If you have a birdhouse in your yard, you should protect it so it doesn’t get damaged by the elements. Rain and sun exposure will degrade wood, but the right finish can prevent this. Spar urethane is a common exterior wood finish, but is it safe for birds?
Yes, spar urethane is safe for birds once it has cured. However, it does emit VOCs (volatile organic compounds) while it is drying, and these may be dangerous.
As long as you let it dry properly before any birds start using it, spar urethane is an excellent durable coating for your birdhouse. This article will tell you everything you need to know about finishing your birdhouse with spar urethane.
Is Spar Urethane the Best Sealer for a Bird House?
Yes, spar urethane is the best sealer for your birdhouse. It’s a tough clear coat that will keep moisture out and it gives great UV protection too, so the wood won’t fade for a long time. Other clear coats like polyurethane give off more VOCs, so they are worse for the environment and more likely to be toxic to birds.
Other sealers like wood oil or stain can be used for birdhouses too, but the protection will not last as long.
Can I Apply Spar Urethane to Bare Wood?
Yes, spar urethane can be applied on bare wood before any other finish has been used. Simply sand the surface down and then paint it on with a brush. If you want to maintain the natural look of the wood, spar urethane is excellent because it is completely clear.
Can I Apply Spar Urethane Over Paint?
Yes, even though spar urethane can be applied over bare wood, it doesn’t have to be. Applying over paint will give you extra protection so the paint lasts longer without flaking off. The combination of high-quality paint and a few coats of spar urethane makes a long-lasting finish for your birdhouse.
Should I Wait Until the Spar Urethane Has Fully Cured?
Yes, it’s a good idea to wait until the spar urethane has fully cured before you put your birdhouse out. Once the spar urethane is touch dry, it is unlikely that it will give off any toxic fumes that will harm birds. However, before it is fully cured, the finish can be a little sticky, so it’s best to let it cure properly.
Should I Avoid Sealing the Entrance Hole?
If your birdhouse is constructed and placed in the right way, you should not need to seal the entrance hole. A sloped roof that extends over the entrance will direct moisture away, so the birds are protected when it is raining. You should also place it in a relatively sheltered area with the entrance facing away from the general direction of wind and rain.
Although you don’t need to explicitly avoid sealing the entrance hole, it is not entirely necessary because it won’t be exposed to too much moisture.
Do I Need to Seal the Inside of the Bird House?
No, if the bird house is constructed properly and the outside is sealed with spar urethane, no moisture will get inside. The birds will be sitting inside the house and even though the spar urethane is not dangerous, it is better to be on the safe side and leave the interior untreated.
Other Alternative Sealers for Bird Houses?
There are several alternatives you can use to seal your bird house. Wood oils like linseed oil or tung oil are excellent for protecting against moisture. Teak oil is an excellent finish for exterior wood too. However, there are some potential dangers to be aware of. Boiled linseed oil (which is treated to reduce drying time) has some harsh chemicals in it and may not be suitable for wildlife. Natural linseed oil and tung oil also take a long time to dry, so if you are looking for an easy option, spar urethane is the way to go.
You could also try wood stain. If you want to change the color of the birdhouse and protect it from moisture at the same time, you can get some great stain products. Just make sure that you let it fully dry and air out as it is a synthetic product.
Read Related: 10 Best Bird Safe Wood Sealers for Birdhouses
What Spar Urethane Can I Buy?
Spar urethane is one of the best options for protecting your birdhouse from the elements. These are some of the best products on the market right now. We have many other clear coats you can check out here too.
Minwax Helmsman
Minwax is a very reliable wood finish brand and their spar urethane is excellent for your exterior wood projects.
Water Based 
The Minwax Helmsman comes in different varieties including this water-based option. Water-based coatings are thinner and apply more evenly. The resultant finish tends to be slightly more brittle. This gives you a solid protective layer, but it is more prone to cracking than an oil-based product.
Oil Based
An oil-based spar urethane gives a softer finish that is less likely to crack. Although the finish is more likely to dent, it doesn’t scratch as easily. A birdhouse is fairly likely to get scratched up, so the oil-based product is probably the best choice.
Helmsman Spray
If you want to make life easier for yourself, use the Helmsman Spray. You’ll get a great even coverage over the surface of your birdhouse with the simple spray applicator. When it comes time to reapply, you can finish the job in no time at all.
Varathane Spar Urethane
This great Varathane Spar Urethane from Rust-Oleum is a great low-odor, fast drying clear coat. It is available in oil and water-based options so you can decide which suits your needs best. It has a nice satin finish that brings your birdhouse to life while also protecting it from the harshest weather conditions.
TotalBoat Gleam Marine Spar Varnish
The TotalBoat Gleam Marine Spar Varnish is excellent for using on a natural wood birdhouse if you want to add a bit of color. It has tung oil mixed into the clear coat to give a nice amber color to the wood and protect it further. Often, people use tung oil before topping it with a clear coat and this great product gives you both in one easy to use option.
Should I Buy Satin, Gloss, or Semi-Gloss for a Birdhouse?
It’s entirely up to you what kind of finish you want on your birdhouse. It won’t impact the birds, so it depends on what you find most aesthetically pleasing.
Final Thoughts
Spar urethane is an excellent finish for your birdhouse. It gives amazing moisture protection and it is very durable. Any of the products listed above will work perfectly and keep your birdhouse in excellent condition for the birds!
Jamie is the founder of The Backyard Pros. When he was 15 years old he started working at a garden centre helping people buy plants, gardening products, and lawn care products. He has real estate experience and he is a home owner. Jamie loves backyard projects, refinishing furniture, and enjoys sharing his knowledge online.