Gulf Construction Online - Guide to keeping GRC products competitive

GRC

Guide to keeping GRC products competitive

Iain D Peter, a technical consultant working with UK-based GRC machinery manufacturer Power-Sprays and material supplier Fibre Technologies International, looks at effective ways of keeping the production costs down of GRC products.

01 MARCH 2001

GRC has proved to be a wonderful material in the Gulf for a whole range of applications but just as the people were receptive to the introduction of GRC, so they are constantly looking at new materials.

GRC manufacturers must be alert not only to threats from other materials but also from imported GRC products from lower-wage economies.

GRC products can be kept competitive by controlling costs at all stages in the design, manufacturing and erection process. Potential savings at the design and detailing stage are often overlooked. The designer must understand the manufacturing process and take it into account. He should visit the production site to see the manufacturing process.

Often, splitting or even joining panels can make production easier. He should try to minimise the number of moulds required when considering panel layout and detail fixing systems that are practical.

The premix process is much less labour-intensive and can be suitable for many smaller products with some redesign.

Major cost

One of the major areas which have a bearing on cost is, obviously, raw materials and here it is advisable to buy the best and control their usage. Buying cheaper materials is false economy - cheap polymers and plasticisers are often diluted and require a larger dose. There is no advantage in buying a cheap glassfibre if it regularly blocks the spray gun, causing wastage and downtime or the last kilogramme collapses in the package and is unusable.

Cheap concreting sands are rarely suitable for GRC production. By the time the oversize is sieved out and the dust shaken out, it would have been cheaper to have bought properly-graded material. Sand only accounts for four to six per cent of the total raw material cost, so potential savings are small but equipment blockages caused by unsuitable sand can be very costly in production time.

Raw materials must not be wasted and costs can be controlled by eliminating storage waste by good stock control and rotation. Frequent stock checks should be carried out on materials in stock and compared to daily usage records.

Accurate control of the mixing process and control of the mixed material are also essential.

Bagged cement is prone to damage and deterioration whilst bulk cement is normally fresher and cheaper. Automatic weighing and dispensing systems fitted to silos allow bulk raw materials to be used and also ensure the correct quantity is used in every mix. Volumetric systems should be used for water, polymer and additives.

Fibre

Fibre is the most expensive raw material with the largest potential savings or losses. When used in the premix process, it should be accurately weighed or bought as roving and dispensed via a timed fibre chopper. In the spray process, the correct percentage of fibre should be maintained by frequent calibration checks verified by 'wash out' tests or using automatic fibre monitoring systems that are now available. These not only show the fibre usage per minute but also allow the accurate daily recording of total usage.

In the premix process, control of thickness and thus raw material usage is relatively straightforward but with a hand spray, the skill of the operator and the effectiveness of the checking process becomes paramount. If a 10 mm GRC skin thickness is required and 12 mm is sprayed, this is 20 per cent 'over usage'.

Obviously, some overthickness is unavoidable if the minimum design thickness is to be achieved and this should be recognised by the estimator. Regular thickness checks by quality assurance (QA) staff - independent of the spray team - and weighing of finished products are also advised.

Automatic or semi-automatic spray traverses lay down GRC very accurately and, when used in conjunction with a folding mould system, can be utilised for a range of products.

For a well-trained spray team, spraying a uniform thickness on a flat mould is relatively straightforward. Complex shapes and corners, where it is difficult to follow the mould profile, usually result in overthickness. The addition of stiffening ribs, fixings and lifting sockets add to the cost in terms of labour and materials. It can often take longer to add these than to initially spray the GRC skin.

The designer can play a big role here by designing the fixings and stiffeners with the manufacturer in mind.

Finishing

Finishing is the process of producing an architectural finish or the occasional repair of small defects or damage. If it is used to overcome poor production practice then labour costs will escalate. If damage regularly occurs on demoulding then redesign the mould. Consider using rubber for complex shapes and for 'cast in' blocks in timber or GRC moulds.

Stone-textured finishes are now very popular but they can be very expensive to produce.

Acid-etching is particularly time-consuming and is potentially hazardous without proper precautions. GRC has a very high cement content and when polymer is added it becomes more resistant to acid, needing a higher-strength acid and more applications.

Sandblasting, dry or wet, is much quicker but again Health and Safety regulations are strict. A cheap alternative is to use a textured mould, which can often produce an acceptable appearance with the minimum of post-treatment.

After producing a first-class panel, care should to taken during the handling, storage, transport and erection of it. Ensure there is a protected area on site to store panels. Repairing panels is skilled work and is expensive, avoid it.

If cost can be controlled, GRC products will continue to be competitive in the Gulf area but if costs are allowed to escalate, then GRC producers may find themselves losing out to other materials.