How to Fix Water Damaged Wood?

Wood by its nature is porous and tends to absorb water when there is significant contact time between the two. This is especially problematic for untreated wood, or wood with damage to its finish – which will allow water to enter undeterred. At this point, you’ll need to assess the extent of the damage, and decide whether to fix the water damaged wood – or simply replace it.

In most cases, the extent of water damage to wood will depend on the length of time the wood has been in contact with water. Long contact periods can cause wood to swell, deteriorate, and sometimes develop mildew or mold.

Even untreated wood can handle periodic contact with water provided it has sufficient opportunity to dry out. Generally, wood that sustains significant water damage tends to be wood that sits in stagnant water for long periods – like the bottoms of fence posts or the corners of exterior wood trim.

It’s for these reasons that wood – especially wood used in exterior applications – is treated or coated with primer/paint, lacquer, or stain. These substances create a water-resistant layer over the wood’s surface, preventing water from penetrating deeply into its pores.

Let’s take a look at the step-by-step process of how to fix water damaged wood.

How to Fix Water-Damaged Wood – Process

Step 1: Assess the damage

The first thing you want to do is assess the level of damage to your wood.

For exterior wood:

If you’re dealing with exterior wood, the potential for more serious structural damage is high. Examine the wood surface and look for conspicuous cracking/peeling paint, or swelling and crumbling wood. When you find this, use a screwdriver or knife to poke into the water-damaged wood – if it pushes through the wood easily, then you’ve got significant damage and will need to remove and replace the soft sections.

For interior wood:

Interior wood is typically less likely to suffer the same level of water damage as exterior wood, the exception would be serious flooding or leaks. In many cases, water damage to interior wood furniture can be fixed by simply drying out the furniture in the sun until any absorbed water has fully evaporated. If the water-damaged surface is not furniture, but something immobile like flooring, then you can use a space heater, fan, and/or dehumidifier to speed up the evaporation process.

Step 2: Remove Any Permanently Damaged Wood

If you’ve found any wood with permanent water damage, then the best thing to do is remove and replace the damaged section. Depending on the extent of the damage, this can mean replacing the entire section or patching and repairing it with something like wood filler or bondo body filler.

using a chisel to remove rotted wood
Removing water damaged wood from exterior window trim with hammer and chisel.

To accomplish this, use a hammer and chisel to extract as much soft water-damaged wood as possible. Then, clean out the remaining gap to remove any leftover splinters or dust.

To make sure the remaining wood is solid, poke it with a screwdriver. Anything that crumbles must be removed to ensure a long-lasting repair.

Step 3: Apply Wood Hardener (Optional)

This step isn’t strictly necessary for every job, but it’s particularly helpful for fixing water-damaged wood. Wood hardener is a liquid that penetrates deep into the wood fibers and petrifies them, transforming any rotten wood into a rock-hard material.

Apply the wood hardener according to the manufacturer’s directions, and allow it to dry fully before moving to the next steps.

Step 4: Prep the Surface and Apply Wood Filler

Before applying wood filler, sand down the surface and if the repair is on the larger side, fasten one or more screws into the gap to act as anchors for the wood filler.

Then, mix up the wood filler or bondo, and apply it to the gap promptly, before it dries too much. Try your best to form it as close to the final shape as possible as sanding it after it’s dried can be time-consuming.

Allow the wood filler to dry, and then sand away the excess until the repair is flush with the rest of the wood surface.

Step 5: Sand the Entire Surface

Sanding and then repainting the entire surface of the repair is useful to ensure it blends in. If the surface in question is large, then a belt sander is likely your best option to strip away the old coating.

sanding away excess bondo
Sanding wood repair in preparation for painting.

Start with a coarse grit sandpaper, and then work your way down to a finer 200+ grit sandpaper. This will help your finish adhere better, plus it will help mask the repair after the paint is applied.

Sand away all of the previous paint or coating and brush the surface clean.

Step 6: Apply Primer/Paint or Stain

You can apply paint, stain, or some other form of waterproof polyurethane coating, although clear coatings won’t hide a repair that involves wood filler. If you aren’t using wood filler, and are simply replacing a rotten section of wood with a new one, then stain or polyurethane are both good options.

If you’re going to paint, then applying primer first is a good idea. This will help your paint adhere to the wood surface better, which will help prevent further water damage in the future.

Apply several coats of paint to the surface, until you can no longer see the repair through the paint.

Denis Gardner

I've loved tinkering and fixing things for as long as I can remember. So, naturally, I gravitated towards DIY and home improvement when I bought my first home. Nowadays you can find me writing about my passions or messing around with my newest tool!

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