Capillary break and footing types
So I was just talking with my GC about applying a capillary break (something I’ve learned here) on the footing. This is something he hasn’t dealt with before and he posed the question, “will the foundation concrete adhere?” Though I’m as green around the gills as one could be and learning as I go, that sounds like a good question to me. I’m not familiar with all the types of footings there are, but based on our conversations I’m thinking the foundation will be cinder blocks filled with rebar and concrete set over the footings as that is typical in our area. My questions, then, are:
1. Does the style of footing matter?
2. Can it impact concrete adherence from the foundation to the footing?
3. Are there any concerns worth being aware of in the design or selection of capillary break product? (I’ve seen the GBA article referenced below, so this question is more in regards to my particular situation)
I should’ve also mentioned that if this introduces this concept to our area and inspectors, then a KISS method is definitely appreciated. The reason I’m even considering the capillary break is because our footings will be located approximately 5′ vertically lower than the road bed in front of our home and though the storm water drainage seems to be okay, I felt like some additional insurance could help improve the longevity of the foundation and footing system. Not to mention tackle any potential rising damp issue early and up front.
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Jason,
Unless you are pouring the footings and foundation walls monolithically, you end up with a cold-joint in the concrete, which has only minimal adhesion. In the past the two were typically connected by a shallow groove formed into the top of the footing with a trowel. Now rebar is the more common method.
Okay, so then if adhesion is minimal, then this shouldn't be a problem or is what adhesion is there considered critical in any way? And then if using rebar, what approach has seen the most success? Or does the current approach really not need the capillary break? (I'm thinking as long as the foundation is in direct contact with the footing, wicking will always be a factor, but thought I'd ask in case there's additional dynamics at play that make it less feasible).
Jason,
I just don't have enough useful experience or knowledge to say. Hopefully someone else can chime in. Right now capillary breaks are confined to a small group of high performance builders. That isn't to disparage them in any way, but it means they are a niche technique most of us aren't that familiar with.
Thanks Malcolm. My GC is a good one and I knew when he wasn't aware of this there was something up. I figured it wasn't typical for the standard in our area. After looking at all the products and realizing the different types of foundations/footings, I can see that.
For an interesting experiment regarding imperfect capillary breaks, stack (top to bottom) a dry piece of paper towel, a plastic film with a tiny hole and then a wet piece of paper towel. Press them together for a few minutes. The dry paper becomes quite wet.
Not sure what to make of it. Thick sheets of EPDM (vs thinner, more delicate alternatives) are better for capillary breaks? Or concrete admixtures? That full gravel surround (under slab, under footings, against walls) is best for dry concrete? Then there are those who claim that wet concrete doesn't matter (while also claiming that a capillary break is important). I see almost no data pertaining to good, modern concrete and the various techniques.
Lol... definitely more questions than answers...
Also, I'm a EE by trade, but work with some CE's and they'll tell you that wet concrete doesn't matter. However, that's from a structural perspective. From a home construction standpoint, this means introduction of moisture into your basement/crawlspace and worse case into your home (rising damp). If the latter occurs, the fix is expensive and involves someone drilling into your foundation and injecting a sealant that will be absorbed by the concrete and setup up to retard the movement. I figure if I'm already aware that moisture will need addressing, might as well get those low-hanging improvements. A few hundred on a barrier now might save a headache's worth of problems later.
Hey Jason.
As Malcolm said, the joint between a footing and concrete foundation walls is typically not a bonded concrete joint. As with your concrete block wall, it's the rebar that will mechanically connect the two. There are membranes that can be used as capillary breaks, but I know some builders find them difficult to install around rebar. Mike Guertin used a fluid applied product--ProtectoWrap’s LWM200--on the FHB ProHome:
https://www.finehomebuilding.com/2016/07/04/capillary-break-coating
Thanks for the link and product info Brian. I've copied both that and the GBA article for my GC and local inspector. I went on the Protecto website and didn't see a dry-time for the concrete before applying. I'll keep looking and may just contact them. Do you happen to know? I know there are some products that are as long as a month before applying and I don't want this to become a large burden for our GC, nor our schedule, such that he never does this again.
Update: Senior moment... per the article I linked above, it can be applied immediately.
Just a thought on the products listed by Martin - If asphalt damp-proofing is going to be used to protect the concrete from water intrusion from the outside, can be applied to uncured concrete, and backfilled quickly, it might be the good choice to use as a capillary break too.
Excellent point. And any excess could be used on the sides.
For what it's worth, I'd also pay attention to the footing drain. Most of us detail it so that the drain channel and material is *below* the top of the footing. This gives water an easier path to continue along than through the footing. However, most contractors shortcut and put the drain level above the top of the footing to save time and money, which just means that the lowest level that the water can sink to is just barely above the cold joint between CMU and footing. They do this because to get the drain below the top of the footing, you either have to "over-excavate" by about a foot and then build formwork in the footing trench, or you have to excavate as normal for a footing, then after it's poured, come back and dig out the foot or so to the outside to lay the drain.
See detail:
https://basc.pnnl.gov/resource-guides/footing-drain-pipe
Jason C,
At the risk of seeming picky, the detail you linked to still is vulnerable because the bottom of the slab rests directly on the footing. Best practice is to have several inches of fill separating the two. This both provides a path for moisture to move underneath the slab, and makes the slab less likely to crack at the edges due to differential settlement of the fill.
Absolutely, a very reasonable observation and solution. I linked that detail simply for the drain location relative to the footing.
Jason,
I've learned from experience that posting a drawing here to illustrate one thing often has people accepting an unrelated part of it as good practice.
I've found a similar problem with design drawings. Clients will often reject an option because of the colour I used on the illustration. "That one is out. I hate yellow!"
Okay, so far the inspector hasn't said no, but hasn't said yes. He has expressed concern that putting another layer between the foundation and the footing would affect the frictional forces. I've sent information (like the Fine Homebuilding article) on it. But so far, no one feels convinced it's the route to go. My GC is already trying to figure other alternatives to pulling water away. And what makes me personally least comfortable is that after talking with some of the representatives for the recommended products (like Protecto Wrap or Epro), it took quite a bit of conversation for them to even understand the application. Although in the end, they said it should work, they definitely acted as though this is not the norm and not in their cross-hairs. Maybe this just hasn't caught on? I'm not sure at this point what else I could do other than show them studies where this has been tested and unfortunately I don't have the feeling that has ever been done.
I have some misgivings as to whether the absence of a capillary break is a problem in most circumstances.
The "rising damp" in British homes comes from the practice of building continuous masonry or concrete structures, that extend from the footing to the roof, which understandably wick moisture up into the conditioned spaces of the home.
The situation in North American stick-frame construction seems to me to be a lot different. Can someone link to the original research that showed this is a significant problem here? I think it came from BSC research, but all I can find is their concern that the salts in soil may cause masonry to deteriorate prematurely.
The biggest issue I can think of is that any moisture wicked up from the foundation to an effectively encapsulated rim joist (assuming good air sealing) is possibly going to cause that rim joist to deteriorate over time.
Bill
We've used two coats of common masonry sealer; seems likely to help We take other measures, but the basements are pretty dry in the end.
Might I recommend the Dorken line of products. Might be worth your time to look and see what they offer?
https://www.dorken.com/en/our-products/residential-products/basement/foundation