I have covered this subject before but we receive so many questions about sealing grout that I thought it worth revisiting. Before I get started on whether grout should be sealed or not, let me first look at the different types of grout that are commonly in use today.There are, broadly speaking, three types of grout:

1. Standard, cement-based (cementitious)
2. Polymer-modified
3. Epoxy

In each case, they can be ‘sanded’ or ‘un-sanded’ As you might expect, they all have different qualities and characteristics. When considering whether a particular grout would benefit from sealing, what we are really doing is considering how easy that grout will be to keep clean and free of stains.

One of the most important areas we can look at is porosity, or to be more precise, we look at the grout’s capacity to absorb water (as this is a good indicator as to how easily the grout can absorb other liquids and therefore accept a stain). Water absorption is measured as the amount of water that can be taken up by the grout, expressed as a percentage of its dry weight. The typical WA figures for the three types of grout are as follows:

Grout Type:

Standard Cement-Based – Water Absorption up to 12%

Polymer-modified (often called flexible, wide joint or similar) – Water Absorption up to 5%

Epoxy (true epoxy) – Water Absorption is 0%

The first thing we can see is that a good epoxy grout typically has a WA% of 0 – it is not porous and will not easily stain. In fact, it is completely impervious and so for this reason it is often specified in food-prep areas and in hospitals. Consequently there is little point in trying to seal an epoxy grout. But epoxy grout is expensive and harder to use, so is not often found in ‘standard’ tiling installations.

So what about the other two? Well clearly they are both absorbent to some degree. To put it into perspective, if we were discussing stones with similar WA figures, for 12% we would have to go to a low density limestone, or good quality sandstone and we would almost certainly recommend sealing them, depending on the circumstances. But, even a high density limestone with a WA of 4 or 5% would often benefit from sealing. If water can be absorbed, even if it is only 5% (bear in mind it is 5% for 100% of the surface) then anything that can be dissolved in water can also get in, only when the water leaves through evaporation, whatever it was carrying stays put. Furthermore, if water can get in so can oil and so can solvent-based contaminants (permanent marker pen for example).

If the grout is a sanded type (in other words as well as cement and maybe polymers, it also has a fine sand for added structural strength particularly in grout designed for floor tiles or other wide joints) then there is the added complication of surface texture that can add to cleaning woes. Furthermore, a grout that can readily accept moisture, or that has a texture (or worse if it has both) can be a perfect harbour for mould, mildew, algae and other air-borne spores to colonize.

By applying a good quality sealer to the grout joints we can dramatically reduce the moisture uptake (whilst retaining a degree of necessary breathability) to provide a sub-surface safety-net to resist deep staining and also significantly reduce the ability of the grout to harbour mould and mildew spores.

So what type of sealer to use? well any premium quality impregnating sealer will help, but a good, modern water-based one such as Grout Sealer by Aqua Mix is ideal, not only is it very user friendly, but it is also one of the best performing sealers we have come across. One additional benefit of Grout Sealer over a standard impregnator is that it also leaves a barely visible film that coats the surface of the grout. This is especially useful on sanded grouts as it coats the sand grains that protrude through the grout and this greatly improves the surface’s ‘clean ability’.

In conclusion, if the grout joint readily absorbs water (just try wetting it and leaving the water for a few minutes. Then it will certainly benefit from being sealed.

Copyright Ian Taylor and The Tile and Stone Blog.co.uk, 2013. See copyright notice above.