The argument over which sealer is the best, solvent or water based, has raged ever since water based products hit the market. Aqua Mix offers both in their premium range of impregnators with the industry standard Sealers Choice and the newer solvent Ultra Solv. I have heard many reasons why one is better than the other, however the fact is that you need both a solvent and a water based sealer to cover the entire range of porous tile and stone sold on today’s market.

The traditional argument for water over solvent has been that water based products do the same job but are safer being non-toxic and non-flammable. Solvent exponents counter this with the argument that their sealers do a better job on dense products such as polished stone. In fact they argue that water based although safer just does not work on dense products such as polished granite, marble and porcelain tile. The justification for this has been that the molecule used in solvent sealers is smaller than water based hence the larger size of the water based molecule makes them unsuitable for many of the dense materials.

This all sounds very feasible until you start to look at the facts. For example the molecular size of Aqua Mix Sealers Choice (water base) is 20nm whereas the solvent based Ultra Solv is 15nm. On face value this would appear to support the solvent camps theory with the solvent sealer having an average molecule 5nm smaller than the water based sealer. However the photos below tell a different story. Figure 1 shows in the top half a photo of the surface of unpolished porcelain. The bottom half is the surface of polished porcelain. The magnification of the top half is x100 and the bottom x1000. The white line towards the bottom of each photo gives you the scale – the top being approximately 1cm = 100 um (microns) the bottom 1cm= 15 um. This makes the size of the pores and the smaller cracks about 1-5 um in size. Remember that a micron is one millionth of a metre. To put this into perspective a grain of salt is about 60um and the human eye can see down to about 40um. However the molecular size of our two sealers is 15nm for the solvent and 20nm for the water based. With a nm (nanometre) being a billionth of a metre it is obvious that both sealers have molecules small enough to enter the 1-5um size pores of either the polished or unpolished porcelain – and porcelain has a smaller size pore than just about any natural stone except perhaps Absolute Black Granite which we all know does not need to be sealed at all.

Therefore the argument that solvent based sealers work on dense products better than water based due to smaller molecules is not true of today’s premium sealers such as Sealer Choice. However if you test both water and solvents on dense products such as porcelain you will definitely find the solvent working better. So if it is not an issue of molecule what is it?

The key to this whole issue is surface tension and surface energy. We are all familiar with the phenomenon of a being able to fill a glass of water slightly higher than the physical sides of the glass. We can do this because of the surface tension of the water. In Figure 2 you can easily see how this works with the molecules on the surface having an unequal force which creates a cohesive bond or compression which creates the surface tension.

 What is less commonly known is that hard surfaces such as tile, stone and timber also have surface energy. This is the energy that holds the particles of the hard material together. Like water the energy at the surface is unequal and hence interacts with liquids that contact it. When water hits a porcelain surface for example it tends not to bead up but rather spreads out a little. This is because the surface energy of the dense porcelain is higher than that of the water and hence the water’s surface tension is reduced.

For a penetrating sealer to enter the dense surface of porcelain it must be able to break down this surface energy almost completely and this is where solvents and water differ. Solvents have a surface tension of 15-20 dynes/cm3 whereas water has an average of 35 dynes /cm3. This means waters surface energy, although not as high as the dense surface, is still too high to enter easily whereas the solvents is lower than the porcelain and can therefore penetrate easily and more deeply as well. This then is the main performance difference between the two carriers. It must be noted we are talking about the carriers (water and solvent) and not the active ingredients carried by them. Solvents are simply a better transport mechanism for active ingredients than water when it comes to dense surfaces such as granite and porcelain.

However the same characteristic becomes a disadvantage when sealing higher porosity surfaces such as limestone and terracotta. In this instance the solvents low surface tension transports the sealer too deeply into the surface creating a seal too deep to be effective on the surface. You can of course saturate the stone or tile to overcome this shortcoming but this is not practical as the cost becomes prohibitive.

This then is the reason why state of the art sealer companies such as Aqua Mix have two premium sealers – water based as well as solvent. One is ideal for dense surfaces (Ultra Solv) and the other for everything else (Sealers Choice). There is no doubt that water based sealers can be made to wet out (low surface tension) like solvents but currently the wetting agents to do this are very expensive making them currently impractical. However with the environment and safety being such important issues it is water based sealer technology that is being developed for the future and companies such as Aqua Mix who pioneered water based tile and stone sealers, are at the forefront of this research.