How To Fix Rotted Wood With Epoxy: The Essential Guide


It can be really disheartening to discover that your favorite wood has been riddled with rot and now it’s weak and you’re wondering whether it can be fixed or if you have to replace it? Well, you may well be able to salvage it using a very simple methodology using epoxy resin and we can show you how. 

How to fix rotted wood with epoxy: the essential guide includes an overview of epoxy for wood repair, the three main epoxy products for wood repair, when to use epoxy to repair rotted wood and then a full process to carry out the most common kind of cosmetic repair using epoxy around the home. 

We walk you through everything you need to know to tackle rotted wood in your projects from the tools that you need to the potential pitfalls you will face, you’ll learn that repairing rotten wood with epoxy is surprisingly easy and how to keep your costs to a minimum while you do it. 

An Overview Of Epoxy For Wood Repair

Epoxy is a word that sounds like it refers to a single thing, particularly, when it’s used in woodworking circles. Yet, it’s not. It’s actually a whole group of different “thermosetting polymers” (that is plastics which cure with an exothermic – heat-releasing – reaction).  They were invented during World War 2. 

They are two-part systems (generally supplied as A and B or different cans) which consist of a resin and a hardener. When you repair wood, you’re going to mix these two together first to form a gel for working with and then to form a solid in the wood itself. 

It’s important to choose an epoxy designed for working on rotting wood because this means it will have been formulated to do the best work. It’s not that you can’t use other epoxies, it’s that they may not last as long or as well.

The Three Main Epoxy Products Available For Wood Repair

There are three main epoxy products used in wood repair:

  1. Epoxy consolidants
  2. Epoxy primers
  3. Epoxy paste fillers

What Is An Epoxy Consolidant?

An epoxy consolidant is used when the wood is roughly in the same shape as it always was but has lost some structural integrity thanks to damage (rot/fungus or sometimes, insects). 

The consolidant is then used to help to reinforce the wood fibers that are still there.

It’s a form of epoxy resin which was designed to be runnier than usual epoxy (i.e. it has low viscosity) and that means it can easily be absorbed by the wood that you pour it onto. 

The theory is that it will penetrate to the deepest part of the damaged wood and seal it to not only return some of the strength to the wood but also to prevent future damage. 

If you need to use consolidant over a large volume of wood it can help to drill some smaller holes along the length of the wood to help increase the absorption of the consolidant and, in fact, you can often purchase small squeeze bottles designed to fill such holes easily. 

One nice thing about working with epoxy consolidants is that they preserve much of the character of the original wood – however, it is worth remembering that you cannot undo work you do with an epoxy consolidant. 

What Is An Epoxy Primer?

An epoxy primer’s job is simply to act as a bonding layer between the wood and the epoxy. There are many different types of primers, each tailored to a specific binding site and it’s important to select the right ones for working on a repair of your specific type. 

What Is An Epoxy Paste Filler?

While consolidants are there to restore the original integrity of the wood under repair, you use an epoxy filler to replace any fiber that has been lost from the wood

When the two parts are mixed, the epoxy paste becomes a sort of gap-filling paste. The epoxy paste filler tends to perform better than old-school wood putty because it can be formulated to flex with the wood, and it bonds with the wood to form a strong, lasting bond.

You can use an epoxy paste filler to replace rotted wood that you’ve removed or to repair voids and holes that have resulted from other minor problems

You can also use it to reconstruct lost wood features, you do this by using multiple layers of the product and then by forming and shaping it.

It is possible to stain and/or paint a paste filler (either during mixing or after the work is done). 

Best Epoxy To Fix Rotted Wood?

The best epoxy to fix rotted wood is simply the right epoxy for the job. As you can see there are three types of epoxy each with a different purpose. You might need all three on the same repair, you might only need one. 

When Should I Use Epoxy On Rotted Wood

Epoxy has become a very popular way of replacing rotted wood. It’s quick to work with and can be very convenient. However, in certain circumstances it may not be ideal for use – certainly, those looking to repair historic wooden items might want to consider using traditional repairs made of wood because using epoxy will change the appearance of the repair and it cannot be reversed.

It’s also worth noting that using wood over epoxy may have cost benefits too. Epoxy is not the cheapest substance to use and for major repairs, it can often be cheaper to replace the wood

However, epoxy can be invaluable when the component you want to replace is hard to remove or might be very challenging to engineer

So, to sum up, epoxy is not always suitable for repairing wood. There are specific circumstances under which epoxy is the perfect choice for working on rotted wood and we’d say they are one (or a mixture of) the following:

  • Only 15-20% of the wood is rotten. Epoxy needs quite a bit of the rotted wood to bond with if you want a good result with it.
  • When the thing you are working on would be very challenging to replace with wood – so anything that requires complicated machining or hours of handwork would be ideal
  • When the thing you are working on can’t be easily removed to be replaced without disassembling the whole of the wooden piece

If you’re facing higher levels of rot, then a dutchman’s patch or a splice or even replacing the entire element are going to need to be considered for your rotted wood. 

It is worth noting that to work successfully with epoxy on wood – you must soak the damaged wood thoroughly in an epoxy consolidant prior to working with epoxy – the purpose of this consolidant product is to fully seal the wood and ensure that the decay is sealed away. This stops further rot and decay.

Your other choice is to completely strip all the decayed wood which is, of course, often easier said than done. Even then, you will either need to coat the exposed wood in an epoxy consolidant or with an epoxy primer. 

One final thing – it’s also important to work out why the wood was rotting and fix it. For example, it might be sitting under an overflowing gutter which is causing it to become too moist. You need to fix the gutter as well as the wood if you don’t want the problem to quickly return. 

The Tools You Need To Fix Rotted Wood With Epoxy

OK, it’s time to get practical and if you want to fix some rotted with epoxy, you’re going to need a few tools – fortunately, we think you’ll have most of these already and won’t need to make a trip to the hardware store to buy them:

  • Chemical Resistant
  • Chisel (for Wood)
  • Drill and Drill Bits
  • File
  • Hammer
  • OSHA approved Vapor Respirator
  • Paintbrush(es)
  • Putty Knife
  • Rasp
  • Safety Gloves
  • Safety Goggles

The Materials You Will Need To Fix Rotted Wood With Epoxy

You will also need to buy a few materials to get working with too. Fortunately, this isn’t going to require a long list of products:

  • A Small Squeezy Bottle
  • Acrylic Paint
  • Epoxy Paste Filler
  • Primer
  • Sandpaper
  • Epoxy Wood Consolidant

How To Fix Rotted Wood With Epoxy

OK, we can’t tackle every type of wood repair in this article because that would take forever – so, we’re going to tackle the most common type of cosmetic repair that you’re likely to carry out in the home.

We’re not tackling major structural repairs here and this is important – if you’re trying to fix a load-bearing timber, it is vital that you get training and/or expert advice on the subject. We don’t want to give you advice that might lead to the collapse of something important and/or expensive. 

Working with epoxy on rotted wood is very easy, indeed, and we think it’s quite a lot of fun too – there’s something very satisfying about restoring a damaged piece of wood. 

We will be using two types of epoxy in conjunction here: the epoxy consolidant and the epoxy paste filler. It’s important to make sure you use the right one at the right time in the job as getting them mixed up is going to lead to some fairly serious and possibly irreversible problems. So, don’t rush this – make sure you’ve got the right tools in hand at each stage. 

Work Out How Much Rot There Is

Possibly the most important part of repairing rotten wood is to work out a.) where the rot is and b.) how to stop the cause of it. 

Typical issues around the home might include leaking gutters, contact with concrete (through which moisture can leach), chipped paint or other coatings which allow water through, etc. 

If you can identify the problem – then you can fix it. You can isolate the wood from the concrete or repair the gutters and in the instance of paint problems (which, for the sake of this exercise, we’ll assume are a guarantee) you can paint a new coat on after the repair.

However, if you can’t identify the problem, you shouldn’t give up and make the repair anyway. You need to ask for help – get in touch with a building contract or even better, ask a housing inspector, and get them to work out what the problem is. 

Once you’ve addressed the problem of what’s allowing the water in (except the paint), you need to allow the wood time to dry. If you work with epoxy on wood that’s full of trapped moisture, then you’re asking for future problems.

It’s not that epoxy can’t tolerate moisture at all but too much of it and the bond will not form correctly between the wood and the epoxy and you may leave moisture trapped below the epoxy which will continue to promote rot and decay.

Once you’ve left it to dry, then you can start to assess how much rot damage there is to your wood. We’d use a screwdriver (or an awl will do fine) and just push it into the wood, the further it sinks in – the more rotten and damaged wood you have. 

It’s important to note that before we can move on to repairing the wood, we’re going to have to remove the rotted wood. 

Get Rid Of All That Rotted Wood

Before you begin removing the wood, you can strip off the paint over the wood – use a paint stripper to get this done quickly and efficiently. You’re going to end up repainting at the end of the job – so, it’s fine to get this done now, as you can’t work without access to the wood throughout.

If you suspect that the paint that you’re removing is old enough that it might contain lead – you should take special precautions to strip the paint (there are specific lead-based paint removal techniques). 

Once that’s done, it’s time to gouge out all your rotted wood – you can use an old screwdriver for this or a chisel or anything else that’s reasonably tough and works for you. You’re looking, wherever possible, to get right down to solid (not rotten) wood. 

Then once that’s done, you want to drill a series of holes about 1 inch apart and about ¼” deep across the surface of the wood. This is going to allow your epoxy consolidant to get deep inside the wood and really bond with the wood. 

If you’re on a vertical surface, angle the holes down slightly so that you can fill them with consolidant without it pouring straight back out again.

If you find that you’ve drilled all the way through your wood so that the hole is now a tunnel rather than a hole – make sure to plug the base of the hole (you can use an oil clay for this) to prevent the consolidant from pouring straight through. 

It’s Time To Add The Liquid Wood Epoxy Consolidant

OK, now it’s time to get to the epoxy wood consolidant. Don’t rush this part as the epoxy is very slow to cure and you’re not going to need to worry about it setting before your work is done.

Also, you should always wear safety glasses, rubber gloves and ideally a vapor respirator too if you are working indoors, if you are outdoors in a very well-ventilated area then you may find that you don’t need the respirator.

You start by mixing the two halves of the epoxy together (that’s the resin and the hardener) this will normally be in a 1:1 ratio but it’s best to check and read the manufacturer’s instructions before you begin – you don’t want to get this wrong because otherwise, the epoxy may be too soft or too inflexible for your needs.

Once you have the mixed epoxy, you will need to work it into the wood – squeeze it into the holes until they are full and over the wood in the whole area of repair. Use a disposable paintbrush to work the epoxy into the wood. You want to saturate the wood with epoxy wood consolidant – so keep going until it is.

Next, you want to make sure that the wood cannot get wet if you’re outdoors – just tape some plastic over it but so that it fits loosely allowing the curing to take place.

You want to allow about a week for the epoxy wood consolidant to cure fully. If you don’t allow for this – it won’t be fully hardened when you start the next part of the work. 

Then Mix Your Epoxy Wood Filler

OK, it’s on to the main event when we use epoxy wood filler to tackle the holes in the wood. This part requires a lot of attention to detail and is conducted under time pressure:

How To Mix It

Mix the two parts of the epoxy wood filler together, you do this on a piece of scrap plywood and use a stiff putty knife to combine the two parts. You want them to be completely blended. 

We’d recommend that you label the containers with parts A and B in them, just to be certain that you don’t get the wrong one while you’re mixing. We’d also recommend that you label your scoops for each part because it’s a bad idea to plunge the wrong one into the wrong container. 

Never put the cap from Part A on Part B or vice-versa as they will glue themselves on at this point.

The Temperature Factor

Epoxy wood filler starts to harden at about 70 degrees Fahrenheit. You can slow down the curing reaction by dropping the temperature and you can heat it up to make it cure faster. This can be very useful if you need more time to mix (work in the shade) and if you want to speed up the epoxy repair – you can take a hairdryer to the finished product.

Get Moving!

You’ve got about 30 minutes to work before the epoxy cures too much and you can’t work with it. 

Never mix fresh epoxy in a space where epoxy was previously mixed and is still present as it may accelerate the curing speed. 

How To Fill The Wood Cavity

OK, this is the easy bit – you press the putty you’ve created into the area with a putty knife. Press down hard – you want to make sure it fills all the voids and creates a very strong bond with the rotten wood below.

Note: Epoxy wood filler is expensive. You don’t want to fill a giant space with it. If you’ve got a really big area to fill, cut up some other blocks of wood and use them to fill most of the space and then use the epoxy to seal them in. Make sure to use wood of the same type and line up the grain if you want it to look right when you’re done. 

When Too Much Is The Way To Go

You want to use more epoxy than you need at this point. Get some chemical-resistant gloves and put them on, if you’re not already wearing them and then use your fingers to shape the excess so that it roughly matches the profile that you’re looking for. Don’t worry about having too much – do worry about having too little. 

Shape The Profile Of Your Epoxy

You’ll want to push the epoxy around with your fingers and possibly a scrap of wood and add any more filler that you need to really be certain that you have the space done. Use enough material that you know you can match the profile of any surrounding pieces when you wear it down. 

You should find that on a warm day – it only takes about 4 hours before you can shape this, though if it’s cold, you may need to leave it overnight. 

Trim The Epoxy Down To Size

Now, it’s probably time to file the epoxy filler down to the right size. You can easily check this – if you can dent the epoxy with your fingernail, it’s not ready. 

If you can’t. It is.

Epoxy is very easy to work with basic woodworking tools and you can easily sand and file it.

Work With The Shape Of The Wood

Get that coarse rasp and use it to remove the biggest bits of epoxy and to get the repair into the rough shape that you want it to be. 

Once you get down to the detail, you might want to grab smaller, finer rasps of different persuasions or you might go old school and grab a dowel and wrap it in 80-grit sandpaper

Be guided by the shape of the profiles around the wood.

Don’t worry if you file off or sand off too much, you can add a second application of epoxy filler if needed.

Retouching is easier if you combine some consolidant with your epoxy filler (mix the two separately and then put them together) as this will make the filler more fluid and easier to work in a more precise manner.

You can expedite the repairs that you make here, along using a hairdryer. 

The Fine Details – When A Plan Comes Together

Now, sand the surface over with an 80-grit piece of sandpaper and then a 120-grit piece. We’d always recommend using a dust mask and some safety glasses when sanding. You can then clean up the dust with a vacuum cleaner. 

Time To Paint

Then to paint the surface, all you need to do is apply some alkyd primer because that seals the repairs. Finally, you can add a couple of coats of acrylic paint (we’d recommend using a good quality paint because it will save having to carry out repairs in the future).

Then finally caulk the joints and apply another coat of acrylic paint. 

You’ll want to check on your paint job annually to make sure that it’s standing up to the test of time and if not, reapply some more paint and/or caulk as necessary. 

Conclusion

We hope that how to fix rotted wood with epoxy: the essential guide has helped you understand what you can achieve for rotted wood with epoxy resin. If you’ve got cosmetic repairs to make to wood – it’s a very simple process which is quite a lot of fun to carry out.

However, we would warn you that if the wood you are trying to repair is load-bearing, you need to talk to a professional before trying to tackle the project as if you get this wrong, the outcome might be very dangerous, indeed. 

Jedediah Arnold

Jedediah has been working with epoxy resin for a couple of years. When he started, he wanted to share everything he learned as he learned it which continues.

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