The Benefits of Sealing all Six Sides of Natural Stone

Stone installations suffering from problems such as picture framing, mineral stains (for example from soluble pyrite, iron sulphide), water marking and even primary and some secondary efflorescence are well known to those who work in the stone industry. Although not all natural stone is prone to these issues there is still a significant number that are. Sealing all six sides of a stone has been advocated by some people in the industry as a fix-all for these problems. Therefore with the ever increasing use of natural stone for both interior and exterior installations the question of whether there are benefits to sealing all six sides of the stone instead of the top surface only is more relevant than ever.

So why would you apply a sealer to all six sides?

The answer is that a sealer, suitable for sealing all six sides, is an important component in a successful system for maximising the management of water in a stone installation. With all of these problems water is a critical component and in the majority of cases the main catalyst. For example soluble minerals such as pyrite and soluble salts cannot react to become a problem without the presence of water. Picture framing and the resulting stains, usually caused by the remaining solid content left behind after the water has evaporated, is again only possible with the prolonged presence of water.

The ph and quantity of water are also critical factors in determining the potential risk for staining and most importantly the degree of staining. The greater the quantity of water and the higher the ph (more alkaline) the greater the risk of staining and degree of staining, becomes. This means the stone is most at risk during the installation phase where there are both significant quantities of water available from the adhesives (or mortar/screeds) and high alkalinity due to the majority of adhesives/mortar being Portland cement based. So in short managing the amount of water that can be absorbed by the stone during this important installation phase as well as managing the water post installation is the best way to reduce the risk of these types of stains occurring.

So back to our question of why seal all six sides? The answer is that it helps reduce the overall surface water absorption of a stone. In doing so it significantly reduces the risk of staining issues such as picture framing, soluble mineral blooms, primary and some secondary efflorescence during the critical installation phase when the majority of these issues are triggered. However for a sealer to work successfully in this environment it must have two important characteristics. The first is that it does not interfere with the bond of the adhesive. The second is that it can perform in the high alkaline environment of the curing cement adhesive or mortar. For years many in the industry have seen sealers as either bond breakers or products that significantly reduce the effectiveness of an adhesive. Therefore they have not recommended or advocated their use for sealing the back and sides of stone or tile, although most have acknowledged the potential ability of sealers to reduce the risk of staining during installation. Contemporary sealer materials and technology along with the expertise of companies such as Custom Building Product’s Aqua Mix® have resulted in sealers that are not bond breakers and can perform effectively in a high alkaline environment making them suitable for application to all six sides of a stone. Our Aqua Mix® ProBlock product is recommended for application on all six sides of a stone when and where required. Being a water-based siliconate compound it performs in a high alkaline environment and is tested both in the laboratory and in the field (with over 20 years of job site use as a six sided sealer) in terms of its ability not to interfere with the bond of an adhesive, cement mortar bed or grout.

As sealers significantly reduce and slow down water absorption but ultimately do not stop water totally, (because they are not waterproofing materials), they are a critical component of a full water management system rather than being a complete solution to these problems themselves. A full water management system should be considered and the appropriate parts implemented across the installation to fully protect the stone or tile from the staining and contamination issues discussed above. This system will also have other benefits in terms of helping to reduce the risk of other water related problems such as freeze/thaw damage and dimensional deformation (warping), a well documented problem with water sensitive stone.

So what are the main components of a water management system? There are a number of components to this system that should be considered when designing, specifying or installing stone and tile. They are as follows:

1. Correct falls – making sure residual water can exit via properly installed drains is imperative to the success of an installation exposed to water. Water that is allowed to pond or stand will increase the risk of water related staining as well as issues such as freeze/thaw damage, efflorescence and warping of moisture sensitive stone.
2. Waterproof membranes, primers or water remediation systems – keeping the substrate underneath the stone/tile as dry as possible is an important part of a successful problem free installation. Water can be sourced both externally and internally. Internal water can come from ground water (exterior on-grade installations) and external from weather that can filter through the installation to be stored in the substrate. So the application of products to address possible ground water (epoxy water remediation systems) or waterproof membranes to ensure the substrate cannot store water supplied from above will greatly reduce contamination issues as well as reduce freeze/thaw and dimensional deformation.
3. Use of appropriate adhesives – using specialised and appropriate adhesives such as polymer modified rather than conventional mortars will help to reduce water in the system. In the case of water sensitive stone using an adhesive that contains no water at all (100% solid epoxy) may be required. Also note that when a sealer is applied to the back of a stone or tile it reduces the surface water absorption close to zero. The sealed surface effectively acts more like a very dense material. Therefore adhesives that are recommended for dense materials such as granite or porcelain tile should be used along with their specific installation methods even if the stone or tile is a naturally less dense material such as limestone, sandstone or similar.
4. Proper placement and use of sealants – movement and expansion joints are important because they manage the natural expansion and contraction of the installation that if not properly controlled can lead to the loss of adhesive bond. Initially one of the consequences is that voids are created under the stone/tile that can collect water resulting in staining and contamination problems. If joint placement is left unresolved they can ultimately lead to the complete failure of the installation.
5. Six Side Sealing – As discussed above.

In summary keeping an installation as dry as possible, both during installation and after, is the key to minimising water related problems such as those discussed. There are major benefits in using a suitable sealer, such Aqua Mix® ProBlock to protect all six sides of a stone from moisture related problems. It works primarily in the initial stages during the installation and cure of the adhesive and is without doubt an important component of a successful water management system.