If the substrate is porous, so that CO2 gas generation can also occur within its pores, the cleaning may not be abrasion free. With porous substrates the deciding factor is the strength of the material. A porous sintered metal will withstand the gas generation, but a friable material like soft wood or plaster will not. Also, composite materials will show differing effects. For example the talc will be leached out of the surface of talc filled plastic leaving the surface roughened, whilst the same plastic without the talc, will clean without damage.
Which surface deposits are hard to remove?
If the solid dry ice particles find it difficult to penetrate the layer that should be removed, cleaning will be very slow or impossible. Typical materials that are hard to penetrate are oven cured paints or enamels and elastic materials commonly used as sealants. Dry ice cleaning is generally slower than an abrasive process on many materials and cannot create any specific surface finish or standard, e.g. SA 2.5.
Can dry ice remove rust from steel?
Physically bonded rust will be removed from steel, but the underlying chemically etched surface created by the rusting process will not be changed, leaving the steel surface clean but still pitted.
What about corrosion?
The same applies to corroded materials, for example, oil, grease and road dirt can be removed from an Aluminium engine block, but the corroded areas, generally caused by road salt, can still be identified after cleaning.
Can Dry Ice remove paint from brickwork?
If the paint is soft and flaky it will be easy to remove with only minimal damage to the brickwork, even if the bricks are on the soft side. However, if the paint is tough and well adhered to the brickwork, but the bricks are softer than the paint skin then the power required to break the paint away will also damage the bricks. Having said this, the same will apply to any other form of blasting technique, and when blasting brick or stone it should always be remembered that these materials, especially when old, are rarely of consistent hardness.