When painting exterior trim, choosing the proper sheen is key. Satin and semi-gloss exterior paints will provide different levels of durability, ease of cleaning, dirt resistance and appearance. While exterior trim represents only a fraction of the surface of your house, it is designed to draw the eye and provide contrast to the body of the house, making it a more visible component than its surface area would suggest. There are several differences between satin and semi-gloss paint that should be considered before painting.
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Semi-gloss paint is more durable than satin paint due to a higher proportion of silica in the paint formulation. Semi-gloss paint is also much smoother than satin paint at a microscopic level, which reduces the effects of many sources of wear. If properly applied to a sound surface, semi-gloss paint will resist the effects of weathering and general wear and tear for longer than satin paint. This is especially important for trim, since the trim around windows and doors tends to see more wear than the main body of the house.
Semi-gloss paint also accumulates dirt and grime more slowly than satin paint due to the microscopic smoothness of the paint film. Satin paint's rougher paint film causes it to pick up particles of dirt, dust and grime more quickly than semigloss paint. This is an important consideration in dry, windy areas where dirt accumulates quickly on building exteriors. Note that some exterior paints are treated with chemical coatings which improve the ability of flat and satin finishes to resist dirt accumulation, which reduces semi-gloss paint's advantages in this area.
Ease of Cleaning
The combination of durability and smoothness make semi-gloss paint easier to clean. Accumulated dirt and grime can be washed away more easily if it is not being held by the rougher sheen of satin paint. The durability of semi-gloss paint means that it can be scrubbed more often than satin paint before beginning to show signs of wear. This is an important consideration for trim, since trim is washed and scrubbed more often than the body of most houses.
Semi-gloss paint produces a much shinier appearance than satin paint, which helps to increase the contrast between the trim and the body of the house and improve its visibility. If the trim of a house is meant to blend with the body rather than provide contrast, satin paint may be desirable, as it mimics the sheen of many forms of siding. A satin paint may also be desirable if the body of the house is painted with a flat sheen, as it will provide contrast without being distractingly shiny.