# Study About the Influence of Diatoms on the Durability of Monumental Limestone
## 1 Introduction  
The protection of historical heritage has become a major concern in recent years, particularly regarding the preservation of historical structures and artwork. The increase in pollutants in the atmosphere and, consequently, in rainwater has accelerated the deterioration caused by natural processes; factors such as growing air pollution levels have accelerated the rate at which these ancient structures and works decay [1, 2, 3, 4]. To address this concern, new techniques need to be researched and developed to prevent the deterioration of works and historical buildings as much as possible and to improve the durability of new ones in a sustainable manner. In this regard, new surface treatments with compounds such as graphene oxide or employing microorganisms have already been considered to achieve protective surface coatings. Promising results have been obtained from innovative processes that involve the use of organisms to enhance properties through biomineralization processes [5, 6, 7]. Biomineralization is a biochemical process by which living organisms stimulate the formation of minerals. Currently, a large number of organisms are known to be involved in mineralization processes:  
* Plants in the formation of silicates. * Invertebrates in the formation of carbonates. * Vertebrates in the formation of phosphates and carbonates. * Microbes in the biomineralization of gold, copper, and uranium. Bacteria are powerful organisms for biomineralizing carbonates, phosphates, sulfates, and silicates. So far, the most studied biomineralization processes to obtain improvements in building materials have been:  
* Precipitation of calcium carbonate by microbial action [8; 9; 10; 11; 12; 13]. * Precipitation of biogenic silica by microalgae [14; 15]. In the present study, a series of tests are performed on limestone samples subjected to precipitation of biogenic silica by diatom microalgae. The goal is to achieve a natural surface treatment by harnessing the silicon biomineralization produced by these microalgae, known as diatoms. These microalgae play a fundamental role in oxygen production on Earth and present characteristics that render them suitable candidates for this type of experimentation. Their cell wall is almost entirely silicon and, therefore, they can easily colonize surfaces by creating biofilms; after their death, the remains composed of silicon are left. Diatoms are a group of microalgae generally unicellular, although they can also coexist, forming cellular chains, fans, or other types of groupings. These microalgae include about 20,000 species and represent one of the most common types of phytoplankton. In addition, diatoms can also live colonizing underwater or even land surfaces known as benthic life forms. These types of microalgae can develop in both salt and fresh water and are able to survive in environments under extreme temperature and salinity conditions [16]. When diatoms die, their frustules are left at the mercy of water currents and, over time, they commonly accumulate and compact, mainly in sedimentary environments, forming the rock diatomite. Due to the nature of its formation, diatomic is a siliceous sedimentary rock widely used for filtration processes in different industries, and diatomaceous earth is extracted from it for various uses, such as fertilizer, insecticide, or building material [17; 18; 19; 20]. Silicon deposition can be achieved thanks to the ability of diatoms to colonize surfaces by adhering to them through the creation of an initial biofilm [21]. Here, the aim is to take advantage of the silicon deposition produced by the frustules of dead diatoms and obtain limestone rock samples with a natural surface treatment, which enable the analysis of any improvements in surface properties. The present work focuses on the engineering involved in the planning and execution of these experimental tests and the analysis of the results obtained. However, the underlying ideas and elements that generated both the experiment and the samples studied cannot be overlooked.