april 2008MODERN STEEL CONSTRUCTION W Properly Prep red steelwise a2008 There’s more than one way to surface prep a member. Your connection to ideas + answers WE aLL WORk haRD TO MakE ThE STRUC- TURES WE DESIgN PERfORM WELL fOR OUR CUSTOMERS. But in addition to meeting saety and serviceability requirements, appearance can also be an important measure osuccess. In order or primers and paints to work as intended, structural steel must go through a surace prepara- tion process. Speciying the correct level osurace preparation is key to achieving the nished lookyou want. Why is steel prepared? When contaminants such as dirt, rust, salts, or oil are let on the steel’s surace and painted over, they have the ability to draw in moisture, which will chip the paint and rust the steel. The most common cause opainting and coating ailure is improper surace preparation. A level osurace preparation that complements the paint specication ensures that the primers and paint will uniormly adhere to the steel and last or the intended service lie. Common surace preparation techniques include solvent cleaning, wire brushing, power tooling, and abrasive blasting. Why are there dierent preparation categories? The level osurace preparation required will vary based on the end use othe steel and the coatings desired. Steel members that will remain enclosed usually require no painting and will receive minimal surace preparation. Pieces that require a high-end nish will require a more rigorous prepa- ration to ensure that the product adheres uniormly . Members that are to be galvanized go through a pickling process to chemically clean them oanysurace oils, dirt, and rust beore being galvanized. Finally , members that will be located in severe envi- ronments, such as coastal areas, industrial acilities, or high-humidity areas, require high-end coatings and higher levels osurace preparation. What must I include on my drawings and specifcations? Members that are to be prepared and painted must be designated in the contract documents. In addition, the level osurace preparation and coat- By Erika WintErs-DoWnEy, s.E. Erika Winters-Downey is an AISC regional engineer basedin Kansas City, Mo. a weuewe buh ee membesspC-sp2. phcuef aiW, s. lu. ing inormation must be included in the specica- tions accompanying the documents. Does AISC give recommendations about surace preparation? Inot, who does? Section 6 othe AISC Code oStandard Practice (COSP) states that steel that is to remain unpainted “ shall be cleaned ooil and grease with solvent cleaners, and odirt and other oreign material by sweeping with a fber brush or other suitable means.” Steel that is to be painted must be prepared to a minimum oSSPC-SP2 (Hand Tool Cleaning). The COSP addresses AESS in Section 10. This section notes that weathering steel must be pre- pared to category SSPC-SP6 (Commercial Blast Cleaning). This is done to remove scale that pre- vents the material rom generating the even patina it is chosen or. However, nowhere in this section are guidelines given or general surace preparation oAESS members. Levels opreparation beyond SSPC-SP2 must be specied by the designer. Industry standards governing the description osurace preparation categories are published by the Society or Protective Coatings (SSPC). The Steel Structures Painting Manual Volume 2, Systems and Spec- ifcationsgives detailed descriptions oeach surace preparation category. The SSPC also publishes its VIS series ostandards; these are pictorial standards that govern visual inspection oprepared steel.
There’s more than one way to surface prep a member.
Your connection to
ideas + answers
WE aLL WORk haRD TO MakE ThE STRUC-TURES WE DESIgN PERfORM WELL fOR
OUR CUSTOMERS. But in addition to meetingsaety and serviceability requirements, appearancecan also be an important measure o success. Inorder or primers and paints to work as intended,structural steel must go through a surace prepara-
tion process. Speciying the correct level o suracepreparation is key to achieving the nished look
you want.
Why is steel prepared? When contaminants such as dirt, rust, salts, or
oil are let on the steel’s surace and painted over,they have the ability to draw in moisture, which willchip the paint and rust the steel. The most commoncause o painting and coating ailure is impropersurace preparation. A level o surace preparationthat complements the paint specication ensuresthat the primers and paint will uniormly adhere
to the steel and last or the intended service lie.Common surace preparation techniques includesolvent cleaning, wire brushing, power tooling, andabrasive blasting.
Why are there dierent preparation categories? The level o surace preparation required will
vary based on the end use o the steel and thecoatings desired. Steel members that will remainenclosed usually require no painting and will receiveminimal surace preparation. Pieces that require ahigh-end nish will require a more rigorous prepa-ration to ensure that the product adheres uniormly.
Members that are to be galvanized go through apickling process to chemically clean them o any surace oils, dirt, and rust beore being galvanized.Finally, members that will be located in severe envi-ronments, such as coastal areas, industrial acilities,or high-humidity areas, require high-end coatingsand higher levels o surace preparation.
What must I include on my drawings andspecifcations?
Members that are to be prepared and paintedmust be designated in the contract documents. In
addition, the level o surace preparation and coat-
By Erika WintErs-DoWnEy, s.E.
Erika Winters-Downey is an AISC regional engineer based
in Kansas City, Mo.
a we ue we buh ee membe sspC-sp2. ph cue f a i W, s.lu.
ing inormation must be included in the specica-tions accompanying the documents.
Does AISC give recommendations aboutsurace preparation? I not, who does?
Section 6 o the AISC Code o Standard Practice (COSP) states that steel that is to remain unpainted
“ shall be cleaned o oil and grease with solvent cleaners,and o dirt and other oreign material by sweeping witha fber brush or other suitable means.” Steel that isto be painted must be prepared to a minimum o SSPC-SP2 (Hand Tool Cleaning).
The COSP addresses AESS in Section 10. Thissection notes that weathering steel must be pre-pared to category SSPC-SP6 (Commercial BlastCleaning). This is done to remove scale that pre- vents the material rom generating the even patinait is chosen or. However, nowhere in this sectionare guidelines given or general surace preparationo AESS members. Levels o preparation beyondSSPC-SP2 must be specied by the designer.
Industry standards governing the description o surace preparation categories are published by theSociety or Protective Coatings (SSPC). The Steel Structures Painting Manual Volume 2, Systems and Spec-ifcations gives detailed descriptions o each suracepreparation category. The SSPC also publishes its
VIS series o standards; these are pictorial standards
What is “surace profle” in reerence toprepared steel?
Surace prole reers to the depth andshape o the microscopic pits and peaksthat make up the steel surace. The depthand shape can be varied to some degreeby the surace preparation chosen and the
abrasive media used. Some high-peror-mance coatings adhere better to a deeperor more angular prole. The prole depthcan be measured and is quantied in mils.Surace prole is also commonly reerredto as “anchor prole” or “anchor pattern.”
The abrasive media must be clean so as notto redeposit oil on the steel. Blasting withabrasives can either be done with com-mercial rotary blasting machines or withnozzles.
What are the dierent categories o
surace preparation? A basic description o the dierent stan-
dards is as ollows:SSPC-SP1 – Solvent Clenin. Oils
used in various cutting and drillingmachines are deposited on the steel. Thesemust be cleaned o prior to applying any coatings. The solvent cleaning process usesan organic solvent that is either wiped orsprayed on the steel to remove dirt, oil,grease, and other contaminants rom thesurace o the steel. This can be ollowed
with detergents or steam cleaning. This
step is integral because it is the only sur-ace preparation process that removes oiland grease rom the steel. Other processes
will roughen the steel but not remove oiland grease.
SSPC-SP2 – hnd Tool Clenin. Hand tool cleaning is usually done with a wire brush or sandpaper. This process willremove loose surace rust and mill scalebut is not intended to remove strongly adherent rust. This preparation is gen-erally not adequate or structural steel
that will remain exposed. This method is
oten used to spot clean areas o a struc-ture that might have rusted, at regularly scheduled maintenance times. It doesnot require a large working area or pro-duce as much dust or noise as power toolcleaning. As a result, it can be perormedin higher prole areas without disturbingthe surroundings. Oil-based alkyd paintsand epoxies work well with hand tooled
preparation.SSPC-SP3 – Power Tool Clenin.
This level o preparation will producethe same results as SSPC-SP2, but usespower tools such as grinders or sand-ers instead o wire brushes or sandpaper.
The cleaning removes all loose mill scale, weld spatter, rust, paint, and other sur-ace contaminants. This level o prepara-tion is usually a minimum or most AESSsteel. The main advantage o this methodover hand tool cleaning is time savings when working with larger quantities o
material.SSPC-SP5 - Wite Metl Blst Clen-
in. Blasting to white metal is the mostrigorous preparation that can be specied.
The surace shall be completely ree o allcontaminants; no surace contaminantsmay be visible. These include oil, grease,dirt, rust, paint, mill scale, and oxides. In a9-sq.-in. area, no rust staining can be pres-ent. Blasting is done in a rotary blaster or with compressed air through hand-heldnozzles. Small abrasives o metal shot ormineral grit are used.
SSPC-SP6 - Commercil Blst
Clenin. This process is common or AESS steel that will receive a high-end n-ish. It is more intense than brush-o blastcleaning but not as rigorous as near-whiteor white metal blast cleaning. No suracecontaminants may be visible. In a 9-sq.-in.area, no more than 33% o the area canbe stained due to rust. It is required ormost epoxy primers and polyurethane n-ish coats.
SSPC-SP7 – Brus-O Blst Clen-
in. This is the least intensive type o blastcleaning. Its main advantages are speed andeconomy. Tightly adherent contaminantsmay remain on the surace o the steel.
SSPC-SP8 – Piclin. This processis most commonly seen as one in a serieso baths used in preparation or hot-dip galvanizing. The steel is dipped ina series o tanks to cleanse, pickle, andlux the material. The pickling materialcan be suluric or hydrochloric acid. It will provide a chemically clean suraceor galvanizing.
SSPC-SP10 – Ner-Wite Metl
Blst Clenin. This category is morerigorous than commercial blast cleaningbut not as rigorous as white metal blastcleaning. It will add signicantly to thecost o the preparation, but when done cor-rectly and with a compatible paint system,
will provide a longer service lie than othersystems. No surace contaminants may be
visible. In a 9-sq.-in. area, 5% rust staining
can be present.SSPC-SP11 – Power Tool Clenin
to Bre Metl. This method utilizespower tools to remove all adherent con-taminants on the surace o the steel. It alsohas a required surace prole that mustbe produced. It usually requires impact-based tools rather than rotary-based tools.It is more rigorous than power tool clean-ing. It is generally specied i the prepara-tion is to be perormed on spot areas inthe eld where there is no blasting equip-ment available.
What about steel that is not exposed orpainted?
Section 6 o the COSP states that struc-tural steel that does not require shop paintshall be cleaned o oil and grease with sol-
vent cleaners.
Will it help my paint system to speciy amore rigorous surace preparation thannoted in product standards?
No. It will add to the cost o your proj-ect and not increase the surace lie o theproduct.
What other resources are out there? The Rocky Mountain Steel Construc-
tion Association (RMSCA) developed amodel specication that addresses somecommon surace preparation and coatingsconcerns. This specication goes beyondthe COSP guidelines as an example o aspecication that can be adapted to a job
with high-end requirements. A cost matrixis included at the rear o this specication
that provides guidelines as to the impactthat a certain action might have on theabrication cost o the member. You cannd the model specication online at www.modernsteel.com/aess2003 . The Journal o Protective Coatings and Linings ( www.sspc.org/books/journal.html)and AISC’s online Engineering FAQs( www.aisc.org/faq) are another couple o resources to search.
incur more costs. Costs vary across thecountry and even rom abricator to abri-cator, depending on the equipment avail-able and the level o experience o shopemployees. Many shops don’t have com-mercial blasting equipment available andsend out pieces that must be blasted. Thecost matrix included in RMSCA’s modelspecication indicates that commercial
blast cleaning (SSPC-SP6) will typically incur a 10% to 20% cost increase on theabrication o those members. Preparingand painting a typical shop prime coat willincur a cost increase o 5% to 10%. Blast-ing to Category SSPC-SP5 (White Metal)is 4-5 times more expensive than prepar-ing to Brush-O Blasting (SSPC-SP7) orPower Tool (SSPC-SP3). (JCPL Applicator
Training Bulletin, Jan. 2005.)
And fnally, a word about unspecifedstandard shop paint...
A “shop coat” is a lower-end primerintended to provide temporary protectionto the steel. A good rule o thumb is that i you aren’t speciying a nal paint coat, youdon’t need a shop primer coat. Steel that will remain enclosed or its service lie doesnot need to be shop coated. In the Com-mentary o Chapter M o the Specicationor Structural Steel Buildings, it is notedthat upon studying long-standing steelrames, the presence o a shop coat is irrel-evant. Speciying a shop primer or aes-thetic reasons is unnecessary and will addto the schedule and cost o your project. I the steel is unprotected in the eld duringerection, there is the chance that it willdevelop a thin lm o “fash” rusting (ironoxide). This is not harmul to the strengthor serviceability o the steel.
ReerencesCbe, Wm. “tg he p u f p:
sufce pe f sucu see,”Mch 14, 2002, www.tebrictor.com
Ce, Che; Mu, thm; d th,Wm. “Ecm see,” ModernSteel Construction, a 2000.
Code o Standard Practice or Steel Buildingsand Bridges, amec iue f seeCuc, Mch 18, 2005.
a membe ex b mche. phcue f Zmmem Me, Deve.
th seeWe qufe f 1 pDH (0.1 CEU)hugh aisC’ “Ex Ced” gm. tuche u ex ced, g www.aisc.org/extracredit d e he equz. need me CEU ced? rege f aisC em. V www.aisc.org/semi-nars ee he d . 12 f fm ucmg de d c.
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