Sealing Natural Stone before Grouting FAQS
Another recent development made by many professional paving contractors working with porous natural stone, is to use GftK’s vdw 950 3-in-1 StainProtect to treat the paving immediately after they have been laid, BEFORE application of the pointing / joint mortar. This approach has proven to be very advantageous with paving that is known to be, or that can be variably, porous, and so it is known that the use of any cement-based jointing, will cause staining and cleaning problems as well as with brush-in jointing compounds, which are prone to staining as well as being generally just not up to the job. This is detailed elsewhere in the Paving Jointing pages of this website, and one of the 2-component epoxy resin based vdw 800 series mortars from GftK is obviously far more ideal.
For example with the 2-part, epoxy resin based GftK Paving Joint Mortar, it is also important to understand that during application over a very porous stone with a prewetted surface as usual, it is possible that in some of the most porous areas, the liquid resin binder could be partially absorbed, subsequently affecting the visual appearance of the stone (darkening in places). Contractors have discovered that by pre-sealing the stone surfaces once the bedding has set, with GftK’s vdw 950 3-in-1, this very effectively prevents any subsequent absorption of any resin binder. There is also the additional benefit that after the grouting is completed, a sealed and protected stone surface is left, with greatly increased resistance to stains from spillages and damage from frost etc. Plus, there is also no longer any risk of efflorescence through the stone surfaces as the impregnation and sealing is made inside and within the capillaries of the stone itself.
Pre-sealing Granite Slabs
Today many types of natural stone sold for use as paving, is very or very variably porous, especially many sandstones, limestones, and a lot of imported granites. Generally these are hard wearing enough for foot traffic and freeze-thaw attack of the surface is not a big problem in most of the UK, but the main problem is the porosity allows rapid staining from water- and oil-borne materials, from coffee, red wine, cooking oils and general grime, to engine oils etc., plus the surface capillaries make perfect growth cells for green algae and then lichens (blackspot), which is always upsetting when you have paid for lovely attractive paving. This porosity also means that the lovely stone surfaces will attract and take up staining from the cement bedding and especially cement grout, as well as brush-ins and some resin grouts – as well as anything else on site during the construction work. These stains can be a very expensive nightmare to remove and an unnecessary cause of conflict between everyone involved, as they can be an expensive nightmare to remove, and some may require replacing.
Therefore a good solution is pre-sealing, usually with an impregnating type of sealer such as GftK’s vdw 950 3-in-1, which is best done after bedding, so as not to affect the bond to the bedding mortar.
Pre-sealing External Porcelain Tiles
It can come as a surprise to many people that it can be a good idea to pre-seal and/or seal the surfaces to protect external porcelain tile paving, but this is an increasing trend. However, this is not because they are porous like some natural stone paving, but quite the reverse and their extremely dense surface and fine slip resistant profile can mean that they can easily pick-up surface staining from their installation grouting, and thereafter in service, which can then be very tough to remove, even by jet washing. To prevent this happening, external porcelain tile pre-sealing treatment is best made using a special surface tension breaking technology, which we have developed as NCC Porcelain Protector, more details are available here and it is available to buy in our Online Shop.