When you start looking to work with resins in your woodwork projects, it can be quite confusing as to whether you need epoxy or polyurethane for the job in hand. We can help you make the decision, that’s right for your project, with this handy guide.
Epoxy or polyurethane for wood? There are many pros and cons of each, here are our top 9 considerations:
- Reactivity with other products
- Reactivity with sunlight
- The cost of the products
- The durability of the products
- The resistance of the products to moisture
- The hardness of the end product
- The scratch-resistance of the end product and more
While these are not the only two options, there are wax, lacquer, oils, and many other in-betweens, this post is going to examine just the difference between epoxy and polyurethane and what common use-cases are.
What Is Epoxy And Why Should I Consider It For Wood?
Epoxy resin is a two-part compound which when you combine the two parts (a resin and a curing agent/hardener) it undergoes a chemical reaction (which releases heat) to become a hard and reasonably rigid substance.
Epoxy has a large number of uses in woodwork (and indeed, in other home and industrial design projects) including:
- As an adhesive. Perhaps the most common use of epoxy resin is simply as an adhesive. Epoxy bonds brilliantly to almost any surface and that makes it quite easy to join two different materials together with it. Once the glue has cured, the epoxy bond is very strong and is likely to deliver a lasting join.
- As paint. Epoxy paints are used in many different settings and, in fact, if you have white goods in your home (such as a dryer or a stove) then they are most likely painted with epoxy-based paints. However, in general, epoxy paint is not used on wood but rather on metals.
- As a coating or sealant. The other most common use of epoxy in-home projects, particularly, is the use of epoxy as a coating or a sealant. In fact, epoxy resin is so useful for coating and sealing applications it can be used to create flooring and countertops too. It is often the most cost-effective option in environments where hard-wearing isn’t a major concern.
- As a repair agent. Epoxy can be really useful for strengthening other materials. In woodwork, it can be used to replace rotten or damaged wood and the final resin product is likely to be at least as strong as the wood that it replaced.
Epoxy is not the perfect choice for every woodworking project but it’s one of the most flexible materials available to woodworkers and it’s likely to be very useful in a multitude of projects at home and even sometimes on a commercial basis too.
What Is Polyurethane And Why Should I Consider It For Wood?
A polyurethane resin is also a two-part compound which consists of a resin and a hardener but unlike with epoxy there is a greater degree of flexibility when it comes to the finished product and it is up to the user to decide the ratio of compound to hardener to use to bring out the right properties in the end product.
There are plenty of uses for polyurethane resins too:
- As an adhesive. Polyurethane will not bond as wide a range of materials as epoxy resin will but in the case of fiber, wood, leather, etc. it creates a perfectly serviceable bond and one which is likely to be clear in appearance as well as strong.
- As a varnish style coating. Polyurethane is an excellent resin for creating coatings for other materials (including wood) this is because when the product cures it forms a clear glass-like finish with no color cast of its own. This can be very important in some projects and it’s often a strong reason for choosing polyurethane as a coating substance.
- As an abrasion-resistant coating. Polyurethanes will absorb impacts and ward off scratches in even the toughest of environments. Untreated steel, for example, will last roughly 8 years in an abrasive environment but if you apply a polyurethane coating it can last up to 25 years!
- As a filler material. Polyurethane doesn’t act in quite the same way as epoxy and it’s not used for strengthening rotten wood, but it can be used to fill cavities and other spaces and it forms a hard-setting aero solid when it is used in this way.
Outside of woodworking polyurethane is used in:
- Automotive parts
- Boat and surfboard manufacture
- Body armor
- Concrete raising applications
- Decking
- Electronic components
- Plant substrates
- Solid-fuel rockets
- Tennis grips
- Textile finishing
- Watch bands
- Water tanks
- Wheel manufacturer
As you can see polyurethane is a very adaptive substance, indeed.
The 5 Pros Of Using Epoxy In Your Woodworking Projects
There are five main benefits of using epoxy resin for your projects and they are:
- The price of epoxy. Epoxy is usually slightly cheaper than polyurethane. We don’t think that price should be the number one consideration when it comes to working on a project but if everything else is even – you’d be better off going with something cheaper than something more expensive. However, we have to acknowledge that certain brands have price tags that are out of line with the general market trend, so it can pay to make sure you’re not overpaying for either kind of resin.
- The durability of epoxy. It’s fair to say that epoxy bonds tend to be stronger and more durable than those created by polyurethane. They can also tolerate the greatest levels of compression strength. This is particularly important if you’re using the epoxy resin to finish a floor or a surface where you expect heavyweights to be placed upon it on a regular basis.
- The chemical resistance is different. Now, it’s very important to note that epoxy is not better than polyurethane or vice-versa in this respect but that they are both simply different from each other. Certain chemicals, such as sulfuric acid, for example, will react less with epoxy than with polyurethane. Depending on where the resin surface is intended to be – this may or may not matter.
- It adheres to a wider range of surfaces. Epoxy is happier to bond with more surface materials than polyurethane. Again, this may or may not be an advantage to epoxy – it depends on your project
- It resists humidity and moisture. This is a clear advantage of epoxy – if the surface is going to be constantly exposed to water then you are going to find that epoxy lasts longer than the polyurethane.
The 5 Pros Of Using Polyurethane In Your Woodworking Projects
There are also several benefits of using polyurethane in your projects and they are:
- The flexibility of polyurethane. While, technically, epoxy is harder and therefore more durable – we’ve found that polyurethane lasts longer because it flexes with an impact and does not abrade as heavily as epoxy. Of course, this isn’t always important but, in some situations, (particularly flooring) it is a very big deal.
- The resistance to solvents and alkalis. As with epoxy, there are certain chemical reactions that simply have less impact on polyurethane products than epoxy ones. Again, this doesn’t make one better than the other, but it certainly means if you intend the product to be in a space where solvents and alkalis are regularly used – you should probably opt for polyurethane.
- The speed of curing. Polyurethane will cure faster than epoxy in most situations. Again, this isn’t always an advantage but in time-sensitive operations or where the resin is needed for a mission-critical application – you’re going to have to consider the advantages that polyurethane brings to getting the show back on the road as quickly as possible.
- The resistance to temperature extremes. The flexibility of a polyurethane coat also comes with another benefit – when the resin goes from hot to cold rapidly (or vice-versa) it tends to flex rather than becoming brittle and breaking. This can be very important for some projects.
- The resistance to scratching. The polyurethane finish is also somewhat less scratchable than the epoxy finish. This is not always a big deal, mind you, but it can be.
The 4 Cons Of Using Epoxy In Your Woodworking Projects
Now that we’ve seen the benefits of using epoxy and polyurethane, it’s time to explore the drawbacks of using epoxy and we think there are four things that may make epoxy problematic for your projects.
- The longevity of epoxy. While epoxy is harder than the polyurethane – the flexibility of the polyurethane means that you’re going to find that you’re going to have to replace an epoxy surface rather more often than a polyurethane one. This can mean a significant uplift in maintenance costs when using epoxy. It can pay to figure this into the project budget calculations.
- The problems in the food industry. There are several chemicals used in the food industry that don’t react well with epoxy resin. In particular, in the dairy industry lactic acid (the acid which is found in milk) reacts very badly with epoxy resin. You can avoid problems like these by thoroughly researching the use of an area in which epoxy resin is going to be used before you start the project. If it’s not suitable, you can switch to polyurethane.
- The curing time. It’s also worth noting that the curing time of epoxy is roughly twice the length of using polyurethane on big projects. That may be OK if you can lay down the epoxy on a Friday night and there’s no activity around the project until Monday morning but in some environments, the cure time is going to seriously interfere with productivity. It’s something you really need to consider when budgeting for the project.
- UV susceptibility. Epoxy surfaces tend to degrade over time when exposed to UV light. This leads to a yellowing of the surface. Now, sometimes this doesn’t matter but if it does matter – you can buy UV resistant epoxy resin, but it costs a bit more than the resin you will normally use on your projects.
The 4 Cons Of Using Polyurethane In Your Woodworking Projects
This is not to say that polyurethane is without its faults, either and again, we think that there are four distinct issues that you’re likely to face on a project which uses polyurethane resin:
- Higher upfront costs. The biggest disadvantage of working with polyurethane is that it’s going to cost a lot more, to begin with. This doesn’t mean that it’s more expensive over time, however, in fact, epoxy needs renewing far more often and polyurethane is better value for money over long time periods but the setup cost is much higher and this can be a real problem on big projects.
- Humidity resistance. In the long run, while polyurethane is water-resistant, it’s not as good at warding off the water as epoxy resin is and if your finished product is likely to spend a lot of time getting wet – you might want to avoid polyurethane.
- Fast set up times. You will find that polyurethane does not have a long gel time and that when working with polyurethane speed is of the essence. It’s not a forgiving material to work with.
- Experience required. You can use polyurethane on a small project without an issue but if you want to do something big – you really need to have experience working with the material. Mistakes on a large scale are hard to undo and can be incredibly expensive. You may even want to consider hiring in some assistance until you’re confident working with polyurethane.
Which Type Of Resin Should I Choose For My Project?
As you can see, this isn’t a simple question – when it comes to choosing whether to work with polyurethane or epoxy, you need to weigh up all the pros and cons and then make a decision based on what works best for your budget, your experience level, and your project.
If you want help choosing – we have recommended epoxy resin for various projects here.
It can help to seek professional advice if the project you are tackling is very ambitious but you should be able to handle most woodworking projects without too much trouble as long as you prepare effectively for them before you start mixing the two halves of your chosen resin.
Conclusion
We hope that our guide to “epoxy or polyurethane for wood? 9 pros and cons of each” has been helpful in pointing you in the right direction for your project. It can seem overwhelming at first to make these decisions but with practice, you’ll find it becomes almost second nature.
Both epoxy and polyurethane resin can add a lot of utility when working with wood in your projects and, in most cases, you’re not going to run into huge problems if you pick the “wrong” one. Just make sure to review potential interactions with the finished product and you should be fine.