Capillary Breaks Above Footings
Capillary Breaks Above Footings
Install a peel-and-stick membrane or a fluid-applied waterproofing product between concrete footings and basement walls
Builders routinely install several types of barriers to avoid damp basements. Examples of these features include a layer of crushed stone and polyethylene under a basement slab; asphaltic dampproofing on the exterior side of basement walls; and sill seal made of thin closed-cell foam between the top of a foundation wall and the mudsill. All of these materials are used to reduce the transfer of moisture from the damp soil surrounding a foundation to the interior of the building or vulnerable framing lumber.
Even when all of the listed features are installed, however, many builders forget to include a capillaryForces that lift water or pull it through porous materials, such as concrete. The tendency of a material to wick water due to the surface tension of the water molecules. break between the concrete footing and the basement wall. While installing such a capillary break isn’t common practice, it’s important.
If you place a large dry sponge in the middle of a shallow puddle, the top of the sponge soon becomes wet. This is a commonplace occurrence, so most people have an intuitive grasp of how capillary action works. Capillary rise isn’t a phenomenon that is limited to sponges, of course; it also happens with concrete walls, CMUConcrete masonry unit. Precast concrete block used to build walls. CMUs have hollow cores that can be filled with concrete onsite for additional reinforcement. The use of stronger, more lightweight types of concrete such as autoclaved aerated concrete (AAC) is becoming increasingly popular in CMU manufacture. walls, and stone-and-mortar walls.
Capillary rise occurs when the forces of adhesion (the attraction between the molecules of a liquid and those of a solid) are stronger than the forces of cohesion (the attraction of the molecules of the liquid for each other). In some circumstances, equilibrium between these two forces is not achieved until the liquid has risen many feet.
In many houses, capillarity is responsible for the rise of water from damp soil under concrete footings into foundation walls. This phenomenon can contribute up to 15 gallons of water a day to a home’s interior moisture load. Capillary action in soils and masonry — called “rising damp” in Britain — is a function of the pore size of the soil under a footing or foundation wall. While small-particle clay soils allow water to rise as much as 20 feet by capillarity, crushed stone permits water to rise only a few inches.
So what’s a “capillary break”?
To interrupt the upward flow of capillary moisture through a concrete wall, we need to install a barrier (also known as a capillary break) under the wall. Typical barriers include some type of sheet membrane or some type of liquid-applied product.
Here are examples of membrane materials that have been used as a capillary breaks between concrete footings and a foundation walls:
- Polyethylene sheeting (a product that isn’t very user-friendly in this application).
- Peel-and-stick products like Grace Ice & Water Shield, Vycor, or Delta Footing Barrier.
- EPDM roofing.
Here are examples of liquid-applied or brush-on products that have been used for the same purpose:
- Asphaltic dampproofing (also known as “foundation coating”).
- UGL DryLok Clear latex masonry paint.
- Thoroseal, also known as BASF MasterSeal 581 (a cementitious coating).
- Tremco TREMproof 250GC.
- Henry CM100 Cold Fluid-Applied High Building Waterproofing.
- Epro Ecoline-R Liquid Applied Membrane.
- ProtectoWrap LWM200.
- Conpro Super Seal.
What about admixtures?
In a comment posted on a Q&A thread, GBAGreenBuildingAdvisor.com reader Malcolm Taylor suggested that concrete that includes Xypex (an additive that can be mixed in with the concrete at the batch plant) will be less susceptible to capillary rise than ordinary concrete.
To learn more, I called up the technical help line at Xypex and spoke with a representative named Jim Caruth. Caruth was intrigued by Taylor's theory, but was not willing to sign on to the idea.
He later clarified Xypex's position in an email. Caruth wrote, “I am unable to provide proven field results to a point that Xypex can recommend its products in this application [to reduce capillary rise]. We expect that Xypex would work to reduce or eliminate rising damp both as an admix in the concrete in the footing or as a coating at the footing to wall joint but again, we do not have proof of this through a track record of documented installations and thus cannot endorse it broadly as would be done in an article such as yours.”
[Photo credit: LgSquaredInc.com - Proud Green Home at Serenbe.]
Over the footing, not under the footing
Some builders have experimented with installing a capillary break (usually polyethylene sheeting) under the footings instead of on top of the footings. But this approach won’t work well.
Why? Because the bottom of a footing is usually lower than the holes in the footing drain pipe. That means that footings are often wet — in fact, in some cases, footings are basically sitting in a puddle. If you tried to install the footing drain pipe far enough below the footing to keep the pipe holes low enough to ensure that the bottom of the footing stays dry, you’ll undermine the footing — and engineers don’t like undermined footings. (For more information on this topic, see How to Install a Foundation Drain.)
Rebar: the fly in the ointment
Of course, when a footing includes protruding rebar, installing a capillary break gets more complicated.
There are two ways that a poured concrete wall can be keyed to a concrete footing: with a keyway (a groove or rabbet) in the center of the footing, or with vertical rebar stubs.
In general, the use of a keyway makes it easier to install a capillary break (especially peel-and-stick membrane) than the use of vertical rebar. But builders have found ways to use membrane barriers even on jobs that have vertical rebar between the footing and the wall.
[Photo credit: Brian Butler.]
In praise of membranes
Mike Maines, a residential designer in Palermo, Maine, told me that he usually specifies the use of “Vycor or equivalent” as a capillary break above concrete footings. “If vertical rebar is spec’d, then two layers of Vycor, meeting in the middle, work pretty well,” Maines said. “I have a personal bias against fluid-applied coatings, as I just don’t like working with them and tend to make a mess. I find membranes and tapes to be easy. But I can see the appeal of fluid-applied products.”
Rhode Island builder Mike Guertin, who is now working with Maines on the Fine Homebuilding ProHome project, told me, “Up until now I’ve used membrane-type capillary breaks to block moisture the migrates through the footing from rising into the foundation walls. The membranes are easy to work with provided there is no vertical rebar.”
In praise of liquid-applied products
In a recent blog posted on the Fine Homebuilding website, Guertin described the installation of a capillary break on the ProHome project — a job with lots of vertical rebar protruding from the footing.
[Photo credit: Mike Guertin.]
“We used a waterproofing coating — ProtectoWrap’s LWM200,” Guertin wrote. “It’s primarily used as a waterproof coating in window and door openings on concrete block walls. … We poured out a stripe of LWM200 along the footing and Bruce spread it with a roller. I followed behind back-brushing it into rough surface areas, pin-holes and around the vertical rebar. I also lapped up any puddles and spread it elsewhere. It only took about an hour for the two of us to coat 130 linear feet of 18-inch-wide footing. By the time we made it around to where we began, the coating was dry enough to snap our layout chalklines and begin nailing down steel track to lock the ICFs into.”
In an email, Guertin elaborated. “I guess the key is getting the mil thickness right,” he wrote. “We probably went too thick, and I’m not sure if that would be a problem with curing. For some contractors who want to move fast, the cure time may hinder them. The material we used was dry to touch in an hour but needed longer to cure before the abuse of setting forms. I think the fluid-applied [product] is simpler when there is rebar and/or a channel. Fluid-applied isn’t as durable as a peel-and-stick. The downside to peel-and-sticks I’ve used is that they required the concrete be primed first, so there was extra labor.”
When I asked Dan Kolbert, a builder in Portland, Maine, about capillary breaks above footings, he told me, “We’ve used Conpro Super Seal. Mix it up in a bucket and paint it on with a stiff brush.”
Check the price
Before specifying a product, you’ll probably want to get pricing information. The online price for 5 gallons of UGL Drylok Clear is $173.
On a Q&A thread on GBA, an owner-builder named Jimmy Nguyen wrote, “Our footers were 18 inches wide and totaled 204 linear feet. … Using two 35-pound buckets of the product [Super Thoroseal], we were able to do two coats with some left over to do a third coat over the keyway. Each 35-pound bucket cost just $25. On another forum about capillary breaks, a product that was mentioned was Tremco TremProof 250GC. I called around to check on the price of that product and it was around $250 for a 5-gallon bucket. I probably would have needed two buckets to cover my footers and so the cost would have been expensive. Also, I kind of liked the fact that the Thoroseal is cement-based and might be tougher than some of the thinner waterproofing paints, especially considering the amount of stomping and scraping it will have to withstand when the workers form the basement walls. … After the first coat, you have to wait 12 hours to apply the second coat. The application is done with a thick block brush. The product is supposed to be applied with a pancake batter consistency, so it’s not exactly like you are painting with thin latex, and it will take some more time to brush on. Wetting the footer will help.”
How long do you have to wait?
On most residential jobs, concrete contractors don’t want much of a delay between pouring the footings and putting up wall forms. Ideally, installing a capillary break shouldn’t delay the foundation work. In some cases, however, it will.
There are two questions here:
- The first question is: How long do you have to wait after the concrete has been placed before you can apply the capillary break?
- The second question is: How long must the capillary break cure before you can set the wall forms?
Conpro Super Seal. To get answers to these questions, I spoke with George Boisvert, a representative for Conproco, the manufacturer of Conpro Super Seal. Boisvert told me that it’s possible to install Super Seal on fresh concrete. However, he advised builders to let the product cure for at least a week before allowing wall forms to be set on the footings. “The Super Seal has to be cured,” Boisvert told me. “You really need to cover it with wet burlap or dampen it with a spray hose 3 or 4 times a day for a week.”
UGL Drylok Clear. Next, I called up United Gilsonite Laboratories (UGL), the manufacturer of Drylok, and spoke with technical help representative Rich Barako.
Barako told me that only one of their products, Drylok Clear, should be used to provide a capillary break above a concrete footing. However, he noted that before applying the Drylok Clear, “You should wait for the concrete to be cured. If you apply it on green concrete, what could happen is that, as the product takes on the water from the concrete, it will never really cure properly. So the concrete must be as dry as possible. There are two lines of reasoning. One is that you should allow the concrete to cure for 30 days. My answer is to allow the concrete to dry for at least a week or two before you put the Drylok on it.”
On the second question, Barako said, “The cure time depends on the drying conditions. You need to wait for the film-forming chemicals to evaporate. High humidity or low temperatures will slow down the cure. You need to wait a day or two, until there is no tack to it.”
Thoroseal. I also spoke with Jason Theis, a technical help representative at BASF, the manufacturer of Thoroseal. (BASF sells its Thoroseal product under two brand names. When sold at Home Depot and Lowes, the product is labeled “Thoroseal.” When sold directly to contractors, the product is known as “MasterSeal 581.” It’s the same stuff, regardless of the label. Super Thoroseal is Thoroseal with an acrylic additive mixed in.)
On the first question, Theis advised, “Thoroseal should only be applied to fully cured concrete, not green concrete. You have to wait until the concrete reaches 80% of its design strength, which takes 28 days. If you apply it early, you might not get a good bond, and you might get cracking.”
On the second question, Theis advised, “You need a two coat-application. Cure time will vary, but generally the cure time is 2 to 3 days.”
Not all liquid-applied products require a 2-to-4-week wait
Of course, ordinary asphaltic dampproofing (foundation coating) can be applied to fresh concrete. So can the following four products: Epro Ecoline-R, Henry CM100, Protecto LWM200, and Tremco TremProof 250GC.
According to Donna Frail, a spokesperson for Epro Services, their liquid-applied membrane (Ecoline-R) can be applied to fresh concrete, “as soon as the forms are stripped.” The product cures in 24 to 48 hours.
According to the manufacturer’s website, Henry CM100 fluid-applied waterproofing can be applied to green concrete. Cure time is about 24 hours.
According to Mike Stout at Protecto Wrap, Protecto LWM2000 can be applied to fresh concrete. The product cures in 24 hours or less.
According to a spokesperson on the technical help line at Tremco, TremProof 250GC can also be applied to fresh concrete. The product cures in 24 hours or less.
Keeping on schedule
So, do contractors who use Drylok Clear or Thoroseal actually wait one to four weeks for the concrete footing to cure before applying these products as a capillary break? Of course not.
Will these products still be effective if builders ignore the advice provided by the manufacturers of these products? The answer to that question is unclear.
Here’s my advice: If you want to install a fluid-applied product, choose a product that can be applied to green concrete (asphaltic dampproofing, Epro Ecoline-R, Henry CM100, Protecto LWM2000, or Tremco TremProof 250GC).
Otherwise, select a membrane product like Vykor or Delta Footing Barrier.
Martin Holladay’s previous blog: “Batteries for Off-Grid Homes.”
- Image #1: Jimmy Nguyen
- Image #2: Hammer and Hand
- Image #3: Roger Normand
Aug 5, 2016 9:09 AM ET
Aug 5, 2016 2:22 PM ET
Aug 8, 2016 6:53 PM ET
Aug 11, 2016 1:05 AM ET
Aug 11, 2016 5:50 AM ET
Aug 11, 2016 10:17 PM ET
Aug 12, 2016 4:36 AM ET
Aug 12, 2016 9:25 AM ET
Aug 17, 2016 6:58 PM ET
Aug 17, 2016 7:43 PM ET
Oct 2, 2016 9:29 PM ET