Should you waterproof the subfloor?

Author: Mrs. Lavinia Wolf  |  Last update: Thursday, July 24, 2025

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.

Should you seal the subfloor?

Subfloor sealing is not required. It is not even recommended, but if bonding is a concern, dont seal the subfloor. Instead, use some clear-set thin-spread vinyl tile adhesive to aid the tile in bonding to the subfloor.

How do you waterproof a plywood subfloor?

The most common ways of waterproofing plywood include treating the wood with epoxy, waterproof glue sealant, or polyurethane prior to installation.

Is it OK for subfloor to get wet?

Subfloor materials are strong, but when water leaks beneath your finished flooring, the results can be expensive and disastrous. Subfloor water damage must be addressed immediately. Wet subflooring is not a problem that can wait.

How do I keep my subfloor from rotting?

How to protect your crawl space from wood rot
  1. Use a commercial subfloor sealing product like LumberKote to make exposed wood water resistant.
  2. Keep your rain gutters and downspouts in good repair.
  3. Inspect your crawl space at least once a year for signs of excess moisture.

Waterproof Under LVP Flooring In Bathrooms

How do you moisture proof a subfloor?

Add a vapor barrier

Adding a vapor barrier entails adding an underlayment below the subfloor in order to keep ground moisture from seeping into the subfloor. If you suspect that the moisture issues are caused by water vapor coming from the ground, this can be an excellent solution.

How much does it cost to replace a rotted subfloor?

The national cost range for replacing a subfloor is between $600 and $2,500. Most homeowners pay around $1,600 for a 200 sq. ft. area in a kitchen or living room using OSB board.

Is the subfloor waterproof?

While there are different types of subfloors, the most common type is made from plywood. This is because it is straight, flat and relatively strong. It is also cheap and while it is not waterproof, it can resist sharp changes in humidity. Plywood also can become water resistant by purchasing a moisture barrier.

Do I need to replace moldy subfloor?

When Should You Replace Subfloors? There are many signs that your damaged subfloor should be replaced with a new subfloor. These include squeaks and other noises, cupping or warping, cracked or popped tiles, sagging or unevenness, the smell of mold or mildew, or bubbling tile.

Does subfloor need a moisture barrier?

Subfloor Material

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).

What is the best waterproofing for plywood?

Epoxy. Epoxy sealers are usually the preferred method of sealing and waterproofing plywood. Epoxy doubles as an adhesive, which gives an additional layer of strength plus protection for the wood, helping it to last even longer.

How do you protect a subfloor from water damage?

One solution to help protect the sub-floor from rainwater damage during construction is to use LP® TopNotch® 350 Durable Sub-Flooring. What is LP TopNotch 350 Durable Sub-Flooring? LP TopNotch 350 Durable Sub-Flooring is an OSB sub-flooring designed to reduce the impact of moisture during construction.

What is the cheapest way to waterproof wood?

The most affordable way to waterproof wood is by starting with a natural wood oil and following with a coat or two of outdoor paint. Though more budget friendly in the short term, you will need to redo this method more frequently, as it is not as long lasting as, say, a pricier, high-quality sealant.

Can I put flooring directly on the subfloor?

Most modern vinyl flooring, such as Happy Feet, comes with an attached underlayment or pad, often with a moisture barrier built-in – unless the pad is cork. If the product you choose doesn't have an attached underlayment, you can almost always install directly over the subfloor without one.

How long should a subfloor last?

However, it plays a major role in supporting certain types of flooring, like hardwood floors or carpeting, which can't be attached directly to the floor joists in your home. A subfloor can last up to 30 years but does eventually need to be replaced.

Is subfloor ruined if it gets wet?

A wet subfloor doesn't always need to be replaced, but it must be thoroughly dried and assessed for damage. Use fans and dehumidifiers to dry it out. If the subfloor is swollen, warped, or has mold growth, replacement is necessary.

How much does it cost to replace mold on subfloor?

Subfloor Cost per Square Foot

Subfloor replacement typically costs about $3 to $10 per square foot. This range can vary based on labor costs, which will add $25 to $30 per hour, and the type of subflooring you choose.

How often should a subfloor be replaced?

Subfloor typically lasts 30 years or more, but if it is consistently exposed to moisture you may need to replace it sooner.

Do you need to seal subfloor?

To summarize, repairing and sealing your subfloor is an important step in ensuring that your finished flooring lasts for many years.

How to tell if a subfloor needs to be replaced?

Here are five signs it's time to replace a subfloor.
  1. Those squeaks could be calling for your attention. ...
  2. Sinking sections are tell-tale signs of subfloor failure. ...
  3. Moisture could be causing your cupping floorboards. ...
  4. Cracked and popping tiles could be a material issue. ...
  5. Possible water damage is always a concern.

How do you fix moisture in a subfloor?

The first way that you can fix a subfloor moisture problem is by removing the finished floor and exposing the subfloor. Make sure that an HVAC system is installed or use a dehumidifier, and then, let the subfloor dry until the moisture levels have gone down.

Does insurance cover rotted subfloor?

Generally, no. Insurance would cover a sudden loss event. A slow leak causing rot over an extended period of time is not a sudden loss event.

Can I replace my own subfloor?

Replacing a subfloor may seem like a daunting task, but with the right tools, materials, and know-how, it's a project that can be tackled by DIY enthusiasts or professionals alike.

Does subfloor rot spread?

Once dry rot occurs, it can quickly spread to nearby wooden structures, causing further damage and increasing your repair costs within a surprisingly short period.

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