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Architects memo no. 92: September 2008

So this is the worst joke in the world! One physicist asks another - 'There are 2 cats on a sloping roof; which slides off first?' Without hesitation the second physicist replies, 'The one with the lowest mew of course!'

The fact that the Greek letter mu is the symbol for the coeffiecient of friction is no excuse for the excruciatingly bad pun above, but it does get us however gauchely into the subject of slip resistance.

Slip is the ability of two surfaces to move with ease, one over the other. This ability is of course highly valued in many areas of engineering, but when the surfaces in question are a shoe and a step or a floor, slip is downright dangerous. The incidence of falling accidents is very high and can lead to a severely diminished quality of life, especially for the elderly with more fragile bones.

The opposite of slip is friction and this is defined as the resistance to movement of two bodies in contact when a force is applied. This resistance can occur at both a molecular level as well as at a macro level. Two smooth blocks of wax will slide easily over each other whilst two, equally smooth, blocks of silicone elastomer will exhibit high levels of friction.

The above is due to how the molecules on the surface interact. There are close similarities to the haptic nature of materials. Some things feel smooth and slippery to the touch while others feel quite 'draggy'.

Even smooth materials become 'draggy' if the physical profile of the surface is changed. If smooth stainless steel is sandblasted it becomes very rough to the touch with high levels of friction.

This technique is often used to improved slip resistance of coatings. Although the majority of coating resins do not have inherently high slip (indeed 'slip' has to be engineered in to coatings), the addition of coarse, texturing pigments can dramatically increase their anti-slip properties.

Texturing coatings with 'sharp' aggregates gives a major plus in the anti-slip area but, like almost all paint technologies, there is a price to pay. Safer, rougher surfaces harbour dirt more easily and are more difficult to keep clean than smoother finishes. They can also cause some nasty grazes should a fall occur.

A compromise is to overcoat a textured basecoat with an untextured topcoat. This will maintain a significant degree of slip resistance while ameliorating the drawbacks of the fully textured system.

Some Resene products of interest in this area:
Resene Waterborne Sidewalk can be used as is for a smooth walking surface or mixed with SRG Grit for a textured non-skid finish.

Or for maximum slip resistance, Resene Non-Skid Deck & Path is a textured waterborne finish, designed to provide a comfortable walking surface for all interior and exterior situations where a non-skid finish is desired. Available in a low sheen finish, Resene Non Skid Deck & Path may be tinted to complement existing dècor, both inside and out. The finish has a comfortable grit texture to give feet and shoes something to grip onto, reducing the risk of accident no matter what the weather. Light colours are ideal for stair edges to highlight the edge and reduce the likelihood of accident.

Resene Non-Skid Deck & Path has been slip resistance tested under wet conditions with a result of 0.74-0.78, which means it meets slip resistance requirements for slopes up to 34 degrees. A very tough finish, Resene Non-Skid Deck & Path may be used in residential, commercial or industrial light wear applications.

View slip resistance test results.

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