Wood Connectors Corrosion Performance

TECHNICAL BULLETIN

PRESERVATIVE TREATED WOOD

Page 1 of 4 UNDERSTANDING THE ISSUES Metal connectors, anchors, and fasteners will There are two primary processes used to hot-dip The following information corrode and may lose load carrying capacity when galvanize (HDG) products – “continuous” hot-dip is a summary of some installed in corrosive environments or exposed to galvanizing and “batch” or “post” hot-dip galvanizing. testing and analysis that corrosive materials. There are many environments Continuous hot-dip galvanizing is a process Simpson Strong-Tie has and materials which may cause corrosion including: completed at the steel manufacturing facility where performed related to • Ocean salt air • Dissimilar metals a continuous sheet of light gauge steel is “dipped” into a molten zinc bath and a protective HDG coating the Preservative-Treated • Fire-retardants • Fertilizers Wood industry’s voluntary • Preservative-treated wood • Fumes is applied to a specified thickness. The steel is then shipped as a coil and used to manufacture many of transition away from the The many variables present in a single building the products produced by Simpson Strong-Tie®. use of CCA-C treated environment make it impossible to accurately predict (The required minimum levels of galvanizing provided wood for residential and if, or when, significant corrosion will begin or reach a by this process are covered by ASTM A653.) Batch critical level. This relative uncertainty makes it crucial or “post” hot-dip galvanizing is generally used on general consumer use. that specifiers and users be knowledgeable of the heavier individual products not capable of being The information is potential risks and select a product coating or metal fabricated from galvanized steel coils and can also intended to help aid in suitable for the intended use. It is also important that be used to galvanize some fasteners and anchors. selection of coatings regular maintenance and periodic inspections are Products are fabricated then shipped out to be “dipped” provided on connectors, performed, especially for outdoor applications. into a molten zinc bath to provide protection against corrosion. The required minimum levels of galvanizing fasteners, and anchors It is common to see some corrosion on provided by this process are covered by ASTM A123 that are in contact with connectors, fasteners, and anchors especially in for individual connectors and by ASTM A153 preservative-treated wood. outdoor applications. Even stainless steel can corrode. for fasteners. The presence of some corrosion does not mean that load capacity has necessarily been affected or that a The corrosion performance of a hot-dip galvanized We continue to research failure will occur. If significant corrosion is apparent product is a function of the amount of zinc on its this evolving topic. or suspected, then the wood, fasteners, anchors, surface. Simply put, more zinc means better Stay informed by visiting and connectors should be inspected by a qualified performance. Historically the connector industry www.strongtie.com/info professional. This individual should evaluate the has used products manufactured with a G60 coating application and make recommendations for any which means 0.60 oz/ft2 of zinc was continuously for the very latest and all remedial action considered necessary. The applied to the steel coil. In recent years, Simpson information. recommendations may include replacing the Strong-Tie made the decision to increase the minimum connectors, fasteners or anchors. standard amount of zinc protection to a G90 coating, 0.90 oz/ft2. This represents a 50 percent increase in Changes in the preservative-treated wood industry protection versus the industry standard and is the have created additional concerns. Effective December minimum level of galvanizing provided on all Simpson 31, 2003, the preservative-treated wood industry Strong-Tie galvanized products. Simpson Strong-Tie voluntarily transitioned from Chromated Copper also offers many products with ZMAX® coating which Arsenate (CCA-C) used in residential applications 2 is a G185 coating, 1.85 oz/ft . to alternative treatments. Testing has shown that certain alternative replacement treatments are Testing has shown that type 304 and 316 stainless generally more corrosive than CCA-C. steel products corrode substantially less than other alternatives when used with the alternative wood Due to the many different pressure treatment treatments. Simpson Strong-Tie has a number of formulations, fluctuating retention levels, and because stainless steel products available and recommends the the formulations may vary regionally or change use of stainless steel as the most effective solution without warning, understanding which connectors, to corrosion risk. However, it is also more expensive fasteners, and anchors to use with these materials and sometimes more difficult to obtain. has become a complex task. We have attempted to provide basic knowledge on the subject here, but it Simpson Strong-Tie testing has shown that relative is important to educate yourself by reviewing our corrosion based on quantitative measurements, visual technical bulletins on the topic, and also by viewing observation, and calculations indicate the alternative information and literature provided by the chemical wood preservatives tested are generally more manufacturers and others. Additionally, because corrosive than CCA-C. The number of variables that the issue is evolving, it is important to get the very affect the rate of corrosion make it impossible to latest information on the topic by visiting our website apply these test results to all product combinations, www.strongtie.com/info. installations, and environmental conditions. These results cannot be correlated to service life. The treated wood industry has recommended the use of stainless steel or hot-dip galvanized fasteners Because increased corrosion from some and connectors for years. This recommendation is preservative-treated woods is a new issue with little still the same for use with the alternative treatments historical data, we have to base our recommendations but additional clarification is needed to insure that on the testing and experience we have to date. It is adequate corrosion protection is provided. Specifying possible that as we learn more, our recommendations 800-999-5099 hot-dip galvanized products is often very generic, as may change, but these recommendations are based www.strongtie.com steel products can be considered hot-dip galvanized on the best information we have at this time. while having various thickness levels. Failure to be © 2008 specific regarding the amount of hot-dip galvanizing Simpson Strong-Tie Company Inc. protection can lead to use of products which may Printed in the U.S.A. not be sufficient for the intended use. T-PTWOOD08 4/08 exp. 6/10

of these items; however, this bulletin only reviews the performance of hot-dip galvanizing with the treated woods. treated the with galvanizing hot-dip of performance the reviews only however,bulletin items; this these of all on results test are there that Note testing. the in examined items the of some indicate tables following The follows: as summarized E12-94 the to similar procedure a using samples 4,000 over on performed also were tests Fastener follows: as summarized procedure test E12-94 the per coupons steel 2,600 over on Strong-Tie Simpson by Testingperformed was TreatedWith Wood.Contact in Metal of Corrosion performedincompliance with the American Wood-Preservers Association Standard E12-94 were tests witnessed independently These anchors. and fasteners connectors, on woods preservative-treated various of impact corrosive relative the assess to tests of series a conducted has Strong-Tie. Simpson used, be may which chemicals treatment preservative of possibilities of number the and available coatings fastener and steel of variety wide the to Due TESTING OF SCOPE

PRESERVATIVETREATED WOOD BULLETIN TECHNICAL Additional testing was performed using barrier membranes. See technical bulletin T-PTBARRIER for additional information. T-PTBARRIERadditional bulletin for technical See membranes. barrier using performed was testing Additional 1 With the exception of ACZA, treatments with ammonia carriers were not included in this testing. this in included not were carriers ammonia with treatments ACZA, of exception the With The corrosion rate was used for comparison purposes only and does not correlate to any life expectancy.life any to correlate not does and only purposes comparison for used was rate corrosion The year.per mils in rate corrosion the determine to used then was which equation an provides standard The • weighed. chamber,and the cleaned from removed were samples The • humidity.90% and 120°F at held chamber environmental an in placed then were Samples • • Several fasteners were installed into the narrow face of a of face narrow the into installed were fasteners Several • weighed. and cleaned thoroughly were fasteners The • A • blocks. wood preservative-treated two between sandwiched then were samples The • sample. each weighing and cleaning thoroughly by prepared were samples coupon Steel • average of the fasteners. the of average an as loss weight percentage the determine to performed were calculations and weighed, cleaned, were Fasteners • wood. the from fasteners the withdrawing of instead chisel a using block wood the from removed were Fasteners • chamber.environmental the in placed was block Each • Copper Azole(CBA-A,CA-B) ACQ-C, ACQ-D(Carbonate) Sodium Borate(SBX/DOT) Micronized CopperQuat ¹⁄₄ Wo " diameter nylon bolt was used on each end to clamp the samples together to provide uniform contact on the coupon. coupon. the on contact uniform provide to together samples the clamp to end each on used was bolt nylon diameter " Borate (other) od Treatment Zinc Borate Untreated (MCQ) CCA-C ACZA 1 SDS, LagScrews&Bolts WA’s, THD’s, PDP’s Various othernails N8, N10,10d,16d Misc. others Fasteners SD8’s ATR ”

preservative Metal Coatings SST graypaint stainless steel Misc. others Batch HDG 304 &316 Uncoated ZMAX -treated wood block. wood -treated G90 ® “ StandardMethod ofDetermining Page 2 of 4 of 2 Page Mechanical galvanization Fastener Coatings EP, ZincDich. Misc. others Uncoated HDG

in the formulation of a treatment can have an effect on the corrosion potential. corrosion the on effect an have can treatment a of formulation the in modification slight a that possible is It etc. performance, corrosion in improvements term repellancy,short providing water improving wood, the penetrating in performance better provide to attempts in modified be may Formulations used. be to wood treated the specifying when exercised be must care so treater wood the and supplier chemical the by controlled are variations These results. the affect can which formulation the in variations of number a be can there etc.) MCQ, CA-B, (Carbonate), ACQ-D (CCA-C, chemical treatment specific a within even that note to important is It results. test the of some of summary general a represents figure following The samples. fastener and coupon steel the from accumulated data the on performed was analysis detailed A RESULTSTEST PRESERVATIVETREATED WOOD BULLETIN TECHNICAL • • AWPA Standard E12-94, and may or may not have a relation to actual service life. service actual to relation a have not may or may and AWPAE12-94, Standard per testing accelerated on based are Testshown samples. results steel galvanized hot-dip continuous G185 and G90 of results the of average an are shown numbers The wood. treated CCA-C with occurred 1 Figure ACQ-D (Carbonate) and CA-B treated wood is on the average approximately two times more times two approximately average the on is wood treated CA-B and (Carbonate) ACQ-D less than seen with CCA-C treated wood. treated CCA-C with seen than less rates corrosion indicates (DOT-Disodiumgenerally Tetrahydrate)Borate Testingwood Octaborate Sodium treated on detail. more for page next the on chart Recommendation Coating Connector the See woods. treated these from demand potential the meet to applied be should ZMAX a minimum a at that Strong-Tie Simpson by recommended is it Thus, CA-B. and (Carbonate) ACQ-D tested the with conjunction in used when protection coating the times two least at be to needs there that reasoned be could it Thus, wood. CCA-C on well perform to time over Strong-Tie Simpson on years for coating galvanized standard the that Note wood. Figure 1 Figure 2. 1. Notes:

ZincBorate ispreservativea treatment for wood composites. together.analyzed and CA-Btreated wood onhot-dip galvanized steel were grouped and (Carbonate) ACQ-D of rates corrosion relative The Relative Corrosiveness compares the average tested relative corrosiveness of several treatments to the corrosion which corrosion the to treatments several of corrosiveness relative tested average the compares 0.0 1.0 2.0 3.0 4.0 and ZincBorate Less than1.0 SBX (DOT) 2 ® coating, which provides approximately 3 times the corrosion protection of G60, of protection corrosion the times 3 approximately provides which coating, CCA-C 1.0 Chemical Treatment

ACQ-D ACQ-D (Carbonate) and CA-B/CBA

4. 3. corrosiveness is somewhat lower than ACQ-D. than lower somewhat is corrosiveness The test results of MCQ (not shown) indicated the relative the indicated shown) (not MCQ of results test The GroundContact or–below (0.40 pcf for ACQ; 0.21 pcf for CA-B). at levels retention with woods on performed was testing All Greater than 2.0 1,3,4 ® connectors was G60 which has proven has which G60 was connectors Page 3 of 4 of 3 Page Greater ACZA than 3.0 corrosive than CCA-C treated CCA-C than corrosive

TECHNICAL BULLETIN

PRESERVATIVE TREATED WOOD

Page 4 of 4 GENERAL SIMPSON RECOMMENDATIONS • Outdoor environments are generally more corrosive with an ammonia base (carrier) are generally known to steel. If you choose to use ZMAX® or HDG coated to be more corrosive. products on an outdoor project (i.e. deck, patio cover), • Using a barrier membrane can provide additional you should periodically inspect your connectors and corrosion protection, see technical bulletin fasteners or have aprofessional inspection performed. T-PTBARRIER. This bulletin is effective Regular maintenance including water-proofing of • Contact Simpson Strong-Tie for availability of ZMAX, until June 30, 2010, the wood used in your outdoor project is also a post hot-dip galvanized, and stainless steel products. and reflects information good practice. available as of April 1, • For wood with actual retention levels greater than 0.40 Due to the many variables involved, Simpson Strong-Tie pcf for ACQ and MCQ, 0.41 pcf for CBA-A, or 0.21 pcf cannot provide estimates on service life of connectors, 2008. This information is for CA-B (Ground Contact), stainless steel connectors anchors or fasteners. We suggest that all users and updated periodically and and fasteners are recommended. Verify actual retention specifiers also obtain recommendations for ZMAX (G185 should not be relied upon level with the wood treater. per ASTM A653) hot-dip galvanized (per ASTM A123 for after June 30, 2010; contact • When using stainless steel connectors, use stainless connectors and ASTM A153 for fasteners and anchors) Simpson Strong-Tie for steel fasteners. When using ZMAX/HDG galvanized or mechanically galvanized fasteners and anchors (per current information and connectors, use fasteners galvanized per ASTM A153. ASTM B695 class 55 or greater) or other coatings from the limited warranty or see • Testing indicates wood installed dry reduces potential treated wood supplier for the type of wood used. However, www.strongtie.com. corrosion. If dry wood is used, see our website for as long as these recommendations are followed, Simpson additional information. Strong-Tie stands behind its product performance and our • With the exception of ACZA, treatments with ammonia standard warranty applies. carriers were not included in this testing. Preservatives Home Office 5956 W. Las Positas Blvd. GUIDELINES FOR SELECTING THE PROPER CONNECTOR Pleasanton, CA 94588 FAX: 925/847-1603 1 Evaluate the Application. Consider the type of structure and how it will be used. Northwest U.S.A. These recommendations may not apply to non-structural applications such as fences. 5151 S. Airport Way 2 Evaluate the Environment Stockton, CA 95206 FAX: 209/234-3868 Testing and experience indicate that indoor dry environments are less corrosive than outdoor environments. Determining the type of environment where a connector or fastener will be used is an important factor in selecting Southwest U.S.A. the most appropriate material and finish for use on the connectors and fasteners. To help in your decision making, 260 N. Palm Street consider the following general exposure information: Brea, CA 92821 Interior Dry Use: Includes wall and ceiling cavities, and raised floor applications of enclosed buildings that have been FAX: 714/871-9167 designed to ensure that condensation and other sources of moisture do not develop. Northeast U.S.A. Exterior – Dry: Includes outdoor installations in low rainfall environments and no regular exposure to moisture. 2600 International Street Exterior – Wet: Includes outdoor installations in higher moisture and rainfall environments. Columbus, OH 43228 Higher Exposure Use: Includes exposure to ocean salt air, large bodies of water, fumes, fertilizers, soil, FAX: 614/876-0636 some preservative treated woods, industrial zones, acid rain, and other corrosive elements. Southeast U.S.A. 3 Evaluate and select a suitable preservative- 2221 Country Lane treated wood for the intended application Low = Use Simpson standard painted and G90 galvanized connectors as a minimum. McKinney, TX 75069 FAX: 972/542-5379 and environment. Med = Use ZMAX®/HDG galvanized connectors as a minimum. Use fasteners which meet The treated wood supplier should provide all the the specifications of ASTM A153 or SDS screws with double-barrier coating. information needed regarding the wood being used. High = Use Type 303, 304, 305 or 316 Stainless Steel connectors and fasteners.6 Eastern Canada This information should include: the specific type 5 Kenview Blvd. Brampton, ON L6T 5G5 of wood treatment used, if ammonia was used in Connector Coating Recommendation – Structural Applications the treatment, and the chemical retention level. If the FAX: 905/458-7274 ACQ-C, ACQ-D (Carbonate), needed information is not provided then Simpson SBX/ CA-B & CBA-A Other Western Canada Untreated DOT Strong-Tie would recommend the use of stainless Environment MCQ ACZA or Wood & Zinc Higher 11476 Kingston St. steel connectors and fasteners. You should also No With Uncertain Borate Chemical Ammonia Ammonia Maple Ridge, BC V2X 0Y5 ask the treated wood supplier for a connector Content1 FAX: 604/465-0297 coating or material recommendation. Interior – Dry Low Low Low Med5 Med High High High Warehouses & Use the chart on the right, which was created Exterior – Dry Low N/A2 Med Med High High High High 4 based on Simpson Strong-Tie testing and Manufacturing: Exterior – Wet Med N/A2 Med3,4 Med3,4 High High High High Eagan, MN; Enfield, CT; experience to select the connector finish or Higher Exposure High N/A2 High High High High High High Gallatin, TN; material. High Point, NC; 2 If a pressure treated wood product is not identified Uncertain High N/A High High High High High High Jacksonville, FL; on the chart, Simpson Strong-Tie has not evaluated 1. Woods with actual retention levels greater than 0.40 pcf for ACQ and MCQ, Jessup, MD; Kent, WA; test results regarding such product and therefore 0.41 pcf for CBA-A, or 0.21 pcf for CA-B (Ground Contact level). Langley, BC cannot make any recommendation other than the use 2. Borate treated woods are not appropriate for outdoor use. of stainless steel with that product. Manufacturers 3. Test results indicate that ZMAX/HDG and the SDS double-barrier coating will perform adequately, subject to regular maintenance and periodic inspection. may independently provide test results or other prod- However, the nationally-approved test method used, AWPA E12-94, is an uct use information; Simpson Strong-Tie expresses accelerated test, so data over an extended period of time is not available. 800-999-5099 no opinion regarding any such information. If uncertain, use stainless steel. 4. Some treated wood may have excess surface chemicals making it potentially www.strongtie.com Compare the treated wood supplier’s more corrosive. If you suspect this or are uncertain, use stainless steel. 5 5. Where noted in the table, applications where the wood is dry (moisture recommendation with the Simpson content less than 19%) when installed and will remain dry in-service may © 2008 Strong-Tie recommendation. use a minimum coating recommendation of “Low”. Simpson Strong-Tie Company Inc. 6. Type 316 stainless steel connectors and fasteners are the minimum If these recommendations are different, Printed in the U.S.A. Simpson Strong-Tie recommends that the most recommendation for ocean salt air and other chloride environments. conservative recommendation be followed. T-PTWOOD08 4/08 exp. 6/10