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out damned spot!

Architect's memo 74: November 2003

Wipeable; washable; scrubbable; fully scrubbable - what does it all mean? Not an awful lot if one is seeking clear guidance to the ease with which soiling can be removed from a coated surface!

One thing is clear; no-one wants their painted surfaces to be marred with unwanted marks, and the ability to readily remove such marks is a very desirable feature in any coating. So what features in a coating lend themselves to soiling resistance? Intuitively everyone realises that hard, smooth, chemically resistant surfaces such as glass, vitreous enamel, stainless steel etc are the easiest surfaces to remove marks from. The dense atomic structure of their surfaces means that stains can not penetrate, and their surface smoothness means that there are few pits or pores in which soiling can lodge.

Does this mean that these surfaces are easy to clean? This would have to be given a very qualified yes. The qualification comes from the fact that smooth polished surfaces also show marks very easily and no-one who has tried to clean and produce a totally smear-free set of ranchsliders would say that glass is easily cleaned!

Brushed stainless steel does not highlight marks as much as its highly polished cousin but the minute scratches in this surface can, in fact, harbour more dirt.

Some organic surfaces approach the surface properties of the above, Teflon and Formica bring to mind two famous brand name examples. Paints can also approach these materials especially if they can deliver a highly crosslinked matrix via two component and/or high temperature, UV or E.B. curing systems.

Typical waterborne wall paints do not come anywhere near such a degree of hardness. The polymers that they are made from are invariably thermoplastic materials and current VOC trends tends to mean that these polymers have to be quite soft to be able to form a film without the use of coalescing solvents. Soft films are more prone to penetration by soil.

There is quite a range of suitable polymers ranging from PVA co-polymers that are quite hydrophilic to styrene/acrylics that are quite hydrophobic. This means that the PVA will be quite sensitive to waterborne stains such as fruit juices but relatively resistant to oily stains such as lipstick or crayon whilst the reverse will be true for the styrene/acrylic.

Flat finishes are much more aesthetically pleasing on broadwall areas but, as noted earlier, the micro-roughness induced to achieve such effects will harbour dirt more than a smooth surface. The trick then becomes to reduce the gloss as much as possible whilst keeping the surface as smooth as possible - quite a balancing act.

Even if the soil can be removed from the coating, the coating itself must be able to withstand the rigours of the cleaning process. Rubbing can induce the softening of thermoplastic polymers and breakage and/or realignment of flattening agents. This can result in the treated area being clean but permanently glossier than its surrounds - out of the frying pan and into the fire.

There are additives that can be used to improve cleanability but these are often impermanent, coming off themselves after the first wash and once more leaving the surface vulnerable.

No memo on cleanability would be complete without reference to 'surfactant leaching'. Under today's technology no waterborne paint can be made without a range of surfactants to hold the system stable, and the greater level of tinter added, the greater the surfactant burden. Under good drying conditions these surfactants simply get absorbed by the film and no harm results. Under adverse drying conditions (cold, humid, poor ventilation) a portion of the surfactants can become deposited on the top of the film.

This fine layer can subtly change the gloss but invariably it remains totally unnoticed until the wall is marked. When the mark is cleaned off the layer of exuded surfactant in the same area is removed showing the true gloss of the film. What was unnoticed in its uniformity now stands out in contrast and often the whole wall needs to be washed with a 'dry bright' cleaner.

Maintaining pristine surfaces is never going to be easy and, at a personal level, the author has responded by increasing his levels of tolerance to a few blemishes. We could also stop breeding, keeping pets and having parties to keep walls pristine, however I for one would rather enjoy these and put up with a few blemishes here and there.

For some useful advice on maintaining your paint finish, read the Resene Caring For Your Paint Finish brochure available from Resene ColorShops or visit to view it online.

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