You have the top layer that is your floor covering (Hardwood, Laminate, Vinyl, Carpet, etc.), next you have the underlayment (usually a thin layer of fiber, foam, rubber), below that you have your subfloor (plywood, OSB, concrete), and lastly you have the joists which are the foundation to your floors.
The subfloor is what creates the stable, level surface you walk on and gives your flooring installers a material to which they can attach the new carpeting, laminate, hardwood, vinyl, or tile. Underlayment is the third layer, above the subfloor and immediately underneath whatever flooring you have chosen.
A: If you have doubts about the stability, condition, or direction of the old subfloor, or if you want to run your new flooring planks in the same direction as the old, it's recommended to introduce a layer of ply over the plank subfloor.
Underlayment is a layer of material between the subfloor and the finished flooring. Underlayment provides a smooth, level surface for installing luxury vinyl tile, laminate flooring, and hardwood floors.
You put rosin paper between the underlay and the flooring.
You have the top layer that is your floor covering (Hardwood, Laminate, Vinyl, Carpet, etc.), next you have the underlayment (usually a thin layer of fiber, foam, rubber), below that you have your subfloor (plywood, OSB, concrete), and lastly you have the joists which are the foundation to your floors.
Therefore, because concrete is porous, it's a good idea to install a vapor barrier over your concrete subfloor before installing your flooring. This way you can stop the vapor drive of water upward to your floors, protecting them from any damage (source).
Underlayment sits between the subfloor and the finished floor covering. They can be made from a variety of materials like foam, cork, felt, and rubber.
Underlayment is a special grade of APA plywood that is attached on top of the subfloor to provide a durable and resistant layer under finish flooring. Underlayment's special face and inner-ply construction resist dents and punctures from concentrated loads.
Half-Inch Plywood
The most common plywood thickness used as subflooring, half-inch plywood is a solid choice for most homes with standard-width flooring joists. Because of the difficulty and cost to replace subflooring, however, be sure that half-inch plywood is strong enough for your job before installing it.
For general residential use, 3/4 inch CDX plywood (3/4 plywood) with tongue and groove edges is a reliable choice. For areas with higher moisture levels, marine-grade or pressure-treated plywood is recommended.
Underlayment does two things that are critical to a successful laminate flooring installation:1. Underlayment takes out any minor deviations in the subfloor. 2. Underlayment delivers superior acoustical performance.
Rather than nails, screws are best to use for subfloors — these fasteners are convenient, easy to remove and capable of providing torque that nails lack. Because of their structure, screws can penetrate plywood more easily and improve the connection, whereas nails can weaken the plywood.
A double-layer subfloor is especially beneficial for high-traffic areas or locations that may experience heavy loads.
If you're gluing the new flooring to the subfloor, use a sander to remove paint, oil, wax, adhesives, sealers or other material and then thoroughly vacuum off dust and debris. Nail-down or floating floors may be installed over existing vinyl as long as it's no more than two layers thick.
Cement board, often referred to as backer board, is a thin layer of concrete with fiberglass mesh on both sides. It's available in sheets of many sizes. Most projects need 3-foot by 5-foot sheets. Whenever you're laying tile on a wood subfloor, you need to first install cement backer board.
Both plywood and OSB are effective choices for your subfloor needs, but OSB may be a better option for a garage than plywood. Plywood is a better option for projects that require a lot of cutting and molding, while OSB is a good option for those who need to cover areas where moisture exposure may be an issue.
You can, and should, use an underlayment on all types of subfloors. On a plywood subfloor, you have your choice of installation methods. You can float your floors, staple your floors, or glue your floors.
The underlayment sheets usually run in the same direction as the plywood subflooring, but it is critical that the seams of the underlayment are offset from those in the subflooring, so the underlayment bridges over the subfloor joints.
Generally speaking, LVP can be installed directly over subfloors such as concrete or ceramic tile assuming they're clean and level. Additional underlayment may be required if installing over existing hardwood or vinyl sheet floors to protect against moisture damage and sound transmission.
Sealing and waterproofing a wood subfloor is an important step in protecting it from moisture and other types of damage. You can seal a subfloor using a sealant specifically designed for subfloors, such as a penetrating sealer or a moisture barrier.
Moisture and mold protection
An underlayment that offers a vapor barrier is essential to protect any flooring installed over a subfloor that emits moisture, like concrete. A thin foam underlayment made of polyethylene or polypropylene usually works best.
Because a vapor barrier is a low permeable barrier, it keeps moisture from passing through. This is beneficial to keep moisture away from a dry surface but will trap moisture behind it if installed on a water-damaged concrete wall, causing the wall to fail further.
Is felt a good choice for hardwood flooring underlayment? Felt can be an adequate choice to use under hardwood flooring, in certain situations. Sometimes cork, rubber, or foam might be more suitable alternatives, depending on the features of the project.