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Product Advisory

The Product Advisory section is intended to provide generic guidance on Corrosion Protection Products.

It is envisaged that the subjects below will serve as a source of reference for 3M™ Scotchkote™ Coating Specifiers and users enabling them to deal with many product issues/queries as and when they arise.

Please note that it is not intended to be relied upon for purposes of product specification and you should contact your sales representative or 3M Technical Centre if specification details are required. Because of the wide variety of processes and conditions in which these products may be used, the user should first carry out tests to determine the suitability of the products for the particular use intended.

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ISO 14001:2004 (pdf, 341KB)
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ISO 9001:2008 (pdf, 341KB)
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1.1 Temperature

It is recommended that all 3M Scotchkote Liquid Coating products are stored between 5°C (40°F) and 30°C (86°F). Storage temperature can affect all products however some products are more affected than others. Generally speaking solvent free (100% Solids) materials are not affected by temperature during storage but solvent based, water based and moisture cured products can all suffer adverse effects if exposed to excessive high or low temperatures.

Solvent based products, if exposed to high temperatures for a prolonged period of time can result in solvents vaporising causing a pressure build up in the can. This may be evident by a swollen container. Similarly amine vapours from solvent free epoxy Activators can also result in a pressurised container.

Water based products risk freezing if exposed to temperatures below 0°C(32°F). This could occur in a matter of hours depending on conditions and product. Once a water based product has frozen it will be unusable, even after thawing.

Moisture cured urethanes and other isocyanate containing products (polyurethane Activators) are affected by moisture which is more likely in humid environments. Moisture in the atmosphere can penetrate the container and will react with the isocyanate constituent and start polymerization. In the case of a moisture cured urethane this becomes evident once the tin is opened and a skin has formed on the top of the coating or in extreme cases the product is solid. A thin skin can carefully be removed and the product underneath should be fit for use. In the case of other isocyanates, traces of moisture can cause gassing which in turn may also result in swollen container with no detriment to product quality. In extreme cases this may result in hardening of the product. If in doubt contact the Technical Information Centre.

1.2 Shelflife

All 3M Scotchkote Liquid Coating products have a quoted shelf life, the time depends on the product. Products correctly stored, but outside the shelf life period should generally still be fit for purpose, however some settlement or thickening may have occurred. If in doubt contact the Technical Information Centre.

In can appearance

2.1 Viscosity

The viscosity of all products is dependant on the temperature, generally speaking the warmer the material is then the lower the viscosity (i.e. the product will appear “thinner”) this is particularly prevalent to solvent free epoxy resins.

2.2 Structure

During storage, or in some cases, shipping some products can develop a “false” body or structure and appear thicker. This “false” body will disappear when agitated, mixed or pressurised during airless spray application.

2.3 Colour

All products should have the colour clearly stated on the label. Some products are matched to particular standards (BS / RAL etc.) and some are even matched to a customers own requirements. However some colours have more generic names i.e. Light Grey, Red etc. It is important to understand that these colours are specific to a particular product and that these colours can differ from product to product. In addition, some products, in particular Solvent Free coatings and some floor coatings, are made using single or multiple pigments and are not tinted before packing. As result, these products are considered approximate shades and can differ from batch to batch. When using these “generic” shades, the applicator must ensure that all adjacent applications are from the same batch.

It should also be noted that generally the product in the can may be a different colour to when it has been applied and cured.

2.4 Settlement

Over a period of time settlement can occur, this is generally most evident in the base component of low viscosity solvent based or water based products. It is recommended all base components are thoroughly stirred prior to mixing.

Application and Curing

3.1 Environmental Conditions

The environmental conditions (temperature, humidity etc.) can have an effect on the ease of application, coverage rate and curing time and can have a detrimental effect on the appearance and performance of all coatings. The environmental constraints are always listed on the data sheet and this should always be taken into account before commencing any application. If two component products have been stored at low temperatures then mixing and application can be difficult, it can also be difficult to achieve recommended film thicknesses, curing will be slower as will over coating windows. Excessively high temperatures can cause products to “sag”, solvent boil (solvent evaporating too quickly leaving bubbles on the surface of the film), and can cause problems due to a shortened useable life. Ideally all products should be conditioned to 20 – 25°C(68-77°F) prior to application. The temperature of the substrate can also affect the application for similar reasons to those listed above.

It is recommended that all two component products are applied at temperatures above 5°C (40°F) otherwise adequate cross linking will be impaired.

Excessive humidity can also cause problems; if the relative humidity is high there is a risk of the dew point temperature approaching the substrate temperature with the potential for condensation forming on the substrate. A waterborne product (which relies on water evaporation for drying) will retain water which can lead to poor appearance and generally poor performance, plus the potential for flash rusting on iron and carbon steel surfaces (See also 4.2).

Applying solvent based products in confined spaces can, without correct ventilation, result in a solvent rich atmosphere which can retard drying leading to ‘sagging’ of the coating and solvent entrapment. A fan can help to create air movement to prevent a solvent rich atmosphere.

3.2 Opacity

Opacity means “hiding power”; generally speaking some colours have better opacity than others. Colours with poor opacity include yellow, orange and some bright shades of red. These colours may require extra coats, especially if applied over a contrasting colour. If in doubt always contact the Technical Information Centre.

3.3 Film Thickness

Typical dry film thickness are quoted on the data sheet for guidance , specific thickness to satisfy project requirements are detailed in the System Recommendation issued for the project. The final dry film thickness should be adhered to for a number of reasons, excessive thickness can cause runs, solvent entrapment, and of course can lead to excessive product been used on a project. Low dry film thickness can lead to poor opacity, subdued gloss levels, poor corrosion or chemical resistance and generally a premature breakdown in performance.

3.4 Gloss Level

Some 3M Scotchkote Liquid Coating products are supplied with a specified gloss level. Deviation from the recommended thinning requirements and dry film thickness can lead to a variation in gloss level. Environmental conditions during curing can also lead to subdued gloss (See also 3.1).

3.5 Coverage Rates

Estimating accurately the quantity of paint required for a particular application is complicated, since the theoretical coverage takes no account of the variable “losses” involved in converting paint in the can to a coating film on the chosen surfaces.

Many factors influence the actual practical coverage rate, these include:-

  • Surface porosity
  • Surface roughness
  • Surface and product temperatures
  • Application method
  • Shape of the surface to be coated
  • Applicator skill

Cured Appearance

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.

In Service Performance

5.1 Colour Stability

Epoxy coating systems are primarily functional rather than decorative will chalk when exposed to UV Light. This appears as a matting down of the gloss level, and an overall white powdery surface effect. This effect is purely aesthetic and is not detrimental to the long term corrosion protection of the coating system.

Where aesthetic appearance is important consideration should be given to the use of an appropriate top coat.

5.2 Effect of Chemicals

Chemical contact can result in discolouration at the surface of the coating material. This is not detrimental to the long term performance of the coating.