4.1 Effects of Environmental Conditions
Amine bloom/ blush – solvent free epoxies are prone to amine bloom – a surface effect caused by moisture in the atmosphere reacting with uncured amine in the surface. This causes a ‘sticky’ layer on the surface. Depending on the final use of the coating, if for example drinking water, this should be removed before going into service. It can be removed by warm water and mild detergent washing. The bloom must also be removed if the surface is to be overcoated to ensure good intercoat adhesion.
Amine bloom can also result in a whitening of the surface (carbamation), particularly noticeable on dark colours. This is caused by the ambient conditions during curing going outside the recommendations – i.e. high humidity, low temperature and moisture. This is purely a cosmetic effect, and causes no reduction in the long term corrosion properties of the coating.
4.2 Solvent / Water Retention
If waterborne products are applied and left to cure in highly humid conditions, the atmosphere is saturated with water, and the water in the coating cannot escape. The result of this can be retarded cure of the coating, as well as the potential for flash rusting on carbon steel or iron substrates.(See also 3.1)
If the solvent in solvent based coatings is restricted from leaving the coating during cure, the gloss level can be affected. If the coating has been cured with high temperature or by heating too quickly, the coating will skin over and the solvent will not be able to leave. This results in fine blisters appearing on the surface – an effect called solvent boil.
4.3 Substrate Porosity
On porous substrates, material will be absorbed into the substrate. This will reduce the overall applied thickness, which can also affect the gloss level and the colour. The wet film thickness will not correlate to the dry film thickness.
4.4 Variation between Wet & Dry Colour
Waterborne colours can show a ‘whiter / milkier’ appearance when wet compared to the dry colour. This is caused by the emulsion within waterborne coatings, which is white when wet, and then dries clear as the water evaporates.
In the wet film the product may appear to give adequate opacity, but then can dry to give reduced opacity.
4.5 Effect of Age on Materials
Age can have various effects on final material appearance.
Semi gloss finishes will generally show an increase in the final gloss level.
Amine based Activators can darken with age to a deep red/brown colour, which, dependent on the colour of the Base, may affect the colour of the applied material.
4.6 Effect of Thickness on Low Gloss Products
If using a matt product as a clear coating / sealer, care must be taken to apply the coating at the correct thickness. The matting agents increase opacity resulting in a white appearance when higher film builds are applied – typically in overlap areas.
For semi-gloss pigmented products, variance in applied film thickness will result in gloss level variation.
4.7 Batch to Batch Colour Variation
Depending on the type of product, Colour will be matched by eye or by colour computer. The requirement is to match within an acceptable tolerance to an established standard. It is entirely possible that two batches both matched to the standard can show a variation to each other. For this reason, it is good practice to use one batch of colour for one application – very much like using one batch of wall paper for one room.
Where practical conditions dictate that the use of multiple batches is required, batches should be segregated so that only material from the same batch is used on areas which have defined boundaries such as expansion joints, doorways etc.
For smaller applications where the only available product is from different batches then it is possible to blend the bases together and re-fill prior to mixing and coating to ensure colour uniformity, for larger applications where two equal sized batches are supplied it is also possible to blend two units (one from each batch) at the time of mixing. This will also ensure colour uniformity.
4.8 Implications for Different Colours
Certain colours, particularly yellows and bright reds, have reduced opacity / coverage than others. Care should also be taken when overcoating dark backgrounds with these colours, as well as some pastel shades including white.