Thursday, October 1, 2009

Avoiding Touch-Up Problems

Paint touch-up can present problems at job sites due to common changes in environmental factors. In order to avoid such problems, temperature, surface porosity. time interval between applications, and the actual application method must be monitored.

An air or surface temperature difference of 110°F or greater between the last finish coat and the touch-up application can cause the touch-up coat to be a different color. This is especially true within the temperature range of 40°F— 60°F. Typically, if the touch- up is done at 10°F lower than the initial application, its appearance will be lighter in color. If the touch-up is done at 10°F warmer than the initial coat, the touch-tip will appear darker in color. At warmer temperatures, the phenomenon described above is not as predictable. The possibility of a touch-up problem still exists, but its cause may be related to other factors such as faster drying film and dry brushing.

HOW TO AVOID THIS: Touch-up work should be done under the same temperature conditions as the initial conditions. Always apply the paint when the ambient air and surface temperatures are above 50°F

Surface Porosity
Porous substrates can cause touch-up differences. both in color and degree of finish, particularly with high sheen eggshells and higher gloss finishes. An unprimed, porous substrate will absorb some of the paint’s vehicle, which results in a slightly lower sheen or gloss level. If a second topcoat is not applied to achieve the correct finish level, any subsequent touch-up will be noticeable, as it will show up higher in gloss or sheen. In this case, temperature makes no difference. A sheen and gloss difference will occur regardless.

Often, poor hiding is misdiagnosed as a color touch-up problem. if an unpainted, unprimed surface is coated with a clean white or transparent color, there may be some gaps in hiding the substrate. In order to provide the best hiding with these lightly toned colors, two topcoats are necessary. These should be applied over a primer sealer. If only one topcoat is applied and a subsequent touch-up is made, the color or sheen difference may stem from insufficient hide.

HOW TO AVOID THIS: Using a primer on porous substrates will provide the required sealing properties. In cases where a dramatic color change is taking place or a clean while or jewel tone color is being used. a pigmented primer will support and augment the hiding ability of the topcoat.

Time Interval
Time can affect how well a touch-up mark blends into the original job. Different types of paints have different final finish times. For example, alkyd based paints can sometimes take several weeks to reach their final appearance, while latexes get to this endpoint quickly. The higher the sheen and gloss, the longer the time required to completely dry and set. Certain ingredients in the paint are slow evaporators, and depending on temperature and humidity, need more time to escape from the film.
HOW TO AVOID THIS: Judge the true success of the touch-up application after a two week period.

Application Method
Touch-up problems will result when different applica­tion methods are used on the same job. A common example of this is when the initial application is done with an airless sprayer or roller and the touch-up is done with a brush. Here, the noticeable differences can be caused by variations in the paint film's profile.
The surface profile from a roller nap is obviously different from one made by a brush. When light reflects off these profiles, it will scatter the reflecting light rays differently, thus causing a color and/or sheen difference. This is why paint formulators use specific ingredients to increase the flow and leveling properties of a paint. Lastly, a touch-up mark can be noticed if there is a significant difference between the film thickness of the touch-up and the initial application. The physical difference in film thickness can cause an optical effect, particularly in higher-sheen finishes.

HOW TO AVOID THIS: Save some of the paint used at each job site for touch-up purposes. Touch-up with the same type of tools (e.g., the same size roller nap and same quality brush). In the case of an airless spray, spray some of the paint material through the gun and store for later use. When applying, do not use too much paint. Minimize the difference by lightly feathering out the touch-up with a short nap roller.
DO NOT 'dry brush' or 'dry roll'.

Other Preventative Steps
Is the finish of the selected topcoat the right finish for this job?
Long walls with light sources at either end are a touch-up nightmare.
So are walls with many surface imperfections.
For these cases, the best solution is to use a flatter finish which is more forgiving of surface and touch-up flaws.

For more information go to

Resource from Technical Bulletin. Benjamin Moore Paints.

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