When installing hardwood floors, one of the most important steps is to make sure the boards are properly aligned. The tongue-and-groove method is a popular way to achieve this, but there is some debate over which side of the board should be nailed.
The main argument for nailing the tongue side is that it provides a more secure connection between the boards. This can be especially important in areas where there is a lot of foot traffic or if the floor will be subject to other heavy use.
Another advantage of nailing the tongue side is that it helps to hide any imperfections in the wood. If you nail the groove side, any gaps or unevenness will be more visible.
However, there are also some good reasons to nail the groove side instead. One is that it can make installation faster and easier since you don't have to line up each board as precisely. It can also provide a stronger connection in some cases, particularly if you're using thinner boards.
In general, either method can work well, so it's really up to personal preference or what's best for your particular project. Whichever way you choose, just be sure to take care when aligning and installing the boards so your hardwood floors look great and last for years to come!