Protection of Natural Stone from Adverse Weather Conditions


Farmington natural Cotswold stone is an Oolitic limestone, laid down in the mid-Jurassic period approximately 165 million years ago. The limestone belt from which Cotswold and Bath stone are sourced stretches from Exeter to Hull.


Farmington natural Cotswold building stone has a fine-grained texture with some shell and compression layers visible. It is creamy in colour, but contains subtle colour variations that add warmth and beauty to the stone. Samples are available on request.


Three major factors influence the weathering of natural Cotswold stone’s colour: surface texture, cleanliness of the environment and position relevant to the prevailing wind and weather. For example, a rough textured field wall will quickly go grey and attract lichens. A smooth vertical wall in a city will mellow to a honey colour but be influenced also by local pollution. Any horizontal feature in the same structure will weather slowly to a greyer shade.


All limestones are composed of stratified layers. To increase durability, natural stone should be laid, wherever possible, on its natural ‘bed’. Full information on bed position for architectural masonry is contained in BS5390 Code of Practice for Stone Masonry.


Density: 2200kg / m3
Compressive strength: 21.8N / mm2
Porosity by volume: 20.8%
Saturation coefficient: 0.72
Durability: Category C/D as determined by the sodium sulphate crystallisation test (BRe digest 269 “The selection of building stone”)
Thermal conductivity: K = 1.9W / m2 (exposed conditions)

Design Loads

Natural stone lintels are suitable for clean spans up to 1 metre. This will adequately support a triangular load from the outer leaf. Lintels over this length are supplied split with a keystone and care should be taken that they are adequately supported during construction. We advise that you seek the guidance of a structural engineer on such matters.


All Farmington stone products are accurately finished – particularly sawn stone and architectural dressings, many of which are finished by hand, signed off with the relevant mason’s mark. All natural stone should be handled with care on site and if shrink-wrapped it is recommended that packaging should be left on until the product is actually required. Natural stone should be stacked on a level flat surface.

Limestone should not be used in close contact with sandstone.

On extraction, limestone contains a certain amount of Cotswold quarry sap and it will also be saturated with water during the cutting process. For this reason, it is advisable to cover stored stone during frosty conditions.


Cotswold building stone is supplied by the bag (approx. 4-4.5m2 per bag). It is supplied as random bagged, or individually coursed and bagged (approx. 125mm on bed in varying course heights). Dry stone walling is supplied in bulk by the bag (one bag of walling stone will produce approximately 2m2 of finished wall face).

Sawn stone and architectural products are supplied palletised and packed according to size and weight.

Any unusual site conditions that may affect delivery should be advised at the time of order.

How to specify/order

When specifying, the following instruction is suggested: “Natural stone to be supplied by Farmington Stone, Northleach, Cheltenham, GL54 3NZ”.

To place an order, please contact our customer services desk and confirm in writing by fax or e-mail. Samples and sample panels for planning approval can be supplied. Our technical department can provide specialist information and advice. Our technical representatives have considerable knowledge and experience on all aspects of natural stone construction.


Farmington has exported its natural Cotswold building stone throughout the world. In Melbourne, Australia, an entire mansion has been built using Farmington Quarry Stone. Farmington can now boast the longest Cotswold building stone wall outside the Cotswolds in Atlanta, USA. Farmington natural Cotswold stone is also exported to various distribution outlets in Japan.

Export enquiries are dealt with by our customer services team.

Code of Practice

Please find set out below references and clauses from BS 5628-3 2005 Code of Practice for the use of masonry – Part 3: Materials and components, design and workmanship.

Clause A. Stone
Deliver the stone from the yard to a suitable off-loading facility on site, and in the fixing sequence. Stack clear of the ground on battens to prevent contamination from moisture and soluble salts in the earth. In wintry weather take precautions to prevent damage to the stones from the freezing of rainwater or residual quarry-sap by covering with tarpaulins or polythene sheet over straw, Hessian or other suitable insulating materials, which contain nothing that might damage or stain the stone. Protect against staining from other building materials, particularly hardwoods, oils and fuels.

Clause A. Mixing in cold weather
Do not mix mortar when the temperature is at or below 3ºC and falling, or until it is no less than 1ºC and rising. Do not use fine aggregate (sand) or semi-finished mortar (lime-sand mixtures) containing ice particles.

Clause A.5 Brick and block walling
A. Cold Weather
In cold weather do not:

Build masonry when air temperature is at or below 3ºC and falling or unless it is at least 1ºC and rising.
Lay mortar on frozen surfaces
Use wet bricks or blocks when there is a danger of freezing.

Clause A. Frost damage
If the mortar is susceptible to frost damage, obtain guidance and instructions before proceeding work.

Clause A. Protection
Cover the tops of newly-built brick and block masonry to protect it from rain and also from frost, if imminent, and at all times when work is not proceeding. If there is any danger of the work being frozen then consideration should be given to the use of insulation under the cover.

COMMENTARY: Unless the work is protected when not proceeding there is always the risk of sudden frosts or showers causing damage. It is important to cover work at the end of each day. These covers should be kept handy for use. Wet covers can freeze in contact with the work. It may therefore be preferable to top the wall with a clean and dry wooden plank, wider than the wall, and place polythene or similar sheeting over the plank, clear of the wall face, in order to provide an insulating air gap. It is important to weight the covers to prevent the wind lifting them.