Application Note | Construction Materials
Drywall Texture & Pitting Using 3D Profilometry
Fast Large-Area Texture Comparison and Pit Analysis of Coated Drywall
Research & Experimental Testing
Duanjie Li
Visual Design & Editorial
Andrew Shore
Introduction
Drywall is prevalently used in the construction of interior walls and ceilings in the States. It consists of two layers of paper sandwiching a layer of gypsum plaster in between. The inherent properties of the materials including gypsum, paper, and organic binders make drywall highly susceptible to moisture and water damage. Paper and gypsum soften upon exposure to moisture, resulting in deterioration of the mechanical properties and exterior appearance. Repairing and replacing the damaged drywall can be very costly and time-consuming. Therefore, primer and coatings are applied on the drywall surface to enhance moisture and wear resistance, as well as to improve cosmetic appearance.
Importance of 3D Profilometry for Coated Drywall
Roughness and texture of the coating is critical in the final product quality and appearance. A better understanding of the effect of surface texture and consistency on the moisture resistance of the coated drywall allows selecting the finest product and optimizing the painting technique to obtain the best result. Quantifiable, fast and reliable surface inspection of the coating surface is needed for quantitative evaluation of the surface quality. The NANOVEA 3D Non-Contact Profilometers utilize chromatic confocal technology with unique capability to precisely measure the sample surface. The line-sensor technique can finish scanning a large drywall surface in minutes.
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Measurement Objective
In this study, the NANOVEA ST500 non-contact profilometer is used to measure and compare two drywall samples with different surface finish. We showcase the capacity of the NANOVEA non-contact profilometer in providing precise 3D profile measurement and comprehensive in-depth analysis of the drywall surface.
NANOVEA ST500 Large Area
Optical 3D Profilometer
Results and Discussion
As shown in Fig. 1, the optical line sensor of the ST500 generates a bright line composed of 192 light spots that scan the sample surface at the same time. This significantly increases the scan speed and enables a detailed 3D scan of an 80 mm × 50 mm drywall sample surface in two minutes. Such a fast speed makes it possible to implement the NANOVEA 3D profilometer into the production line for quality control of the product in situ. In addition, the portable JR25 model allows users to directly measure the drywall in use.
Two sets of drywall samples with different surface finish are evaluated in this study. Fig. 2 compares these two samples under the microscope at different magnifications. Sample 1 shows a relatively smooth and dense surface texture. In comparison, it is observed that small pits distribute on the surface of Sample 2, making it more vulnerable to mold and moisture.
The pseudo-color view, cross section profile and roughness of the two drywall samples are compared in Fig. 3. The 3D view of the drywall samples is compared in Fig. 4. Sample 2 shows a lumpy surface texture with a higher roughness Sa of 0.126 mm, compared to an Sa of 0.0683 mm for Sample 1. Sample 2 also possesses small pits all over the surface represented as small black dots in the pseudo-color image.
| ISO 25178 parameter | Sample 1 | Sample 2 |
|---|---|---|
| Sa (mm) | 0.0683 | 0.126 |
| Sq (mm) | 0.087 | 0.155 |
| Sp (mm) | 0.357 | 0.548 |
| Sv (mm) | 0.645 | 0.459 |
| Sz (mm) | 1.00 | 1.01 |
| Ssk | −0.0389 | 0.184 |
| Sku | 3.37 | 2.72 |
Table 1: Roughness of the two drywall samples (from Fig. 3).
In order to further investigate the effect of the pits on the resistance of the drywall, a higher resolution surface scan on Sample 2 is performed and analyzed in the following section.
The false-color view and pitting analysis of Sample 2 at a higher resolution are displayed in Fig. 5. It is clearly seen that Sample 2 shows small circular pits present on the sample surface. The pitting analysis allows us to locate the pits and calculate the statistics of all the pits. The pits, highlighted in blue color on the pitting analysis image, take up 2.26% of the projected area and have a total volume of 0.091 μm³.
Fig. 6 exhibits the 2D profile analysis on one of the pits on Sample 2 as an example. The measured pit has a “cone” shape with a maximum depth of 494 μm and area of 2.2×10⁵ μm².
| Pit profile parameter | Value |
|---|---|
| Maximum depth | 494 µm |
| Area of the hole | 223473 µm² |
| Maximum height | 1.08 µm |
| Area of the peak | 9.51 µm² |
Table 2: Pit profile analysis (from Fig. 6).
Conclusion
In this application, we have showcased that the NANOVEA ST500 3D Non-Contact Profilometer is an ideal tool for analyzing and comparing the surface finish of drywall samples. The small pits on the drywall surface play a critical role in the susceptibility of the drywall to moisture and mold. The high resolution scan and comprehensive analysis tools including 3D and pitting analyses by the NANOVEA profilometer enable comprehensive and quantitative evaluation of the surface finish, which is critical in assessing and optimizing the product quality.
The data shown here represents only a portion of the calculations available in the analysis software. NANOVEA Profilometers measure virtually any surface in fields including Semiconductor, Microelectronics, Solar, Fiber Optics, Automotive, Aerospace, Metallurgy, Machining, Coatings, Pharmaceutical, Biomedical, Environmental and many others.
Frequently Asked Questions About Drywall Surface Inspection
Why measure the texture of coated drywall?
Drywall’s gypsum and paper soften with moisture. Primers and coatings protect it and improve its appearance, and the coating’s roughness and texture affect both its moisture resistance and the final look.
How fast can drywall be scanned?
The line sensor projects 192 light spots at once, scanning an 80 mm × 50 mm drywall sample in two minutes, fast enough for in-line quality control; the portable JR25 can measure drywall in place.
How did the two drywall finishes compare?
Sample 1 was smoother and denser, Sa 0.0683 mm; Sample 2 was lumpier, Sa 0.126 mm, with small pits all over the surface that make it more vulnerable to mold and moisture.
How are surface pits analyzed?
A higher-resolution scan and pitting analysis locate every pit and compute statistics: on Sample 2 the pits covered 2.26 % of the projected area, and one cone-shaped pit was 494 µm deep with an area of about 2.2×10⁵ µm².
Does contact matter on drywall?
The chromatic confocal sensor measures without touching the surface, with no influence from reflectivity and no sample preparation.
Which instrument was used?
The NANOVEA ST500 3D non-contact profilometer with an optical line sensor.
