Our aim is to season our stone after the material has been extracted. This removes the ‘quarry sap’ from the stone before it is used thus showing any possible natural defects that maybe in the raw material.
As with most limestone, Marnhull Stone performs better when laid in the same orientation as it was in its natural bed, known as ‘on bed’. Occasionally it is used ‘out of bed’ for example with internal decorative products.
We will always advise if our stone is suitable for varying applications and if it is not we would recommend a suitable replacement.
There are many things to consider when constructing with natural stone which can effect its performance over the years. For example an adequate damp proof course (DPC) is a must to stop moisture from rising into the stonework and thus helping to keep the material from being continually saturated with water as this can lead to damage to the stone in freezing temperatures.
Contact with soil should be avoided when using a porous stone as soils can be heavily contaminated with mineral salts which can damage and stain the stone.
If using a porous stone as a facing material to a block work retaining wall, then an impervious membrane is required to stop moisture coming through the block work and penetrating the stone face.
A coping stone is highly recommended to cap porous stones to prevent water from penetrating the stone. We advise that the coping should exceed the face of the stone by at least 50mm and have the correct weathering detail to provide maximum water run off and a raindrip on the underside of the coping to stop the water from running back onto the stone.
We do NOT advise using a ” Kings and Queens ” capping or a cement mortar capping as this is not adequate to protect against the weather with a porous stone.
We do NOT advise the use of a porous stone for coping, water features, rockeries or any application where the stone is not in compression and has high exposure to the various temperature and climate changes that come with the seasons.
We also rely on the historical buildings of the area dating back some 500 years to view a stones performance over the centuries and have noticed that incorrect mortar mix (i.e. too hard) repairs and coping without overhang from the face of the stonework etc have directly led to damage to the masonry on the buildings throughout time.
Mortar
Mortars used for stonemasonry will vary according to the type of stone used and the structural requirements. The strength of the mix which may be acceptable with one stone type will not necessarily be acceptable with another.
The mortar mix should be no less porous than the stone itself which in turn will allow the stone to breathe. If a mortar mix is too hard then the moisture can become trapped and damage the stone in freezing conditions.
When building a rubble wall the strength of the wall will largely depend on the setting properties of the mortar. The mixing of the ingredients is a very important factor in its ultimate success. The use of lime in the mortar aids workability.
The STRONGEST basic mortar mix when using cement with our stone would be as follows:
6 building or washed sand / 1 Hydrated lime
2 flooring grit sand / 1 white Portland cement
This is an 8 parts Sand : 1 part White cement : 1 part Hydrated Lime mix and will provide a good colour match to our stone. Usually a weaker mix of 10 parts Sand : 1 part White cement : 1 part Hydrated Lime would be used to be more porous.
Whenever possible either Hydraulic Lime or Lime Putty should be used. A good stonemason will provide the correct advice.
Our stone has been tested to meet the CE Marking requirements, please contact us for more information.
