Why is mold growing on new drywall and not old drywall

Asked July 27, 2013, 3:24 PM EDT

Two years ago I left tub water running and flooded half of my one story house and my basement. My insurance covered this and hired a contractor to repair the damage and another to clean the mold (I did this the night before leaving for a 4 day out of town weekend). I have never had a mold problem before this. Just recently we had an unsual heat wave. But before the heat wave I noticed white circular mold on the ceiling drywall of the basement. It grew only on the new drywall. During the heat wave it spread but only on the new ceiling drywall. My basement is not finished. I called my insurance company and a man from the mold removal company (same one as before) came to investigate. He could not find a new source an said there was no moisture or leak. Then my insurance company came with an adjuster, a man from the contractor that installed the new dry wall and my agent. They could not figure out why the mold is on the new drywall only. They said the humidity in my basement is very high (this was during the heat wave). They asked me if I ran my dehumidifier. I said no and that I rarely had to use it. Now, my insurance is refusing to cover this saying the humidity caused it. I could understand this if the mold was on both the new and old dry wall. The mold stops in a straight line between the new dry wall and the old dry wall. Can you tell me why this is happening and what should I do? Thank you.

Rensselaer County New York new home design and construction mildew and mold control

2 Responses

All mold needs is moisture, warmth and a food source to grow. The paper of the new drywall is an excellent food source. You have recently had weather that would be normal for us in the mid-south that provided surplus warmth and moisture. Mold spore are always present. They just need the other 3 to have a go.

How to prevent it is to control the elements that you can control, the moisture levels in your home. We really need to keep the humidity levels in the home down in the low to mid 50%. I doubt that you want to lower the temperature to below 40 F. Cost and comfort prohibit that action. Nearly all our building materials are a food source.


Why didn't the old drywall get moldy? One of 2 things, first the picture showing the old drywall next to the new looks like green-board. Green-board is normally used in bathrooms and other wet locations. It is moisture resistant and thus has some level of mold resistance. Second, some sealing paint primers have a mold and mildew resistance mixed in so that they can provide some protections to mold and staining.


What you can do! Use ventilation or a dehumidifier to reduce the indoor humidity in the home. Clean the walls and ceiling to remove all the mold. Be sure to use the precautions listed below. Keep the indoor humidity low so that all the building materials can dry out. The dry out process may take several months. Then use the sealing paint primer mentioned above.

Follow the directions listed at the links below. It is the process we use for mold clean-up after a flood. Mold does not care where the moisture cam from, warm humid summer air or flood water.

The U.S. Environmental Protection Agency website contains information on mold cleanup and remediation in homes, schools and other large commercial buildings.The Centers for Disease Control and Prevention website includes general background information about mold health hazards and mold safety recommendations.

Mold Cleanup Guidelines

Tips and techniques
The tips and techniques presented in this section will help you clean up your mold problem. Professional cleaners or remediators may use methods not covered in this publication. Please note that mold may cause staining and cosmetic damage. It may not be possible to clean an item so that its original appearance is restored.
  • Fix any moisture problems as soon as possible. Dry all items completely.
  • Scrub mold off hard surfaces with detergent and water, and dry completely.
  • Absorbent or porous materials, such as ceiling tiles and carpet, may have to be thrown away if they become moldy.
  • Mold can grow on or fill in the empty spaces and crevices of porous materials, so the mold may be difficult or impossible to remove completely.
  • Avoid exposing yourself or others to mold (see discussions: What to Wear When Cleaning Moldy Areas and Hidden Mold).
  • Do not paint or caulk moldy surfaces. Clean up the mold and dry the surfaces before painting. Paint applied over moldy surfaces is likely to peel.
If you are unsure about how to clean an item, or if the item is expensive or of sentimental value, you may wish to consult a specialist. Specialists in furniture repair, restoration, painting, art restoration and conservation, carpet and rug cleaning, water damage, and fire or water restoration are commonly listed in phone books. Be sure to ask for and check references. Look for specialists who are affiliated with professional organizations.

What to Wear When Cleaning Moldy Areas

It is important to take precautions to LIMIT YOUR EXPOSURE to mold and mold spores.

  • Avoid breathing in mold or mold spores. In order to limit your exposure to airborne mold, you may want to wear an N-95 respirator, available at many hardware stores and from companies that advertise on the Internet. (They cost about $12 to $25.) Some N-95 respirators resemble a paper dust mask with a nozzle on the front, others are made primarily of plastic or rubber and have removable cartridges that trap most of the mold spores from entering. In order to be effective, the respirator or mask must fit properly, so carefully follow the instructions supplied with the respirator. Please note that the Occupational Safety and Health Administration (OSHA) requires that respirators fit properly (fit testing) when used in an occupational setting; consult OSHA for more information (800-321-OSHA or www.osha.gov).
  • Wear gloves. Long gloves that extend to the middle of the forearm are recommended. When working with water and a mild detergent, ordinary household rubber gloves may be used. If you are using a disinfectant, a biocide such as chlorine bleach, or a strong cleaning solution, you should select gloves made from natural rubber, neoprene, nitrile, polyurethane, or PVC (see Cleanup and Biocides). Avoid touching mold or moldy items with your bare hands.
  • Wear goggles. Goggles that do not have ventilation holes are recommended. Avoid getting mold or mold spores in your eyes.
See the CDC and EPA websites for more information.

Here is more information from a housing construction specialist:
There might be a chemistry subtlety within the manufacturing of the paper facing. Probably a combination of the newer, replaced gypsum board with a more susceptible ingredient (perhaps an adhesive starch), vs. the original gypsum board being resilient enough not to be affected. I’ve run across oddities like this with plywood roof sheathing, where I believe some panels were manufactured from all juvenile or sap wood and ended up performing poorly. A thought; I wonder if the original gypsum was from a traditional material supplier, while the newer gypsum from a big box store.

There seem to be no easy answers to the mold question. Yet, I hope the information received from eXtension is of some help to your dilemma.