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Six-Sided Sealing: Its Role in a Water Management System for Natural Stone and Tile

THE PROBLEM – MOISTURE Natural stone today is as popular as ever among customers who value its beauty, durability and uniqueness. The unique inherent qualities of natural stone can pose challenges when installing stone (and certain natural clay or cement tiles) for interior and exterior residential and commercial applications. Many installa tions suffer from problems such as picture framing, soluble min eral blooms and staining (for example from soluble pyrite, iron sulphide), water marking including picture framing, and even primary and some secondary efflorescence are well known to experienced members who work in the stone industry. (Photos 1 and 2) In other cases, the base of stone veneer and seat walls may be stained from moisture wicking up, bringing impurities that permanently discolor the installation. (Photo 3) Although not all natural stone and tile are prone to moisture issues, com monly used marbles, limestones and granites, terracotta and cement tile among others are prone to moisture issues. There fore, the question of how to prevent moisture issues with seal ing all six sides of the material, instead of the top surface only, is more relevant than ever.

jority of adhesives/mortar being Portland cement-based. So in short, managing the amount of water that can be absorbed by the material during the important installation phase, as well as managing the water post installation, is the best way to reduce the risk of moisture types of stains occurring. Preventing water from being absorbed into the material during the installation and resultant cure of the mortar and grout is crit ical. Other sources of moisture can have an equally damaging effect. Moisture in a concrete slab can migrate through capil lary action into the assembly and cause damage. Environmental exposure to weather conditions, interior wet areas, accidental spills and joint fillers are other causes of irreversible staining.

Photo 4: Alkalinity staining on limestone

HOW CAN YOU KNOW IF SIX-SIDED SEALING WILL HELP?

Often, certain stones are known to have potential risks, such as white Carrara marble with iron staining. In some cases, pre vious experience with a stone history is valuable. The stone quarrier, importer or supplier may caution about such potential issues prior to installation. If the stone history is not provided, asking for any data and testing can produce useful information. But given the amount of natural stones we see today (as well as some non-porcelain products such as encaustic cement tile), and with new natural stones being discovered frequently, there is no substitute for a mock-up to assess and ensure that all vari ables and risks have been addressed up front when all other av enues fail. (Photo 5)

Photo 1: Picture framing on granite Photo 2: Iron staining on marble

Photo 3: Moisture wicking of impurities

The pH and quantity of water are critical factors in determining the potential risk for staining, and – most importantly – the de gree of staining. The greater the quantity of water and the higher the pH (more alkaline), the greater the risk and degree of stain ing. Moisture staining in certain types of limestones is common along with other stones. (Photo 4) Stones are most at risk for moisture staining during the installation phase. During instal lation, there are both significant quantities of water available from the adhesives/mortar, and high alkalinity due to the ma

Photo 5: Mock-up test showing sealed stones vs. an untreated piece

NTCA Reference Manual | 2024 / 2025

Chapter 6 | Natural Stone Installations

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