Frequently Asked Questions

We’re always happy to answer your queries on concrete engineering. Here are some of the topics we’re often asked to comment on.


What sizes and lengths of Macalloy bar are held in stock?

We typically hold quantities of 26.5, 32, 40 and 50mm fully threaded high tensile carbon bars in stock in our branches. Larger quantities are held in our Auckland warehouse but our branches in Wellington and Christchurch hold smaller quantities on hand for urgent projects. All bars are sold in 5.9m lengths and we have couplers, nuts and washers available to suit every bar size. Non-stock sizes and lengths are imported to order and take around 12 weeks to arrive depending on specification and quantity.

How long does it take to get a special Macalloy order delivered to NZ?

Typically its about 4 weeks from time of order to manufacture and prepare for shipping. Its then approximately 9 to 12 weeks to ship to NZ. You should allow four to five months from time of order to make sure you have it when you need it. The shipping time can be reduced by air-freighting to less than two weeks.

Can I get Macalloy in stainless steel?

Yes, Macalloy bar is available in limited sizes in stainless steel to suit sites where corrosion may be an issue or where finish is important to the client. We don’t stock stainless bar in NZ but would place a special order from the factory for delivery to your site in NZ.


What sizes and lengths of Drossbach duct are available?

The standard sizes are ???. We generally keep stock lengths up to 5.8m as this length are easier to transport. We can cut duct to any length required for a small additional cost.

How long will it take for my Drossbach duct order to be delivered?

It depends on how many orders we have stacked up. If we have the right size in stock then we can generally turn an order around in a few days, plus shipping time. Larger orders may require a little longer.

PT Slab on Grade

How thick are these PT Slabs?

Minimum 150 mm for lightly loaded retail floor. Maximum 300 mm for Container handling pavement. Warehouse floors are typically 160 to 190 mm depending on loads.

What is the main advantage of PT Slabs?

No sawcuts and minimal construction joints. This is because all concrete drying shrinkage is directed to the floor edges, eliminating potential for internal floor cracks. This also eliminates expensive lifetime maintenance of sawcuts and joints.

Who designs the PT Slabs?

BBR Contech provide full design and drawing service for PT Slabs on grade. We will also advise designers if they would rather undertake the design themselves.


How is Sewpercoat different than other Biogenic Corrosion Coatings?

Sewpercoat both repairs the damage caused by Biogenic Corrosion and protects the structure from on-going Biogenic corrosion by introducing a “bacterio-static effect” that drastically slows down the acidophilic bacteria ecosystem, inhibiting the acid generation at the source itself.

How is Sewpercoat normally applied?

Sewpercoat can be applied as a Wet or Dry Spray Mortar, or for small applications, by hand.

Does the surface I am applying Sewpercoat to have to be dry before I apply it?

Sewpercoat unlike most other protective systems, is a cementitious material that actually needs a damp substrate prior to application. This is advantageous in live wastewater environments where getting the substrate completely dry is very hard to achieve.

Can I buy a bag of Sewpercoat and do the repair myself?

Yes, we supply Sewpercoat from our Auckland warehouse in 20kg bags. Contact us at [email protected] to place an order.

What is the difference between Sewpercoat and a normal concrete repair mortar?

Unlike normal mortars that use Ordinary Portland Cement and natural aggregates, Sewpercoat is a 100% Calcium Aluminate product, with both the Binder Cement and the Aggregates composed of Calcium Aluminate.

Post Tensioning

What size multistrand tendons are available in NZ?

We can supply an extensive range of tendon sizes to suit almost any project. By having one of the widest ranges of tendon sizes we can optimise our solution to the capacity you need, not a size much greater. This results in efficient design solutions and means that you only pay for what you need.


Who specifies the level of corrosion protection?

The level of corrosion protection is specified by the designer and described in the contract specification.

What classes of corrosion protection are available for ground anchors?

Two classes of corrosion protection are provided:


Class 1 – Double corrosion protection by encapsulation of tendon or bar pre-grouted under factory condition inside a corrugated plastic sheath and then grouted into the anchor hole.


Class 2 – Single corrosion protection using galvanised or fusion bonded epoxy coated bar grouted into anchor hole.

What international standards are used for ground anchoring?

We recommend adopting BS8081:1989, US FHWA Geotechnical Circular No.4 and BS EN 1537:2013 for the specification of multi-strand ground anchors.

What is post-grouting?

Post-grouting is additional pressure grouting of the fixed anchor length to enhance anchor performance in weak ground conditions. This technique can enhance anchor pull out capacity and minimise anchor creep.


What is a Codemark Certifed FRP system, and why should I specify a Codemark FRP system?

Evidence of compliance with the New Zealand Building Code


A CodeMark Certificate of Conformity is evidence that the stated FRP system has been independently tested and confirmed as meeting the following key requirements of the NZ building code:


– B1 Structure: clauses B1.1, B1.2, B1.3.1, B1.3.2, B1.3.3 and B1.3.4
– B2 Durability: clause B2.3.1
– E2 External moisture: clauses E2.3.2, E2.3.3,and E2.3.5
– F2 Hazardous building materials: clause F2.3.1


An FRP system with Codemark cannot be rejected by a New Zealand consent issuing body as being unsuitable for the purposes defined in the Codemark application.


Independent annual audits of quality processes


To ensure compliant installation, there is a local and independent annual audit undertaken on CodeMark Certified FRP installers to ensure sufficient training and quality systems are in place and being consistently applied. This ensures the CodeMark Certified FRP installer is sufficiently experienced and qualified to install FRP in accordance with the NZ building code.


To ensure compliant materials typically means that an FRP system with Codemark has been tested and is subject to audits in accordance with a standardised acceptance criteria such as AC125 (issued by the International Code Council (ICC) based in the USA). The key elements of the materials testing in AC125 is accelerated durability testing in a range of exposure environments and a requirement for regular audits of production facilities.


See link for CodeMark Certificate validity verification from MBIE:



What is the difference between precured laminate FRP (e.g. Sika Carbodur), and wet lay-up Fabric FRP (e.g. Sikawrap range)? AND Why would I specify a wet lay-up system rather than a precured system?

Precured FRP products consist of carbon fibres combined with resin in factory conditions through a process called pultrusion where the fibres and resin are pulled through a die and cured. The precured FRP product is delivered to site as a solid plate or rod which is then bonded to the structure using a thixotropic epoxy such as Sikadur 30. The key advantages of precured FRP products is that they are usually quick and unobtrusive to install, and they typically have greater tensile strength and modulus properties than wet lay-up products due to the greater fibre content that is achieved by the pultrusion process.


Wet lay-up FRP systems consist of a dry fabric consisting of woven carbon or glass fibres that is delivered to site in a roll. The fabric is saturated on the job site with epoxy resin, and then applied to the surface of the structural element to cure. Key advantages of wet lay-up FRP systems include their flexibility and ability to conform to the shape of the structure, their ability to wrap around columns or beams and provide confinement and to be anchored into or through adjacent structural elements with FRP anchors. Wet lay-up FRP solutions are typically more cost effective for a given degree of strengthening than a pre-cured solution.

Can FRP be used as a concrete repair system?

It is possible to use FRP to restore the strength of a structure that has deteriorated due to loss of reinforcing steel. However, the FRP will not typically prevent further deterioration from occurring so the underlying cause of the deterioration must be addressed. Furthermore, because the FRP is typically bonded onto or into the cover concrete it is essential that the integrity and durability of the FRP, the cover concrete and the bond is ensured.


For example, in the case of a structure affected by corroding reinforcement and spalling of cover concrete, the cause of the corrosion must first be addressed and concrete repaired in order for FRP to be considered otherwise future corrosion and spalling will cause delamination of the FRP and potentially brittle failure modes.

What are the relevant design standards for FRP?

There are a number of accepted design guides for strengthening structures with FRP. The most commonly used in New Zealand is ACI440.2R, the most recent version was released in 2017. Many other countries have also published FRP design standards which have varying balances of ease of use/computation and conservatism/efficiency. Notable examples include TR55 (UK), fib Bulletin 14 (Europe), SIA 166 – SIA 262 (Switzerland), and CNR-DT 200 R1/2013 (Italy).


Sika have developed a comprehensive design software package which is available free of charge from the website below:


Ready to get some help with your project design? Get in touch

Get in touch by phone or by completing the enquiry form below, and we’ll be happy to discuss your project needs and schedule an initial consultation. Together, we’ll create structures that stand the test of time.