Guide to finding & buying low-toxicity building caulk or sealant products:

This article describes non-toxic caulks & sealants used in buildings, aquariums, water cisterns or springs and similar applications.

We answer a reader question about how to seal a leaky water container for a spring, and we list several low-toxicity caulk brands for which we include key properties (and in some cases warnings) from the caulk MSDS data.

Guide to Choosing & Buying Non-Toxic or Low Toxicity Caulks & Sealants

Question: what to use to patch a leaky springwater container

I have a hand dug and stone and cement spring at my camp which isn't holding water very well.

I want to patch the inside with something that can stay wet and won't be toxic, any ideas?

- D.H. 4/3/2013

Reply: approaches to sealing a spring or other container intended to contain potable water

Below we describe several products that may be suitable and successful in making a patch to a leak for a concrete (or other) container that is used to hold drinking water.

But before advising patching I'd need to understand how your water system is constructed. When I was a kid our spring-fed water supply entered up through sandy soil in the bottom of a spring-fed springhouse that was surrounded by concrete and covered with a roof.

[Click any InspectApedia.com image to see an enlarged detailed version.]

We tossed our watermelons in there to stay cold during the summer. But if the spring water level in that design dropped it wasn't a leak in the springhouse it was a drop in the groundwater levels.

Watch out: at SPRINGS as WATER SUPPLY we describe other more broad concerns with the safety of cisterns and springs as drinking water sources.

• Hydraulic cement,
  
  high in portland content, is compatible and as it's essentially the same as what you've already got - concrete - about the same in toxicity. But if the cracks and leaks are because the concrete structure you built to contain springwater is tipping, bending, breaking, leaks will probably recur until you fix the underlying support.
  
  Since we include warnings in MSDS sheets for the other sealants discussed below I note that while cured cement has been used for centuries as a successful and low-toxicity container for water in cisterns and springwater enclosures, cement or concrete can be highly toxic and caustic during construction or repair.

• Aquarium sealant:
  
  an alternative that is surely not toxic would be to try a silicone or similar sealant sold for use in constructing an aquarium.
  
  If we have a product that doesn't kill the fish that's a good sign.
  
  As you will see from our clip of advertisements for aquarium sealers in our photo above these are generally silicone sealant products sold by Ag, DAP, DOW, Marineland, Perfecto, and other manufacturers.
• Swimming pool or marine product (boat) sealants
  
  An alternative for which you'd need to read the MSDS but that might work well would be swimming pool patching compounds. We list some approaches to sealing swimming pool leaks in our resources list below, including Atlas Pool Putty and Fix-A-Leak that may have special application depending on where the leak is located.
• I am hesitant to recommend caulks and sealants in generic form
  
  one should first check the caulk's ingredients, solvents, and chemistry. But in general, the most toxic chemical in some caulks would be mineral spirits (possibly a source of benzene, a carcinogen, for example). Acrylic / latex caulks, do not contain mineral spirits.

Silicone or acrylic compounds in caulks and sealants are key ingredients in forming their waterproof properties when cured.

Watch out: the Mother Earth Living website contributor Debra Lynn Dodd[1] (author of Home Safe Home [7]) recommended three caulks as "non toxic" that I list below.[1]

However a look at the product MSDS sheets is further informative so I include some excerpts, noting that the possible toxicity of caulks, sealants, and coatings may be quite different between when the product is opened and applied and when it has cured, as VOCs and other products diminish during the curing and drying process.

Certainly in the various caulk & sealant MSDS data sheets it is apparent that the risks discussed focus on exposure to the product "out of the box" or container, that is, before it has been applied, cured, diluted, etc.

List of Non-Toxic or Low-toxicity Caulks & Sealants

• Dap Acrylic Caulk - http://www.dap.com - MSDS cites ethylene glycol, an automotive type antifreeze, and formaldehyde in the MSDS for Alex Plus Clear Latex Caulk.
  
  From the product MSDS:
  
  Emergency Overview: A white to off-white paste product with a very slight ammonia odor. WARNING! May cause eye, skin, nose, throat and respiratory tract irritation. May cause eye or skin irritation. Harmful if swallowed or absorbed through the skin. This product contains ethylene glycol.
  
  The MSDS Section 11 - Toxicological Information notes the following:
  
  Significant Data with Possible Relevance to Humans: This product contains trace amounts of free formaldehyde. OSHA and NTP identify formaldehyde as a potential carcinogen.
  
  IARC identifies formaldehyde as a human carcinogen. Formaldehyde has been shown to cause mutations in a variety of in-vitro test systems, the significance of which to humans is unknown. There should be minimal risk when used with ventilation adequate to keep the atmospheric concentration of formaldehyde below the recommended exposure limits.
  
  Maintain adequate ventilation to prevent exposure above current OSHA / ACGIH exposure limits. Workplace monitoring of the air to define formaldehyde exposure levels may be necessary.
  
  In a two-year inhalation study, rats showed carcinogenic effects in the respiratory system at 15 ppm of formaldehyde.
  
  Section 12 provides this statement: Ecological Information: Ecological injuries are not known or expected under normal use.[2]
  
• Dow Corning 100% Silicone Sealant - http://www.dowcorning.com - (Watch out: the company has so many products lines and products that you will have to navigate a forest of web pages often ending at a dead-end)
  
  The Dow MSDS for Dow Corning® 790 Silicone Building Sealant, Gray, MSDS section on Potential Health Effects from acute exposure includes warnings for Eye: Direct contact may cause severe irritation, Skin: May cause moderate irritation, Inhalation: Irritates respiratory passages very slightly, and Oral: Low ingestion hazard in normal use. Effects are different in cases of prolonged or repeated exposure.
  
  The Dow Corning Silicone Sealant MSDS Section 11 states:
  Contains Bis(N-methyl acetamido)silane which liberates N-methylacetamide (NMA) during cure. NMA has been shown to cause birth defects in laboratory animals.
  Section 12 Ecological Information states "Complete information is not yet available."

• Durham's Water Putty - has been produced by the Donald Durham company since 1932 and is a plaster-based product. Some builders refer to this product as "durock" which in our opinon is not correct.
  
  The Durham company notes that
  
  "None of the ingredients are toxic or harmful to humans" which I take as should mean it does not contain asbestos.
  
  Note: This product may endure on exterior surfaces if the surface is kept sealed against water and moisture.
  
  Contact: Donald Durham Company P.O. Box 804 Des Moines, IA 50304 USA Tel: 515-243-0491 Website: http://www.waterputty.com/ conforms to ASTM D-4236 Standard Practice for Labeling Art Materials for Chronic Health Hazards
  
  Website excerpt - instructions:
  
  Durham's will withstand weather if kept painted, but paint will peel from damp water putty. Durham's will absorb moisture, like from underneath porch floors or decks, condensation within walls, and humid environments like showers or bathtub enclosures, which will prevent Durham's from completely drying or adhering.
  
  Durham's is meant to fill voids, not spread in thin layers over large, smooth surfaces. Where, for example, the first good slam of the door may cause Durham's to pop off. Do not use Durham's for structural or load-bearing applications, where there is movement, expansion, or contraction like between floor boards.
  
  Do not use on smooth concave surfaces, because Durham's may "pop" as it dries and expands slightly. If you add a great deal of powder or liquid paints, hardness and performance may be compromised.
  
  ASTM D-4236 Abstract
  
  This practice describes the standard procedure for developing precautionary labels for art materials to provide chronic health hazard and precautionary statements based on knowledge that exists in the scientific and medical communities.
  
  These statements concern hazards known to be associated with a product or product component(s) when it is present in a physical form, volume, or concentration that in the opinion of a toxicologist has the potential to produce a chronic adverse health effect.
  
  This practice applies exclusively to art materials packaged in sizes intended for individual users of any age or those participating in a small group, and does not apply to products appropriately labeled for known chronic health hazards.
  
  Also, this practice does not specify test methods for determining whether a substance or product presents adverse chronic health effects.
  
  Labels should include the signal word WARNING, list of potentially chronic hazards, name of chronically hazardous component(s), safe handling instructions, list of sensitizing components, information sources, labeling content and product size, and other supplementary information.
• Safecoat Caulking Compound (modified acrylic polymer) - http://www.afmsafecoat.com - describes this product as Safecoat Caulking Compound is a not-toxic, elastic emulsion type caulking compound designed to replace oil caulk and putty for windows, cracks and general maintenance work. [4]
  
  Significantly the MSDS states
  
  Section 311/312 Categorizations (40 CFR 370): Not a hazardous chemical
  
  Section 313 Information (40 CFR 372): This product does not contain a chemical which is listed in Section 313 above de minimis concentrations.
  
  The Safecoat Caulking Compound MSDS for Safecoat 7130 White, does not contain a Section 11 on Toxicology nor a Section12 on Environmental impact.
  
  The product contains Propylene Glycol (for which the acute oral toxicity is stated by sources such as Wikipedia as "very low"), Titanium Dioxide (used in sunscreens, possibly toxic in sunscreens [5] and separately, especially in dust form), and of course other materials. Hazards would occur principally from swallowing or inhalation of the product. [4]

Note: For a helpful discussion of just what constitutes "adequate venitlation", see Offermann, Francis (Bud) J., P.E., C.I.H., ASHRAE & Mark Nicas, Ph.D., MPH, C.I.H., USE WITH ADEQUATE VENTILATION ? [PDF], ASHRAE Journal, May 2018.

Other Caulks or Sealants for Pools & Water-Containers

• Atlas Epoxy Bond Pool Putty, Atlas Mineral & Chemicals, Inc is a two part resin and hardener epoxy repair product that can be used to seal holes or cracks in swimming pools and capable of working under water provided the surfaces have been cleaned of slime and algae or loose particles and debris. This product is specifically formulated for use on concrete or Gunnite swimming pools.
  
  Watch out: the product data sheet (www.atlasmin.com/products/epoxybond/pdf/5-61pi--6-06.pdf) is not in our OPINION a valid MSDS and takes care to include this warning:
  
  The materials referred to in this Data Sheet present handling and potential health hazards. Consult Material Safety Data Sheets and the container labels for complete precautionary information.
  
  We did eventually find an MSDS for this product that identifies its potential hazards as:
  
  Hazards Identification:
  
  Routes of Entry: Inhalation: YES Skin:NO Ingestion:NO
  
  Reports of Carcinogenicity: NTP:YES IARC:YES OSHA:NO
  
  Health Hazards Acute and Chronic: EYES: MAY CAUSE IRRITATION. SKIN: MAY CAUSE IRRITATION & SENSITIZATION.
  
  Effects of Overexposure:IRRITATION.
  
  Medical Cond Aggravated by Exposure:RESPIRATORY PROBLEMS, ALLERGIES, ECZEMA.
• Fix-A-Leak [swimming pool sealant], Marlig Industries, Niagara Falls, Ontario. is a product that is poured into the pool plumbing system, circulates through the system and in theory flows to and fixes leak points.[8][9]
  
  This product might be tempting to use if the leak in a spring-fed or cistern-fed water supply system has not been pinpointed but we need to be convinced that the compound is harmless in drinking water and that it will find, seep into, and repair a leak in a cistern type structure. The Fix-a-Leak Pool Sealant MSDS includes this summary statement:
  
  Hazard Identification: This product is classified as a hazardous substance and as dangerous goods according to the classification criteria of NOHSC and ADG Code (Australia). Warning! Contents under pressure! Highly flammable liquid and vapor! Vapor may cause flash fire! Keep away from heat, sparks, and open flames.
  
  Do not puncture or incinerate. Do not store above 130°F. Use only with adequate ventilation. Keep containers closed when not in use. Keep away from children.
  
  Routes of Entry: Inhalation, Skin & Eyes, Ingestion [10]
• See CAULKS & SEALANTS, EXTERIOR for details about selecting and using these products
• SPRINGS as WATER SUPPLY discusses that topic and issues around assuring that water remains potable and sanitary.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-09-15 by Anonymous

Thank you. We have used AFM products though (1) they aren't always ideal in a wet room setting because they have no mildewcide or fungacide (it's hard to find the sweet spot btwn low VOC and practical needs). Meanwhile, we found out the specific product our contractor used and the amount of VOC in it is off the charts.

Whereas most similar products have VOC levels btwen 30 and 50, this one had a level >300. So we bought a different one, did a test, and it was fine after about 24 hrs. Live and learn! (Lots of the latter on this website.)

On 2020-09-11 - by (mod) -

IMO silicone is among the most-inert stable sealants we can use, and is very long-lived. There is a "vinegar-like" odor at first application, that quickly dissipates.
Silicone sealant doesn't contain other solvents that may be irrritating as do some other products.

Companies who say they offer other "hypoallergenic" or non-irritating caulks and sealants include

AMF Safecoat

and Greenguard

On 2020-09-11 by Anonymous

Thank you. We had excellent ventilation, heat and humidity, and didn't mix sealants. But my wife is chemically sensitive and it was a nightmare. Not sure what other options we have and were hoping you might have some ideas. Thanks for all you do at this site where you have such a wealth of info that you share so generously with people. Very grateful.

On 2020-09-10 - by (mod) -

Anon

IN my experience silicone caulk offgasses and is odorless very quickly in normal use;

Ventilation + heat speeds the process.

Beware of mixing sealants; recently at a shower installation I used a silicone sealant that was not the right color at the shower base; I was sold a silicone substitute, tried it and found it would not bond to the existing silicone; had to peel it all out and start over.

On 2020-09-10 by Anonymous

A tile installer just installed a Corian backsplash in my bathroom that needed to be replaced. He used a Dapp brand silicon caulk to attach it and the odor is awful. After a few days with little improvement in the smell, I removed it and am now trying to figure out how to re-attach it to the painted drywall with product that won't stink.

I thought I'd found one made by ChemLink, but after speaking w/someone at the company they said none of their products would be appropriate for a bathroom application and recommended using thinset mortar. But after doing some research online it seems everyone recommends using silicone caulk for this kind of a job, so now I'm completely at a loss and am seeking your assistance.

What kind of product would you recommend I use to attach Corian to painted drywall? And, do you know of a brand that is low VOC? Thank you for your help!

On 2020-03-08 - by (mod) -

Most cement patching compounds ought to be fine once cured. For example Red Devil makes a pre-mixed acrylic-based cement patching compound. I've tried to find the actual MSDS for these patch products without success - perhaps you'll have better luck.

On 2020-03-08 by Anonymous

I meant we are looking for a non-toxic caulk, putty, or sealant to repair our sand cast cement bird bath.

On 2020-03-08 by americanprana@gmail.com

We need to plug up holes in our sand cast cement bird bath. We are looking for a job toxic caulk or putty or sealant for the repair. Any suggestions?

On 2017-08-12 - by (mod) -

Yes, Carolyn, breathing ethylene glycol fumes can be harmful, according to a typical Ethylene Glycol MSDS provided by Fisher Scientific. Of course we can't know what was your level nor duration of exposure, but if you are having breathing difficulty that is severe you should seek immediate medical attention.

Otherwise you should take your question to your doctor.

Here is an example MSDS

https://inspectapedia.com/hazmat/Etyhylene-Glycol-MSDS-Fisher.pdf

On 2017-08-12 by carolyn

i used a product to seal tile in my kitchen called wet look sealer by behr interior /exterior that containes ethylene glycol. i have astma and can this product cause breathing problems

On 2017-08-08 - by (mod) -

I'd use an Aquarium sealant as we discuss above.
Or look at the other non-toxic sealants or low toxicity sealants we discuss in this article like the Safecoat product line.

DynoSeal
Safecoat DynoSeal is a sophisticated, low odor, all weather, waterproof, vapor proof coating and sealer that remains flexible for years. It is highly resistant to flame spread and temperature change, and when cured is also highly resistant to gasoline, oil, grease, fungi, acids and alkalines. It has very low odor upon application and is odor free once cured.
Contact http://www.thegreendesigncenter.com/product/afm-2oz-samples

Manufacturers include

AllGlass, clear silicone sealant,
Aqueon Silicone Aquarium Sealant, Black
Aqueon 100 cleare silicone aquarium sealant
DAP Silicone aquarium sealant
DAP Household/Aquarium Adhesive Sealant. ASTM. Id: C920
and similar products

I looked at pourable sealants as an appealing solution for your birdbath but didn't quickly find one that sported an MSDS assuring safety for animals.

You might try talking with some of the manufacturers such as
L.H. Dottie Company
6131 Garfield Ave.
Commerce, CA 90040
(323) 725-1000

Watch out: all of these products warn that the surfaces to be sealed must be perfectly clean and usually dry too, for a successful seal.

On 2017-08-07 by Dee

I am looking for something to seal the whole surface of a pebble type bird bath . It does not have a crack , instead, the whole thing seeps water. I want something clear and safe for the birds and animals to drink from.

...

Continue reading at CAULK & SEALANT CHOICES, products list for our full list of caulk & sealant products & manufacturers or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

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CAULKS, NONTOXIC at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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