Permaban’s Silver Birch Dryshake strives to be a success within the Construction Industry.

In response to market demand developments have occurred in materials available to achieve very light coloured floor surfaces for retail warehouses and for improved curing of dry shake and concrete power-trowelled floors. The testing, environmental and safety implications are discussed. 

Light Coloured Dry Shake Concrete Floors

A development prompted by one of our retail DIY warehouse customers has been to produce the new ultra-light coloured dry shake hardener (Silver Birch) for concrete floors. In a retail environment sales and business go better if the sales space has a light and airy "feel". The use of a very light coloured floor minimizes both the cost of lighting, energy usage and the environmental impact. Also dry shake coloured and hardened concrete floors are monolithic and ultra-durable. They have long maintenance-free lives requiring only routine housekeeping and we have examples of these dry shake floors still performing perfectly after more than 20 years in demanding environments.

Permaban have commissioned light reflectance testing of Silver Birch colour to the new (draft) BS 8493: 2008 Light Reflectance Value. Results are quoted on a scale from 0 to 100 where utter black is 0 and perfect white is 100. We can't achieve such a light colour with real concrete so the introduction of our "Perfect White" colour will have to wait! The average of 36 values achieved by a light coloured Natural dry shake was 33.50 and for Silver Birch was 50.97, an improvement of 52% in light reflectance. The introduction of Silver Birch to the floor would provide the end user with a reduced lighting level requirement and consequently reduced electricity cost

Following the development work, the recently opened B&Q Flagship store at New Malden, Surrey (see photo nos.1 & 2 - exterior and interior of this store), had floors installed by Stuarts Industrial Flooring under main contractor Simons Construction. The concrete floor surface was hardened and coloured by Permashake Quartz Silver Birch. The project also used another Permaban material, Aquacure, which had been developed to assist our retail DIY warehouse customers to improve the carbon footprint of new stores and also to reduce the incidence of surface crazing.

Crazing

The process of repeat power-trowelling a concrete floor is highly beneficial to the properties and performance of the floor surface. The vast majority of high-performance concrete floors these days are constructed with repeat power-trowelled surfaces and this will surely continue to be the case.

High surface temperatures are created during the final trowelling operation at a time when the slab itself is beginning to generate heat through the cement hydration. This causes the surface to lack moisture. Once the conventional (solvent dispersed) acrylic curing agent is applied this lack of moisture will be compensated by moisture rising from within the depth of the slab.

Crazing is a network of visible cracks. These are not considered to have structural significance, have minimal depth but are visually unattractive. Deryk Simpson and Neil Watson of The Concrete Society have discussed this effect ("Concrete" September Issue 2002). They suggest a number of factors contributing to the incidence of crazing but were of the opinion that curing was only a minor factor. They did however say that the "predominant mechanism is drying shrinkage". 

Our customers operating retail warehouses had asked for assistance to reduce or eliminate the occurrence of surface crazing in their floors and Permaban developed this new type of acrylic curing agent in 2007. Aquacure is spray-applied, quick drying, high efficiency curing agent and imparts a sheen to the floor surface. It also comprises 50% more acrylic resin, and in this case, as an emulsion dispersed in water. We have formulated this product so that the water content will have a beneficial effect on the tendency of power-trowelled concrete floors to show crazing. This material has been used for over a year now and we have observed no significant crazing on the floor slabs. In fact we have now re-written our specifications to call up Aquacure for curing all our coloured and natural dry shake floor hardeners.

Permaban's recent experience is that applying this high efficiency water-based curing agent immediately after finishing does seem to eliminate crazing. We conclude at the moment that this is because one is applying water (the acrylic/water emulsion) to the surface at this very early age, ensuring it doesn't lack moisture, and of course achieving thereafter of good curing conditions. We suggest that concrete needs moisture at all stages to cure properly and the temporary lack of moisture at the surface cause a danger of surface crazing. Rising moisture under a curing membrane continues for many months but may not prevent the effects of the initial lack of moisture in the very top surface becoming apparent in due course.

Environmental Factors

The use of water-based high efficiency non-silicate curing agent has reduced emissions resulting from the construction process and thereby improved the carbon footprint.

There are also safety and transport advantages of this approach and the construction of concrete floors in building extensions need not cause the employees in the buildings to be evacuated on account of solvent smells.

Curing agents for power-trowelled concrete floors are usually spray applied late at night and sometimes in poor visibility. It has long been felt that it would be helpful if the curing agent would be light coloured to ensure no areas are missed. By using a water/acrylic emulsion this is achieved (the liquid sprayed being a milky white emulsion) and the surface dries, in an hour typically, to a clear resin membrane similar in appearance to the solvent-based acrylic.

This article has shown how some recent developments have assisted retail clients to make atmospheric and environmental improvements at low cost. We always recommend new clients considering dry shake should view the actual colours under consideration in service elsewhere.   It should be remembered that lighter coloured dry shakes do make more demands on the workmanship and practice - e.g. steady and consistent concrete supply rate and quality become more critical. High efficiency water-based acrylic spray applied curing membrane is now available and this also reduced the incidence of surface crazing.