About Sub-Tropical Testing Service's Exposure Testing Program

Selecting a Test Facility

Outdoor or Natural Weathering Exposure Rack

There are many factors to consider when selecting a weathering test station to conduct your test program. It is important to know what to look for when considering which test site to trust with your valuable test specimens.
Location: The test site must be located in a clean pollution free area within the geoclimatic region to be used. This is important for the prevention of unnatural effects on the specimens.
Location: Within the local area chosen, there must be no isolated sources of pollution or deleterious atmospheric contamination. This could result from construction, emissions from a manufacturing plant, or chemical spraying in farming areas.
Location: The layout of the test field itself is very important. The characteristic manner of the test field will be determined by the location of the surrounding area. For example, if the field is enclosed by trees, the test area will be affected by mildew spores, lower sunlight levels, and possible lower temperatures. If the field is on low land and poorly drained it will flood in times of heavy rainfall, humidity will be higher, algae growth, and dirt attachment will increase.
Maintenance:The exposure maintenance program followed by the test site will also play a major role in determining the accuracy of testing. It is important for the specimens on the test racks to be correctly maintained. This involves ensuring the correct mounting method, and constant follow-up attention to maintain the quality. The racks themselves are in contact with the specimens. The racks must be cleaned regularly to remove any dirt, mildew, or algae which would otherwise contaminate the specimens.
The selection of the test site should be based upon all of the above factors. This is what will determine the success of the weathering program. When selecting your weathering station consider the following:
Sub-Tropical is located in a clean residential neighborhood atop green grass covering a coral rock base, providing excellent drainage.Our racks are sparkling clean and we offer the finest hurricane protection plan for your valuable specimens. You can trust your test program to Sub-Tropical. We have been in business since 1929. Sub-Tropical is committed to providing you top quality exposure testing and services. We invite you to visit our test site.
TYPES OF EXPOSURE TESTING:
All of our test sites offer direct weathering, black box, and under glass exposures. Our Miami, Florida site also provides a tropical forest simulation. All these exposure types are available at any required angle of exposure and facing direction.

Direct Weathering

	For direct exposure the specimen is mounted on the exposure frame open backed or solid backed, and subject to all atmospheric effects. This type can be used at a number of exposure angles. The standard angles used are 45, 5, and 90 degrees, or an angle equal to the latitude at the location of exposure. (All angles are referenced from a horizontal angle being 0 degrees). The angle chosen should be one that matches as closely as possible the position of the end use of the material. In addition to the choice of exposure angle, the racks can be adjusted through 360 degrees of rotation in order to face any direction. To maximize solar radiation accumulation, the racks are normally positioned to face the equator. The standard racks used by Sub-Tropical Testing are designed to hold the specimen firmly in place while providing a mask area over the top portion of the specimen. If controls are not available this area can be used for visual comparison of the changes occuring on the specimen.The racks are made of anodized aluminum, which is an inert material, and will not cause any contact corrosion effect. Our racks are cleaned on a regular basis to remove mildew and algae, which would otherwise contaminate the specimen, and affect the test result.


Black Box Weathering

	The black box exposure is used primarily to recreate the exposure conditions of the horizontal surfaces of an automobile. The "box" creates an enclosed air space beneath the panels which form the top surface of the box. The modified environment is similar to that of a parked automobile. The black box can be used at a number of exposure angles. However, for automotive testing, the black box is usually placed at 5 degrees. The box is made of aluminum, painted black, with the test panels forming the top surface. The black box also serves to lower the panel temperature overnight below that of the surrounding air, creating a longer condensation period.

Tropical Forest Weathering

	The Tropical Forest is a localized micro-environment that accelerates fungal and algae growth at a significantly faster rate than standard outdoor weathering. Since microbial resistance of paint and paint films is a very important characteristic of such paints, considerable attention has been given in developing a field test that provides the optimal conditions for the accelerated growth of mildew and algae. In turn, companies that need to test their algicides and fungicides in paint and paint films, can do so in a much shorter period of time. The following brief description of our Tropical Forest site will enable you to understand how we can accelerate microbial growth. Specimens are exposed on a standard aluminum frame with a vertical North orientation. Specimens should ideally have a wood or styrofoam substrate that will also allow for water capillary action from the sample sitting on the test rack. Once the specimens are on exposure, the micro-environment has a natural canopy of native foliage that surrounds the test specimens allowing only shaded light and lower ambient temperatures throughout the day and night hours. In addition, the forest area has a built-in overhead waterspray three times per day that significantly increases the time of wetness on a specimen while also increasing the surrounding humidity to a near constant 100% during the summer months. Since the inception of our Tropical Forest site a few years ago, we now have an area that is green with algae covering tree limbs, surrounding rocks, and our test racks. In essence, we have what we consider ideal conditions for testing the biological deterioration of paint films. In conclusion, we strongly recommend this type of outdoor weathering for companies that are testing for microbial resistance. Exposure time has been dramatically reduced, which leads to lower exposure costs, and real-time results that you can depend on.

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Under Glass Weathering

	This exposure technique places the specimen behind a glass covered frame, protecting the specimens from any direct rainfall. The solar transmittance properties of the glass filter out a significant amount of the harmful ultraviolet. This method is used to test interior materials.