Go Ahead - Skimp on Your Masonry Thru Wall Flashing

Thru-Wall Flashing is typically an after-thought on a project. The total cost is often amounts to a rounding error so contractors and designers rarely scrutinize their Thru Wall Flashing system. Until it goes wrong. Anyone who has had a flashing problem gets a case of the “shouldas.” As water leaks into their building, wetting drywall, damaging windows they think “I shoulda spent the extra nickel per sq ft to buy a material that would actually perform.”

So the question you have to ask yourself before you cheap out and buy some bargain basement flashing material is: “Do I Feel Lucky?”

Just to illuminate the features, benefits, and cost of different flashings, York Manufacturing came out with this awesome grid. Take a look and see what a minimal increase in material cost gets you in terms of performance.

York Flashings' Products Have Been Added to MasterSpec!

Stupid Question: What is the point of mortar in masonry construction?

I was looking at an architectural detail the other day and came to the stunning realization that I didn’t really know the purpose of mortar in masonry construction. I know, I know…I sell masonry materials for a living. How did I miss this? I know a lot about masonry. I could answer, “What is mortar?” I could answer, “Where is mortar?” I could even answer, “How is mortar?” But I couldn’t answer, “Why is mortar?”

I had always had some kind of vague idea that it was the glue that held a masonry wall together. But as I looked at a detail for a York Thru-wall Flashing (which ideally goes through the entire thickness of the wall), I caught myself thinking, “But wouldn’t that be a bond breaker? Wouldn’t a line of copper or stainless steel going through the wall interrupt the adhesion? Wouldn’t adding that cause the whole wall to fall down!?!”

How does this not ruin the wall? How!?!?!?!

Catastrophizing is a forte of mine.

There must be an obvious answer. Brick buildings have had thru-wall flashings on them for years and years with no issue. So how does this work?

Whenever I have questions about masonry I turn to the International Masonry Institute. The IMI provides education, technical support, research and training on all topics masonry. I spoke to Brian Trimble and Casey Weisdock, both Directors of Industry Development & Technical Services for the IMI. “The flashing does act as a bond break, but you have the weight of masonry bearing on the flashing and that flashing has some coefficient of friction that helps hold the wall in place.,” Brian said. “Also weight/gravity keeps the material in place.”

Casey reminded me that while “mortar isn't an adhesive with a capital A”, it's bonding capacity does play a role bonding the bricks together. The bricks need to stick together somewhat in order to have “panels” that are secured back via a brick tie to the structure of the building.

In short:

While mortar does serve as an adhesive, holding masonry units together, it also serves as a cushion to create full bearing between units. Walls are primarily held together by their own weight and because they are typically anchored to the structure of the building. That’s why the addition of a thru-wall flashing doesn’t compromise the structural integrity of the wall.

Become a ThermaZee Zealot!

Zealot /ˈzelət/ - a person who is fanatical and uncompromising in pursuit of their ideals.

Z-Girt /zee-girt/ - an antiquated way of putting cladding onto a building that would often severely hinder the effective R-value of an exterior wall.

You know Knight Wall from their award-winning CI, HCI and MFI systems. In fact, you may have seen them on some recent projects, including one of the first certified Passive House projects in Pittsburgh. That reputation continues as they the launch a new product that should make increasing the effective R-value of your wall assembly even easier!

Knight Wall’s ThermaZee employs a specially designed, hollow, thermal isolation strip complimenting other performance enhancements at the web of the girt. The webs unique punch pattern has a substantial reduction in metal penetrating the insulation – about 75% – which decreases heat-flow through the girt. With up to 93% exterior insulation effectiveness, the Knight Wall ThermaZee easily meets the requirements of the IECC in all climate zones (maximum U-Value 0.064) with only 3.5” of exterior mineral wool insulation without the need for interior batt insulation.

Like traditional Z-furring, the ThermaZee can be installed either vertically or horizontally, attached to a variety of substrates such as steel studs, wood studs, CMU and concrete. Also, like traditional furring, a variety of claddings can be attached directly or with secondary rails. These include fiber cement, metal panels, HPL panels or aluminum composite material (ACM), among others.

It’s got thermal performance. It’s got ample drainage. What more could you want????

Read more about it on Knight Wall’s website.

Crusting: Good for Bread; Bad for Concrete

A great many of us have turned to baking our own bread while under quarantine. We’ve learned how to make our own sourdough starter, boil our own bagels and fry our own doughnuts. So if there’s one thing we’ve all learned while performing this newfound hobby, it’s that a good crust is key to a good pastry.

Unfortunately the exact opposite is true when it comes to concrete. “Crusting” of concrete happens when the very top layer of concrete hardens prematurely, giving the impression that the concrete is ready to finish when in fact the layer just below is still soft. If a concrete crew attempts to start finishing operations, the soft jelly-like concrete underneath can bulge out, producing wavy or cracked surfaces. It’s typically caused by “differential stiffening” within the concrete placement. Basically the top layer gets hard way faster than the rest of the placement.

If you, for some absurd reason, want crusted concrete. I included a recipe below.

Recipe for Crusted Concrete:

• 1 cup of temperature difference between subgrade and the concrete

• 2 TBSP’s of wind, sun or other environmental factors that might prematurely dry the concrete

• 2 dashes of Concrete Mix designs that inherently reduce bleedwater rate (air entrainment, silica fume, high cement content).

• Bake in the sun and wind.

In order to avoid concrete crusting, try to eliminate the factors that cause differential stiffening. Keep your subgrades closer to ambient temperatures through heating blankets. Use a fog spray to keep the surface humidity relatively high. Spray a monomolecular film like Euclid’s Eucobar on the surface to prevent rapid evaporation of bleedwater.

With this advice in mind, in the coming months we’ll hopefully only see crusts on people’s Instagram pretzels.

Engineering for Dipsticks: Does Stronger = Longer ?

After my last installment of Engineering for Dipsticks, I got some feedback from a number of structural engineers on topics they’d like me to cover. One of them asked if I could cover the topic of compatibility in concrete repair specifically, “The compatibility of “stiffness” when it comes to repair material selection (i.e. is there such a thing as a material being too strong for an application). 

An age-old aphorism within the concrete repair community is “Repair like with like.” This means that if you are going to repair an existing concrete slab that has a compressive strength of 4,300 psi, then your repair mortar should be relatively close to the original concrete in strength. The International Concrete Repair Institute has even spelled out these guidelines in their Technical Document: Spall Repair in Horizontal Concrete.  “Compressive strength should be greater than the original concrete and should not be less than 4000 psi.”

On it’s surface, it makes sense that you wouldn’t repair concrete with weaker material. But there are some occasions where a “stronger” material can actually make repairs less durable.

A great example of this is in the treatment of control joints in warehouse environments. Often times, the shoulders of control joint are one of the first things to spall. This is because they are subjected to lots of wear from forklifts, hard-wheeled hand carts, etc. rolling over them all day long.

Overhead view of a typical deteriorated warehouse control joint.

A lot of designers and/or contractors say, “That thing is a pain in the butt to maintain. I’m going to fill it with the hardest, most durable material I can find.” This leads many to use a structural epoxy to fill the cracks. However, typical structural epoxy will have three times the compressive strength and potentially twenty times the tensile strength of the existing concrete!

“Great!” you might say. “That should give me a long lasting repair.” However, there are other factors to consider. What if the original cause of the cracking is due to movement or deflection between the slabs? Now the control joint, which was designed to crack, is filled with an ultra-hard, ultra-stiff material. If the movement continues, then the stress will migrate to the areas adjacent to the control joint, causing the concrete to crack further away from the original control joint.

Movement cracks will likely re-occur near dotted lines if control joints are filled with a structural epoxy. The control joint isn’t allowed to crack because of the extra-hard material, so it cracks somewhere else and makes the spall worse.

If the control joint was filled with the appropriate material [COUGH Euclid’s QwikJoint UVR polyurea COUGH], then we might not have that problem. A slightly softer material could still provide adequate load transfer yet allow for some movement. This would keep the cracking where it’s supposed to be, in the control joint. On paper, a softer polyurea might not be as impressive as a structural epoxy (less than 15x the tensile strength, etc), but it’s more likely to be the right choice for long repair.

Investigation into the root cause of the failure should determine the approach to repair. Stronger is not always longer.

Understanding Hydrostatic Pressures

In these trying times, it’s nice to know that there are some things that stay consistent.  The sun rises in the East and sets softly in the West.  The birds sing to each other as they have for eons.  And it is raining like a son-of-a-*$&#@ here in Pittsburgh.  Pittsburgh is one of the “Dreariest Cities in America.”  Please…please…hold your applause.  On average, Pittsburgh has 140 days per year of precipitation.  It gets a little wet around these parts and it can affect how designers protect a building against the intrusion of groundwater. 

A typical beautiful day in Western Pennsylvania.

You may have read the term “hydrostatic pressure” when skimming through geotechnical reports. Hydrostatic basically means “resting water”.  As the water level rises, it creates pressures which can force water into areas where it otherwise might not go.  This is because water is heavy.     

It can even crush cars!

Ideally, you want to build the foundations of your building above the water table.  The water table is the upper level of an underground surface in which the soil or rocks are permanently saturated with water. The water table fluctuates both with the seasons and from year to year because it is affected by climatic variations and by the amount of precipitation used by vegetation.   

Now, to make things a little bit more confusing.  Almost, every project will see hydrostatic pressure at some point, maybe after a big rain or a snow melt (Intermittent Hydrostatic Pressure).  But typically, once the rain stops or the snow stops melting, the water table will lower back to normal. When a foundation wall is above the water table and may only see some intermittent hydrostatic pressure, a designer may add some kind of perimeter drainage system to help keep the structure dry.  This could be a Trench Drain, a sump pump system, or a French Drain (that’s just a normal drain…with tongue). 

However, some projects require that the foundation walls sit below the water table (constant hydrostatic pressure).  If the project has walls that will sit below the water table, then there’s really no point in designing drainage, is there?  Because there is a constant source of water, pumping it or directing it elsewhere is tantamount to Sisyphus pushing the rock up the hill for eternity.  It is a fruitless endeavor.  The water will always be there, no matter what you do.  Take a look at the CETCO Waterproofing Membrane details below. The one marked “Non-Hydrostatic” shows a drainage board, likely directing the water to a drainage system of some kind. The one marked “Hydrostatic” doesn’t have a drain board, because there is no where for the water to drain to!

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Remember that water is the #1 source of construction litigation today.  So to combat water, you need to think like water.  Understanding the difference between intermittent and constant hydrostatic pressure is a great starting point. 

Engineering for Dipsticks: Shear? Sheesh...

To borrow a premise from comedian John Mulaney, I think I was supposed to be a nerd. I think in heaven they made 3/4 of a nerd but forgot to flip the final switch before they sent me out the door. So I got all of the obsession with Lord of the Rings and X-men, but unfortunately very little of the useful math and science skills stereotypically reserved for nerds.

 This brings me to my topic today: shear. This is a term I’ve heard a multitude of times over my brief construction career. Shear walls, shear failure, etc. So while I always kind of got the gist of it, this particular term in mechanical physics never quite made as much sense as it’s cousins compression and tension. 

I think this is about right.

So, on a VERY basic level, shear is when parallel internal surfaces are laterally shifted in relation to one another.

Fun side note: this is actually what my lower back looks like too.

Shear walls are used when designing buildings to resist the lateral loads that are put on the structure (namely wind/earthquakes). The wind or earthquake wants to shift the building one way and the building’s foundation wants to keep it in place. These parallel forces put shear stress on the wall. A shear wall will typically use a structural sheathing (DensElement / OSB) to stiffen it up, or can be constructed of masonry or reinforced concrete to keep the building from falling down at the first breeze.

You might also see shear when talking about concrete bridge construction. Bridges are subject to dynamic loading and needs something to resist the forces placed upon it. On the picture below, the orange arrows can be both the dead load of the bridge itself and any dynamic live load that crosses it (ex. Semi-Trucks filled with dumbbells, buses full of offensive linemen, etc). The bridge wants to push down in one direction and the piers want to resist that force in the other direction. These forces cause shear stress at the circled locations.

Obviously, I’m not an engineer. I’m just a guy with a liberal arts degree trying to make sense of all this stuff.

The Legal Implications of Shop Drawings

Have you ever looked at an FTP site for a construction project and browsed through the bajillion pages of contract documents (Specs, Drawings, General Conditions, etc) and thought to yourself, Isn’t this all a bit much? There is so much to consider for a contractor when putting together submittals, it can sometimes be overwhelming. They need to review the spec, data sheets, and in many cases come up with their own shop drawings. The term shop drawings can mean different things to different people, but generally it is defined as drawings meant to express how the contractor plans to build the designed project. However, while shop drawings and other submittals are important, they do not supersede the actual contract documents.

Recently, I read an excellent article in the American Concrete Institute’s monthly publication (CI International) on the topic of shop drawings. Here are some important excerpts from that article:

“A common misconception is that submittals dictate the work to be performed. The AIA documents are clear however, that the contract documents define the work and the AIA General Conditions state specifically, ‘submittals are not contract documents.”

“Before sending the submittal for review, a contractor must review the submittal for compliance with the requirements of the Contract Documents and approve the submittal. When contractors send submittals to the design professional for review, contractors represent to the owner and the architect that the (1) reviewed and approved the submittal, (2) determined and verified materials, field measurements, and field construction criteria [this often time included substrate preparation], and (3) checked and coordinated the information in the submittal with the contract requirements.”

“A contractor is prohibited from performing any work covered in a submittal until it is approved by the architect or engineer. Once approved, contractors must perform the work in accordance with the approved submittal. There is a word of caution: even if the architect approves a shop drawing that includes a deviation from the Contract Documents, the contractor’s obligation remains compliance with the Contract Documents - not the shop drawing.”

I have seen this first hand. A reputable sub-contractor was hired to perform some below-grade waterproofing work. They submitted shop drawings showing the waterproofing just going on the foundation walls. These drawings were approved by the GC and the designer. The sub-contractor purchased material and coordinated labor to begin the job. Then came the pre-installation meeting. The Project Manager for the GC informed everyone that the Contract Documents stated that the walls AND the floors were to be completely waterproofed (thus more than doubling the area the subcontractor was responsible for). The sub-contractor was stunned. He protested, saying that all of his shop drawings showing just the walls in the scope had been reviewed and approved. Although this was the case, it was in conflict with the original contract documents. The sub-contractor ultimately had to eat his mistake and waterproof both the floors and the walls.

Was this sub-contractor wrong? Yes, legally speaking. Would it have been nice for either the GC or the architect to call out this mistake much earlier in the process and avoid the delays in schedule, loss of money and ill-will associated with this mistake? Without a doubt.

So much of commercial and industrial construction relies on legal power to be able to get a thing done, when in reality, a little better communication at the onset would have resulted in a better project and less stress all around.

Bottom line is that Contract Documents are king. Shop drawings are necessary, but they will never take the throne.

What's a Pour Strip?

This is one of those things that you don’t run into a lot, but it’s still nice to know what it is. A pour strip is usually 3 -5 ft wide area of concrete slab that is left open (or “un-poured”, if you will) in order to control shrinkage. 

Why are we interested in controlling shrinkage? On large slabs, shrinkage can result in serious cracking. Therefore a contractor may pour two sides of a large slab first, leaving a pour strip in the middle. This allows the two slabs to shrink freely, reducing the slab’s tendency to crack. After a prescribed period of time (usually 30+ days) the slabs are hopefully done shrinking. After that, the pour strip is filled in with normal concrete to provide a continuous floor.