Drywall. Sheet rock. Gypsum. It’s the same thing but there are several names you can choose from when searching for this popular building material commonly used in North American houses to build the walls.
Drywall is relatively easy to use and fix which is why it’s so prevalent in homes. If you’ve ever experienced water damage in your home however, you know the challenges of fixing a house with wet drywall.
Beyond a visual inspection of a drywall for moisture, you can also feel the drywall for dampness and use an electronic moisture meter to measure the weight in water relative to the weight of the drywall when bone dry as a percentage.
Having said that, we’re about to find out that simply looking at or even measuring drywall for moisture isn’t the only think you need to do.
Drywall damage is on a case by case basis and depends on the water exposure
We had a flood in my parents’ basement during a heavy rain storm one year. The water started backing up in two of the window wells and then began coming through the window cracks and from behind the wall itself. The house was 33 years at that point so the drywall was original.
The next morning we started drying the walls with the gas heater and another portable heater we had at our disposal. We also ran the dehumidifier to get rid of excess moisture.
Amazingly we didn’t have to replace the drywall but quickly drying it as mentioned above certainly helped. We didn’t experience any mold growth either.
If you’re facing wet or damp drywall, you might wonder how to tell exactly how wet it is and when it needs to be completely replaced.
Let’s take a look at how to measure moisture in drywall, the maximum level of moisture you should experience, when you need to replace wet drywall and more!
How much moisture is too much in drywall?
If there is any doubt as to how wet the drywall is, replace it. That’s the simplest way to look at it.
Moisture is measured as Moisture Content (MC) which is shown as a percentage (%). The equation to calculate MC is as follows:
MC = (Gross Weight – Dry Weight) / Dry Weight
So a 50 lbs (average weight) piece of drywall that has 0.5 lbs of water has a MC of (50 lbs – 49.5 lbs) / 49.5 lbs ≈ 1%.
1% seems like a low enough number, right?
But it doesn’t mean that it’s acceptable for drywall specifically so I decided to do some further checking and contacted the Gypsum Association
which since 1930 has represented gypsum board (i.e. drywall) manufacturers in the United States and Canada.
The easiest way the Gypsum Association sums up the question of how much moisture in drywall is too much is as follows:
If there is any doubt as to how wet the drywall is, replace it.
They don’t even list a moisture percentage that you shouldn’t exceed and there are several reasons why.
How do you check for moisture in drywall
You can use a moisture meter to check drywall but how effective are they? The problem with measuring moisture in drywall is that you can only visually see the surface of the drywall and can’t see inside it or on the other side.
Again, I consulted the Gypsum Association and they bring up a number of interesting points regarding the use of moisture meters to measure dampness and water content of drywall following an event like a flood or leak:
- Moisture meters need to be calibrated to work properly. If you calibrate it incorrectly or misread the results, you may not get an accurate reading and answer.
- Moisture meters are typically good for measuring moisture in a substance that has uniform composition throughout, such as wood. Drywall has several material components (paper and gypsum commonly) which have different compositions and thus might yield conflicting levels of moisture.
- Drywall can have different levels of moisture depending on the surrounding temperature and humidity. Drywall in a bathroom could be expected to have less moisture in a room such as a bedroom than a bathroom or basement. And a basement is typically cooler than a bedroom, too.
- Handheld moisture meters only give you a reading of drywall that is relatively dry compared to nearby drywall that is relatively moist, and vice versa.
So a moisture meter can be good when used to properly give you a relative reading of drywall but it still only gives you an indication of dampness. It doesn’t let you know about mold or mildew that is growing inside the drywall or behind it which can cause health and structural problems.
You should still use common sense when it comes to drywall replacement and remember the adage:
If there is any doubt as to how wet the drywall is, replace it.
Does mold and mildew grow on drywall?
Yes, mold and mildew can both grow on drywall. Mold grows in the presence of humidity, water or moisture and the more that exists, the better the chance that mold will occur. When drywall becomes wet or overly moist, mold spores and mildew can develop on the outer paper surface which can create both structural and health concerns.
Mold on drywall often appears first as small black or green dots and will grow and expand to large areas if not treated. Mold loves to grow on cellulose so drywall, paper (which drywall has) and wood are common sources for mold to occur.
Addressing mold and mildew on drywall first means eliminating the source of the moisture to begin with. You can then figure out how to address the associated mold problem whether by getting rid of surface mold or replacing the drywall completely.
Remember that mold can grow inside or behind the drywall where it’s not seen by the naked eye, too. Even if you eliminate the visible mold on the outside surface of the drywall, that doesn’t mean that the mold has been completely eliminated.
Health symptoms from mold on drywall
Mold is dangerous to your health and can be responsible for a number of health-related symptoms including:
- Dry or blocked nose
- Dry and sore throat
- Sinus problems
- Watery and red eyes
People with respiratory problems can experience more serious health concerns.
The bottom line with drywall that has been exposed to water or moisture is to replace it when you’re unsure. The side effects from both a health and structural perspective mean that trying to simply dry the drywall and paint over it may not be your best decision.