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Sweep blasting before galvanizing?

Q. My name is Sreejith. I am working in a aluminium and steel fabrication company as a quality controller. I want to do painting on some steel fabricated items. The pretreatment given:
1. sand blasting
2. hot dip galvanising
3. sweet^SWEEP blasting
4. painting. I want to know, is this much preparation before painting necessary? (structural steel items)
5. What is sweet^SWEEP blasting?

Sreejith M.N.
quality controller - Dubai, UAE
October 19, 2008

Ed. note: We changed the title of this inquiry to "Sweep Blasting" after reading Geoff Crowley's response below

A. Someone has given you poor information.
1. You don't need to shotblast if you intend to galvanize the steel unless it has previously been painted. If it's new steel, it needs no blasting to galvanize it.
2. Galvanizing is a corrosion protection. If protection is what you need, then you don't need to paint it. If you need a special colour, or a highly aesthetic finish then you could paint.
3. There is no such thing as "sweet" blasting. There is "sweep" blasting. (could be a typo?). This means a very light blast by "sweeping" the nozzle over the work. It means a very light blast. Its a poor pretreatment method for preparing galvanized steel for painting. It's expensive, messy and ineffective.
4. Painting. You can paint steel that has been blasted but not galvanized. In this case, shotblast, prime, paint. If the steel has been galvanized, then you need a pretreatment or the paint will not adhere properly. There are a number of proprietary brane chemical pretreatment systems available. You apply (spray or brush apply) the pretreatment, then after drying you paint.

Good luck, hope you get a "sweet" job.

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK
crithwood logo
December 11, 2008

Q. What would be the surface profile for sweep blasting the stainless steel substrate, and what should be nozzle pressure?

Mahesh sk
- Doha, Qatar
January 26, 2012

A. Hi Mahesh. I am not seeing a specification for "sweep blasting" by any standards body, so it remains mere slang rather than detailed instruction. To hot dip galvanizers it is a pre-paint process and involves lightly blasting with a soft media, at an angle, and at low pressure --

The Galvanizers Association of Australia says: "Blast pressure 40 p.s.i maximum, Abrasive Grade 0.2 - 0.5mm (clean ilmenite), Angle of blasting to surface 45 angle, Distance from surface 300-400 mm, Nozzle type min 10mm of venturi type. These controls will ensure that the severity of blasting does not damage the galvanized surface and should remove only 10 µm of surface zinc." (see

The American Galvanizers Association says: "Some materials that have been successfully used to sweep blast galvanized steel include aluminum/magnesium silicate, soft mineral sands with a Mohs hardness rating of five or less, organic media such as corn cobs or walnut shell abrasive [affil link], or stone materials such as corundum and limestone. Particle size for abrasives should be between 200 and 500 micrometers, Blast angle should be between 30 and 60 degrees relative to the steel surface, Blast pressure should be 40 psi or less. Finally, the substrate should be maintained at least three degrees centigrade above the dew point." (see

In your case the substrate is stainless steel, and we don't know why you are blasting it (preparation for painting?) -- but it seems reasonable to interpret "sweep blast" pretty much the same way the galvanizing associations do. Good luck.


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey
April 2014

Q. Hi. My name is Saber. I have a question: please describe sweep blasting method.

Abbas Saber
- Iran, Tehran
April 21, 2014

A. Hi Abbas. This thread explains sweep blasting in pretty good detail. But what are you blasting and why?


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey
April 2014

Q. Dear all,

I wish to know about the percentage of Price difference between Shot blasting and Sweep blasting to accommodate in my estimate for pipe painting. The materials include LTCS Galvanized pipe and SS 304L & SS316L pipes.

Can anybody please advise me??

Anil Kini A
- Kazakhstan, Atyrau
May 30, 2014

Mechanical preparation (Blasting) for Hot Dip Galvanized substrate

Q. Hi,
Please confirm whether we can use Stainless steel shots for blasting (brush off/sweep blasting) hot dip galvanized (Zinc) substrate. Is there any chance of bimetal galvanic corrosion. We have been advised not to use steel shots.

Sellappan Thiagarajan
Applicator - Mumbai, India
June 28, 2016

Q. We make portable towers that get hot dipped galvanized. There are problems with drip lines and galvanize buildup. Some of the material we use in fabrication has a "varnish" like coating that we have sandblasted off.

I have had a theory in my head that this may be the cause of some problems with buildup on those parts. Now I have read in this thread that using steel shot is not recommended. My theory involved the belief that the sand used to blast is silicon. Is there any information on the suitability of steel shot or sand as a blasting media?

Robert Mandrell
- Tulsa, Oklahoma, USA
August 2, 2016

simultaneous replies

Shot blasting is one of the way to prepare the surface for Galvanizing. SS shots No prob but expensive.

Umesh Dalela
Galvanizers & Consultant - Delhi. India
August 4, 2016

August 4, 2016

I'm surprised to hear of anyone shotblasting using sand anymore. The high risk of silicosis has made this inadvisable in all situations, and illegal in many countries.

Blasting (any media) will reprofile the steel surface, which in turn will cause a thicker galvanized coating. This is the main way to get a thicker coating, which is sometimes required in aggressive environments.

The runs and drips will more likely be caused by the angle of dipping, and that is influenced by a number of factors such as:
* length of kettle in relation to the item being dipped
* provision of sufficient diameter vent and drain holes for hollow sections
* operator practice

A steeper angle facilitates better drainage of surplus zinc, avoiding runs.

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK
crithwood logo

August 19, 2016

A. Sweep blasting by means of sand or al-OX/ garnet is limited to Air-pressure blasting and generating huge amount of dust !

Nowadays Stainless steel shot is being applied :
SS Chrome steel with hardness 280 - 400 Vickers and or mixed with Stainless steel grit (one Size-grade finer) as Sweep or brush blasting media.
Major international HDG'ers have approved such media since meeting spec for Brush / Sweep blasting/

Such media can be applied in Air Pressure as well as in Centrifugal wheel shot blasting equipment.

New ways are right now also in practice tests: the use of Zinc/Al-Alloy shot or respective Zn/Al-Alloy cut wire:
Hardness of such media is > 70 HV as like usual zinc cut wire but less than 120 HV in use.

Since hardness of these media is significant higher than hardness of HDG layer, the brush / sweep blasting can be realized to way lower cost and by means of more efficient centrifugal wheel shot blasting machines !

Herb Gray
- Austell, Georgia, USA / Hagen - Germany

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