Crawl spaces can be creepy places anyway and when they are wet and musty they can be even more creepy, not to mention nasty. That musty smell is probably due to mold and mildew that has grown in it’s favorite environment, a wet one. If your crawl space is like this then you probably should consider getting a crawl space dehumidifier.
Crawl spaces are dark, cramped and hard to work in but if you are going to fix the problem you are going to have to get in there and get busy.
First, assess the situation, get enough light in there to see well and look around to see if there is any standing water anywhere. If there is then mop it up with a rag or towel. If it returns then try to figure out why. Check pipes for leaks and fix them yourself or hire someone to come in to fix them before you go any further. If the pipes are free of leaks then check for a way for rain or snow to get in from outside.
The puddles may only be due to condensation or even the ground water. In these cases the dehumidifier will only do so much. You will probably have to encapsulate your crawl space to get it to stay dry.
Before you get to work on the encapsulation, run the crawl space dehumidifier for a few days to make your working conditions a little better. Do not forget to empty the collection container or you will just have to start all over again.
Next, you need to make the floor of the crawl space as even as possible to help the puddles stay gone. You could even bring in some sand or use a few bags of cat litter to help absorb moisture on the dirt floor of your crawl space.
Now you need to get the liner in there and fasten it to the walls with an industrial adhesive. The liner you use should be antimicrobial and have zero permeability. If this is confusing for you ask an expert. The liner should be installed no less than 18 inches up the walls of the crawl space.
Make sure to overlap the liner on the walls and when you roll it out on the floor. Secure the seams with duct tape to prevent gaps. This is obviously not a one day job but when it is all done you will have a nice, dry, better smelling crawl space and will have effectively saved yourself a lot of repairs as mold and mildew will destroy wood and other materials used to build your house.
When the crawl space is dry and encapsulated, you should still run the dehumidifier as needed to keep it from getting musty again. Remember, if the crawl space is cool, and it probably is, make sure the crawl space dehumidifier is one that will operate efficiently at low temperatures so it does not freeze up. If it freezes up it will not work as efficiently as it should and coould even shut down completely.