I want to go over the issue of how waterproof membranes work with a sealer to provide protection as in many markets the use of membranes is still not common practice.
In many markets around the world sealers and waterproof membranes are seen as addressing different building site problems. Waterproofing is installed to stop water travelling from one area into another such as in a shower cubicle. Sealers are the products used on tile, grout or natural stone to reduce the likelihood of staining. However in many cases the solution to a problem is the proper use of both a sealer and waterproof membrane in partnership, each enhancing the performance of the other.
I cannot cover all of the problems that are addressed by using these two materials together. However I will use as an example one of the major stone installation problems seen around the world that of below surface staining. The photos at the bottom of this article show a quite common application of Sandstone around a water feature and planter box. The stone is clearly stained by both dark and white residues. The stains are most likely of three types. Firstly white efflorescence. This is soluble salt coming from both the stone, cement setting materials and grout as well as salts from the soil in the case of the planter box. Secondly darker stains coming from minerals leached from the soil in the planter box. Lastly and also manifested as dark marks are soluble minerals from the stone itself. In all three cases the catalyst for these sources of contamination is water. If the stone was dry none of this staining would occur. This type of staining is widespread in all countries and markets and yet in most markets an understanding of how to reduce this occurrence is poor to non-existent.
The first step in addressing this problem is to use a waterproof membrane. In most cases when this is mentioned the common response is that it is not required because there is no critical dry area to protect. In other words many believe waterproof membranes are only applicable when you are protecting a living space. This is in my opinion completely incorrect. You will not address our problem of below surface staining unless you protect the stone from both of the two major sources of water that ignite the contaminants. The proper installation of a waterproof membrane to the inside of the water feature and planter boxes is critical in controlling the amount of water that can evaporate up through the sandstone in this example. In many markets waterproofing is attempted in these cases by applying cement based renders. These do not work well because not only are they not water tight but they also contain soluble salts and minerals that will eventually evaporate through the stone. The membrane must be totally waterproof.
The other source of water is external; rain and runoff from other areas. In many markets this is the only source of water that is addressed in a stone installation of the type in our photos. Many believe that sealers will complete this task keeping the stone totally dry and hence stain free. This belief leads people to apply sealers on all six sides in anticipation of having a totally dry stone for all time. This is a common misconception so lets put the record straight. Good sealers are not waterproof. Sealers are made to allow vapour transmission so that the stone can breathe. To do otherwise would result in damage to the stone caused by entrapped water vapour ever present in all natural stone. What the sealer does achieve is a dramatic reduction in the porosity of the stone and in doing so reduces the amount of catalysing water and hence staining. In the case in question you can never guarantee that some staining will not occur. However what you can do is put an installation in place that vastly reduces the risk of this happening. A waterproof membrane or sealer in isolation will not maximise protection against this type of staining. Only the use and marriage of both technologies will do this. There are of course other procedures one can take to enhance the membranes and sealers performance in extinguishing such contamination such as using latex modified grout and mortars, using washed sand etc. However it is the use of a waterproof membrane and sealer together and not in isolation that addresses 95% of this problem.
So the next time you specify or design a stone or tile installation where water is present think of how you can use a sealer and a waterproof membrane together, as this partnership will result in performance that far exceeds that of using the two materials in isolation.