Natural stone has traditionally been used from erecting buildings to sculpting statues. This is mainly because of the durable and imperishable nature of natural stone. However, nothing is everlasting and even natural stone weathers. The causes of weathering are very diverse and the weathering processes can be biological, physical or chemical in nature.
Restoration options for weathered stone are at least as diverse. From the complete replacement of the damaged stone to the minimal restoration of the natural stone. When repairing natural stone, both minor and major repairs, replacement mortars are impossible to do without.
Restoration options
Major and minor repairs may be required during a restoration. The repairs can be divided into 3 types: full stone replacement, inserts and mortars. In full stone replacement and inserts, existing damaged stones are fully or partially replaced with a new stone.
We can classify stone repair mortars according to the binder: this can be a synthetic resin (acrylic, epoxy or polyester) or a mineral product.
Synthetic resin-bonded mortars are generally not very compatible (hardness, elasticity, water (vapor) permeability, weathering...) with the natural stone. They have a (too) good adhesion, but due to differences in thermal expansion they can tear off and pull original stone with them. E.g. mortars based on polyester resin are not frost-resistant; epoxy mortars discolor very strongly. Such mortars are sometimes an option for interior applications such as stair treads.
Among mineral binders, we distinguish mortars based on lime, zinc oxide and cement.
Cementitious mortars have fast curing properties; however, they are often too strong, too hard and too inflexible relative to the original stone.
Zinc oxide mortars are composed of crushed natural stone with zinc oxide and an inorganic binder. Their properties approach those of commonly used natural stones. They have fast shrinkage-free curing. They are usually applied with an anchorage.
Lime mortars best approximate the properties of the stone. Namely, they have good bond strength, water vapor permeability, capillarity, modulus of elasticity and water absorption.
There are different types of lime; for this we refer to our article "the benefits of lime in construction" .
Reynchemie offers ST.ONE , a stone repair mortar based on Saint-Astier natural hydraulic lime, available in a full color palette and various hardnesses.
ST.ONE is easy to apply and machine with traditional tools.
Reynchemistry Laboratory
Reynchemie has years of expertise in choosing the right repair mortar with appropriate color and hardness.
In Belgium and the Netherlands, we find several types of natural stone: bluestone, Tournai, Euville, Gobertange, Balegem or Ledesteen, Savonnières, Mergel, Portland, St.-Maximin, ...
There is a standard color palette for RC Amonit and St. One. If no standard color is satisfactory for a particular type of repair, a color analysis can be done in our lab based on a piece of stone.
