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Building with stone
What is the difference between traditionally laid and light weight sawn/glued stone?
What is the difference between traditionally laid and light weight sawn/glued stone?
All New Zealand buildings have a structural frame in addition to the stonework. Even traditional thick stone work is treated as a cladding rather than structural component of the building. This is due to our susceptibility to natural disaster such as earthquakes, as a result buildings are engineered to a high standard designed to keep people safe in natural disasters.
Traditional stone work uses solid stone which has been cut to a specified width in a quarry (usually to fit on a 150-200mm footing). The stone is laid against the structure of the house using brick ties attached to the framing and mortar to cement it in the same way that brick is laid. Traditionally laid stone requires a concrete footing and additional bracing of the structure. These requirements usually mean a structural engineer must review and approve the design.
Lightweight stone is real stone sawn or cut to a thin (usually around 30-40mm) veneer. This thin stone is lighter than traditional stone and has to be glued to a backing board in much the same way that tiles are. Lightweight stone does not require additional footings or bracing and is useful for areas where space is limited or where complex engineering requirements make traditional stone inappropriate.
Both systems are covered by the NZ building code.
Traditional stone vs thin veneer
The use of stone with simple cement and lime mortars has stood the test of time, indeed many significant buildings worldwide are constructed of stone. Thin stone veneers are ultimately an attempt to replicate the aesthetics of stone without the weight or mass of natural stone. Thin sawn stone veneers glued to a substrate is a relatively new technique which allows great flexibility to have stone in areas it would be difficult to install otherwise.
Traditional stonework has a lot of benefits such as:
The main reason that people love traditional stonework so much is that it offers such a timeless and robust beauty to any home, church or place of business. The thicker nature of the stone adds to its depth and dimension, creating an even stronger illusion of a building that has been entirely constructed with stone or masonry materials.
There are a wide range of different types of stone available, making it easy to achieve the right look. Whether your style is modern and cool or traditional, you’ll find exactly what you’re looking for.
Traditional stonework can be easily customized as full sized stone retains its strength and integrity, allowing the stonemason to trim and dress each stone to suit the required finish. Masons can be more flexible in this area because there is more stone to work with and the material isn’t fragile.
In many instances larger, Traditional stonework is more practical for a large area of wall that needs to be covered. Traditional stonework will have a better range of larger sized pieces than thin veneer. This is because thin stone veneers work better in smaller sizes in order to reduce breakage in both fabricating and handling.
One of the greatest advantages of traditional stonework is the material is strong, durable and resistant to the elements. The thickness of this particular type of stone comes with many benefits.
Full size stone has a mass which helps to protect the stone from issues with rain, snow and ice. When combined with an unrestricted cavity for ventilation and drainage is allowed behind the stonework, you can fully enjoy the peace of mind that that any wood framing or wood sheathing will be fully protected.
Traditional stonework is built onto a solid foundation with the weight of stone directly on the foundation, supporting the stonework. Wall ties are used to anchor the stone to the framing and are there in case of earthquake to ensure the stonework doesn't pull away from the framing during vigourous shaking.
Traditional stonework is less susceptible to damage that may be inflicted by season changes and temperatures fluctuations such as freeze-and-thaw cycles.
The weight and strength of full sized stone also helps to prevent unwanted blemishes inflicted by Mother Nature. It will not easily crack, chip or scar when faced with heavy winds, rain or even hail. Very little maintenance is required on this type of natural stone cladding.
Thin Veneer stone work:
Using New Zealand schists or local stone cut down to a thin 40 mm veneer is more expensive than traditional stonework as the stone must be cut down adding costs in extra handling. Thicker fibre cement board and increased waterproofing also add to the cost. In addition thin veneer is no quicker than laying traditional stonework and in some styles it's slower.
One of the most common misunderstood aspects of using veneers is weight. Thin veneers are glued to fibre cement boarding that is screwed onto the timber framing, so the weight of the veneer stone is placed directly onto the framing while traditional stonework is laid on a foundation and the weight load is on the foundation. Thin veneers don’t require additional foundation or bracing which makes them a good option for remodelling of existing structures and above roof lines where heavy lintels would have to be used to support traditional stone, however the weight of stone is hanging on the backboard and strength is dependent on correctly applied glues and installation.Sawn/glued stone veneers are not an environmentally friendly option.
How to understand and avoid efflorescence
Effervescence in masonry:
New building bloom is typically fairly uniform across the wall surface. New-building bloom tends to occur shortly after construction ends, due to normal water loss during post-construction drying. Efflorescence that reappears after this initial period is likely due to water entering and remaining in the wall.
Effervescence is a crystaline deposit on surfaces of masonry, stucco or concrete. It is whitish in appearance, and is sometimes referred to as "whiskers". Efflorescence has been a problem for many years, and is a topic of much controversy. The formation of these salt deposits are not mysteries. They are, for the most part, water-soluble salts that come from many possible sources to mar and detract from an otherwise beautiful and serviceable structure. First of all, there must be water present to dissolve and transport the salts. Groundwater is often a source of efflorescence. For water to carry or move the salts to the surface there must be channels through which to move and migrate. The more dense the material, whether it be brick, stone, stucco or concrete, the more difficult for the water to transport salts to the surface. Conversely, the more porous the material, the greater the ease with which salts are transported and deposited. Salt-bearing water, on reaching the surface of a structure, air evaporates to deposit the salt. When humidity is low, the water may evaporate before reaching the surface of the structure, leaving the salt deposit beneath the surface, and unseen. When the humidity is high, water evaporation is slower allowing more opportunity for whisker growth. Growths which project 15-25 mm below the surface have been reported in some areas.
Since humidity has a definite effect on whether or not the salts appear, it can be assumed that efflorescence is a seasonal problem. The intensity of efflorescence increases after rainy winter seasons, decreases in spring, and by summer has practically disappeared. This cycle may repeat for months or years, but generally the intensity of the efflorescence decreases in all but very extreme cases, and by about the third year it should be practically eliminated.
The mechanics by which efflorescing salts are carried to the surface of structures by moisture and capillary action through porous materials, is understood. The amount and character of the material deposited varies considerably, depending on the nature and source of the soluble materials.
Composition of Efflorescence:
The problem of efflorescence, or the deposit of water-soluble salts on the surfaces of masonry, stucco or concrete, is an old one, and one that has been studied and reported on as early as 1877. These reports are all in common agreement that efflorescence originates from more than one source, and may be made up of more than one or two compounds.
Sources of Efflorescence:
There are many sources for water-soluble salts with some salts more soluble than others. The movement of groundwater into building foundations and by capillary action, or wicking, upwards into masonry, stucco or concrete, is very often the cause of efflorescence. In the case where soil conditions exhibit water soluble sulfates, precautions should be taken to preclude the passage of this sulfate-bearing water to the structure. Low absorption is the best assurance against efflorescence. Properly graded aggregates, low water-cement ratio, good compaction and proper curing practices will produce concrete of maximum density and low water absorption.
Sand and gravel, in their natural state, may or may not have been associated with salt bearing water or soil. If they have, and these salts are not removed by washing, this can be a possible source for efflores cence. Most rock, sand and gravel plants, however, are conscientious in washing material so that any contribution made to efflorescence from this source is negligible.
When mixing-water used for mortar, stucco or concrete is obtained from a natural source which has been in contact with a sulfate-bearing soil, the resulting structure may exhibit efflorescence. The adherence, again, to a good concreting practice of low water-cement ratio, will help reduce the appearance of salts from this source.
It has also been noted that the occurrence of efflorescence bears a relationship to the type of mortar used. With a particular type of brick and a certain mortar no efflorescence may occur, whereas, the same brick with different mortar may produce a wall heavily coated with salt deposits. The appearances of sodium and potassium salts (as sulphates) usually suggest Portland cement mortar as the origin. The use of low alkali cement in mortar and grout will minimise efflorescence, at least from this source.
Since, for the most part, concrete masonry is somewhat porous, evaporation of the salt bearing water usually takes place before reaching the surface when exposed to a drying atmosphere. The hydroxides are converted by reaction with the carbon dioxide of the air to alkali and calcium carbonates. Efflorescence in the form of alkali chlorides and sulfates is formed when the structure is surrounded, exposed, or in contact with salt-bearing water or soil and appears as columnar or whisker-like crystals.
Some of the sources of water-soluble salts have been covered. These may be deposited on stucco, masonry or concrete walls as efflorescence. Practically any building materials in direct contact with the earth are potential sources for water-soluble salts. This fact has been recognized by the various producers of building materials, and steps have been taken to reduce their presence to a great degree.
Removal of Efflorescence:
Several methods are suggested. One is to use water under pressure or one of a number of products available from stone dealers; another is muriatic acid with subse quent flushing with water. Acid applied to brick masonry, without previous wetting, may cause "burning" or discoloration of the brick and may also eat into the mortar. The Handbook on Reinforced Grouted Brick Masonry Construction suggests the use of light sandblasting for removal of stubborn efflorescence (after many months). Allowing the surface to dry thoroughly and then using a stiff brush, prior to washing with water, has helped prevent re-penetration of the surface by the salt.
Various methods have been used in attempts to remove efflorescence from masonry structures. It has been found that when efflorescence is caused by soluble alkali salts, the salts will dissolve in water applied to the structure and migrate back into it. These salts would then reappear on the surface as the structure redried. It was learned accordingly, that the best way to remove these soluble salts was to brush the surface thoroughly with a stiff brush. Water, however, has been satisfactory for removing efflorescence from the face of concrete structures, since concrete is fairly well saturated with water. In fact, efflorescence in the form of alkali salts will be washed from the surface of concrete structures, if exposed to rain, over some period of time. If the coating is largely calcium carbonate or calcium sulfate, it adheres rather strongly and is difficult to remove by brushing. The practice developed in this case for masonry surfaces, has been to saturate the structure as thoroughly as possible with water, and then wash with diluted Spirit of Salts, followed immediately with an alkaline wash, then washed with water. The acid recommended is five (5) parts Spirit of Salts to one hundred (100) parts water, or twenty (20) parts vinegar to one hundred (100) parts water. The alkaline wash recommended is diluted household ammonia.
Much care must be taken in applying acid to Portland cement products. The acid will attack, not only the calcium carbonate and calcium sulfate efflorescence, but also other calcium compounds to produce calcium salts such as calcium chloride. It is, therefore, very important to neutralize the acid before it can attack other compounds.
Choosing A Stone Mason
How do I choose the right tradesman for the job?
Currently in NZ there is no Licenced Building Practictioner (LBP) for Stone Masonry. Initially MBIE included Stonemasonry with Brick and Block, however this was retracted once the differences between the trades were highlighted. There is also no requirement for councils to inspect stonemasonry as part of their building consent schedule. A good deal of our focus as an Association is to address these issues including working with the government and training platforms to obtain recognition for our trade. However, in this current unregulated climate, it is imperative that clients/designers/builders take the time to choose their stonemason carefully. Insist on recommendations from previous clients, examples of completed work by your proposed stonemason should be scrutinised in conjunction with our Code of Practice.
One of the benefits of choosing a NZSMA member is that should issues of dissatisfaction arise for whatever reason, we offer the service of appraising the work via the committee. If such work is deemed substandard, or business/trade ethics have not been adhered too, then we shall instruct the stonemason to comply and act as a third party intermediary.
Preparing For Stone
Where can I source natural stone from?
There are a number of quarries who specialise in preparing natural stone for building in New Zealand. It is good idea to start with narrowing down a type of stone you like then locating a quarry.
There is a list of specialist natural building stone quarries in the affilated membership area of the website. There may be other companies offering stone for sale and it would always be a good idea to ask to see their permits and licences to ensure they are operating legally.
In some districts the local council allows the collection of limited quantities of stone to be handpicked from riverbeds or lakes.
How do I know if a quarry is operating legally?
Ask the quarry operator if they have their permits and licences. There are three permits and licences required to extract natural stone legally in New Zealand.
- Mining permit - are issued by New Zealand Minerals and Petroleum (https://www.nzpam.govt.nz/).
- Resource Consents - are issued by the district council and regional council. A land use resource consent would be the minimum requirement.
- The Quarry Manager must hold a current Certificate of Competency (COC) and be approved by Worksafe.
There are advantages to using stone that has been legally extracted. Generally legal quarries will be operating to a high standard both in terms of health and safety and quality of product. In addition the quarry is more likely to still be in business in the future should you ever want to do any additional work with stone or renovations.
Can I use the stone off my land?
In some cases yes, however there are a number of characteristics that natural stone must have to make it a suitable building material. Some stone found on ground surface can be weathered and weak making it unsuitable, or the stone may be unworkable by the stonemason making it difficult to get a good finish. An experience stonemason will be able to tell if you your stone is suitable. If you wish to extract stone from your land using machinery such as diggers and guillotines and/or explosives you will need a qualified quarry manager approved by Worksafe to oversee the operations.
Why use natural stone?
Humans are instinctively attracted to the unique feeling of strength and solidity that stone structures represent. Natural stone is an interesting building material with varied texture and pattern. Natural stone is permanent and low maintenance which can result in a low whole-of-life cost compared to products that may be cheaper to install but require ongoing maintenance.
Is stone a sustainable material?
Stone is a naturally formed building material with limited mechanical inputs resulting in minimal carbon footprint. Massive quantities of rock exist in nature and are continually forming meaning that the resource is unlikely to ever by exhausted. There are no toxic substances used with the traditional installation of natural stone, and no ongoing applications of chemicals required.
How to prepare structures for natural stone?Typically stonework on a building will require a bespoke design by a engineer, however below are some examples of approved substrates typical design details.Polyblock requires ties to be built in., , , ,