Decorative Finish | Sweep Blasting | Thicker Galvanized Coatings | Galvanized Steel in contact with Timber | Steel Detailing | Safe Buildings | Imported Steel Products | Advantages of After Fabrication Galvanizing | Standards Update | Materials Handling & Conveyors | Lintels and Shelf Angles | Zinc for Human Health | Atmospheric Corrosion Resistance | Paint over Galvanizing | Abrasion Resistance | Use of Galvanized Reinforcement | Repair of Field Welds | Wet Storage Stain | Distortion | Thickness on Flame-Cut Edges | Coastal Construction

In the case of lintels and shelf angles, corrosion durability failure has severe & early effect on masonry cracking and disfigurement as steel size significantly expands as it corrodes.

Since embedded steel items are not accessible for inspection after being installed, initial treatment must be reliable and adequate as no in service maintenance procedure is possible without dismantling and replacement. This may be simply disruptive or more likely extremely costly, where mortar cracking of many levels of brick is involved.

Responsibility for this installed quality rests variously with regulators, designers, suppliers, builders and ultimately building certifiers.

The current AS/NZS Standard AS/NZS 2699 which serves AS 3700, offers specification choice from eight (8) differing systems of durability, which provide for five (5) distinct levels of corrosive severity. For this purpose a durability colour coding identification is required. All manufacturers must be in compliance with this coding.

Standards criteria for products used for lintel protection, direct extracts from AS/NZS 2699 are as follows:

Paints

Zinc Silicates

• AS/NZS 3750.15 to either type 4, for mild service or type 3 or 6 for severe service.

Epoxy Paint

• AS 3750.14 or AS 3750.1
• AS/NZS 3750.13 or 3750.14

Appendix E (normative) – Impact test
Appendix B (normative) - CSIRO durability of zinc silicate & organic top coats
Appendix D (informative) – General compliance
GPC (APAS) Approval certification

Galvanizing

• AS/NZS 4791 Top coated with epoxy for mild service
• AS/NZS 4680 for severe service or Duplex top coated for very severe service

Appendix A (normative) – CSIRO durability test
Appendix D (informative) – General Compliance

Galvanizing Duplex

All criteria from paints for organic top coats only

Stainless steel

• AS 1449 / 316
• AS 1449 / 316 L (UNS 31600 or 331603 respectively)

Informative appendix C – Molybdenum test
Informative appendix D – General compliance

These quality test requirements are frequently overlooked, or are misjudged in relation to geographic rates of corrosion and fail to meet anything approaching 50 years protection.

Specification decisions and details are therefore most important, where corrosion of these steel elements will cause mortar damage and remedial cost out of all proportion to the initial cost of appropriate lintel protection.

Consumer concerns and inclination to seek redress on such errors, strongly suggests that lintel procurement should include a clear statement of durability classification and protective treatment.

Built in items for masonry construction AS/NZS 2699-2-2000 Lintels and shelf angles

Introduction

Following the Newcastle earthquake it was determined that an upgrade and revision of building standards take place.

This included steel items, which were included in the masonry code AS 3700.

Given the critical load bearing and long service life required of these components, the reliability of corrosion control was given special attention by technical subcommittee BD 28 representing interested parties in Australia and New Zealand.

The new Australian Standard setting of a 50 year life to serve homebuyers and their next generation is a reasonable and worthy objective.

Industry has a moral duty to make this the first and principle objective of the standard.

It also carries the legal liability of any failure to deliver.

Standard AS/NZS 2699 Outline

• There be no loss of function of the Lintel or adverse effects on the masonry over a design life of not less than 50 years
• Durability criteria to ensure that the steel be inherently corrosion resistant or treated to ensure that the design life is achieved
• Identification to determine durability correctness over 5 normal and one extreme atmospheric exposure. This classification mark to be visible after installation
• Coating repair of any site damage to the components to exceed the original coating thickness
• Paint coating options shall be high performance systems tested and approved over 6 years exposure by APAS the Australian Paint Approval Scheme (formerly Government Paint Committee - GPC Scheme)
• A measure of impact resistance of a protective coating used to achieve the appropriate level of durability

Lintels and shelf angles are typically handled like black steel, subject to very severe impact and abrasion in transit, during site storage and at installation.

Galvanized metallic coatings, of adequate thickness will resist such treatment however many paint or thinly galvanized coatings will require scrupulous multicoat repair particularly on edges.

Failure to address this need may mean failure of the item.

Dispatch Detailing

Since in theory many grades of protection are described in the standard and at least 5 zones of corrosion severity have to be properly matched, the coordination or permutation of options of protection to corrosion severity is complex and difficult.

Any miss match of insufficient protection with a more severe exposure than appropriate will result in failure and consequential masonry damage of substance and significant cost.

While such failure may not mean early collapse of the lintel the three-fold increase is steel size when corroded will typically fracture the mortar and crack bricks or other wall surfaces.

The cost of correction and replacement will quickly show that no economy exists in lowering protective quality, where it is clearly preferable to design conservatively, and install superior, rather than insufficient, protective grades of lintel protection.

From the consumer stand point, matching and delivering a correct level of steel protection cannot be left to chance. Currently five zones of corrosivity can be supplied by any one of eight systems.

It can be argued - who is finally responsible for selection? The end user however will suffer the cost of repair.

The unreasonable task of the lintel distributor best - guessing delivery point zones of corrosion is grossly unfair but may not set aside liability.

Economics

From the recent round of cost reductions, construction is fast reaching the point that trade offs of quality for cost reduction are all that remains.

Rising litigation and insurance collapses are proof of this position.

In this respect the consequential costs and risks within the forgoing advice, are real and immediate, so too are the availability of security and reliability but only if pursed with absolute discipline.

The cost of top grade corrosion and abrasion protection are probably less than $100 per home on average. With time reliability, efficiency and tolerance to site congestion probably more an offset.

This is now a critical detailing decision and delivery challenge.