Mud bricks exposed to water will eventually erode, lose strength and swell. That is because mud contains clay and that attracts water, bricks swells and lose strength when wet. Many adobe bricks, under water can even disintegrate. Swelling can cause plasters to break off causing cracks from which more water can enter. Exposed walls or earthen domes can erode, crack, and maybe even fall. Given enough time, exposed to water, adobes will get severely damaged. Either you protect them from water reaching them or if that is not easy or desirable you can stabilize them with cement, lime, asphalt, oils or many other possibilities. Stabilisation has as goal to decrease the swelling, erosion and loss of strength of the adobe. I am building domes and vaults with mud bricks, therefore I am interested in avoiding risks.
The following test, on the video, shows how 4 different adobe bricks, with different proportions of added cement and or lime, perform under a constant water drip on a focused spot. The best stabilization that I found for my earth bricks is the one with equal parts of lime and cement, I suppose it could be because of the relatively high amount of clay in my earth.
The drip test is a simple yet insightful test, it allows you to see how much your bricks are eroded by water. It gives an idea of the loss of strength and lets you see how much they swell. By comparing different bricks you can have a fairly good idea of which serves you better. It is straightforward and gives you a faster idea of the kind of mud bricks you have than passing a long time reading on the internet. You can adjust the amount of falling water, the time if falls, the angle at which it falls and the height, you can also fix the bottles or let them swing in order to simulate a smaller or bigger drop area.
Best wishes to all and sorry about the bad video quality, I messed the audio up by blocking the microphone sometimes when I was filming.