How to Repair and Prevent Door Rot

Rot is a problem that’s plagued timber for as long as human beings have been making things out of it. It’s especially troublesome in the case of doorways, which not only need to look great, but which also serve an important security function. Let’s take a look at rot in doors and how best to deal with the problem.

What Causes Door Rot?

‘Rot’ is what happens when a material is eaten by microscopic organisms. In the case of wood, fungi are usually responsible. As they chew through the wood fibres, the timber begins to lose its structural integrity, until it eventually falls apart. If the wood is supporting something, then this can be disastrous!

The sorts of fungus that cause wood to rot need moisture to survive. If the timber is soaked through, then they’ll spread rapidly. That’s why timber storage facilities insist on such tight humidity controls; even the slightest variation can have disastrous consequences.

Timber rot comes in two forms: dry rot and wet rot. The former requires just 20% moisture content to get started, the latter closer to 50%. In both cases, you’ll need to deal with the source of the moisture to prevent the problem from recurring.

How can You Tell if Wood is Rotten?

Rotten wood evidences itself via a few different symptoms. Let’s take a look at dry rot first:

1. To begin with, dry rot will look a little bit like a sheet of cotton spread over the wood. These are the hypnae.
2. When the hypnae germinate, they will form into large clumps.
3. Finally, you’ll see these clumps form into actual fungus which will release more spores.
4. Timbers which are infested with dry rot will begin to split and crack. Look for long cracks running across the grain.
5. Eventually, dry rot will cause the timber to weaken. Apply some light pressure with your fingers. If the wood buckles, or even crumbles, then you have a dry rot infestation.

Wet rot is not quite as dangerous as dry rot, but it’s still worth looking out for. Concentrate your inspection in places where moisture is likeliest, such as outdoor porchways.

1. Check finished surfaces by applying pressure with a thin knife. Healthy timber should offer a bit of resistance; if the blade sinks in easily, the chances are strong that you have a problem.
2. You can repeat this inspection with your fingers; a spongy texture indicates that all is not well.
3. Rotten timber also looks different. The timber will tend to look a little bit darker, even beneath a coat of paint.

How to Fix Door Rot

Let’s look at how to repair door rot. Rotten wood needs to be removed and then replaced. The way you do this will depend on how far the rot has spread. 

1. Start by removing the rot. If it’s just a small area, then you can do this with a Stanley knife or other sharp tool.
2. Next, it’s time to fill in the gap. Do this with a polyester-based wood filler. If you’re fixing a natural-grain door, then pick a wood-coloured filler. If you’re fixing a white door, then choose a white filler.
3. Spread it into the recess so that it sits slightly flush from the surface.
4. Allow the filler to dry.
5. If necessary, apply another coat.
6. Sand the filler down to a smooth surface.
7. Using a damp cloth, wipe away any loose dust.
8. Finally, it’s time to prime and finish the wood. If you’ve done everything right, the transition should be seamless.

In some cases, the rot might be so extensive that you need to cut out and replace large portions of the trim (or the frame). The procedure in such cases is similar; you’ll just be applying wood-filler to the crack between the joins, so that you get the appearance of a single uninterrupted length.

How to Prevent Door Rot

Prevention is better than cure – and this is especially so when it comes to rot in your external doors.

Inspect your doors occasionally. Make a point, once a year, of going around and looking for any cracks that might have appeared in paintwork.

If you notice cracks, then moisture will have a point of entry. Sand down the offending surface and refinish it.

Before you assemble a new door, you can cover the adjoining walls in sealer. This will prevent moisture from spreading in from beneath.

Once the timber is in place, you can prime it. If you do this before attaching the hardware, you’ll be able to more easily cover the entirety of the door.

Finally, it’s worth looking into a weatherboard. This is an angled strip of material that sits at the bottom of an external door and prevents water from collecting at the base of the frame.

You can also limit the amount of water that falls on your door frame in the first place. If there’s a gutter overhead, make sure that it’s regularly cleared to prevent it from spilling down onto the door. 

In Conclusion

Timber rot can be a big problem, but if you catch it early, then you can intervene before it does too much damage. Prevention is key, and thus it’s important to inspect all of your wooden doors for problems proactively, and that you take steps to remove the source of any damaging moisture. External doors, along with those in kitchens and bathrooms, should be considered a priority.