GUIDE TO BLAST CLEANING

This is intended as a very basic guide to the equipment required for operating a mobile
abrasive blast cleaning business.
It is written as a result of numerous requests for information emailed to my Ebay site and is
intended simply as a guide for the total beginner. Thus , I have steered well clear of
technicalities and techniques, and have only included just one essential chart.

                                                                          
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A blast cleaning set-up consists of just 6 main pieces of equipment, with associated
accessories, and abrasives.

1) COMPRESSOR
You will require a diesel engined mobile compressor. They are rated on their air output cfm
( cubic feet per minute)……… usually 140, 180, 260 & 350 cfm, and manufactured by the
likes of Atlas Copco, Ingersoll Rand, Compair & Kaeser.......

90 to 140 cfm : The lower end of the scale. These are small, lightweight, easy to tow with a
small van, easy to source and miserly on fuel. But you are limited to cleaning just lightly
soiled stone, brick, steel and wood, and the cleaning rate will be generally slow.

180 cfm : Firm favourite with one-man band businesses, my favourite size compressor, as
again they are light, easy to tow, fuel efficient, and not too tiring to use all day. Formidable
when used with 1440 blast pot; I have always owned this combination and have been able to
clean virtually every job I have encountered. Biggest problem is that they are quite rare and
difficult to find, as they are too big for road gangs and too small for other industries.

260 cfm (as in photo above) : Very popular with small/medium size businesses and hire
companies. Weighing in at around 1400kg , you need a decent size van to tow. Can be used
with any size blast pot and is fairly common. Makes rapid work of large areas of stone, brick
and rusty or painted steelwork……. Ideal for large buildings, allows use of long lengths of
compressor and blast hose without losing too much power.

350 cfm : The biggest of the mainstream mobile compressors. For use where a seriously
fast cleaning rate is required on heavily corroded steelwork…. ships, bridges, structures,
heavy machinery, etc. Heavy on fuel and cumbersome to tow. A few days use can be very
tiring …… just about every muscle in your body will know about it !

                                           

2) BLAST POT
Four sizes available : the ½ bag 1028, 1½ bag 1440, 3 bag 2040 and the 6 bag 2452.
Each suitable for a variety of applications. Pots are supplied with manual controls ( two onoff
ball valves), or with a remote valve, controlled by the operator using a deadmans handle
at the end of the blast hose......

The 10A holds just 25kg of abrasives, enough for 10 minutes of continuous blasting. Useful
for small or limited access jobs, for snagging & touching up, fine detail restoration work, or in
workshops for occasional blasting.

The 14A  holds approx. 75kg of abrasives, enough for 30minutes of blasting. Easily the
most popular size pot with jobbing one man businesses. Very manouverable on building
sites and easy to load in and out of van.

The 20A holds 150 kg of abrasives, enough for a full hour of continuous blasting. Popular
with firms involved with medium / large cleaning projects.

The 24A holds 300kg of abrasives, sufficient for 2 hours blasting. Monster size pot for for
big projects where as little down time as possible and a rapid cleaning rate is required. In
reality a full pot (allowing for inevitable stopping and starting) will last half a shift.

3) BLAST HELMET
Available in many guises, an essential safety requirement to basically allow you to see and
breathe whilst blasting. The genuine red Apollo 60 is probably still the market leader despite
it’s hefty price tag and the availability of other cheaper and equally good helmets like the
Scorpion. The helmet must be used in conjunction with a ……………

4) BREATHING AIR FILTER which is a free standing large charcoal filter pack designed
to remove oil mist, moisture and odours from your compressed air supply.

5) BLAST HOSE
The 10A pot uses ½” i.d. blast hose, and the other pots are normally used with a ten or
twenty metre length of 1½” i.d. hose with a two metre long 1” i.d. whip hose at the end.
The whip hose allows for greater flexibility and easier handling.
Blast hoses are made of very hard wearing materials. When used with small compressors and
fine abrasives they can last a long time ….. and so on to the ……

6) NOZZLE
Smallest item, but massively important in determining the final workface impact of your
abrasive / air mix. There are three basic types available…….

Boron alloy : Entry level throwaway nozzles. Cheap and cheerful, don’t last very long, and
are designed for use in projects where management requires precise costing , or for the
occasional use blaster.

Tungsten carbide : Very popular and versatile nozzle. Very hardwearinglining in a lightweight
 jacket , allows for excellent operator comfort and increasedproductivity. Good quality products
will last a long time, choose carefully though, there are alot of dealers selling trash from the Far East.

What size do I need ? The size of nozzle you require depends on the output cfm of your
compressor and the surface you are cleaning. There is an optimum nozzle for each size of
compressor to achieve full pressure (100 psi). There are however many occasions where you
simply do not need full whack output…. 60 or 70 psi is often quite sufficient for cleaning
stone, brick or wood. The chart below is self explanatory………

     NOZZLE             AIR (CFM) TO           AIR (CFM) TO           AIR (CFM) TO
        SIZE                 ACHIEVE 60 psi        ACHIEVE 60 psi         ACHIEVE 60 psi
   1/4” ( 6.5mm)                 54                                68                                  81
  5/16” ( 8mm)                   89                              113                                137
   3/8” ( 9.5mm)               126                              161                                196
  7/16” ( 11mm)               170                              217                                254
   1/2” (12.5mm)              224                              280                                338

100 psi : Required for corroded or painted iron & steelwork, & to remove millscale. To clean
 hardwoods, and painted stone & brickwork.

80 psi : Required to lightly etch steelwork, and to clean heavily soiled stone & brickwork.

60 psi : To clean lightly soiled stone & brickwork, softwoods, and
to etch bright metals.

THIS IS A VERY GENERAL LIST... ALWAYS CARRY OUT TEST PANELS TO
DETERMINE DESIRED PRESSURE AT NOZZLE.

OTHER ITEMS
You will require two compressor air hoses … one ¾” i.d. to connect to the helmet filter and a
1” or 1 ½” i.d. hose for the blast pot. A 15 metre length of each is usually sufficient for
most jobs, but it is prudent to carry an extra length of each.
You will also need a 20 metre length of ¼” i.d. helmet air line, again it’s always worth having
a spare coil.

ABRASIVES There is a multitude of different abrasives available, and this isn’t the time or
place to delve into it all. Suffice to say that we normally stock just two types, which are a fine
and a medium grade mineral slag and they cope very efficiently with 95% of jobs.
Silica sand : is still very widely used because it is cheap and cleans most surfaces with
great efficacy.
There is massive confusion as to whether silica, ( A.K.A. kiln-dried and block paving sand) is
illegal to use for blast cleaning. It is banned ( wet or dry blasting) for cleaning so called
‘articles’, (ref : Factories act 1949 & 1961 ) which according to HSE guidelines encompasses
a wide variety of objects from small castings to ships . These objects do not include
buildings and even bridges . However, normal risk, duty of care and COSSH assessments
prevail and the safest and most effective media available for each particular job should be
used. See section 4 of link below…….
http://www.hse.gov.uk/foi/internalops/fod/oc/200-299/273_18.pdf

HOW MUCH CAN I EXPECT TO BLAST IN A DAY ?

                                     

Lots of variables of course, but if everything’s running smoothly, the weather and access is
good and there is nothing to mask or neighbours to worry about, then 250 to 350 metres of
lightly soiled brickwork is achievable in a good day. As an example , the long elevation and
gable end in the photo below , an area of approx. 200 sq.mtrs was cleaned in just under four
hours with a 260 cfm compressor, 14A pot and approx. 700 kg of sand.

And finally..... look out for the cheap and nasty cloned products with their dodgy ISO 9002
ratings flooding the market from the Far East. Particularly Apollo helmets, silicon nozzles with
super thin linings, nylon CQP couplings that shatter after a week, very thin CQ couplings,
and garbage blast hose.

DISCLAIMER :
THE ABOVE IS PROVIDED FOR GENERAL INFORMATION PURPOSES ONLY, AND DOES
NOT IMPLY ANY SPECIFICATION. THE DATA HAS BEEN COMPILED FROM SOURCES
CONSIDERED ACCURATE. THE USER SHOULD SATISFY HIMSELF THAT ANY PRODUCT IS
ENTIRELY SUITABLE AND SAFE FOR HIS OWN PARTICULAR PURPOSES. IT IS THE
RESPONSIBILITY OF THE USER TO DETERMINE THE BEST PRECAUTIONS NECESSARY FOR
THE SAFE HANDLING AND USE OF ANY PRODUCT FOR HIS UNIQUE APPLICATION. THIS
DATA SHOULD NOT BE CONSTRUED AS ABSOLUTELY COMPLETE, SINCE ADDITIONAL
DATA MAY BE DESIRABLE WHEN PARTICULAR CONDITIONS OR CIRCUMSTANCES EXIST.
CENTURYWISE LTD. DO NOT ACCEPT ANY LIABILITY WHATSOEVER ARISING OUT OF
THE USE OF THE INFORMATION, OR ANY USE, APPLICATION, ADAPTATION, OR
PROCESSING OF THE PRODUCTS THEREIN, AND EXPRESSLY DISCLAIMS ANY LIABILITY
FOR ANY INJURY OR LOSS ARISING FROM THE USE OF THIS INFORMATION OR THE
MATERIALS DESCRIBED.
                                                                                                    Date of Preparation : November 2009