Oxides - FAQ

Boral Oxides - FAQ
Q: How much oxide do I require?
A:   Total amount of cement in the mix will determine the amount of oxide required. As an example, a typical 25MPa concrete may require 15Kg of oxide for approximately 5% oxide by weight of cement or cement plus Flyash. This may give a mid-range colour intensity, with the dose of oxide recommended range from 1% to a maximum of 10% by weight of binder content. We would recommend doing a trial to determine the desired oxide content.
Q :  Can I get more oxide colours?
A: Yes there are a multitude of colours available (Refer to our oxide colour chart» available on this web site). Different shades of these colours can be achieved by adjusting the % of oxide used in mix design.

Varying colours can also be achieved using Grey Cement, Off White Cement or White Cement.

Generally darker colours use Grey Cement but if trying to achieve pastel colours, Off White Cement or White Cement would be more suitable.
Q : Is it possible to dust/sprinkle oxide onto wet concrete and rub in instead of mixing through the entire mix?
A: It is possible to do this, but it requires considerable experience and may be done by an experienced tradesman, who would normally dilute the oxide with cement or a similar material to ensure that a durable and even colour is produced. Patchy and loose surface may result from uneven or careless application of oxide directly onto freshly placed concrete.
Q:  If I use the dust/sprinkle method, do I need to seal the concrete?
A: Yes, it would be in your interest to apply a suitable concrete sealer such as Blue Circle Slate-N-Stone Sealer.

The dusting/sprinkle method only has the oxide colour millimetres below the surface and if a sealer is not applied,

      (a) Oxide colour may come off particularly in wet weather, causing you to walk colour
            throughout various parts of the home etc.

      (b) The colour may also rub off in main traffic areas leaving the grey colour of the concrete.

The sealer will need to be refurbished at some stage depending on the intensity of foot or vehicle traffic.

Note that in some cases in heavy traffic areas the sealer will not stop the oxide from being rubbed off.
Q:  Can I obtain oxides in larger quantities?
A: Yes, oxides are sold in varying pack sizes.The standard colours come in handy pack 500g containers  up to 4kg as well as 20 to 25kg bags.

Other colours are also available but these are supplied in 20 to 25kg bags.
Q :  Do oxides fade?
A: Oxides do not fade but some may gradually change their appearance due to weathering of the surface of the concrete or mortar and the deposition of dirt and grime. If efflorescence develops on the surface, the oxide will appear dull and lighter in colour.
Q:  Can I mix different oxide colours to get a special colour?
A: Yes, but we suggest that you should first examine the range of existing colours available, as small variations in proportioning and mixing of your own colour will result in colour variability that cannot be easily detected. Readily obtained colours like Sandstone, Terracotta, Tuscany and others are consistent from batch to batch. Speak with your local supplier about the colour you have in mind and you may find a similar colour is already available.
Q: Why does Yellow oxide appear to be a green shade when dried in concrete or mortar mix that has grey cement?
A: The green hue from the cement tends to envelope the oxide to give the yellow oxide a yellowish green colour/shade.

It is suggested that if a cleaner yellow colour is required - Blue Circle Off White Cement or even Blue Circle Southern White Cement be considered in your mix design.
Q:  How do I remove salt bloom/efflorescence?
A: Salt bloom and efflorescence can visibly affect coloured surfaces if the surface is overworked or too much water is used in the process. Impurities from the sand or aggregates and hydrated lime from the cement can travel to the surface, leaving a patchy whitish appearance. Although it may disappear in time, it is possible to remove the deposit by carefully applying and washing off a dilute Hydrochloric (Muriatic Acid, Spirit of Salts) acid solution. Apply a solution of one part Hydrochloric acid to 30 parts water, lightly brush and wash off fully. In obstinate cases a somewhat more concentrated solution can be used, but never so concentrated as to remove any oxide from the surface.

Observe the necessary precautions when using acids and remove all traces from the surface and finally mop the surface dry. Repeat with care if necessary. Note, Chloride residues from acid can cause rusting or corrosion in metals.
Q:  Are oxides dangerous/toxic?
A: Oxides used to colour cement-based products are harmless very fine non-toxic powders. Care must be taken to avoid breathing in any dust, including oxides, and eye protection should be used. Oxides should not be disposed into water systems as they will produce a long-lasting visual pollutant if not set hard with cement.