A: Yes, premium T&G OSB subfloor can be used in a bathroom under plank vinyl flooring, but there are important considerations. While OSB is structurally sound, it's more susceptible to moisture damage than plywood.
OSB is not appropriate for a subfloor. Especially in a bathroom.
The best way to waterproof the OSB is to to use an oil based primer and put at least two good coats on it. Before you prime it, get a paintable silicone caulk and seal all of the joints in the subfloor, then apply the primer.
The strength of OSB boards makes them ideal for firm support in a heavy-traffic environment. If looking to install OSB as underflooring within a high moisture environment like a kitchen or bathroom, it's important to choose a moisture-resistant model.
Plywood is the correct substrate for a bathroom floor really - it has the best moisture resistance. While, ideally, your subfloor shouldn't actually get wet, there is always a puddle that seeps past a compromised mastic joint or something somewhere that gets it wet eventually.
The best flooring options for bathrooms are floors that can withstand moisture and humidity, aren't slippery when wet, are easy to clean, and comfortable underfoot. In terms of withstanding moisture and humidity, luxury vinyl tiles (LVT), vinyl roll, and porcelain or ceramic tile are the best bathroom flooring options.
A thickness ranging from 5/8-inch to 3/4-inch in plywood or OSB is typically sufficient. This thickness ensures enough rigidity to prevent the carpet from feeling spongy or uneven underfoot.
OSB is not waterproof or water resistant. Like most wood-based materials, OSB tends to expand and contract as moisture is wicked into and expelled out of wood fibers. The wood fibers exposed to the elements swell as they interact with moisture in the air and water droplets.
“The major disadvantage of OSB is that if it gets exposed to significant amounts of water or moisture, the edges expand by up to 15% ... especially if they are cut edges. This swell will then telegraph onto the shingles or some flooring," according to PATH.
There are three main methods we recommend for making OSB waterproof: sealants, waterproof paints, and waterproof membranes. Each has its advantages, and the best choice depends on your specific application.
Yes. Hardwood flooring is quite sensitive to moisture and it's always worth adding a moisture barrier during installation. It is a necessity with concrete subfloors and damp areas, but water-resistive underlayments should be considered with other subfloors as well.
As a waterproofing agent CuSTOM's RedGard will protect the OSB from moisture in the thin set mortar and subsequent surface exposure. As an anti-fracture membrane CuSTOM's RedGard will prevent any movement in the OSB from transferring to the tile assembly.
Furthermore, plywood generally has better moisture resistance than OSB, maintaining its structural integrity even when damp. Structurally it holds up well but visually, there are a few things to consider.
Backer boards serve as a stable and moisture-resistant surface to support and protect tiles from damage and moisture-related issues. As a result, they are commonly used in wet areas like bathrooms, kitchens, and showers, as well as for exterior applications.
Using OSB Safely
When installing in vertical applications such as wall sheathing, you'll want to orient the smooth or stamped side facing out. The smooth side has a better moisture resistance and will ultimately provide better performance against weather.
Underlayment is the material placed on top of the subfloor that assists in the installation of the tile or other type of flooring.
OSB can be manufactured into panels that are larger than plywood. OSB is more uniform, so there are fewer soft spots, such as those that can occur in plywood. OSB is less expensive than plywood. To build a typical 2,400-square foot home, OSB may cost $700 less than plywood.
Formaldehyde is a volatile organic compound that can cause respiratory problems and other health issues, so using OSB instead of materials with higher levels of formaldehyde can contribute to a safer indoor environment.
Although the surfaces of the boards repel water, their edges are somewhat more vulnerable. Whereas moisture causes ordinary wooden boards to warp, OSB panels that become wet or moist tend to swell at their edges.
Cement board is best suited for: Ceramic and Porcelain Tile: Cement board is specifically designed to be a moisture-resistant substrate for tile in high-moisture areas like bathrooms and kitchens.
If you use exterior paint, it can add another layer of weather resistance. However, paint will not make OSB weatherproof. To truly waterproof and weatherproof OSB, you will want to cover it with a sealer once you're done painting it and have it looking the way you want it to look.
Wood based sheathings (plywood, OSB) shall be at a moisture content of 19-percent or less. Some experts require a moisture content of 16-percent or less.
Both plywood and OSB are effective choices for your subfloor needs. 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.
OSB aka chipboard is a sheet material that's composed of layers of flat flakes of wood sealed together with phenolic resins. Most builders and renovation contractors insist that the best choice for a bathroom subfloor is plywood. And that too a thicker plywood to ensure that moisture doesn't absorb into it.
Assuming your subfloor is in good shape and level, your next step is waterproofing. Use a layer of unmodified thin-set mortar on your substrate, then add an uncoupling membrane, like Schluter®-DITRA & DITRA-XL. Then add another layer of thin-set mortar on top of the membrane, and finally, you place your tiles.