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A World of Stone Ltd
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We are proud to work closely with the stone suppliers in New Zealand and are currently recommended consultants for
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Hydestone Schist Wall Cladding System
Hydestone System Installation Manual
Technical information on the Rigid Stone System PDF's
Rigid Stone Cladding Column Detail
Stone System Rigid Base Detail
Stone System Rigid Block Detail
Stone System Rigid Wall Detail
Stone System Rigid Window Detail
Technical information on Veneer cladding 40mm PDF
New Zealand Stone Masons Association 2012
Best Practice Guide
The primary purpose of this document is to provide guidance to members of the New Zealand Stone Masons Association (NZSMA) on current best practice in construction stonemasonry within the New Zealand building environment.
The first part of this guide demonstrates how stonemasonry must comply with the New Zealand Building Code (NZBC).
The second part of this guide deals with other elements of the stonemasonry craft that may not relate directly to the NZBC.
Apart from offering guidance to stonemasonry practitioners, this document is also intended as a useful resource for other industry stakeholders including architects, designers, councils and clients.
Origins and Limitations
This document has been compiled and written by NZSMA members and endorsed by the NZSMA membership. It is intended to provide guidance only. The advice provided in this document must always be considered in the context of independent engineering and architectural advice on a project-specific basis.
Stonemasonry and the New Zealand Building Code
New Zealanders have been using stone as a building material since the beginnings of colonial history. After a slump in use in the mid-20th Century, stone has emerged in the last 20-30 years as an attractive and popular cladding material in both the residential and commercial sectors, and especially at the upper end of the market.
In the vast majority of cases, stone is now used as a non-structural cladding material. Stone cladding does not normally carry any of the structural load in contemporary building designs. However there are structural implications of the strength of the cladding itself, and these are covered later in this guide.
As a cladding material, stone must comply with the NZBC in a number of ways. These are covered below.
1. Durability *
As a building material stone must meet the durability requirements of the NZBC. Clause B2.2 states:
Building materials, components and construction methods shall be sufficiently durable to ensure that the building, without reconstruction or major renovation, satisfies the other functional requirements of this code throughout the life of the building.
Under clause B2 the minimum life of a stone cladding is 15 years. (NZBC: B2/AS1.2.1 (b) & (e))
The NZBC requires that verification of the durability of stone cladding must take into account one or more of the following:
1. The durability of stone supplied by commercial quarries can be verified by statements of “in service history” (B2/VM1.1)
2. Relevant laboratory testing can also be used for verification of durability of stone supplied by commercial quarries. (B2/VM1.2)
3. Stone supplied from non-commercial quarries, demolition or recycled stone can be verified as durable by comparison with similar materials. (B2/VM1.3)
Assessment of Stone Durability
Assessing a stone’s durability and its suitability as a cladding material is an essential skill of the experienced or qualified stonemason.
In most cases the stonemason will have knowledge of a similar material to the one intended for use. It is this knowledge that allows the assessment of the material’s durability.
Durability assessments should take into account:
• The geological composition of the stone
• The stone’s source or origin
• The environment in which the stone will be used
• The specific application of the stone within the project
• The stone’s maintenance requirements
• The compatibility of the stone with other materials
Where any limitations to use or durability exist, These should be clearly identified and evaluated.
In addition, NZS 4210 Masonry Construction: Materials and Workmanship stipulates (C220.127.116.11):
The properties of a proposed natural stone material should be carefully assessed for the use to which the stone is put. Consideration should be given to compressive and tensile strength, splitting properties, mortar bonding characteristics and weathering aspects such as porosity and abrasive and chemical durability.
Durability of other materials used in stonemasonry construction
When stonemasons use standard masonry veneer fixings, the NZBC’s acceptable solutions and NZ Standards regarding sea spray zones should be used to ensure the durability of fixings. See “Durability”, NZS 3604 Timber-framed buildings Section 4.
Durability of Ties
To ensure durability, masonry ties should always have a minimum cover of 15mm of mortar from the front face of the masonry.
Ties should also be fully encased in mortar in the bed joint.
All ties used should meet AS/NZS 2699Built-in components for masonry construction. When fixing systems require Specific Engineered Design care should be taken that the elements of the fixing solutions are compatible and therefore durable.
2. External Moisture and Cavity Systems *
Drained and ventilated cavities are a means of dealing with moisture that may enter through a building’s exterior envelope. The NZSMA strongly recommends the use of cavity systems when cladding a building with stone.
A number of Acceptable Solutions are detailed in Clause E2 of the NZBC. At present these solutions do not deal specifically with the use of stone as a cladding. The reason for this is that stone generally exceeds the weight range of these Acceptable Solutions. This means that the design of stone cladding is usually undertaken by an engineer on a project-specific basis, presenting a number of different cavity options.
Despite the lack of a “one size fits all”solution, the use of a cavity is strongly recommended, especially when cladding a timber-framed building. A number of different systems are in use:
• Where the tie spans the cavity
• Where the tie sits on the outside of the cavity and is fixed through a cavity batten into the stud work. Whichever system is used some basic principles for drained and vented cavities should always be applied.
• The foundation on which a masonry wall sits must be at least 50mm below finished floor level and should be sealed with a waterproof membrane.
• At the base of the cavity the foundation should fall toward the outside of the building.
• A compliant wall underlay needs to be installed directly over the timber framing with a minimum of laps and flashing tape.
• Cavity battens must be a minimum of 25mm for a dry cavity (ties on the outside of the backing sheet) and 40mm for a wet cavity (ties crossing the cavity). Cavity depth must not exceed 75mm.
• Timber cavity battens must be treated to a minimum of H3.1 and should not be ripped from larger members.
• Cavity battens must be fixed on the stud line with a layer of damp proof course between batten and backing board. Where ties cross the cavity, battens must be offset or spaced to allow ties to be directly fixed to studs.
• When a rigid backing sheet is used it must be of a material that is resistant to moisture transfer and sealed appropriately.
• The backing sheet must be kept at least 50mm above the footing to prevent wicking. A temporary thin piece of sheeting (later removed) should create the final 50mm of cavity.
• Pipes and services may pass though the cavity but must not be placed inside it.
• Cavities must be drained from the bottom by weep holes a minimum of 75mm in height and a maximum of 12 mm wide at 800mm centres, or other dimensions that provide vermin protection and at least 1000mm2 per lineal metre of ventilation.
• Similar vents or a continuous 10mm gap between wall and soffit must be provided at the top of the cavity.
• The cavity must be sealed off from the floor and roof space.
• Flashings must be provided at openings and other interruptions. The exact configuration of the flashings will be determined by the type of cavity being used.
[insert fig 1 and 2 examples of cavity systems]
3. Grout Durability and Strength *
In general the use of mortars and grouts should follow those specified in NZS 4210.
Any variation from the above requires:
• Consultation with an engineer when specific engineered design is required for a project.
• Consultation with an engineer and heritage architect when restoration work is carried out on historically significant stonemasonry.
Some general tips for mortar preparation
• Mortar shall have a minimum compressive strength of 12.5 MPA
• Mortar shall be protected from drying out in hot or windy conditions.
• In warm weather or conditions that are likely to accelerate the mortar, The shelf life would be under 1.5 hours. Where the mortar is kept cool and damp a 2 hour shelf life may be possible.
• Mortar shall be dry enough that it stays in a heap on the trowel.
• Mortar shall be wet enough that it stays in lumps when dropped from a trowel at a height of 1 meter.
• When laying directly on set stonework, the bed must be free of loose debris an be dampened down.
• Both sand and cement shall be measured in the same volume or gauge bucket.
• Mortar can have a plasticiser additive.
• Mortar should be mixed for a total time of approximately minutes.
• Mortar should be made in the following stages.
1. Add most of the water and measured amount of plasticiser for one mix.
2. Add half the sand.
3. Add all the cement.
4. Add remaining send and additional water if needed.
• As a rough guide a 4/1 ratio mix will be between 12.5 and 22 MPA after 28 days.
4. Ties and Fixings *
If the weight of the stone veneer is less than 220kg per m2, the general recommendation for tie fixings set out in NZS 4210 must be followed.
If the weight of the stone veneer exceeds 220kg per m2, a specifically engineered design is required. Stonemasons should meet with the project engineer to provide input into the proposed design.
Some general rules for ties and fixings:
• Ties should extend approximately two thirds the width of the veneer
• Ties should slope five degrees toward the outside of the veneer
• Ties should be fully encased in mortar
• Ties should not be placed on top of work that has already set
• The amount of ties around openings and at the top and bottom of work should be increased
• Fixings need to be stronger than the tie
• Ties should be installed as per manufacturer’s recommendations
• Ties and fixings should be of compatible materials
Other Areas of Stonemasonry Best Practice
1. Bonding *
While all stonemasons have their own particular style of work, some basic rules regarding the way in which stone units are combined (“the bond”) should always be followed:
• Stone should not be face bedded and in general sedimentary stone should be laid on its natural bed unless a specific architectural purpose requires otherwise;
• Each stone should overlap the stone below by at least 25% to avoid running vertical joints.
• Stone should always be laid on its widest and deepest face.
• Stones at corners should be laid in alternating directions.
• Top and capping stones should have substantial height and depth.
• Where stonemasons work in a team, they should be made aware of the desired composition of the wall and regular oversight of its visual composition should be carried out.
Insert figure 3: Bonding
2. Dry Stone Construction *
Dry Stone Construction is the oldest form of masonry and it still has a relevant place in contemporary New Zealand landscape construction.
Some basic principles of dry stone construction include:
• The use of a flexible compacted hard-fill foundation.
• The use of batter on walls.
• All stones being laid as headers running back into the wall not as stretchers.
• Double-sided dry stone walls having through stones at regular intervals for strength.
• Walls being backfilled with free draining material.
Insert fig 4: Dry Stone
Restoration and preservation are amongst the most important processes that stonemasons undertake. As such, they should only be undertaken by those who have had experience in this area. Where a stonemason undertakes to up-skill in this area, it should be done in a gradual way in consultation with experienced stonemasons and other experts.
Detailed principles of restoration practice can be found in the Charter of the International Council on Monuments and Sites (ICOMOS),
These should be considered before any restoration work is undertaken.
4. Cleaning and Protecting Stonework *
If excess moisture via rain/snow is allowed to settle on fresh stonemasonry work efflorescence can result. Work can also be damaged by frost. Stonemasons should take care to cover and protect fresh work at the end of each day.
At the conclusion of the job stonework should be brushed and washed down to remove mortar dust and loose material.
|Advice on products to use
Maintenance and Cleaning Stone Restoration
Current building practices
Reports on faulty work