Healthy exteriors/gardens

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”.

Application:

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.

Next steps:

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.

A safe non-toxic option to disinfect a birdbath that won’t degrade the tung oil is food-grade hydrogen peroxide. You can also use borax or baking soda to help scrub out and clean the birdbath.

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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There are two main ways to go with chemical-free sealants (and stain) for raised garden beds or planters.

The first option is to use a non-toxic water-based stain on the exterior with a safe water-based painted on membrane on the interior of the box. (The water-based stains used on the exterior won’t hold up inside the bed).

The second option is the most food-safe option, which is to use a totally natural penetrating oil on the inside and outside of the garden bed or container garden.

Some of these are only wood stains/sealants and some can be used on concrete and plastic planter boxes as well.

This post contains affiliate links. Upon purchase, I earn a small commission at no extra cost to you.

1. Non-Toxic Stain & Sealant

Vermont Natural Coatings PolyWhey is a stain and sealant for the exterior of raised garden beds.

This is one of the most durable water-based (non-toxic) wood stain/sealers out there. This is a semi-transparent stain and sealer in one. It is a waterproofer that has some UV resistance (you get more UV resistance the darker you go with the stain color).

It can be used on new wood, pressure-treated wood, and weathered wood. Pressure-treated wood needs 6 months to a year to fully dry before this (or any) sealant is applied. It’s not for use on exotic super dense woods.

It could be applied over older oil-based stains or finishes, as well as water-based finishes if it’s been fully sanded first so that it can penetrate into the wood. No product can go over top of this in exterior applications.

This sealant is non-toxic, low odor, and low-VOC, and does not contain biocides, fungicides, or anti-microbial agents. The pigments act as natural UV inhibitors.

This coating is great for the exterior of raised garden beds with AFM Dynoseal for waterproofing on the interior.

You can buy PolyWhey online at Walmart and sometimes via Amazon.

2. Non-Toxic Invisible Waterproofer

Vermont Natural Coatings Penetrating Waterproofer with Juniper is an invisible-looking option for the exterior of raised planters.

This is another water-based sealant. This is a penetrating sealer that does not form a film on the surface; therefore it leaves the wood looks totally bare after applying it.

This sealant provides waterproofing but it does not provide any UV or abrasion resistance. The wood will gray out naturally from UV exposure.

It is used on the exterior of planters, and like all water-based sealants and paints, it is not suitable for subterranean or submerged wood. 

For the inside of the planter, you will need a product that can resist moisture and prevent rotting – use AFM Dynoseal for this purpose.

It can be used on new wood, weathered wood, as well as pressure-treated wood. For pressure-treated wood allow 6-12 months for drying out before applying this sealant. It can work on teak and other oily woods and it is a good choice for cedar, pine, spruce, and fir.

It cannot go over or under another product.

It is zero-VOC and contains no solvents, dyes, biocides, or fungicides.

You can buy Penetrating Sealer From Walmart and you can sometimes find it via Amazon.

3. A Non-Toxic Waterproofer for Inside the Beds

AFM DynoSeal is for the interior of garden beds.

For the interior of the bed, the most durable non-toxic coating is AFM SafeCoat Dynoseal.

You paint it on and when it’s dry it acts as a waterproofing membrane that prevents moisture intrusion from the soil into the wood (preventing rot) and it stops tannins or chemical treatments in the wood from leaching into the soil and getting to the plant’s roots.

You can use this on the inside of planters made of wood, plastic, or concrete. It’s not for use on the outside of the planters, it doesn’t hold up to UV light and doesn’t look great either.

The partial ingredient list is: Acrylic Copolymer Emulsion and Pigment Dispersion. It’s listed at 19 g/l VOCs.

On the exterior, you can use PolyWhey, Penetrating Sealer with Juniper (listed above), or tung oil, linseed oil, or paint (listed below).

4. All-Natural Tung Oil Sealant

Outdoor Defense Oil is an all-natural tung, pine, and zinc mix that can be used for the interior and exterior of planters.

Pure tung oil is an all-natural product. The brand I use contains no synthetic, metallic, or other harmful additives.

It is non-toxic, and safe to use on organic garden structures that have contact with food supplies, including raised garden beds, chicken coops, and greenhouses.

Tung oil is very durable for a natural oil. It’s by far the most durable of the natural penetrating oils which is why it can be used on the inside as well as the outside of the garden bed. It seals moisture out of wood and its elastic properties help it hold up to movement and temperature changes. It’s very durable to mold.

Outdoor Defense Oil is an all-natural oil sealer made from pure tung oil, pine oil, and zinc.

You can also use this over Milk Paint to protect it from the elements or you can mix (some types of) pigments into the tung oil.

You can use this on all wood types. Extremely dense woods such as teak and ipe, etc may require thinning with more (natural) solvent. Because it needs to penetrate the wood it does not go over new oil-based sealers/stains or other finishes. You can use it over aged penetrating oil finishes (like aged linseed oil).

Some highly chemically sensitive folks have preferred these natural oil coatings to synthetic coatings like PolyWhey (others would find the opposite preferable).

Always test for your own tolerance and I would recommend not using or being exposed to the natural solvents used with tung oil (pine oil or citrus oil) when they are wet if you are sensitive.

Buy it through the Real Milk Company. You can use code mychemicalfreehouse for 10% off.

PS. To clean tung oiled wood, you can use gentle soaps, but some non-toxic cleaners can damage it – this post goes over the best options.

PPS. My in-depth look at tung and linseed oils goes into more detail on what these oils offgas.

5. Linseed Oil Stain & Sealant

Rubio Monocoat linseed-based stain & sealer can be used on the exterior of planters.

Rubio Monocoat Hybrid Wood Protector is a modified linseed oil and wax penetrating oil finish that is applied with just one coat.

This product is for exterior use, it provides protection from water and UV (except for the color “Pure” which has no UV protection).

It works well over almost all wood types including oily exotic woods (ipe, teak, etc).

It is solvent-free, technically zero-VOC because it’s a natural product. (Though see my in-depth review of Rubio Monocoat and other linseed oils for information on naturally occurring VOCs).

Rubio Monocoat is preferred to plain linseed oil in many ways because it’s lower in odor than the other brands. You need a part B accelerator, be sure to test that out as well.

You can buy it directly through their website.

6. Non-Toxic Paints

AFM or ECOS non-toxic paints can be used on the exterior of raised garden beds.

If you have older planters start by sanding off any rough areas or peeling paint and then prime the surface with AFM SafeCoat Transitional Primer. Next, paint the surface with AFM Safecoat Exterior Satin Paint.

Painting ultimately gives you the best protection against UV damage and other natural elements.

If you go with the painted option, you can’t use any penetrating sealant or oil-based stain and sealer over or under the painted surface.

If you prefer ECOS Paint brand you can use their exterior paints and primers.

What I wouldn’t use:

• “Teak oil” – any mix that contains tung and/or linseed with unknown ingredients or metallic driers would not be safe on the interior side next to the growing food.
• Linseed oil on the interior of the planter beds/container garden. It’s just not durable enough to hold up in here.
• Hemp oil or walnut oil – while you can use these two other penetrating drying oils on the exterior side they are not nearly as durable as linseed or tung oil. I would not be keen to use these outdoors.
• Jojoba oil – this is not a drying oil, it’s not a good finish for exterior wood.
• Milk Paint without a super durable top coat is not going to hold up outside.

Corinne Segura is a Building Biologist Practitioner with 7 years of experience helping others create healthy homes.

Did you find this post helpful? If so you can buy me a coffee to support the research behind this blog. Thank you!