Mould Oils for High Quality Precast

WHY MOULD OILS?

The surface finish of concrete structures and products is a major quality measure. Voids (“bug holes”) at the surface are unsightly and reduce the “value”.

They lower the value of the finished product and can be expensive to remedy. If coatings are to be applied the holes will require filling to avoid blistering of the coating. Crete Lease products are a new type of mould release agent that contains hydrophobic and hydrophilic surfactants (surface active agents). By combining the ease of release of an oil with the finish performance of a water based release agent (Crete Lease 20-VOC) it is the ideal material for all formwork types where a high quality finish is required.

Mechanism of Air/Water Void Reduction

The air/water bubble is formed at the interface of the concrete and release agent. Hence, “bug holes” can be reduced by either:- using an oil with a hydrophilic surface (CL880 and CL20) or improvement of the mix designer water or air causes the bugholes. In addition excess release agents also produce bugholes…the very small ones. The ones the size of a pencil eraser and smaller. Bugholes larger than that are a mixture design or mixing or vibrating problem. Good vibration along with properly applied Crete-Lease contribute to much or all of the bughole reduction.

Release Agent

Conventional oil is commonly and efficiently used as a mould release agent. Unfortunately, oil is hydrophobic while the fresh concrete is hydrophilic. Cresset uses some hydrophilic double action surfactant in the oil containing release agents. This is why the oil based Crete-Leases also effectively diminish bugholes.

The surfactants in 20-VOC and Crete Lease 880 make a hydrophilic layer on the surface of the release agents oil layer.

Superplasticiser

The extent to which a bubble forms is dependent on the difference in the surface tension of the concrete and the release agent. The surface tension of concrete with conventional superplasticiser is 70Dyne/cm2. Using superplasticiser this is reduced to 30Dyne/cm2, about the same as the surface tension of an oil mould release agent. This virtual elimination of the barrier is why Cresset products work so well.

All Crete Lease® Release Agents:

  • Are non-toxic, non-flammable and biodegradable.
  • Increase surface durability.
  • Apply easily even at temperature extremes.
  • Promote clean stripping and stain-free surfaces.
  • Eliminate concrete build-up.
  • Cut labour costs of form clean up.

Cresset Concrete Standards