Freezing temperatures and the hot sun affect concrete birdbaths – if you leave yours in the elements without a sealant you will likely get pitting and cracking.
Sealing the surface with a non-toxic sealant helps your birdbath to be less porous so it holds water well and limits the freeze-thaw effects.
Of course, we want a sealant that is totally non-toxic to the birds and doesn’t leach any chemicals into the water. It’s also important to have a sealer that is safe for the humans who are applying it.
This article outlines one truly non-toxic, no VOC, natural, non-leaching option that is safe for birds and humans, as well as one synthetic option.
These sealants work on stone/rock, terra-cotta birdbaths as well. The first option works on metal birdbaths.
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1. A Natural Non-Toxic Sealant for Concrete, Stone, Terra-Cotta & Metal Birdbaths
Tung oil, also called china wood oil, is an all-natural, food-grade compound that’s safe to use on concrete, stone, terra-cotta, and metal birdbaths. It will help to waterproof the birdbath and help prevent cracking and pitting in porous materials. It helps prevent rust on metal.
Even though it’s a natural oil, tung oil is tough. It’s the most durable of all the natural finishes. It’s historically used to seal wood boats.
Tung oil from The Real Milk Paint Company is 100% pure oil from the seeds of the tung tree. It does not contain any other oils, solvents, drying agents, or other additives.
Be careful with any tung oil you find in a hardware store, I have not seen any in the major stores that are 100% tung oil.
One other thing to know before you start is that, although it’s a transparent sealant, it will darken the look of the concrete, stone, and terra-cotta.
What I would not use to seal a birdbath:
- Acrylic sealants which don’t hold up to water.
- Shellac, despite this article by Martha Stewart, shellac will not hold up to water in this situation.
Instructions for a Concrete Birdbath
Prep the Concrete for Tung Oil
Start with clean, dry concrete, stone, terra-cotta or metal. You may want to use a garden hose to wash it out with some pressure and then a brush with a non-toxic outdoor cleaner to help remove dirt, grease, and debris.
Move the birdbath into an enclosed area out of the sun and rain. Wait at least three or four days to make sure the concrete, stone, or terra-cotta is fully dry.
You can use a food-grade silicone aquarium caulk sealant to fill cracks in concrete and stone if needed. This is non-toxic, it does not contain mildewcides or leach any chemicals once cured, so it won’t harm the birds.
Application of Tung Oil on Concrete
You can apply tung oil sealant only to the inside of the bowl or to the whole birdbath. Applying it to the whole birdbath will help to extend its lifespan if you have a cold winter climate.
Conditions for the application:
- Above freezing temperatures on the day of application and for 15 days after.
- Make sure the birdbath is protected from rain and the sun while working. Exposure to the sun while it’s drying can make it turn “frosty”.
For concrete, you usually do not thin the tung oil with anything – no solvent or thinner is likely needed. However, if the bath is polished concrete, it may need some thinning to help it absorb (you could use the all-natural citrus solvent).
Pour on a small amount of oil and rub the oil into the concrete, adding more as the oil absorbs.
You’ll need to apply several coats, usually 2-5 coats of unthinned tung oil. But it could be as many as 6 or 7. Let each coat dry for at least half an hour before moving on to the next coat.
If you apply 3 coats and they completely absorb within 40 minutes, you’ll want to continue applying. Apply as many coats as will absorb in one day, then the next day “top off” the concrete again with another coat (or more if it still absorbs).
Use a rag to rub in the oil rather than letting the oil dry on the surface of your concrete.
Wait 30 days before filling the bowl with water. (The initial cure time is long, but subsequent touch-ups will be much easier and shorter).
How to Maintain your Tung Oil Sealed Birdbath
Touching up the oil:
If you feel that your concrete needs more protection, you can simply add another coat of 100% unthinned tung oil at any time without sanding it, stripping it, or other prep.
Because the concrete is submerged and outdoors, you may need to wipe it down with some oil annually for the best protection.
All you have to do is clean it, dry it out, dampen a rag with the tung oil and wipe it down. Wait 3 days for the oil to cure before introducing water again.
Cleaning and disinfecting the birdbath:
When it comes time to disinfect your birdbath, don’t use vinegar on the tung oiled concrete, it will damage the sealant.
The National Audubon Society advises against using soaps and other surfactants to clean your birdbath because they can strip the oils off of bird feathers (source).
Sealing a Terra-Cotta Birdbath With Tung Oil
You can also use Tung Oil for a non-toxic sealant on terra-cotta just like you would with concrete birdbaths.
Unglazed terra-cotta is super porous so it will take tung oil well. Check to see that it is unglazed and with no coating on it so that it can absorb the oil.
The tung oil can bleed all the way through if the terra-cotta is not very thick, so that would leave you with dark spots on the outside if you only sealed the inside. However, this has not happened to me when sealing terra-cotta pots for plants (which are quite small and thin). You can seal the outside as well if that happens.
For the application follow the same instructions for concrete outlined above.
Sealing a Stone Birdbath With Tung Oil
For stone the instructions would generally be the same as with concrete and terra-cotta. Stone tends to be less porous, so, more than likely the Tung Oil would need to be thinned with citrus solvent.
If it’s polished and/or repels water, then the tung oil probably won’t work.
Sealing a Metal Birdbath With Tung Oil
If the metal is something like cast iron or it’s heavily rusted then the oils could work. Typically you can use the Pure Tung Oil (thinned or not) on them like you would on concrete. Metals that do absorb the oil don’t typically need a lot so, 1-2 coats would be a good.
A light coat rubbed onto steel is an effective rust inhibitor.
Where to Buy
PS. In the UK, this brand of tung oil is good.
2. An Epoxy Sealer for Birdbaths
The other way to go is the opposite side of the spectrum, with something totally synthetic. Epoxy sealants are very thick and waterproof so this is ideal for use inside the bowl of the concrete or stone birdbath.
Not all epoxy sealants are low-VOC and non-toxic to people applying them or to birds.
Pond Shield by Pond Amor is non-toxic to birds. It’s also marked as low-VOC on the Home Depot website description and the company says it’s lower odor than a latex paint. However, when asked by email about VOC levels more precisely, the company would not put anything in writing.
It’s a two part product that is very thick and very waterproof to line ponds and birdbaths made of concrete or stone/rock. It comes in Black, Charcoal Gray, Chocolate Brown, Clear, Competition Blue, Delta Blue, Gray, Moss Green, Sky Blue, Tan and White.
Application of Pond Shield
Concrete needs to be etched with an acid stain first. This is not toxic once it dissipates.
Pond Shield needs to be applied at a minimum of 10 mils thick (like three sheets of paper thick). A rough surface usually requires that you thin Pond Shield which means the Pond Shield will not hang at 10 mils in one coat. So two coats applied at 5 mils can work. A smooth surface the easiest to apply Pond Shield to and in those instances, you may be able to apply it in one single 10 mil thick coat.
Reviewers have found the application tricky.
It normally cures in 24 hours, though in colder seasons, you might wait an additional 12 hours. Make sure that there are no tacky spots anywhere on the surface of the coating before adding water. When it’s dry you can add water to the birdbath.
Where to Buy
You can buy it on Amazon or through local retailers.
Corinne Segura is a Building Biologist Practitioner with 8 years of experience helping others create healthy homes.