**1. Introduction**

The number of newly constructed apartment complexes in South Korea continues to increase each year. In particular, apartment complexes containing more than 304,432 dwellings were constructed in 2016 [1]. Because the exterior finishes of these apartment complexes normally require painting, the increase in the supply of newly built apartment complexes will result in an increase in the demand for exterior wall painting. Moreover, in the case of existing apartment complexes to which exterior wall painting has been applied, full-scale repainting on the entire outer wall of an apartment should be performed every five years using a fresh coat of paint according to the long-term repair plan of the Korea Housing Act [2] to enhance the long-term durability and sustainability of the buildings. An analysis of the repainting frequency for 50 apartment complexes in metropolitan areas of South Korea showed that exterior wall repainting was performed every 5.34 years on average. Therefore, it is expected that the market for exterior wall painting of apartment complexes will grow even more in the future considering the enormous number of dwellings in apartment complexes in South Korea.

Exterior wall painting for apartment complexes is performed by laborers working from a suspended scaffold. Therefore, there is a high risk of accidents, such as falls or collisions with the outer wall. Moreover, there is a high risk of safety accidents, such as falling objects hitting pedestrians passing by below. In particular, the intensity of an accident would be very high when it does occur because exterior wall painting work is performed after the safety structures (safety net, flared shield in, etc.) have been removed from the exterior walls. Thus, the inherent problems, such as various risks and the number of insufficient skilled laborers involved in the exterior wall painting work of apartment complexes in South Korea, are expected to worsen in the future.

Recently, a unique Gondola-type Exterior Wall Painting robot (GEWPro) was developed to resolve the above problems related to the conventional exterior wall painting work of apartment complexes in South Korea [3]. To determine if this construction automation technology is attractive and acceptable in the field, it is important to verify quantitatively the benefits gained using the automated method by a comparison with the conventional method. Over the last three decades, a number of automated or semi-automated construction machines or systems have been developed and demonstrated in the construction industry [4–8]. On the other hand, few studies have verified the superiority of such automated methods based on a comparison and analysis of their overall performance in terms of productivity, cost, safety, and quality [9]. As a result, their practical use in the field has been underestimated.

In this study, the conventional process of the exterior wall painting of apartment complexes in South Korea and its problems were identified, and the automated method using the developed GEWPro was assessed. A model for performance evaluation and Life Cycle Cost (LCC) analysis [10–12] of GEWPro was developed in an effort to enhance the sustainability for the practical use of robots on construction sites.

Based on the model and data collected from several field trials, the overall performance of GEWPro was analyzed and its LCC was then compared with that of the conventional method to verify the benefits obtained from automation. Multiple laboratory and field tests were conducted to acquire essential data for the performance evaluation and LCC analysis. Conclusions and recommendations are made regarding the value of implementing and commercializing GEWPro. Finally, the performance evaluation and LCC analysis methodology and the model presented in this study can be adapted to analyze the performance of any other construction automation machine or robot.
