Metastar is a purpose-made pozzolanic additive of the metakaolin family. Its manufactured from selected kaolins (clays) which are refined and calcined under conditions designed to give optimum pozzolanic reactivity. Most other pozzolanic materials are by-products and may be highly variable in chemical composition e.g. pulverised fly ash (PFA) and ground granulated blast furnace slag (GBFS).

Metastar readily disperses in the mortar mix, and being hydrophilic it does not tend to form lumps. Its reactivity, determined using the Chapelle test, shows it combines with slightly less (90%) than its own weight of lime (calcium hydroxide) which makes it up to 10 times as reactive as GBFS and between 2 to 5 times as reactive as PFA. It typically reacts with the available calcium hydroxide within a fortnight at ambient temperature, forming cementitious compounds such as hydrated calcium silicates and gehlenite hydrate.

The effect of Metastar on the microstructure of the mortar mix may also be beneficial. Tests with cement/metastar based binders and limestone and granite aggregates show greater binder-aggregate bond strength, with suggested benefits from reduced thickness of the interfacial zone between binder and aggregate.

English Heritage:

As part of the Smeaton project to test various lime mortar mixes for their characteristics, mixes incorporating Metastar are being evaluated as part of the Phase III. Final publication of the data and conclusions are awaited.

Supplies:

We supply two variants of Metastar; 402 and 501 with similar reactivities. We hold substantial stocks for immediate delivery throughout the UK and abroad. Metastar is supplied in individual 25kg bags, or up to 48 bags per pallet.

Usage:

• external pointing - 8 -12% by volume (0.5 -1 bag of Metastar per tonne of lime putty mortar)
• rendering - 12 - 30% by volume (1 - 2.5 bags of Metastar per tonne of lime putty mortar)
• copings - 24 - 48% by volume (2 - 4 bags of Metastar per tonne of lime putty mortar)