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 the only truly non-toxic, no VOC, natural, non-leaching option that I know of that is safe for birds and humans.
While other options like epoxy paint can certainly be safe once fully cured, they are harsh at first for the people applying it and they can take some time to fully cure to get to the point of truly not leaching any chemicals.
This sealant works on most stone birdbaths as well.
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Tung Oil – Natural Non-Toxic Sealant for Concrete Birdbaths
Tung oil, also called china wood oil, is an all-natural, food-grade compound that’s safe to use on concrete and stone birdbaths. It will help to waterproof the birdbath and help prevent cracking and pitting.
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 the wood on 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.
Prep the Concrete for Tung Oil
Start with clean, dry concrete. 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 is fully dry.
You can use a food-grade silicone aquarium caulk sealant to fill cracks 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 Bird bath
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 in this case, 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).
Corinne Segura is a Building Biologist Practitioner with 7 years of experience helping others create healthy homes.
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