Pool contractors use metakaolin to "make
plaster more resistant to erosion and corrosive chemicals.
The white additive brightens plaster and improves workability
to reduce trowel bum and mottling.
While metakaolin should have no impact
on surface, applied coatings, special consideration must
be given when using penetrating stains, Paris explains. "Because
metakaolin increases the density of concrete, it may reduce
the ability of stain to penetrate the surface. In addition,
pozzolans consume some of the lime in concrete and can reduce
the ability of chemically active stains to react with lime
and develop their color."
David Kucera, president of David Kucera
Inc., Gardiner, N.Y., a fabricator of precast concrete ornamentation
and architectural cladding, points out a further tip on finishing
concrete with metakaolin. "Metakaolin makes my concrete
more resistant to acid rain, but it also makes it more difficult
to use an acid wash to expose the aggregate. I now have to
work twice as hard to remove the cement paste." He admits
that this is an ironic testimony to the effectiveness of
metakaolin in improving the density of concrete. On the other
hand, he says, metakaolin simplifies sandblasting. "Me
harder concrete makes it easier to keep an edge on a piece,
and comers don't get rounded off as easily.
