How do I prevent mold from growing on a damp wall?

Inside or outside?

Spray the mold with bleach

What is the wall made of and what is causing the moisture?

Hydrogen peroxide....must dry out and then use a sealant paint like KILZ

http://blacktoxicmolds.com/borax-kill-mold.php

You have a couple of choices but they are all dependent upon whether or not you are the owner of the property.

If you are not the owner of the property you can:

1. Spray or wipe down the wall in question with bleach (be sure to wear a good respirator which you can purchase at home depot or lowe's so that you're not inhaling bleach fumes and you will also need it for the 4th step.
2. Attempt to dry the wall with either a dehumidifier or a fan. (Could take a while.)
3. Seal up any sources that you can see of leaks with a silicone sealant.
4. Paint at least 2 thick coatings of a product called UGL on the wall which will prohibit moisture from penetrating the wall. If you get the oil based version, the fumes will get you higher than a kite and you won't realize it until you get out into fresh air so you'll need the respirator for this step also. If you get the latex version, you should be ok sans the respirator.
5. Now you can paint the wall as desired but I would still be leery about mold growing behind the scenes.

If you are the owner of the home, you can do the above but what you need to do is find and repair the source of the moisture. If this is a basement wall that's leaking, can you dig it out and seal the wall in question? I wouldn't want to play around with any type of mold situation because it can quickly get out of hand. Also do not hesitate to call in the professionals to handle this problem.

If digging outside is not an option then you can:

1. Remove the wall that has the mold (assuming that it is some type of framed drywall/plasterboard over cement block or poured cement foundation.
2. Do steps 2-4 from above.
3. Install a vapor barrier.
4. Reframe the wall if necessary and redrywall/replaster the hopefully now sealed and dry wall.
5. Now you are ready to prime and paint to your liking.

Hope that this helps. Good luck and keep us posted!

Where i live, there are many buildings with this recurring problem, because the way they are built lets moisture from the outside seep in. There are anti-mold cleaning sprays you can buy in the grocery store, which i know people spray/wipe the wall with a few times a year to keep the mold from growing on the interiors of the wall.

If it is on an inside wall, clean well with bleach, buy a de-humidifier, and treat your room with a diffuser with "Thieves Oil"...an essential oil from Young Living. Works great. We had that problem with our former home...did these things, no more mold problem!