Installation of Ōamaru Stone veneers
For a list of Stonemasons and Block Layers with experience in installing Ōamaru Stone, please visit our Installers page.
Specifications for handling and laying, beyond what is detailed here, should comply with relevant building bylaws.
Ōamaru Stone limestone is a natural material, not a manufactured product, with a proven performance record as a building material spanning over 100 years.
When quarried, the limestone contains natural moisture. As the large quarry blocks are stacked, the stone gradually dries and hardens.
After the limestone is milled, it is placed on timber pallets (up to 1.60 tonnes of limestone per pallet). These pallets are covered on top when they leave the quarry but are generally not fully wrapped, allowing airflow around the stone for the evaporation and dispersal of moisture.
If the limestone has been shrink-wrapped for transport, the wrapping should be removed as soon as the stone is placed on site. As the stone continues to dry, it hardens, making it more resistant to damage. If Ōamaru Stone is not sufficiently hardened, it is more susceptible to damage.
On-site, pallets should be stacked clear of mud, with any shrink-wrap removed to enable side ventilation and continue the drying process. The top covering of the pallets can remain to protect against weather exposure.
For all foundations, whether concrete or filled concrete block, apply three coats of D.P.C. (such as Mulseal) to the top of the foundation to create a damp-proof barrier before laying the first course of stone. This step is essential to prevent rising damp from entering the stone.
After milling, there may be slight variations in the stone’s height. Layers should conduct random checks on sizes before setting out story rods. The maximum bed depth should be 6-8 mm.
Mortar mix
Sand may be washed beach sand or clean sharp sand, which has been passed through a 5mm sieve. Using 6 parts of dry sand to 1 part hydrated lime, thoroughly mix and store dry until required for use. Use 9 parts of this prepared mix, add 1 part of cement, thoroughly mix dry, prior to adding water. Add sufficient water for the mix to become pliable.
Joggling
Sand may be washed beach sand or clean sharp sand, which has been passed through a sieve. It is recommended that all stones over 100mm high shall be joggled or have a vee cut in the perpendicular joint. This vee cut shall be a depth of approx. 12mm and be approx. 60mm wide in the centre of the 100mm blocks.
Ties
Ties shall comply with all provisions of NZS 4210. Ties must be heavy duty ties with a durability that complies with NZS 4210. The ties must be contained within the middle of the mortar bed. The ties must be located at a maximum horizontal spacing of 600mm and a maximum vertical spacing of 400mm. This equates to approximately 2 ties per block or 11 ties/m². The ties must be fixed to studs and nailed to the stone at all times.
Pointing mix
Use 2 parts of dry sharp sand, to 1 part hydrated lime, to 1 part dry Ōamaru Stone dust. Mix thoroughly and pass through a 1/6 sieve. Use 4 parts of this mixture to 1 part of white cement and add water to suit.
Weep holes & ventilation
The normal method to provide weep holes is by omitting mortar from part of the vertical mortar joints. With this method, the weep hole should be at least 75mm high and be provided in each vertical joint on the bottom course. The spacing of the weep holes must not exceed 750mm. Ventilation must be provided around the top of the Ōamaru Stone veneer. This may be achieved in a similar manner to that used to form the weep holes.
Laying instructions
After the foundation has received the damp proof coating and all lines set out and prepared, spread mortar as for normal brick or block work.
Lay first course to line, do not wet the blocks, perpendicular joints are to be no greater than 5mm. When all first course is laid in the area where working, vee joints shall be filled prior to laying the next course of stone. To fill these vee joints take mortar and by adding water, thin this mix to a grout. Pour this grout into the vee joint with the use of a dipper, topping up until completely filled, prior to bedding the next course.
In laying the next course, only spread sufficient mortar bed for one stone at a time. Before placing this mortar bed, the stone shall be wet by pouring water from a dipper.
As each course is laid, repeat the system to fill all vee joints.
Bedding mortar shall not be used for pointing. All joints shall be raked to a depth of approx. 8mm to allow for pointing.
Prior to pointing, it’s possible to take a tool such as a rasp and straighten all horizontal and perpendicular joints. This gives nice clean edges to the stone and removes any minor chipping.
Once these joints and lines are straight, pointing may continue.
At no time shall the veneer bed width be less than 90mm.
Seal all stonework after laying and pointing has been completed and after the limestone has dried to an even colouring. This is done with a waterproofing silicone such as Aquellux.
Any fungus or mould apparent before this application can be removed by wire brush and if necessary, sprayed with a moss or mould killer.