas, only the
displaced soiling/coating requires collection
and disposal but care must be taken in
confined or low lying spaces to avoid the risk of
asphyxiation. Cleaning damp, porous surfaces
must be avoided or cracking or spalling may
occur. When used on a large scale, the noise
caused by the high velocity of air emission
from the nozzle is a significant problem.
Further Information
N Ashurst,
Cleaning Historic Buildings,
Donhead, Dorset, 1994
C Daniels,
The Stone Restoration Handbook,
Crowood Press, Wiltshire, 2015
English Heritage,
Practical Building Conservation:
Stone,
Ashgate, Farnham, 2012
English Heritage,
Practical Building Conservation:
Concrete,
Ashgate, Farnham, 2012
A Henry et al
, Stone Conservation; Principles
and Practice,
Donhead, Dorset, 2006
JAMIE FAIRCHILD
is a former materials
engineer in the quarry industry. He has
25 years of experience in masonry cleaning
and is a director of Restorative Techniques
Ltd (see below). He provides training
and consultancy including tuition for the
Masonry Cleaning Master Class at West Dean
College, Chichester.