When it comes to installing a subfloor, if you're dealing with a moisture-prone surface or concrete, you need to make sure you have a layer of protection against moisture. A moisture barrier underlayer is the best way to ensure your laminate floors stay safe from water damage for years to come. If the amount of moisture exceeds what the bottom layer can handle, then yes, you'll need a moisture barrier. If it's within the capacity of the bottom layer, then it can do the job.
Almost all floor installation instructions require the use of a vapor barrier or moisture barrier beneath the floor. This is because manufacturers don't want their product to be exposed to moisture, and it helps keep your flooring durable. When water comes into contact with laminate or any type of wood base material, it can cause damage over time. If you're used to other types of flooring such as solid wood, vinyl, and tile, which don't require a subfloor, you may be surprised to learn that a bottom layer is practically essential for laminate floors.
The only case where no subfloor is needed at all is when the laminate floor already has one attached to its underside. In addition to spills from above, the moisture content of the subfloor can also play an important role in keeping your floors healthy. Common foam underlays can inhibit moisture, but there are types of subfloors that require an additional 6mm vapor barrier. Most floor manufacturers require the installation of a 6mm vapor barrier to protect their products from moisture.
The installer we had assured us that the glue he was using would protect the floor from moisture, which was not true. Solid wood or engineered wood can easily cover small gaps and go directly over imperfections without needing an underlayment. Also known as a moisture barrier, a vapor barrier for floors is usually a sheet of plastic that prevents moisture from passing through walls or subfloors. In reality, it's used for both walls and floors, but when it comes to floors they're mainly referred to as moisture barriers. Premium subfloors designed specifically for noise reduction can make up a large portion of your apartment bill.
Because laminate floors can be tricky to install on surfaces that are even slightly uneven, an underlayment is recommended. If you're installing a new floor over an old or new concrete subfloor, you should make sure no moisture gets in and ruins your investment in new floors. The subfloor will help increase the sound-absorbing qualities of the laminate, but only slightly. A rare feature just a few years ago is that more and more laminates with pre-bonded underlays are becoming available.
