Installation of Ōamaru Stone veneers
Specifications for handling and laying other than set out below shall comply with relevant building bylaws.
Ōamaru Stone is a natural material, not a manufactured article and its performance as a building material has been proven over the past 100 years.
When the stone is removed from the quarry, it has a large moisture content, and when the milling of the stone is complete it will stay damp and soft for some considerable time.
When milling of the stone has been completed it is placed on timber pallets up to 1.60 tonne in weight. These pallets have the top covered when they leave the quarry but are not usually wrapped, to allow air movement around the stone and to allow the dispersion and evaporation of water.
If the stone has been shrink wrapped for transportation purposes, the wrapping should be removed immediately once the stone is placed on site. It is important to remember that as the stone dries it becomes harder and stone shall not be laid until 3-4 weeks after milling. If stones are not sufficiently hard enough they are more easily damaged.
On site pallets should be stacked clear of mud and have any shrink wrap removed. This will allow for side ventilation to continue the drying process. The top covering of the pallets can remain in place to stop weather penetration.
On all foundations, whether they be concrete or filled concrete block, three coats of D.P.C. such as Mulseal, shall be applied to the top to form a damp proof cover prior to the laying of the first course of stone. This is essential to prevent any dampness rising into the stone.
There may be a slight variation in the heights of the stone after milling, and the layer should have random checks on sizes prior to setting out story rods. Maximum bed depth shall be 6-8mm.
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.
Sand may be washed beach sand or clean sharp sand, which has been passed 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 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 5 ties/m². The ties must be fixed to studs and nailed to the stone at all times.
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.
- 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 till 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 is 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 stone work after laying and pointing has been completed and after stone 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.