Wire or steel wool can actually work quite effectively at sealing up holes that rats and other rodents use to gain entrance to your home. It doesn’t work as a long-term approach, and it usually doesn’t work alone, but combined with other efforts can give you a short-term fix for what could end up being a very long-term and costly problem.
Rats have very sharp teeth that are able to chomp and tear through most materials, but hard metals seem to give the rodents a bit of a hard time. Certain softer metals can still be tackled by the surprisingly lay strong interlopers, but steel wool can actually provide a barrier that the rats can’t chew through with ease.
As well as being one of the toughest materials against an animal like the rat, steel wool is also flexible and moldable, meaning that you can fit it into any number of gaps and spaces. You can use wire wool in large holes and small, sliver-like cracks. With the assistance of a screwdriver, multi tool or similar, a bit of poking around will usually fill most spaces quite nicely.
Adding to that, steel or wire wool is relatively inexpensive and easy to get your hands on, making it perfect for those weekend DIY jobs after you start noticing rat droppings around your home. If you have large holes, or a lot of holes to fill, buying lots of steel wool might be the most viable, cost-effective option.
Finally, using sealing methods that are designed to keep the rodents out is considered to be one of the most natural rat control methods. You will still need to find a way to physically evict rats from the building, obviously, but sealing the building itself will go a very long way to making sure internal rat populations do not grow. You can then deal with the rats inside the building using traps — kill traps or live traps, or other methods.
You will almost always need to use steel wool with another material to fill a hole effectively against rats. You can use expanding foam squirted into the space to help secure the steel wool a little better, and this will also add another physical barrier, although not one that you can use by itself. It would take the average rat no time at all to chew through the soft expanding foam material.
There are other “fixing” materials that you could use for a slightly more hardy and permanent finish: concrete repair, other fillers, adhesives, etc.
You CAN use steel wool to seal a rodent hole and keep rats out of your home, but only when you make sure that you are sealing all holes, that all rats inside the building are evicted, and that all sources of food and rat waste/debris is all cleared away. If you do not complete ALL steps, the rats will get back in and you’ll be right back at the start again.