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topic 12526

Sand blasting standards: Swedish SA 1, SA 2, SA 2.5, SA 3 vs. NACE and Ra

A discussion started in 2002 but continuing through 2018


Q. I need to know the technical details about the following- Surface preparation - Cast Iron part (gratings, used for cooking ranges); the surface needs to be prepared by sand blasting as per Swedish Standard, SA 2.5 or better as per Swedish Standard, SA 3. If it is possible then please inform about the surface finish value (Ra, Rmax) which can be achieved by the above mentioned process.

Please respond as early as possible.

Best Regards,

Souren Pal
steel company - Ahmedabad, Gujarat, India
similarly 2002

Q. Dear Mr. Souren Pal,

I am also interested in the relationship between the SA standards SA 1, 2 2.5 and 3 and Ra. An interesting answer on your question which may be of help to me?

Best Regards,

Laure Spriensma - Jirnsum, The Netherlands




Surface Preparation and Finishes for Metals
from Abe Books


Surface Preparation ISO 8504-2:2000
from Techstreet



A. Mr. Souren Paul , Laure Spriensma, Mr. FADI MUSALLAM,

Surface preparation standards are stipulated by various bodies throughout the world to designate the cleanliness condition of blasted steel, prior to applying a protective coating. The applicable cleanliness standard is usually called for by either the protective coating manufacturer or the owner of the structure to be painted. The most commonly referred to standards are SSPC, NACE, and Swedish Standards. Each standard is divided into four standards of cleanliness, broadly described as follows; brush off, commercial, near white metal, white metal. Whilst each standard may differ slightly in requirements and terminology the following cross reference chart indicates the close approximation of each level of cleanliness for each standard.

A brief description of each of the four levels of cleanliness is as follows:

I hope the above info is useful to you. We are setting up a shipyard and are installing a plate preparation shop.


Bijit Sarkar
shipbuilding - Calcutta, WB, India




Q. May I know the surface profile difference between SA 2.5 and SA 3 in microns?

Shahaji Doltade - UAE

February 17, 2012

A. Dear Mr. Shahaji Doltade
We know that sa 2.5 & sa3 are cleanliness levels not Roughness levels.

Sohail-Hashmi - Karachi,Pakistan

March 19, 2010

Q. Dear sir,
I want to know about measuring instrument for surface finish SA 2.5. I also want to know about from which size of grit we can achieve surface finish SA 2.5.

Your sincerely


March 19, 2010

A. Hi, Prashant. The above discussions lead me to believe that Sa2.5 is not a "surface finish" but a visual standard for cleanliness and is not related specifically to grit size and surface roughness standards like Ra / Rz, and it cannot be measured with a profilometer. Do you have a copy of ISO 8501-1 handy, with its description of Sa2.5? Thanks.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

May 5, 2010

Q. Thanks for the information that SA 2.5 is not measurable in Ra, but we have seen specifications, such as in containers manufacturing that surface finish to SA 2.5 to achieve 25 to 30 micron finish. Is it correct!

- Kolkata, India
May 5, 2010

A. Hi, S P S. Hopefully someone who is more knowledgeable about this will answer, because I don't see how you can measure things that are covered by Sa 2.5, like discoloration, visible oil, and greyness with a profilometer. Nor can I see how you can reasonably expect a given surface profile from performing operations that comply with a blast cleaning specification that is unconcerned about surface profile, and which apparently permits the use of any blasting material of any size for any amount of time.

However, you can certainly specify both requirements, just as you can specify that you want to buy a car with 5 seats and of red color. The color red is neither included nor precluded by the car having 5 seats.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

November 1, 2008

A. I hope this will clear your queries on Blasting and surface preparation..

grade - BS 7079 SS 05 59 00
description, when viewed with the naked eye

SA 2
thorough blast cleaning:Commercial finish 65% clean
The surface shall be free from visible oil, dirt and grease, from poorly adhering mill scale, rust, paint coatings and foreign matter. Any residual contamination should be firmly adhering.
SA 2.5
very thorough blast cleaning: Near white metal 85% clean
The surface shall be free from visible oil, dirt and grease, from poorly adhering mill scale, rust, paint coatings and foreign matter. The metal has a greyish colour. Any traces of contamination shall be visible only as slight stains in the form of spots or stripes.
SA 3
blast cleaning to pure metal: White metal 100% clean
The surface shall be free from visible oil, dirt and grease, from poorly adhering mill scale, rust, paint coatings and foreign matter. The blasted surface must have a uniform metallic colour.


Following is a table giving a clear indication of the comparative blasting grades applicable to national and international standards:

SSPC steel structures painting council
BS 7079 British standards
SS 05 59 00 Swedish standards
BS 4232
NACE, National Association of Corrosion Engineers

white metal (SP5) SA 3
1st quality
grade 1

near white metal (SP10) SA 2.5
2nd quality
grade 2

commercial finish (SP6) SA 2
3rd quality
grade 3

A Surface mostly covered with adherent mill scale, with little or no rust
B Mill scale has begun to flake, rust has started to form
C Mill scale has rusted away or can be scraped off easily and slight pitting has taken place
D Mill scale has rusted away and general pitting can be seen with naked eye
Sanjay Mungee
- Baroda, Gujarat, India

June 11, 2009

Q. Dear sir
We want photographs of standard blasting profiles like Sa 2, Sa 2.5, Sa, 3 etc.

KIRIT D. PARMAR - coatings - Vadodara, Gujarat, India

August 13, 2009

Q. I want sand blasting profile books for SA2 and 2 1/2 with complete pictures. Please let me know where can I find this.
Thanking you in advance.

Shivaraju Ramarao - contractor - Vizag, AP, India

October 21, 2012

A. Hi Kirit; hi Shivaraju.
HMG Paints Ltd. offers a free 24-page PDF with pictures of these surfaces at:

But I think you'll want to try to get a look at ISO-8501-1, which is a hardcover 74-page book, and the actual official reference.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

August 26, 2009

Q. I want to know what the term "Sa" in blasting standards actually stands for.
My boss always asks me and I cannot answer. Help me please...

Ahmad Sanusi
Painting Executive - Johor, Malaysia

September 5, 2009

A. SA stands for Standard Abrasive ... Similarly ST means Standard Tooling

Rahul T.
- Mumbai, India
October 28, 2009

A. Sa Simply stands for Sand as that is the abrasive medium that they used to determine the blasting standards on the 4 Rust Grades for ISO 8501-1 [link by ed. to spec at TechStreet].

Remember Sand was the most widely used abrasive back in the days before the health risks of silicosis were identified.

Alternatively St stands for Steel sorry its nothing more technical, but that's it guys, and the reason I know is that I asked SIS years ago when I first started Inspection to settle an ongoing debate between myself and a colleague.

The relationship between the standards Sa3 and 2.5 is practically identical except that a 2.5 allows for staining or traces of contamination i.e. Very thorough blast cleaning. When viewed without magnification, the surface shall be free from visible oil, grease and dirt, and from mill scale, rust, paint coatings and foreign matter. Any remaining traces of contamination shall show only as slight stains in the form of spots or stripes.

And Sa3 does not have any visual contamination present it is a white metal finish.

For a more definitive view at amounts of contamination which are allowed visually to be included in a blast please take a look at the joint Nace SSPC blasting standards which are equivalents, however not identical to the ISO 8501-1 standards. These standards give a better representation of the actual amounts of contamination which should be present.

Nace 1, SP5, Sa 3 = 0%
Nace 2, SP10, Sa2.5 = 5% Staining
Nace 3, SP6, Sa2 = 33% Staining
Nace 4, SP10, Sa1 = 100% as long as its tightly adherent

Lee Wilson Nace Level 3 Coating Inspector, Nace CIP Instructor & Lecturer, Icorr Level 3 Painting Inspector
inspection services - United Kingdom
February 5, 2010

thumbs up signThanks a lot everyone. It was really helpful.

Priya Suryakant
- Bangalore,Karnataka, India

ISO 8501-1

June 4, 2010

Q. Dear Sir,

I want to know about the detail of SA 2.5 about blasting for steel equipment.


Shanthi K
project engineer - Chennai,Tamil Nadu, India

June 4, 2010

A. Hi, Shanthi. The general meaning of Sa 2.5 is explained above.

My understanding is that the full details are covered by specification SS 55900, available from the Swedish Standards Institute at -- but that this standard was actually canceled in 2001 and is now superseded by ISO 8501-1 [link by ed. to spec at TechStreet].

Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

June 9, 2010

A. The blasting standards as depicted in ISO8501-1 are visual standards for surface cleanliness

Once a substrate is abrasive blasted the blast achieved is then compared to the visual reference pictures which are contained within ISO8501-1 and a comparison made between the blasting standard achieved and the standard required.

When you speak of Ra you are speaking of surface profile, roughness or anchor pattern which is the peak to trough amplitude of the blast profile usually expressed and specified in microns and created during the blasting process this is usually measured with surface replica tape, surface comparators or surface profile needle gauges however surface profile is not an indication of the surface cleanliness do not get confused surface profile and surface cleanliness as depicted in ISO8501-1 are separate requirements.

I hope that this helps

Best Regards

Lee Wilson Nace Level 3 Coating Inspector, Nace CIP Instructor & Lecturer, Icorr Level 3 Painting Inspector
inspection services - United Kingdom

January 17, 2011

Q. I would like reference/guidance for the relation between cleanliness standard with steel structural condition/type. Example: SA-2.5 is applicable for a structure on what conditions? Or what grade is suitable with what condition of structure?

Yuhanas Yuhanas
structure engineer - Jakarta, Indonesia

May 11, 2011

A. Sa.2.5 is expected for existing structure, while Sa.2 is for new installation.

Joseph Okoye
- Ikoyi, Lagos, Nigeria

May 5, 2011

Q. Sir
Can we use silica sand in following Sa 2.5 & Sa 3? If not, which kind of sand do we use?

Rana Akbar
employee - Rahim Yar Khan, Pakistan

August 21, 2011

Q. Which term to follow regarding surface preparation of storage tanks, whether surface cleanliness or surface profile or both because both seems two different requirement of surface preparation for applying coating on metal surface.

A. Aziz
- Karachi, Pakistan

October 1, 2011

A. It seems there is a whole book to be written on the blasting standard requirements, the differences between the required grades and surface profiles.
In short, our company approach the problem as follows:
The client needs to decide (or be advised depending on the application) what type of coating will be applied to the steel, this will decide the required blasting grade as specified by the coatings manufacturer (the norm seems to be SA2.5).The coatings manufacturer will also specify the required DFT (Dry Film Thickness) of the required coating to be applied.The DFT requirement is what needs to be looked at when one decides the roughness of a surface profile in microns.

Hans vd Linde
- Alberton, Gauteng, South Africa

October 26, 2011

Q. Please advise me how to inspect sand blasting for steel structures like I beam, channel, plate.
1. What the pressure should I maintain to get the fine surface preparation.
2. What microns should be there after sand blasting.

Mohamed Jaseem
quality control - Saudi Arabia

October 28, 2011

Q. I have a similar question to the one asked on October 26. For us we are being asked to prepare metal surfaces by Sandblasting to a Sp-10 level finish. What does that entail and how do we inspect for this?

Carlos M [last name deleted for privacy by Editor]
manufacturing - Stockton, California

thumbs up sign Hi Carlos. Some people spend their entire careers helping people answer that question, so I can't pretend that it's easy. But if you have a copy of SP-10, please try your best to phrase your questions in terms of what information you feel is lacking in that specification. If you don't have a copy of SP-10 in your possession yet, well, you probably shouldn't proceed until you do :-)

Luck and Regards,

Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

December 31, 2011 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Is it possible to achieve surface roughness 6.3 Ra from initial surface roughness 12.5 Ra by grit blasting with SA1 or SA1-1/2? Material forged steel.

Abdullah Ansari
wind energy - Pune, Maharashtra, India

January 19, 2012

A. Are you sure you are talking Ra? I don't think you can achieve those results using any blasting media.

tony kenton
AF Kenton
Hatboro, Pennsylvania

February 1, 2012

Q. For example: machined surface roughness Ra 12, can we blast it to SA 2.1/2 and achieve surface roughness 6.3 Ra?

Abdullah Ansari [returning]
wind energy - Pune, Maharashtra, India

February 2, 2012

A. Hi, Abdulah. I think AF (Tony) told you "no". To the best of my knowledge, blasting is for cleaning (removing surface contaminants), and I have personally never heard of anyone attempting to polish an article by blasting, so I think he's right.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

P.S. Jan. 2015: Upon re-examination, Abdullah is talking about 6.3 microns not 6.3 microinches; this is not "polishing" and probably is achievable by blasting in some fashion; but I do not have the necessary experience to answer the question of whether or not it is practical to simultaneously blast forged steel to Ra 6.3 microns and Sa 2.5.

January 25, 2012

Q. What is the size and specification of SA2.5 iron grit?

Ashok Kumar
- India

February 17, 2012

A. Dear Mr. Ashok Kumar, Sa 2.5 is a surface cleanliness level. So how can know grit size?
Sohail Hashmi

- karachi, Pakistan

April 13, 2012

Q. 1.What is the max.percentage of humidity to conduct sand blasting of steel structures?

2.How to measure the profiles SA2,SA2.5 & SA3 at site?

Please help me by answering these questions

B V Ganeswara Rao
- Vishakhapatnam,AP,INDIA

May 8, 2012

Q. Dear Sir,
What is the specification grade for normal surface cleaning by hand before painting?

Subramanyan V A
- Calicut,Kerala, India

July 10, 2012

Q. How can we convert Sa 2.5 to millimeters?

- thrissur, kerala, india

July 10, 2012

Patron: "Waiter, my strawberries & cream have mud in them! Did you wash them?"

Waiter: "No problem sir, we can re-slice the berries smaller if the chunks are too large for your taste".

A. Hi cousin Sunilantonyt --

Please start at the top of this page and read it slowly and patiently to understand that Sa 2.5 is a visual standard for cleanliness, like the patron is talking about. It is not a measurement of surface profile like the waiter is talking about -- and no conversion between the two is possible. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

August 21, 2012

Q. Could you tell the difference between rust grades A and B blasted to Sa3?

Almer G.
- philippines

October 16, 2012

Q. What is the meaning of "Degrease" according to SSPC SP1, and Profile 75, Profile 75µm

Javeed Akhlaque
- Pakistan

August 11, 2013

Q. I want clear Visual Photo or Reference of Sa 1 to Sa 3 value after Shot Blasting on HR Sheet (thickness 8-10 mm).

- Jamshedpur, Jharkhand

July 2013

A. Hi Arijit. Please carefully read the page. I already answered that question on October 21, 2012: "HMG Paints Ltd. offers a free 24-page PDF with pictures of these surfaces at:". Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

August 25, 2013

Q. Sir,
What surface profile is for Sa 2.5 sand blasting?

- AbuDhabi, UAE

August 2013

A. Hi Boby. Perhaps we continue to misunderstand each other's words and phrases, but many people have tried to make it clear that Sa 2.5 is a visual standard for cleanliness and it has nothing to do with surface profiles, which are measures of roughness not cleanliness.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

September 12, 2013

Q. As per customer, requirement is sa2.5 -- but we did sa3. Is there any problem?

thiruppathi manikandan
oil field services - hidd, manama,bahrain

September 2013

A. Hi Thiruppathi. I'm not an expert in this subject, but I can't imagine how it could be a problem. It sounds to me like you've simply removed any doubt that the surface is clean enough to comply with Sa2.5. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

October 15, 2013



Manufacturer of LPG Cylinders - DELHI INDIA

October 16, 2013

A. Hi Shriram. This is available for Rs 130 either from Jain Book Agency at or direct from the Bureau of Indian Standards at

Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

February 24, 2014

Q. Dear sirs,

What is the full form of Sa In Swedish Blasting standard?
My answer was degree of cleanliness in an interview. But interviewer was not satisfied with my answer. The interviewer was From United States in SADARA project at Jubail in Saudi Arabia. So please send answer as soon as you can.

birendra Kumar Kathbaniya
- Dammam, Saudi Arabia

February 2014

A. Hi Birendra. Some have said Sa stands for "standard abrasive", others say it stands for "sand". I say it doesn't matter and you can't translate abbreviations from one language to another anyway :-)

But perhaps the interviewer's problem with your answer is that "degree of cleanliness" may not have quite conveyed the nature of ISO-8501-1 and the ratings like Sa 1, Sa 2, Sa 2.5 and Sa 3 that are associated with it. I think the main point, which is made several times in this thread, is that it is a standard which includes 24 photographs and is a guide for "Visual assessment of surface cleanliness". Please download the short free booklet from HMG Paints that was previously mentioned and I think you will understand it thoroughly. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

May 13, 2014

A. SA:Sweden Airblast
ST:Sweden Tool

Derek Satre
- Medicine Hat, Alberta, Canada

July 29, 2014

Q. Dear sir,

I want to know about the Swedish standard SA-2.5, i.e., to check surface roughness in microns.

With regards


Rohan jena
- Odisha,india

July 2014

A. Hi cousin Rohan. Please study this thread and you will learn that your question isn't properly formed -- because SA-2.5 has nothing to do with microns or surface roughness. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


October 8, 2014

thumbs up signHi Ted,

I said 'Arrrgh' so many times when reading this page. You are a very patient man, and generous with your knowledge. If I could apologise for the blatant ignorance, I would.

Thank you


Matthais DeSOUZA
- Mumbai, Maharashtra, India

October 2014

Thanks Matt. I have the world's best job: I receive & post people's questions & answers from my own home on my own schedule; I can interject my personal opinions at my leisure, and I'm free to google around whenever I find anything interesting -- and get paid for it all through advertising revenue. Yes, I sometimes have to deal with repetition -- but that's a very small price to pay for not having to deal with the much harder stuff that most workers face :-)

I wish I could save the fast learners from the boredom of repeated answers, but since I haven't figured out how to do that, all I can do is try to make the site a fun and pleasant place to visit. Thanks again!


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

January 10, 2015

Q. Dear Sir,

I read the entire communication on this page since from the beginning ...

It is clearly mentioned that "Surface roughness" cannot be the outcome of blasting process and it isn't measurable also - NO standard calls...

But I observed one table for standards of surface preparation for steel in which ISO 8503-1:2012 calls for surface roughness characteristics of blast-cleaned surface..

Anyone can assist me in getting more details in the same?

Adik Chavan
- Pune, India

January 2015

thumbs up signHi cousin Adik. Thanks for your patience in reading the whole thing.

Unfortunately I do not have all of the standards that people mention on this site, but ISO 8503, which you are talking about, is not the ISO 8501 that other people were talking about. ISO 8501 is the "visual standards for cleanliness", and this cannot be equated to surface roughness because it is a visual standard for cleanliness and not a roughness standard. We gave an analogous example that strawberries can be clean or dirty irrespective of the size of the slices.

ISO 8503 appears to be "surface roughness" standards, not visual cleanliness standards.

I don't believe that anyone said that surface roughness "cannot be the outcome of a blasting process and it isn't measurable". The whole point of ISO 8503 seems to be that it can be the outcome of blasting and it is measurable. Anthony Kenton and myself did express the opinion that it was probably not practical to achieve an Ra 6.3 polish by blasting, but I think I may have been too hasty :-(
I, and probably Mr. Kenton, was thinking in microinches instead of microns, but upon re-examination microns were intended and Ra 6.3 microns is probably doable by blasting -- which is not to say that Abdullah Ansari will necessarily be able to achieve what he wants; I don't know.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

February 25, 2015

Q. I want to know if it is necessary to measure temperature & humidity of surface which is to be sand blasted.

Yogesh Bhujbal
- Satara, Maharashtra, India

February 2015

thumbs up sign Hi Yogesh. I hope some reader fully understands the context of your question because it is too abstract for me. If you are a local weld shop offering to clean up a customer's old lawn mower, the answer is no. If a specification you are processing to requires it, the answer is of course yes. If you are an aerospace shop involved in processing airliner components, the answer is possibly yes.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

March 3, 2015

A. To add to Ted's answer. We also need to know what materials you are working with. You should also be aware that oxidation is always a problem which is caused by temperature and humidity.

tony kenton
AF Kenton
Hatboro, Pennsylvania

February 14, 2015

Q. I understand from reading the posts that we need to differentiate between surface cleanliness and surface profile.

An earlier post indicated that surface profile can be related to overall DFT.

Are there any guidelines as to what surface profile should be provided for differing DFT's?

Also, I see specifications from customers that stipulate different Ra ranges for carbon steel and stainless steel for the same paint system and DFT - why is this appropriate if the DFT is consistent?

- Manchester, United Kingdom

March 18, 2015

A. Hi Rob. One thing to keep in mind is that a thick coating on a very smooth surface does not stick as well, in many cases, compared to the same coating on a lightly roughened surface due to a smaller surface/contact area. Therefore, if adhesion is critical and the coating is fairly thick, 63 Ra or higher may be appropriate. On the other hand, if a given coating is very thin, perhaps a very fine finish such as 8 or less will work fine. Another example is a case where visual differences are desired. If a thin coating is placed upon a highly polished surface, the article will possibly look very different (shinier) than a case where the same coating is placed upon a mill finish or roughened article. However, if the DFT is quite high, the underlying Ra is less noticeable. After plating, the surface roughness should not change very much in most cases.

blake kneedler
Blake Kneedler
Feather Hollow Eng.
Stockton, California

May 23, 2015

A. Hi Guys

Surface Roughness and Paint Thickness (DFT) is proportional to each other. when we paint shoprimer the requirement of DFT is 20 microns. We cannot apply on 70 Micron Roughness surface. Because its give you high paint consumption. Same thing reflects for high thickness paint. Also, the adhesive effect is not good.

Stanley C.T
- Madurai Tamilnadu India

March 21, 2015

Q. Dear sir.
I want to know about SA-2.5 & SA-3 profile of sand blasting because I don't have the SSPC standards
at present.

Ali Hassan
PES Consultants - Skardu, Pakistan

May 2015

Q. Hello Ali. Bijat has told us:

Sanjay had told us:
- white metal (SP5) SA 3
    1st quality
    grade 1
- near white metal (SP10) SA 2.5
    2nd quality
    grade 2

And I have told the readers that --
HMG Paints Ltd. offers a free 24-page PDF with pictures of these surfaces at:
But that ISO 8501-1 [link by ed. to spec at TechStreet] is probably the best reference. Let us know if you seek something further.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

May 26, 2015

thumbs up signDear Sir,

Thanks a lot for providing such informative things.

Ali Hassan [returning]
PES Consultants - Skardu Pakistan

June 6, 2015

A. As far as any blasting I have done in the past the SP-10 was considered a white blast...
As far as profile, we were always asked to get a certain average Mil reading usually about 2 mils was a 30 grit sand which is pretty fine. If we used a 16 grit we could get up to a 10 mil average profile.

When You are reading mil thickness on paint, however, the peaks will have less mil thickness due to paint flowing to the low spots. If you use a really rough sand, ex. 16 grit, you will get a lower average mil reading when checking the coating thickness. If you are trying to get a wet mil thickness this even makes it lower because the wet mil gauge will only measure from the highest spots. An electronic Mil Gauge is a bit more accurate but still reads less than the actual mil thickness due to peaks and valleys. I hope this helps anyone wondering about why you may not be getting the proper mil thickness after coating the blasted metal.

If you try to save time blasting by using a really coarse sand, you can actually cost yourself a lot of money later when trying to achieve a certain mil thickness with an expensive coating.

Dave Freer
Freer Specialty Coatings - Great Falls, Montana, U.S.A.

July 1, 2015

Q. As i know, if we talk about roughness after blasting, we should refer to ISO 8503.
If we talk about surface cleanliness from rust, we should refer to ISO 8501.

Sometimes no tight correlation between SA and millimicron.

Is it correct?

Dwitas Ananda Sutomo
united tractors pandu engineering - Cikarang, West Java, Indonesia

July 2015

thumbs up signHi Dwitas. Yes, that is my understanding exactly.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

November 6, 2015

Q. Dear Sir,

Will you Please Clarify the Following Queries:

1) As a Practice and associated, can we mention DIN 55928 for Sand Blasting/Painting in the note of the Dwg.(though part of the information of ISO 8501-1 originates from the said DIN spec'n?);
a) If already mentioned in the Docs as DIN 55928, is this considered as deviation?
2) If not, any other equivalent DIN spec'n is prevailing?


Balachandran Ananth
Freelancing Engineer - Chennai, INDIA

June 28, 2016

Q. If I will do shot blasting with 1.2 mm dia. steel balls for 30 min in blasting machine, which SA standard I can achieve SA2 or SA 2.5?

Ankur srivastav
- Jamshedpur,India

June 2016

A. Hi Ankur. My guess is SA 2.5, but it's only a guess. Do you have any experience with different diameter balls or longer/shorter blasting times that would give us some basis for refining such guesses?


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

August 31, 2016

A. If you are blasting a surface like this you get Sa 5 at least :D

Each part of the surface is only blasted for a few seconds to attain Sa3 (which decreases to Sa 2 1/2 (not Sa 2.5) within a few hours depending on climate). On usual S235 the attained roughness is medium(S), on S355 maybe less but can be optimized. In a blast machine you have surfaces depending on the parts shapes, which are not orientated optimally (low blast angle) so you have to slow down to get your Sa 2 1/2 there which means, better oriented surfaces have Sa3 by far...

Ben Blake
corrosion protection - Dresden, Germany

June 29, 2016

Q. Dear Sirs,

I read all of the Q&A.

I understood that Sa grades are just for cleanliness.

Now, I have a question.

Is there an exact difference between Sa2 and Sa2 1/2 except optical points (like percentage difference)?

Best regards,

G.H. Mun
- Ulsan, Korea

July 15, 2016

A. Dear All;
I was reading TOTAL Company Standards for Offshore and Onshore oil Projects. Following seems to be useful in the discussion:

Apart of "Cleanliness Requirement", there is "Roughness Requirement" as below:

All surfaces shall be blast cleaned to obtain a total angular roughness Rt included :
- between 30 and 50 microns when total thickness of the coats of paint applied is less than 400 microns,
- between 50 and 80 microns when total thickness of the coats of the paint applied is greater than 400 microns.
Only dry blasting techniques are allowed. Compressed air for abrasive blasting shall not contain any trace of oil or water.

Hadi Kh.
Desalination Industry - Tehran,Iran

August 31, 2016

This should give an idea of what the surface preparation grades acc. to ISO 8501 are. The complete standard ISO 8501-1 [link by ed. to spec at TechStreet] costs about 400£)

A. The surface preparation grades acc. to ISO 8501-1 / ISO 12944-4 are visual categories only. ISO 8501-1 is a collection of photographic comparison samples.

Roughness on blasted surfaces depends on the abrasive used and the material blasted. If Slag of 0 to 0.25 mm is used, a finer roughness is achieved than by using 2 mm chilled iron grit (density and size).
An angular abrasive leads to a sharp profile (grit) and a round one (steel "balls") to a profile rounded in the pits (shot). And some are less angular than others...
Needless to say, but it also depends on the strength, the ductility and the hardness of the material to be prepared. (high => low roughness, low => high roughness).

Roughness (surface profile) is judged according ISO 8503-1 to 5, yet the only real mobile method is the comparator procedure acc. to ISO 8503-2 with a sample consisting of four segments of Ry5(µm) 23-28/35-45/60-80/85-115 (shot(s)) and 23-28/50-70/85-115/130-170 (grit(g)) so there are 2 times 6 grades of surface profile (with (g or s) each): finer than fine (finer than Segment 1), fine (1-2), medium (2-3), coarse (3-4) and coarser than coarse (coarser than 4).

Usual coating materials have no special demand of roughness by themselves, but coarser leads to a larger surface and therefore to a better adhesion (That's why some Clients demand a roughness of 80 µm or more without really knowing what they demand, it is sometimes just expensive and sometimes not possible without really helping much, have a look below). Some examples for exceptions are most zinc rich primers ( Zinc(R) EP or ESI) - medium (G), some abrasion-resistant coats - up to coarse (G).
Medium(G/S)are somewhat of a trade standard.

On many materials higher grades cannot be attained, at least not by economic means:
-many stainless steels - on some not more than 20 or 30 µm,
-hardened steel surfaces (flame cut edges!)- almost none even with chilled iron grit of 1.5 mm
-cast iron - usually fine

I hope this information is of some help ;)


Ben Blake
corrosion protection - Dresden, Germany

August 31, 2016

A. I just found a few question to answer, so here's a supplement...

In the technical data sheets (not the safety data sheets!) of professional coating materials there has to be a section where the demanded surface preparation grade is described, example:
Usually most materials need a Sa 2 1/2 to fulfill the intended protection (=> ISO 12944-5, tables annex A). Some (e.g. zinc rich alkali silicate) need Sa3, some surface tolerant primers only need a tool cleaned surface, example:
and so are suitable on sites where blasting is not possible. But blasting would improve the protection and therefore is the preferred method.

Silica sand causes silicosis and therefore should not be used for blasting. In most countries it is forbidden anyway... As a replacement slag tap granulate is used.
If you have a rust grade A or B (mill scale on full or parts of surface) you need "heavy" (high density) grains to hammer the hard and brittle scale off the surface. So a steel or chilled iron abrasive is the best choice. Higher pressure and less abrasive helps as well (higher speed of the single grains and as E = m/2 * v2 ... ;) )
On rust grade C or D (rust with/without scars) "lighter" abrasives like Slag (single-use) or garnet (reusable) should be used. The same goes for removing paint.

On non-ferrous surfaces (e.g. galvanized steel, stainless steel or aluminum) non-ferrous abrasives should be used because of small amounts of ferrite cause galvanic corrosion; (only white used) garnet or special "de-feritted" slag are the abrasives of choice.

There should always be finer grains in the abrasive (e.g. 0-2 mm when using 2 mm) as they make the "fine cleaning" in the pores.

Depending on climate (in particular air humidity) the preparation grade diminishes within a few hours. In 50% and above an Sa 2 2/1 lasts only maybe 4 hours or less. In 30% and below it can last 1 or two days...

For a few years roughness is considered for DFT measurement acc. to ISO 19840 (Correction values: fine: -10 µm, medium: -25 µm, and coarse: -40 µm) due to coverage of peaks. I think there have been several cases of damage in the past and this was the conclusion... I'd say, there was just bad surface preparation - because of this no coat would "fall off". Maybe for single coat systems with 80 µm or less this is one small issue but not for 160 µm or more. This correction value has to be added to the applied thickness and can cause real problems (e.g. zinc rich ESI, NDFT 80 µm+25 µm..., zinc ESI shouldn't be applied with more than 60 µm NDFT anyway. Anyhow only 30 to 40 µm have an electrochemical effect due to the inner resistance of the binder) so this correction value should be relocated to the intermediate coat.

A roughness demand of e.g. 30 to 40 µm in specifications should never be accepted as the values spread wide and after all it is handwork and if some looks really close it could be very very expensive... . You can not blast to an exact roughness like you can machine surfaces. So the grades acc. to ISO 8503-2 should be agreed upon.

We've coated parts for Stat Oil, Petronas, Siemens and a few others and the deviations listed above (if they were) have always been accepted when the matter was explained thoroughly... Even material changes (ESI to EP) where possible.

Btw. with the right combination of abrasive and material you can reduce a primary roughness but this would never be as exact as mechanical processing and why should you when a coat of a few hundred µm is applied anyway ;)

And there's a list with the different preparation grades I got from a manufacturer. They are not exactly the same but very similar.:

SSPC         NACE ISO 8501-1

SP 5    1      SA 3
SP 10  2      SA 2 1/2
SP 6    3      SA 2
SP 7    4      SA 1
SP 1          solvent cleaning
SP 11      ST 3 with Rz = 30 µm
SP 3      PMa

Ben Blake
corrosion protection - Dresden, Germany

January 1, 2017

Q. Dear sir,

Please advise if the blast profile or amplitude is higher than required, what is the remedy to reduce the profile?

arthur donat
xervon - Doha, Qatar

September 6, 2017

A. Dear Mr Arthur Donat go for centrifugal blasting with ONLY steel shots to compensate higher amplitude profile.

Rahil Shaikh
Protective Coatings - Dubai, United Arab Emirates

March 19, 2017

Q. Blasting metal surface using garnet 2040, finished with rust spots. Due to contaminated garnet or technical issues?

Joanne Chin
FRP Products Co Pte Ltd - Singapore

April 4, 2017

Q. Dear sir,
How can I check the cleanliness of grit+shot blasted surface... is any visual comparator available to check for the mix of both, unlike individual comparators.

Yaswanth Vallaturu
- Trichy, chennai , india

August 14, 2017

Q. Let me know about blasting profile samples. How many samples we can take? Any standard describes it? As SSPC PA2 describes area and readings; is there same like that any standard for Profile sample?

- Dammam Saudi Arabia

September 14, 2017

Q. Hi.
I have this question that if SA 2.5 is a standard for visual appearance of cleanliness, then why only blasting is specified in ISO 8501-1 ? We can clean rust by Zinc phosphating also. One of my customers is asking for SA 2.5 and we have Zinc phosphating process in-house, but customer is insisting on Blasting only.
Please advise.

Soumitro Deb
Desmi Equipment Pvt. Ltd. - Mumbai, Maharashtra, India

May 3, 2018

Q. Sir, required profile is 40 to 70 micron but after blast clean profile is 120 micron. For reducing the profile I did sand blasting again, blasting with small size of abrasive with 45 degree angle of nozzle
Now the profile is 90 micron .. please tell me how I can achieve the requires profile. I need the answer because in an interview they asked.

Tariq Aziz
- Abqaiq, saudi arabia

May 30, 2018

Q. What is the blasting type for the interior of an existing petroleum storage tank that's been unused for some period. Note. It has been blasted and primed before use. Now a little pore of corrosion exists. Thanks

Lot aura international limited - ETHIOOE west, Delta state, Nigeria

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