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Relatively non-toxic concrete joint filler/sealing material that will last?

rossn1 | Posted in Green Products and Materials on

I have a failed cove joint in my below-grade level, and need to replace part of the fiber board joint material that exists between the slab and foundation wall. I need it to be a permanent type repair, as it will be difficult to get at the joint after my remodel, and I have radon present in my soil.

Does anyone know of a product that both works well (i.e may have a 20+ year life on concrete, remaining attached and flexible) and isn’t highly toxic or classified as a carcinogen?

Most of the products I’ve looked at have a pretty discouraging SDS sheet, though that isn’t entirely a surprise.


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  1. GBA Editor
    Martin Holladay | | #1

    The answer to your question depends on your definition of "relatively non-toxic."

    Used as directed, caulks and sealants sold for residential use will not poison the homeowner. In that sense, they are non-toxic. Needless to say, you don't want to eat them.

    Some caulks have solvents (VOCs) that evaporate for a few hours or days after installation. If that worries you, leave a window opening and install a fan for a few hours or days.

    If an MSDS sheet lists a carcinogen on the ingredient list, that doesn't mean that homeowners will get cancer if the product is used in the home.

  2. rossn1 | | #2

    Understood it is a spectrum which is why I mentioned relative. The question is if there is a product that has a good reputation as being a green product on the less caustic end of the spectrum that works well. Sometimes they do exist and people who work with these products regularly may know.

    Anyone have any ideas?

  3. GBA Editor
    Martin Holladay | | #3

    Here are some possibilities from the GBA Product Guide:

    Loctite Construction Adhesive

    Safecoat Construction Adhesive

    Sherwin-Williams GreenSure Caulk

    Smart Zero-VOC 1408-1-61 Elastomeric Caulk Sealant

    The last of the products in this list is recommended for concrete as well as for interior use.

  4. rossn1 | | #4

    Thanks, Martin! I didn't know that guide existed and will check it and the products out.

  5. onslow | | #5


    I am sealing the perimeter and post supports in my own basement against the possibility of radon intrusion whether or not it exists. I have been using polyurethane sealant formulated for concrete made either by Quickcrete or Sika's Sikaflex. Both are available at Home Depot- probably elsewhere, too. I favor the Sikaflex as it self levels better than the Quickcrete and it come is 29 oz tubes that are much more economical (relatively speaking). Both take days to dry enough to work near.

    I would personally advise against construction adhesive based on my observing its characteristics over time. During some remodeling projects, I had to tear out elements that had been glued. It was a bear to be sure, but the relevant point is I found the aged glue to be bordering on brittle. Formulations may have changed over the last 10-15 years, but as the polyurethane concrete sealant is available and is specifically made for the situation you have, I would push for using these products.You only get one chance. They are a bit stinky but just ventilate. The amount of stretch in the material is superior to any caulk I have my collection, even silicones.

    The assorted caulks, acrylic, siliconized, etc. I have used, show limited flex range. None I have used stretch like the two I mentioned above. I also found the adhesion to raw concrete less than impressive when I have used them to tack items to walls. I did take to wet wiping the areas to be sealed before I invested the time and money using the polyurethanes so perhaps that would help the less stinky caulks as well.

    Since you are intending to seal against radon, I hope you are leveling or cutting down the fiberboard and sealing over the gap between slab and wall fully. The polyurethane sealants do require a minimum profile thickness, so cutting the board down below slab height is the best way to go. I am grinding a bevel on the edge of my slab to ensure proper setting. I am also stuffing the gap between slab and wall with the round caulking rope foam to prevent material draining down into the gap uselessly. Don't forget to seal around support posts and do the best you can to seal sumps. Floor drains are a problem which fortunately I don't have to deal with. Best of luck.

  6. onslow | | #6


    Back with a small addenda which is not meant to be snotty or ignore the concerns of people with chemical sensitivities. Finding products that are non-toxic or at least non-carcinogenic are something I think all GBA readers strive for when obtainable. However, it would seem that the long term goal of protecting yourself and others from the known effects of radon trumps the very short term dangers of modern sealants. If natural and safe choices were available and performed as you ask, they would be readily found. Unfortunately the desired combinations of long term flexibility and adhesion seem to only be found through modern chemistry which is not the purist path. The sealant I advise you to use is indeed listed as toxic and a known carcinogen (in CA) and should only be used with good ventilation.

    Radon is a long term issue that needs a solid fix to ensure long term control. Your sealant chemical exposure is for the short term,of a limited volume of chemicals, and easily handled with ventilation. The chemicals in sealants, construction adhesives, etc are toxic and dangerous mostly to those making the products or using them daily in poor conditions.

    It worth noting some chemicals that we eat or wash in, while not listed as dangerous on the products, place the workers making them at grave risk. A good example are the unfortunate workers who produced microwave popcorn products with fake butter flavor. Daily exposure to the vapor resulting from the heated goo added to the bags resulted in devastating lung damage. Still the popcorn is sold to millions with no warning. Individual exposure is relatively trivial.

    I guess the bottom line is not focusing on a small risk when a much bigger risk is looming. Sorry if my views on the value of modern materials is at odds with the general GBA readership.

  7. Jon_R | | #7

    I don't know about toxicity, but an EPDM gasket will work best and last the longest.

  8. rossn1 | | #8

    Roger -- thanks for taking the time to provide your feedback.

    I have a two year old, another one possibly on the way, and we live in the other half of the home that is not being remodeled. I think it's worthwhile to seek out less caustic products to use on the project.

    I spoke to Sika some time back, and they sternly advised against using the sika product I think you were referencing above (it's the only one Home Depot really carries) for interior uses. When you look at the SDS sheet you can see why.... 2-5% xylene, etc. Of course, I learned this after using a lot of it on the interior in another section of the house, next year. Shame on Home Depot for recommending it for interior use. Instead Sika recommended SikaFlex 1A for interior, but for my purpose, they told me to not use their product at all. It seems their product is not just incompatible, but l listed as reactive with asphalt impregnated fiber board. I haven't found other manufacturers who can tell me about compatibility.

    I've recently come to the conclusion that I can use a layer of sand over the top of the remaining portio of the fiberboard (as an isolation layer), and in this older section of the home it seems there is less or no asphalt in the fiberboard, so I won't have some of it sticking to the walls of the joint. I had considered grinding it out with an angle on one side, but if I can remove the top inch without going to that effort, then less I don't see the value.

    With the sand isolation layer approach, I can probably get away with the sikaflex 1a, but it's sds sheet isn't exactly inciting, which is why I'm reviewing alternatives.

    Jon -- I had seen some prior references to EDPM gaskets (like 6 months ago), and will check into those. Thanks for the thought. In some areas, I have more variability of joint width, where I think the sealant will be required. Maybe shove some gasket down in the lower part of the joint and put a layer of sealant on-top. I'll have to think through how that would affect gasket function.

  9. onslow | | #9


    Back again with a question about the details regarding the fiberboard between the slab and wall. Is the slab finished smoothly? Does the fiberboard sit flush with the slab or stickup random amounts? Are you able/willing to grind at least a little to clean the slab edge?

    I am puzzled by the phrase cove joint as I would take that to mean the slab to wall intersection is curved. I am not familiar with a detail like that as the only finished curves/coves in most of the cement work I have seen occur at the bottom edge of the riser portion of cast steps or slab level changes. Fiber board would not be used in these locations.

    If your walls are smooth and "square" and the slab is smooth up to the fiberboard, you might have a few options yet. I did not mention a product that is much more benign, partly out of failing memory and also it is not a terribly good product outdoors where I have had to use it. It is another Quikcrete product at the Depot Model 864000/SKU738883. The SDS is the usual CYA lawyer/government standard form that is very confusing and unclear. The product does have the unusual distinction of being one of the few things California has not declared a known carcinogen. (unlike coffee) Quickcrete disavows the use for sealing against radon, so you will have to decide what to make of that.

    The product is much like acrylic latex paint with fine sand in it. It is sold as a pourable self leveling sealant for cracks in patios. It will stay flexible in full sunlight and weather for at least five years. Staying attached to the sides of the crack - not so much. Maybe inside it will behave better for longer. Basement slabs are hopefully less actively thrown around by frost.

    Cutting down the fiber board at least a 1/2' below slab top will be necessary for the pour to be deep enough to set and seal. If you grind the edge of the slab at a 45 angle sufficiently deep,you can cut the fiberboard with a utility or linoleum knife. The result will be a one sided V. Grind the surface of the wall where the pourable sealant will contact and wipe well with water and let dry. Dust is the doom of any sealant bonding (and your lungs so don't forget the vac and mask). Pour the sealant in the V.

    If the fiberboard is too "gappy" to keep the liquid in place, pack the cracks with foam caulking rope. If the cracks are too small there is a trick I have used successfully. Using the cheapest latex caulk, I cut the tip wide and flood the bottom of the V and smear it down with a small plastic spoon. I second round of touch up if needed. Once the V trough is safe to fill, flood in the sealant and fill to slightly proud of the slab top.

    If that is all too much, one more approach might work for you. Garage door seal adhered to the wall and slab - spanning the fiberboard and gaps might be a workable answer. The door seal is available in bulk rolls of 100 ft at the Depot Model/44823-Internet202016393. The trick will be finding a suitable adhesive with the nontoxic profile desired. The corners will be a bit awkward too.

    Last but not least. What have you done to collect and vent the radon? Is there an under slab pipe system? If you don't have a negative pressure under the slab, I am not sure if sealing the edges will be sufficient. Have you conferred with anyone on this? Best of luck.

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