Types of Damage in Stone

Stone can weather, break, crumble and split. In cast stone, there can be separation of the core and surface layers, and either deterioration of the aggregate or the cementing matrix. All types of stone can be damaged by the decay of iron or steel reinforcements or fittings.

Intact stone has no surface loss and shows the original tooling marks.

This table describes typical damage and problems and the usual method of repair.

Condition	Description	Repair
Biological growth	Moulds and algae.	Remove by chemical cleaning.
Cracking	A fracture in the stone of variable width or length that could result in the movement of adjacent parts, perhaps cause structural failure and allow water to enter.	Clean out larger cracks and repair with lime grout. Epoxy adhesive can be injected into fine cracks. A pin may also be required.
Minor disaggregation	Minor loss of surface material in powder or granule form by deterioration and erosion of the binding material; the stone is crumbling.	Tool the surface to restore a sound profile.
Embedded ferrous anchors or pins	Anchors or pins may corrode and cause damage to the stone. These fittings may be used or disused, for example for an iron fence that has been removed.	Remove abandoned anchors. Install new non-corrosive anchors as necessary.
Exfoliation, flaking or scaling	Separation of the layers of a stone, usually in a uniform thickness, creating contoured depressions parallel to the material surface.	For minor loss, tool the unsound surface material to restore a sound profile. For major loss, install a Dutchman repair.
Guano	The accumulated excrement of birds. Guano may cause staining and encourage pests.	Remove by chemical cleaning.
Previous inappropriate or failing patches	Repairs preformed with materials or methods, which cause damage to, do not match the original material's physical or visual characteristics.	Remove the patch. For minor loss, tool back the surface of the stone to match the original surface. For major loss, install a Dutchman repair.
Salt Efflorescence	The formation of surface deposits, often white in colour, crystalline in form, powdery to the touch, and composed of soluble salt.	Brush off the crystals or wash down with light water rinse.