Advice and answers from Blue Circle products

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Frequently Asked Questions

What cement should I use to level the floor under my garage door?

You want a high strength cement that will resist abrasion and trafficking. The best option would be a Portland cement (CEM I) such as Blue Circle Procem. Make sure that you keep it moist for a few days after placing so that it develops its full potential strength.

What cement should I use for concrete directly exposed to sea water?

A Portland-fly ash cement such as Blue Circle Sulfacrete is a good choice for concrete in these circumstances (look for the designation CEM II/B-V +SR) as it get progressively more impermeable with time and has a greater chemical resistance to the chlorides present in sea water. Sea water does not significantly attack good quality concrete, but it can cause rusting of any embedded metal which may eventually crack the concrete. Concrete exposed to sea water should always have a low water/cement ratio (below 0.55), high strength (C30 or above) and must be properly cured in order to develop its full resistance to seawater penetration. For reinforced structural concrete seek specialist advice.

Removal of stains from slabs?

Obviously, it is better not to stain slabs in the first place, but if staining occurs then there are several solutions. Ideally the stain should be removed as soon as possible by extensive flushing and scrubbing of the affected area. If this is not possible to remove immediately, then physical abrasion or a mild brick cleaning acid may be required to remove. These can sometimes do more harm than good to the slab as they may have to be excessively strong to remove the stain and hence a small trial area is recommended. In general, the longer the stain is left before treatment, the harder it will be to remove.

Concrete or mortar is dry so why is it not strong?

The cement in concrete and mortar hardens by a chemical reaction with water so if there is no water present then essentially no further strength development will occur. It is thus vital that the mix is kept in a moist condition for the first few days after it has set.
Common causes of moisture loss from exposed concrete or mortar surfaces are: high ambient temperatures, exposure to direct sunlight, drying winds and excessive suction of moisture by surrounding porous materials.
Common prevention methods are to cover with damp hessian and/or plastic sheeting (being sure that this does not mark the concrete) to prevent evaporation, prewetting of surrounding porous materials, misting (for use especially with mortars and renders) with light water spray at regular intervals and pooling water on horizontal surfaces.

What is lime bloom and how can I prevent/remove it?

Lime Bloom is a crystalline or powdery deposit that forms on the surface of cement based products and brickwork. It is normally white in colour. Efflorescence occurs when soluble salts in the concrete, mortar, render or brickwork come into contact with the atmosphere. As the construction dries out, water dissolves the soluble salts, carrying them in solution to the surface where they are deposited when the water evaporates. It tends to form predominantly in cold, damp conditions.
Although efflorescence is unsightly, it is not usually harmful to the concrete or masonry and can normally be removed by stiff brushing or in severe cases a mild brick cleaning acid.

How much water should I use for Blue Circle Postcrete and can I put the Postcrete in before the water?

Blue Circle Postcrete should be used as per the method on the bag. Fill the hole one third with clean water and add the Postcrete on top of the water. Allow 5-10 minutes for the initial set. You will be able to hang a fence panel in as little as 10 minutes!