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T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 1 6

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.uk

T: 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.