Constructed out of a gypsum-based core with a paper coating on all sides, drywall is the most common interior wall surfacing material used in modern construction. Despite its prevalence in the construction industry, achieving a uniform and even finish when painting new drywall can prove challenging. While the painter may appear responsible for an uneven or patchy finish, these defects can often be attributed to how the drywall was prepared.
Why does this happen?:
One of the reasons an even and uniform finish is so difficult to achieve when painting new drywall is due to the variance in texture and porosity between the paper coating and joint filling compounds. The paper coating is less porous and therefore will absorb paint at a slower rate than the filler compound, resulting in an uneven finish.
Using a high quality latex primer sealer will help to offset this difference in porosity by sealing the more porous surface joint filling compound and the less porous paper surface. This provides a continuously sealed surface with relatively uniform porosity and is the first step required to accomplish an even and smooth finish on new drywall.
The Importance of Primer Sealer and Surface Defects:
Although minimizing the variance in porosity is the first step in ensuring an even finish when painting drywall, it often is not the last step. This is because defects in drywall can be very difficult to detect until the prime-coat is applied. This occurs because greater light reflectance tends to make surface defects more noticeable and thus the uncoated drywall may have small surface flaws that are practically invisible until some coating is applied.
Addressing Drywall Defects Before Moving Forward:
Even with a thorough review of the unpainted drywall surface, it is quite common for “new” surface defects to become visible after the prime-coat has been applied.
The next step from here is to call the drywall contractor back onto the jobsite to repair and fill any deficiencies in the substrate. Once repaired, the painting contractor will spot-prime these areas before scuff-sanding the prime-coat in order to prepare the surface for the application of the intermediate coat. Ideally, this would be the final step before scuff-sanding the intermediate coat and applying the final finish coat; however, this is not always the case.
How Lighting and Temperature Affect Drywall Finishes:
Often, when painting work on new drywall commences, the lighting and heating systems of the finished project have yet to be installed. As the project moves forward, these systems are set up, both of which can impact the appearance of the drywall.
Improved lighting makes surface defects in the drywall much easier to see (as well as the application of a higher sheen intermediate coat), and changing the temperature of the exposure environment causes movement in the walls and seams, creating additional defects. These newly identified surface irregularities will be need to be repaired by the drywall contractor. The painting contractor is only liable for surface defects found AFTER the applying the finish coat, however the scenario above highlights how difficult achieving a quality, uniform finish when painting new drywall is. Perhaps the worst part of the scenario described above relates to what happens when drywall repairs are made after the intermediate coat.
Why Consistent Coating Application Matters:
To achieve a smooth uniform appearance in a typical 3-coat system, each coat must be applied over a level and even surface. In the scenario mentioned above, one wall could consist of the following combinations of coatings and filler:
- Drywall, Sealer, Intermediate Coat
- Drywall, Filler, Sealer, Intermediate Coat
- Drywall, Sealer, Filler, Sealer, Intermediate Coat
- Drywall, Filler, Sealer, Intermediate Coat, Filler, Sealer, Intermediate Coat
If coating combination A were to appear directly beside coating combination D, the variance in texture would not create a visible profile to the naked eye; however, it would definitely give the wall a blotchy, patchy appearance as if the wall was painted with the 2 different batches of the same product. The variance in surface texture created by applying uneven layers of filler, sealer and intermediate coat across an entire wall is what causes the inconsistent appearance of the finish.
At this point, the painter would apply the final coat to the drywall; however, the final appearance will still be uneven and patchy (assuming the painter had done a perfect job). The only remedial action the painter can take is to apply additional coats to level off the surface; which, given the variance in surface texture, could take significantly more coats.
The Role of Dried Film Thickness and Application Errors:
Although these defects and flaws will look like application errors, the reality is that these defects have nothing to do with the quality of paint or application methods used. Paint alone cannot fill these defects and level the surface. Because the dried film thickness (DFT) of a single coat of conventional latex is roughly 1/3 the thickness of a 5-dollar bill (1-2 mils), it is impossible for these defects to be masked or filled by a single coat.
How to Avoid this Problem:
One solution that could have been used is for the specifier to require an ASTM Level 5 Drywall Finish, which requires the entire surface of the wall to be coated with a thin skim-coat of drywall compound to create a smooth and level surface. It is important to note that although a Level 5 finish will produce consistently better results than a Level 4 finish, it does not guarantee a defect free surface in critical lighting conditions.
Seeing as a Level 5 finish is not commonly specified, all parties involved in the project should be aware that all drywall repairs should be made before the intermediate coat is applied. Only small minor repairs like dents or scratches from moving furniture/equipment should be made after the intermediate coat is applied. Additionally, the interior temperature of the building should be at 60°F or higher before any painting commences to avoid movement of the drywall that can create new surface flaws. To assist in identifying any surface imperfections in the drywall before application of the intermediate coat, ensure that good lighting has been installed.
Furthermore, if the painting contractor believes the raw drywall is not ready for paint, he should inform the general contractor, point out exactly where the problems lie, and ask that the drywall contractor make the necessary repairs before painting work begins. Repair work is much harder to execute effectively after paint is applied.
Recap:
- New drywall can be difficult to paint as there is a difference in texture and porosity between the paper surface and the joint filling compound used. Additionally, repairs made after painting work has commenced will create an uneven surface that results in an uneven and blotchy appearance after being painted. Although these defects and flaws will look like application errors, the reality is that these defects have nothing to do with the quality of paint or application methods used
- Use a high-quality latex primer sealer when painting new drywall to provide a continuously sealed surface with relatively uniform porosity.
- Although using a high-quality latex primer sealer is an important first step, many defects in the drywall are practically invisible until the prime-coat has been applied. This means the drywall contractor will have to return to the job site and make repairs.
- Ensure proper lighting is in place and that the interior temperature is above 60°F before commencing painting work. Proper lighting makes defects in the drywall more noticeable, and the change in temperature causes movement in the walls and seams of the drywall, which can create new surface flaws. It is far more efficient to have these repairs made before painting commences.
- Never make drywall repairs after the intermediate coat has been applied. The variance in surface texture created by applying uneven layers of filler, sealer, and intermediate coat across an entire wall is what causes the inconsistent appearance of the finish.
- Specifying a Level 5 Drywall Finish (application of a thin skim-coat of compound across the entire surface of the drywall) can produce consistently better results than a Level 4 Finish when painting new drywall; however, a Level 5 Finish does not guarantee a flawlessly painted surface in critical lighting conditions.
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