Frequently Asked Questions

How do I produce consistently coloured concrete products?

Pigments should be purchased from a reputable supplier to ensure consistent colour strength and shade from batch to batch.

In addition, using different base pigments, or varying the weight of pigment in your batch can create a wide spectrum of colour tones and shades. The amount of pigment added is usually expressed as a percentage (by weight) of the batch cement content. Cement, pigment, aggregates and admixtures must be measured into the mix accurately. Water must be metered accurately as the water-cement ratio will significantly affect the final colour of the product.

What is the maximum dosage of pigment in a concrete or mortar?

Every pigment has a colour saturation point, after which further increases in the dosage rate will fail to make an appreciable difference to the colour intensity of the final cementitious product.  Pigments with high tinting strength reach their saturation point at a lower dosage rate. For example, black iron oxides have the highest tinting strength, generally achieving saturation at 6 % dosage, on weight of cement. Brown iron oxides have a slightly lower tinting strength, levelling-off at approximately 7 % dosage, followed by 8 % for red grades and 9 % for yellow grades. However, these figures will vary significantly for different shades of each pigment type. The current European standard for pigments in cementitious products [BS EN 12878] requires that pigment dosage rates  be limited to a maximum of 10 % on weight of cement because the strength of your finished product could be reduced owing to the displacement of cement

How much pigment do I need to colour a cubic metre of concrete?

A typical concrete mix contains 350kg of cement per cubic metre, and therefore a 5% dosage of pigment by weight of cement would require 17.5kg of pigment per cubic metre of concrete.

The finished concrete surface is dusty how do I avoid this?

Dusting on the surface of concrete products is usually caused by too high a fines content and is most common when fine limestone aggregates are used. Reducing the amount of fines in the mix and using an appropriate super-plasticiser to allow a reduction in the water content should eliminate this problem.

The surface of the concrete is patchy or mottled. What is causing this?

In wet-cast concrete products, either over-vibration or too high a proportion of coarse aggregates in the mix can cause some of the aggregate to migrate to the surface resulting in a mottling effect. Other possible causes are an uneven application of mould oil and/or insufficient curing time allowed before mould stripping.

How do I reduce airborne dust when using pigments and stop my workplace and employees getting dirty?

Iron Oxide powders are classified as nuisance dusts but the level of airborne dust must be kept below 10 mg per m3  8 hour Time Weighted Average. This is best achieved by careful handling of the open pigment bag, and (if necessary) the use of local exhaust ventilation at the point of use. Careful disposal of the empty bag will also reduce the risk of small spillages.

Please see our safety data sheets for further details on the safe handling of our products.

Other ways to reduce or eliminate airborne dust include the following:

Please contact our Sales Department if you would like information on these alternative delivery forms