# Study About the Influence of Diatoms on the Durability of Monumental Limestone
## 2 Materials and Methods
### Methodology
#### 2.2.2 Water Absorption Test at Atmospheric Pressure  
The next part of the study consists in determining the amount of water the test cubes absorb at atmospheric pressure and detecting the differences in behavior between the samples with diatoms and the control samples. The test method used is described in the UNE-EN 13755:2008 [32] standard and based on completely immersing the test pieces in water at atmospheric pressure to study their absorption capacity. The process consists in drying the test cubes until they reach their constant mass and then completely submerging them in a tank or container with water until all the samples reach saturation. Knowing the difference between the mass of the test tube saturated in water and the mass of the dry test tube, the amount of water absorbed by each of them was determined expressed as a percentage according to the expression (1):  
\[A_{b}=\frac{m_{s}-m_{d}}{m_{d}}.100 \tag{1}\]  
For this test, six cubic specimens with 50 mm edges were used: three treated with diatoms (d1, d2, and d3) and three as control specimens (c\({}^{\prime}\)1, c\({}^{\prime}\)2, and c\({}^{\prime}\)3). All specimens were waterproofed with fiberglass paint on the face opposite to the surface under analysis.  
Initially, the specimens were dried in a ventilated oven at 70 \(\pm\) 5 \({}^{\circ}\)C until reaching a constant mass; specifically, they were kept for 5 days at 68 \({}^{\circ}\)C to prevent potential damage to the deposited biofilm by a higher temperature. As in the previous test, diatom-treated samples with the lower surface isolated were used to compare surfaces potentially containing diatoms with those known to be free of them. Also, a random face was isolated in the control samples. Following this initial drying phase, the specimens were returned to the oven for an additional 4 days at 68 \({}^{\circ}\)C, again until constant mass was achieved. Once dried, each specimen was weighed to determine its dry mass (m\({}_{\rm d}\)) and then allowed to cool in a desiccator.  
The specimens were placed on supports (plastic grids), maintaining a minimum distance of 15 mm among them. Tap water at 20 \(\pm\) 10 \({}^{\circ}\)C was then added to reach half the height of the specimens, and the container was sealed. This moment is defined as t\({}_{0}\), marking the start of the test.  
After approximately 60 min (t\({}_{0}\) + [60 \(\pm\) 5] min), water was added to reach three-quarters of the specimen height, and the container was resealed. After about 120 min (t\({}_{0}\) + [120 \(\pm\) 5] min), additional water was added until the specimens were fully submerged, with a 25 \(\pm\) 5 mm layer of water above them, and the container was closed once again. The specimens remained submerged in the closed container, as shown in Figure 6. After \(48\pm 2\) h (t\({}_{0}\) + 48 h), the specimens were removed, lightly cleaned with a damp cloth,  
Figure 5: (**a**) Samples submerged in water and (**b**) hydrostatic weighing.  
weighed, and their masses recorded. Once weighed, the specimens were returned to the water, and the container was resealed. From this point, the process of removing, drying, and weighing was repeated every 24 \(\pm\) 2 h to track mass changes.  
The test was considered as complete when all specimens reached their saturated mass in water (m\({}_{\text{s}}\)), defined as the point at which the difference between two consecutive weighings is less than or equal to 0.1% of the first of these two recorded masses.