Topping yourself the way forward
November 1st 2004

Alex Dennis of Sika-Armorex looks at the use of dry shake toppings in creating durable floor finishes in industrial applications

Ever since the discovery of cement in Roman times man has been trying to exploit and improve the performance of cement bound materials in one way or another. Nowhere is this more relevant than on the concrete floor of a modern warehouse or distribution centre, where the cost of remedial work is intolerable in terms of disruption.

This article looks at the use of dry shake toppings as durable and cost effective floor finishes. Use is broadening from industrial facilities to commercial environments where the natural aesthetic quality of coloured dry shake is as important as its superior mechanical properties. Dry shakes have recently been installed in trendy wine bars, luxury apartments and high street retail stores.

So what is a dry shake and why should you use one?

The concept is relatively simple and develops the ‘granolithic topping’ theme of improving durability of concrete by the broadcasting and trowelling of hard aggregates into the wearing surface. In a refurbishment situation this ‘case hardening’ is readily achieved by binding such aggregate into a resin matrix and reprofiling the worn surface. But how about doing this from day one?

The concrete

The most frequently ignored fact in industrial flooring is that a floor finish must generally rest on or bond to a concrete substrate. As we have the opportunity in new build to design the concrete mix correctly, why not do so? It is well known that the following characteristics are desirable for such flooring concrete: • Sufficient compressive strength (N/mm2) • Low or Negligible shrinkage (mm/m) • Good workability (slump ) • Project specific mix design (trials) • Low water:cement ratio

It is argued that shrinkage would be a better specification parameter than strength, as shrinkage of concrete and subsequent curling of slabs is responsible for a large number of failures, slip/trip accidents, damage and repair bills the world over. Yet even now most concrete mix designs call for little more than a minimum cement content (typically 400kg/m3) and minimum compressive strength (typically 35N/mm2).

Shrinkage performance is rarely specified. It is time to move up a gear.

The current trend is for increasingly slender slabs (175mm is common) using a steel/synthetic fibre reinforced concrete and a polycarboxylate superplasticiser such as Sika Viscocrete. Whilst the cautious among you will suggest that this all sounds expensive, risky and unnecessary, the proof is all around and the industry accepts the great advantages of the system.

• Concrete quality is consistent (better) • Costs are reduced through cement savings (cheaper) • Slender slabs mean less excavation and concrete volume (quicker)

With all of this fibre reinforced concrete being used, something must be done to stop the fibres from protruding through the top surface of the concrete and causing a nuisance. In addition the durability and wear resistance of the surface is not addressed by the above discussion. This is where the basics of dry shake technology come in to play.

The wearing surface

It is easy to forget that the floor finish is the one part of the structure that cannot be avoided once the building is operational, so correct specification is essential to avoid catastrophic failure and expensive maintenance. Selection of a floor finish is best achieved through analysis against a matrix of performance criteria including; Traffic and Mechanical Wear * Chemical Resistance * Temperature * Slip Resistance * Impact * Hygiene * Conductive/Anti-Static properties * Sound Deadening/Comfort * Crack Bridging * VOC content * UV resistance * Installation speed * Cleaning Regime * Floor coating to green/damp concrete

Once the priorities are agreed and an idea of budget and service life is known, the type of floor finish can be selected. At this stage, whole life costing is an appropriate mechanism to assess the true value for money of various systems.

Good quality dry shake hardeners offer exceptional value for money in this analysis. They are dry powder blends of specially selected aggregates, cements, pigment and admixtures that are sprinkled into the surface of wet concrete before powerfloating. Once floated, finished and cured it offers an exceptionally durable surface or 'armour plating' to the concrete.

All Sikafloor dry shakes will act as fibre suppressants (to stop the steel fibres protruding through the concrete surface) and offer degrees of improvement to surface wear characteristics.

The differentiation of one dry shake from another is important, as performance and cost vary considerably depending upon their make up. As ever, generic specification of ‘dry shake’ will tend towards the lower quality and quantity of material.

There are three broad categories for dry shakes that are based upon the aggregate fraction of the material. Even within these categories there is clear differentiation between the performance of specific materials.

• Natural Mineral • Synthetic mineral • Metallic or alloy

In comparing aggregate quality used for such floorings, the most commonly used parameters are hardness, measured on the Moh’s Scale [1 (chalk)- 10 (diamond)], AAV (aggregate abrasion value) and PSV (polished stone value).

In the FerroSilicon material Sikafloor-1 MetalTop, which is in essence a metallic titanium containing alloy with complex bonded iron (i.e. not free to oxidise/rust) you achieve an extremely dense material with exceptional abrasion resistance and hardness. This metal is produced as a byproduct of the arc furnace process. This provides a floor that will outlast the rest of the structure.

In the FerroSilicate [note how it sounds very similar] material Sikafloor-2 SynTop, you have a synthetic mineral containing complex bonded metal oxides, which offers good abrasion and hardness values. These materials, a by-product of copper production, are more readily available and as such offer good performance with a lower cost.

Curing

Once applied and floated, it is imperative that curing is timely and efficient. For this the application of acrylic, resin based curing, hardening and sealing liquid compounds such as Sikafloor-ProSeal is necessary.

The application must be immediate and helps prevent rapid drying out of the floor and limit the associated shrinkage, cracking and curling. The guidance of BS 8110: Part 1: 1997 on curing should be observed and the slab protected from strong drying winds and extremes of temperature.

The everlasting floor

Far from being a proverbial holy grail it is possible to specify and have installed a floor which lasts with the building and requires little or no maintenance other than a good cleaning regime.

The use of the high quality materials such as MetalTop, is now being seen as cost effective, as developers switch strategy to one of leasing space and

footing maintenance bills directly. On a 50 000m2 project the increase in build cost is potentially some £200 000 for the enhanced performance, but with floor repair bills starting at £40/m2, only 10% of the floor area being repaired over the coming years will eat up this same money, and still the repairs will not offer the order of durability.

A recent example where we have been consulted to examine repair options for a distribution centre in the West of England, now has the owner facing repairs to 8000m2 of floor every four to five years at a budgeted cost of some £64 000 each time.

The facility is only five years old and the original dry shake topping has worn through on the aisles. The topping was an inferior material, applied at the minimum thickness, in the absence of a performance specification.

Compared with the initial outlay of a similar sum to achieve a 25 year maintenance free life using a metal alloy topping, the argument to install the best is compelling.

Future

As more people appreciate the advantages, it is clear that the use of dry shake flooring can expand. The possibilities to exploit the extreme cost effectiveness and durability could prove good partners for increased use in the commercial world. The use of Sikafloor-1 MetalTop as a polished ultra tough floor is seen as desirable for its aesthetics as well as its ‘indestructible’ mechanical properties and thence added value.

More articles from Sika Limited: