If mortar contacts the face of the stone, allow it to dry slightly and then pick the mortar from the face. If removed when very wet, the mortar can smear and cause more work later. If a bonding admixture is used in the mortar then remove the mortar as soon as possible by dry brushing and then damp sponge. Do not attempt to smear the mortar. It is suggested to wet the stonework down with water and then to apply a mild cleaning detergent with a soft bristle brush to remove any dirt or mortar smear left from the installation. DO NOT USE ANY TYPE OF ACID. Always wet the stone first before applying any cleaning solutions to prevent over-absorption of the cleaning solution, and always ask your dealer for a recommended cleaner. Cleaners perform differently and your needs will vary depending upon the stone used.
If a sealer is required, first check with the natural stone supplier as to a sealer that may be recommended for your stone. Topical sealers and impregnators are available for application when enhancement of the color or water repellency is required. Make sure to choose products which are not harmed by ultra-violet rays, alkali, do not yellow, and do not interfere with evaporation of moisture through the stone. Always test a small area before full application. Once sealers are applied to the stone it must be considered that re-application of the sealers will be necessary over time. Longevity varies and re-sealing times can range from 1 year to 10 years depending on the product, application, and exposure. The sealer should not be applied until the stonework and mortar has time to completely cure. EXTREMELY IMPORTANT: The installation instructions by the sealer manufacturer must be followed.
Article by BSI Building Stone Institute