How much water does it take to create a water stain/damage to a plaster ceiling? Updated 2/26/24

Water leak?: How much to cause ceiling damage?

A test 

Started February 18, 2024

So my curiosity, I want to know how much water it takes to create a water stain, and damage to a plaster ceiling.

So using some debris from a recent plaster job, I have a fairly large piece of plaster- 2x3' its rocklath, plaster base, finish and its been painted multiple times over the last 75 years.

So I set this up, and started with a table spoon of water on the back side to simulate a water leak. 


 1 Teaspoon of water

8 hours later:


So 1 teaspoon didn't do anything. So I tried a new spot, with tablespoons. This is day 2- different spot, I dripped 2 table spoons of water onto this spot. The 2nd tablespoon is still puddled and wet the next day.

I will see what this looks like when I get home from work. So far no staining on the other side of piece. 

Some notable observations: Water beads up on the back side of the rocklath, and it takes a long time for the water to soak into the paper. A lot longer than I thought it would. This piece is about 3/4" thick so it might take a bit before we get a stain. Water stains are usually caused by water disturbing the dirt on the surface. 


 I keep adding water, 1 table spoon at a time.

Update: 2/21/24: 

Water soaks into the rocklath very quickly if its at all damp (1-3hours its wet, puddle is gone). The beading effect is completely gone. Still no stain/corrosion.
Current table spoon count: 11 - About 1/2 cup of water

The rocklath feels damp prior to adding more water. no stain yet.

Update: 2/23/24:

 I missed one day, but the area that has had 12 tablespoons of water applied to it feels damp. Added another tablespoon. (13) Side note- water stain may not show up, I am using a piece of a wall, and not an actual ceiling piece. Not sure if that would make a difference.

Update 2/25/24:

Current tablespoon count is 21. The area is constantly wet, damp. I also began adding water to the joint between the two piece of rocklath. I noticed the water soaks into the bare plaster a lot faster than even the wet paper. The wetter the plaster/rocklath the faster it soaks up the water!

9:46PM + 1 tablespoon

9:51 PM

In a period of 5 minutes, it soaked up a lot! 

This is the side view of the crack. But this is cheating a little because the water is running over the edge and dripping off. So the water is getting into the plaster from 2 directions.

Still no stain.

Though it looks like there could be something there. Next time this is 'dry' I need to make my stand a little taller  Its sitting on 2x4's on a table


midnight 2.5hrs later:

The dark is wet.. not damp but actually wet. And that is an actual puddle. I wonder if the plaster is becoming water logged?
Table spoon count: 21, just under 1 cup of water.

Update: 3/22/2024

I need a better way to simulate dripping water.

Any ideas?


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