It is the temperature to which a volume of air must be cooled in order to reach saturation. The dew-point temperature is the temperature at which moisture will begin to form on a steel surface. Therefore, it is important to check the specifications of the coating. Some coatings, however, require moisture to cure. For this reason, the maximum RH at which coatings or linings can be applied and cured is generally set at 85%. Therefore, high RH can retard the rate of solvent evaporation. Moisture-laden air cannot hold as much solvent as dry air. Relative Humidity (%RH)Ĭure rates are directly affected by RH-the amount of moisture in the air expressed as a percentage of the total amount (saturation) possible at a given temperature. A surface that is too hot may cause the coating solvents to evaporate so fast that application is difficult, blistering takes place, or a porous film results. The maximum surface temperature for coating application is typically 125✯ (50✬) unless clearly specified otherwise. Paint specifications may further state that painting should not be undertaken when the temperature is dropping and within 5✯ (3✬) of the lower limit. It may be as low as 0✯ (–18✬) for “cold-curing” one or two-component systems or 50✯ (10✬) for conventional two-component systems. The coating manufacturer should specify the maximum and minimum surface temperatures for applying a coating.ĪSTM D3276, “Standard Guide for Painting Inspectors (Metal Substrates),” 1 states that the minimum surface temperature for coating application is usually 40✯ (5✬). Application at incorrect temperatures can cause defects such as: blistering, pinholing, cratering, dry spray & mud cracking. Since surface temperature is often different from air temperature especially for work performed outside, both temperatures should be measured to avoid application problems should air or steel temperatures become too hot or too cold for satisfactory film formation. During the day, it absorbs heat and is usually warmer than the air temperature. At night, steel work usually radiates heat and is cooled below air temperature. The first parameters necessary to assess the risk of moisture formation on a substrate are the temperature of the surface to be prepared or coated and the temperature of the air near that surface. How do Environmental Conditions Affect Coating and Paint Performance? Air and Surface Temperatures Dew point temperature should be compared to the surface temperature to ensure the two are far enough apart that moisture formation is unlikely.Ĭareful observation of atmospheric conditions and a good understanding of their impact on the quality and long term health of coating and lining applications are important to all contractors and inspectors. Tests should be performed to calculate the dew-point temperature before, during and after the coating process. Rather than detect this moisture, instruments are used to help assess the risk of moisture forming in the first place. Light condensation on blasted surfaces can be difficult to observe. Trapped between a coating and a substrate, moisture will likely cause the applied system to fail prematurely. Moisture will cause unprotected steel to rust. Moisture forms on a surface when warmer, moist air comes into contact with it-a process called condensation. Less understood is the impact surface moisture has on the life and performance of materials. It is commonly known that most coatings will not dry properly at low temperatures and high relative humidity (RH). The difference between the surface and dew point temperatures.A variety of instruments are available to measure the five conditions that should be observed and tracked: Surface preparation and the application of coatings and linings should be performed under optimum environmental conditions to help prevent failures. It also covers several mechanical and electronic measuring devices and discusses proper use of each instrument. This article presents the five environmental conditions that should be observed and measured and the effect each condition has on a successful job. Optimal environmental conditions are essential for surface preparation, application, and curing of coatings and linings to maximize successful performance. Why is it Important to Measure Environmental Conditions before the Application of Paints and Coatings? David Beamish, DeFelsko Corporation Originally published in: Materials Performance (February, 2004) Coatings & Linings Section Updated: October, 2021
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |