Does Pressure Treated Wood Rot?

One of the most troublesome problems with wood is rot. Natural wood will only last a year or two, maybe even less if you’re unlucky before it starts the horrible rot journey. In a bid to prevent this, people have turned to pressure treating wood.

But does that make the wood truly rot-resistant? Sadly, no. Although it resists rot far better and lasts longer, pressure treated wood used outdoors can still rot under certain conditions. The good news is, you can prevent it.

So, does pressure treated wood rot? Let’s examine the causes of rot in pressure treated wood and how you can stop it.

Does Pressure Treated Wood Rot?

Yes, pressure-treated wood will rot in a few years if not protected underground or if you go for the wrong grade. The chemical preservative improves its resistance to bacteria, insects, fungi, but this doesn’t last forever. For any DIY projects, pick the right grade for the intended use.

What Is Pressure Treated Wood?

Pressure treated wood is wood that’s treated with chemicals under pressure. The name sure gives away a lot. For years, people have treated wood with chemicals to make it resist rot better and last longer.

The same principle applies with pressure treated lumber, with the difference being the whole pressure treatment process is conducted in a pressure vacuum for the chemicals to be forced into the wood pores, replacing air. The chemicals used are arsenic, chromium, and copper.

Using pressure treated lumber indoors is not recommended due to the potential release of harmful chemicals. Opt for suitable untreated wood for indoor projects.

See Also: How to tell if lumber is treated

What causes pressure-treated wood to rot

Most pressure-treated wood rot because of fungal attacks. Fungi spores and water are a lethal combination. Fungi and fungi spores are present everywhere. Fungi will feast on moist and easy-to-eat wood and cause wood rot and decay.

But that’s all, let’s dive deeper into each one of them;

Fungal and Microbial Infestation

Builders and constructors love wood, and so do microorganisms. Fungi and bacteria are the most common culprits of microbial infestation on wood. These microorganisms grow in moist environments, meaning wet wood is a safe breeding ground for them.

Microorganisms multiply rapidly, constantly eating up the wood. Eventually, the deck starts to soften and decay, causing rot as we know it. Before long, the deck gives up and breaks apart.

The only aspect you can control in this is the moisture around the deck. Fungi spores are everywhere, always on the lookout for a suitable spot to start their growth cycle. But with dry wood, the fungi don’t grow at all or as well.

Water Damage

Water penetrating wood never ends well. Woods with high moisture content are more prone to rot. Aside from the obvious fact of the moisture damage of the wood, it also provides a microorganism-friendly environment. Note that microorganisms rarely grow in dry environments.

Pressure treated wood has its pores sealed during the treatment process, but cracks and bends can provide an avenue for water to get into the wood. This is common in cupped decks.

Chemicals reactions

Pressure treated wood, as we discussed above, is wood treated with chemicals under pressure. It’s the chemicals that are responsible for preserving the wood and making it resistant to rot. 

But being that they are chemicals, they can still undergo chemical reactions with galvanic nails or screws driven into the pressure treated wood. This kind of rot is known as galvanic rot.

It’s usually difficult to detect or solve galvanic rotted wood, usually requiring a replacement of the galvanic nails and screws.

Checking for Rots in Pressure Treated Lumber

First things first, What does rotting wood look like? Read to find out.

The way to check for rots in pressure treated lumber is similar to natural, untreated wood outside. Use your hands to feel the wood, looking out for any soft spots or areas that crumble easily under slight pressure.

For pressure treated decks, the most liable areas to rot are the supports and beams, so pay extra care around these areas. Also, the base of wood stairs and areas where two pressure treated wood trims meet are liable to rot.

How to Prevent Pressure Treated Wood Rot

Pressure treated wood will at long last meet the fate of all woods – rot – if the storage conditions aren’t optimal. Fortunately, you can prevent this rot, or at the least, retard it to the barest minimum.

Using sealers

Sealers are substances that seal wood’s surface, as the name suggests, providing an extra layer of protection. They involve paint, stains, varnishes, sealants, oils, etc. These substances will improve the durability and longevity of your pressure treated deck. Nowadays, you can find sealers that are specially made for pressure treated wood.

The good news is these sealers are readily available at local wood hardware stores and cheap, so you save money. The bad news – their protection isn’t absolute. This means you still need to reapply the sealers after they wear off. Some sealers need to be reapplied more frequently than others.

For instance, sealants, which protect pressure treated lumber from moisture, need to be reapplied every year. You can also get longer-lasting sealants but at a higher cost.

How to seal pressure treated wood

Ensure your deck is completely dry before applying the sealer. You may need to wait months for the deck to be dry in some cases. To know when your pressure treated  deck is completely dry, sprinkle some water on the surface. 

If the water absorbs into the deck, then it is dry, and you can proceed. However, if the water beads on the deck surface, you need to wait some more.

Letting the wood dry is critical for the activity of most sealers, although some sealers are still effective on wet wood. Using a brush, coat your pressure treated lumber with the sealer. You should pay close attention to the ends of the wood, as they are the easiest way moisture and insects can get inside your wood.

Some sealers may require pressure spraying. For these, ensure the pressure isn’t too high to protect the integrity of your wood surface. Brush out the wet coating after you are done spraying.

After sealing, you can sprinkle water on the deck surface and see how fast the water is absorbed into the deck. If it’s quite fast, you need to recoat the deck.

The same procedure applies for recoating, emphasizing letting the deck dry before applying your sealer.

Read also: How to seal pressure treated wood cuts.

Using mildewcides

Mildew is a form of fungus. By implication, you need to prevent them from growing on your wood. One way to do this is by cleaning the wood with mildewcides. This is nothing out of the ordinary, as many commercial cleaners in hardware stores can kill mildew. 

For best results, you should clean the pressure treated lumber with mildewcides and let it dry before coating.

Application of UV stabilizers

UV stabilizers are additives that impart UV resistance properties to wood preservation coatings and finishes. This is crucial because pressure treated wood, like natural wood, isn’t resistant to UV rays.

UV light. This implies that exposure to sunlight can alter the appearance of pressure treated decks and fences. To prevent this, the finishes and coatings used for the pressure treated decking should contain UV stabilizers.

Frequent inspection

Frequently inspecting your pressure treated wood deck in itself cannot prevent it from rotting. But, it can let you know when your wood is already or about to start rotting. 

It also lets you know when you need to reapply coatings or finishes to the wood, particularly with sealants that need to be reapplied periodically.

Recommend Reading: How to keep untreated wood from rotting

Disposal of Pressure Treated Wood

Pressure treatment involves forcing chemicals into the wood at high pressure. The chemicals are what prevent wood decay. And as with all forms of chemical treated substances, you need to be careful when handling or disposing of pressure treated wood.

Under no condition should you burn the wood. Don’t even think of it. This is because burning will heat the chemicals, and they can be released as fumes that are toxic when inhaled. Also, you need sufficient protection when handling the pressure treated. 

At the minimum, you need to handle the decking with a dust mask and hand gloves in a room with proper air circulation.


What keeps pressure treated wood from decaying?

To prevent pressure-treated wood from decaying, use a high-quality wood preservative or sealer. You can protect your treated wood against elements such as water and UV rays that cause decay by applying stains, paints and sealants. Just make sure the wood is dry enough before using any treatment.

Related read: Does bleach prevent wood rot?

Is pressure treated lumber safe?

To a certain degree, yes. Health hazards only arise when you try to burn the wood or break it apart without adequate protection. Burning the lumber can release the chemicals in it in the form of toxic fumes. You should also refrain from pressure treating kitchen cutting boards. Besides, you have little to worry about in the safety department.

Can concrete rot pressure treated wood?

No. Pressure-treated wood put on concrete do not rot. It is resistant to rot and perfect for outdoor use like decks and patios on concrete surfaces. Before installation, prepare the concrete properly. Then, securely nail pressure-treated wood boards onto the concrete for durable and long-lasting applications. Concrete won’t cause rot in pressure-treated wood.

When should I use pressure treated wood?

The primary reason for using pressure treated wood in the first place is its longer durability and improved resistance to rot than natural wood. They are used for outdoor projects because of the higher probability of moisture and insect damage. Some wood, like cedar and redwood, are insect repellent, and pressure treated wood may not be a necessity in such cases.

Read this guide on the difference between cedar and pressure treated wood.

Is sealing necessary?

Sealing is important for lengthening the life cycle of pressure treated wood material. Although they are more resistant, pressure treated wood will still rot after some time. This rot can be prevented by sealing the wood with paints, stains, sealants, waxes, etc. After sealing, periodic inspections of the wood are important to ensure the sealers are still in place.

Can I paint pressure treated wood?

Yes, you can paint pressure treated wood. The only condition is ensuring it is dry before applying the best paint for treated wood. To be sure the wood is dry, carry out the water test. Sprinkle some water on the wood. If the water seeps in quickly, you can proceed with your painting; if it forms beads on the surface, you need to wait some more. You may also need to paint before the deck is installed.

Can I pressure-treat wood myself?

Pressure treatments aren’t easy procedures by any means. They require a depressurized holding tank and high technical expertise to carry out successfully. Therefore, it’s almost impossible that you will be able to carry out the process yourself, even if you have the necessary equipment. Also, the chemicals used are dangerous, and ingestion, even in small quantities, can result in serious health hazards.

How long does pressure treated wood last?

Pressure treated wood isn’t all the same. Some will last longer than others. Deck boards and floors may last about ten years, while poles and fences may last 40 years. Wood exposed to high humidity will last less than those exposed to dryer conditions. In essence, what determines how how long pressure treated wood lasts is the climate, type of deck, and coatings.

Does Treated Wood rot?

Pressure treated wood is wood that’s treated with certain chemicals under pressure. The pressure forces these chemicals into the wood, replacing air in the wood. The added preservatives make the wood products more water repellent and resistant to insects.

However, this protection isn’t absolute, and even pressure treated wood will rot after some time. Luckily, this rot can be prevented or limited to the bare minimum by adding sealants, paints, stains, mildewcides, UV-stabilizers, etc. These provide additional protection for the lumber.

A word of warning, though – never burn pressure treated wood because it can release toxic fumes. You should also handle the wood with adequate protection.

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