How To Replace Wood Under Kitchen Sink: A Complete Guide

So, your kitchen sink has leaked for some time without you noticing it. The particle board making up the under-sink cabinet’s floor is all soaked and presents signs of mold. Now what? Fixing the plumbing issue won’t stop the cabinet floor from rotting. The only thing you can do is replace it.

To replace the cabinet floor under the kitchen sink, remove the floor’s middle section first, then remove the edges with a pry bar. You can then install new plywood flooring. Alternatively, you could consider installing pressed-cement backer board for a more durable, water- and rot-proof solution.

How Much Does It Cost To Replace Wood Under Sink?

Replacing the wood under your sink is cheap if you can tackle the project yourself and already have the power tools. Sandeply and oak plywood are your cheapest options, a four by eight feet sheet with a thickness of 1/4 inches costing between $18.97 and $25.97.

For a more solid option, such as 3/4-inch thick 5-ply birch, you can expect to pay about $44.97. Pressed-cement backer board costs more or less the same.

If you don’t have a circular saw and drill driver, you could rent these power tools from your local hardware or home improvement store. A saw would cost you about $62 per day or $42 for four hours. A drill driver will cost you about $24 per day or $17 for four hours. 

Even so, you can still save some money compared to hiring a professional. If you don’t feel like replacing the cabinet floor yourself, a contractor can charge up to $250 for labor alone, depending on where you live and the actual times it takes to do the job.

Things You Will Need

While replacing a cabinet floor could seem complicated, the project is easy and suitable for beginners and advanced DIYers alike. Before getting down to business, gather all tools and supplies listed below.

  • Plywood sheet
  • Framing square
  • Circular saw
  • Pry bar
  • Measuring tape 
  • Pencil and paper
  • Jigsaw
  • Drill driver
  • Plywood screws
  • Oil-based polyurethane 
  • Paintbrush
  • Pipe wrench
  • Goggles 
  • Mask with respirator 
  • Gloves 
  • Caulk 
  • Caulk gun 
  • Headlamp 
  • Sandpaper 

How to Replace A Rotted Cabinet Floor: Step by Step Guide

Have you gathered all the necessary tools and materials? Here’s how to replace the under-sink cabinet floor.

Step 1 – Clear the area under your sink 

Replacing the cabinet floor requires ample working space since you’ll have to operate a number of power tools. 

Perhaps you’ve emptied the cabinet already, but you also have to remove the P-trap if it hinders your movement. 

To do that, turn off the water valves under the sink and place a bucket under the trap. Use a pair of adjustable pliers to unfasten the ring nuts connecting the trap to the sink’s tailpiece and the wall drain, then remove it.

Step 2 – Remove the old cabinet floor 

If you haven’t done so already, put on and turn on your headlamp. Then, proceed to remove the old cabinet floor. 

There is no right or wrong way to do this, but most people find it easier to cut and remove the middle section first. Use the circular saw and cut as close to the edges as possible. Work your way around the perimeter, then use the pry bar to lift the base and take it out.

After you’ve removed the middle section, use the drill driver to unfasten the screws holding the old edges in place, then use the pry bar to remove them from their place.

Step 3 – Measure and cut the new floor 

Use the measuring tape to measure the interior of the cabinet. Write down the numbers on a piece of paper, then use the framing square and the pencil to mark the plywood section you have to cut. 

Place the plywood sheet on sawhorses and cut along the lines you’ve marked earlier with a circular saw. When you’re done, you can smooth out the rough edges with a piece of sandpaper if you want to.

Now, place the new floor inside the cabinet to check if it fits and to mark the spots where you should cut the slots for the water supply tubes. 

Step 4 – Cut the water supply tube slots 

Remove the new floor from the cabinet and place it on sawhorses again. Use a jigsaw to cut the slots for the water supply tubes.

Step 5 – Install the new floor

When you’re done cutting the slots, place the new floor inside the cabinet and fix it to the base with plywood screws. Fasten them using an electric or cordless drill driver for a secure fit.

When placing the new floor inside the cabinet, pay attention to route the water supply tubes through the slots you cut earlier. Otherwise, you may damage them as you’re installing the board.

Step 6 – Caulk around the edges 

Under-sink cabinet flooring is exposed to a lot of moisture, and water can seep under the new floor if you don’t seal it. Caulk does an excellent job in keeping water out and is relatively easy to apply with a caulk gun. Seal along all edges, then let it dry for a couple of hours. 

Step 7 – Seal the cabinet floor

You can extend the cabinet floor’s lifespan by sealing the surface with an oil-based polyurethane coat. Apply the product with a paintbrush, following the instructions on the paint tub. Let it dry as instructed and apply a second coat if necessary.

After this protective coat has dried, you can decide whether you want to paint the floor in the cabinet’s color or leave it as it is.

Step 8 – Install the P-trap 

Once the top coat is dry, reinstall the P-trap by fastening it to the sink’s tailpiece and wall drain. You can now place all the supplies you’re holding under the sink back into their place.

If you want to prevent future water damage, you can follow the same steps but replace the plywood with a pressed-cement backer board. You’ll need more advanced skills, though, since the pressed-cement is harder to cut and install compared to plywood.

How To Prevent Water Damage Under Sink: Tips and Techniques

Unnoticed leaks can be expensive to fix if they ruin your kitchen cabinets. Soaked wood can swell, damaging the cabinet finish. Mold and mildew will start growing, posing health risks, and the material will eventually rot. To prevent this, here are a few tips and techniques to use.

Seal the area around the sink

Using your kitchen sink means splashes, so sealing the area around your fixture is essential for preventing water damage. Apply caulk all around the sink and let it dry completely before using the fixture.

Seal the cabinets 

Waterproof top coats have been invented for a reason, and using them is only wise. Why risk spending hundreds – if not thousands – of dollars to buy new kitchen cabinets when you can take care of the ones you already have?

A polyurethane top coat is your best bet. Apply it on all wood parts, including a wooden countertop and inside the cabinets – especially on the walls and floor of your under sink cabinet.

Check your plumbing 

Leaks are sometimes hard to spot, so make sure to check your plumbing regularly. Don’t rely on eyesight alone. Use your hands and feel the area around your plumbing joints to make sure that everything’s dry and in good working order.

Keep the cabinet under your kitchen sink organized

As mentioned above, spotting a leak is often hard. Even more so when your under-sink cabinet is cluttered. Not only will all that stuff hide the water damage, but you could even damage the plumbing yourself as you’re rummaging through the things. Use containers and organizers to keep cleaning supplies and other items neat and tidy.

Use under-sink mats 

Under-sink rubber mats act as a barrier between the leaking pipe and your cabinet’s floor. These mats are available in various sizes, or you could cut them to size. 

Seal the under-sink cabinet floor with vinyl 

If you don’t like under-sink mats for one reason or another, consider protecting the cabinet floor with vinyl. Like the rubber mat, vinyl acts as a physical barrier between the cabinet floor and any leaks. 

Frequently Asked Questions

Replacing the wood under your kitchen sink could be intimidating if you’ve never done something similar before. Here are the answers to some questions you might be asking right now. 

What kind of wood goes under a sink?

Particle board is the most common material used in the making of kitchen cabinet floors, but we wouldn’t recommend using it. Manufacturers use particle board because of its low costs and because it’s easier to cut and shape than plywood.

However, particle boards absorb water faster and are more prone to rotting. For this reason, you should use quality plywood when replacing a damaged kitchen cabinet floor.

What happens if the particle board gets wet?

When a particle board gets wet, the material absorbs and retains the moisture. In time, it will swell and start to rot. Mold, mildew, and bacteria can also develop between the wood particles, feeding on organic matter. Not only will it become an eyesore to look at, but it can be bad for your health.

Next Steps

You now know how to replace the wood under the kitchen sink, but your job is not done. Before getting to work, find the leak source and fix it. Otherwise, the new floor will eventually rot, too, and you’ll have to keep replacing it over and over again.

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