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Chris Walcher

Boothe Concrete

1906 Richcreek Rd
Austin, TX, 78757
United States

512-737-5006

How To Videos/Articles

Tips for Building with Board Form Concrete

Valerie Zapien

Journal of Light Construction, May 2017 Article

Tips for Building with Board Form Concrete

Click here for the PDF version of this article.

 

On the Job

BY MATT RISINGER

Tips for Building With Board-Form Concrete

Architects drool over it and clients love it, but frankly, board-form concrete can be a little daunting for a concrete sub or a builder. In this article, I am going to discuss some tips I’ve learned over the years from doing a number of architect-designed homes that have featured board-form concrete walls.

THINK “ART FORM”

Most poured-in-place concrete walls in residential construction are for basements, which have wall surfaces that are either underground or, if exposed on the interior, are considered part of an unfinished space. What we are talking about here is still a structural wall, but it is also a finished surface for aboveground walls.

It’s really an art form, or a sculptural process, that accentuates the surface and intentionally highlights the pattern and grain of the form boards. In many ways, board forming is an old technique; it’s how all poured concrete walls used to be done before we had aluminum and plywood concrete forms. But it has been revived by architects looking for a dramatic, textured wall nish.

NOT YOUR AVERAGE CREW

A good concrete crew is essential. This is not blow- and-go work, and you need a crew that will listen and come up with solutions.  Concrete guys know an amazing amount about how concrete behaves and how to get it to do what you want. I’m lucky that I’m able to work with Chris Walcher and the crew at Boothe Concrete here in Austin. It helps that the end product is an art form that features their work. If the job goes as planned, it makes them look good, and the project becomes their art form that we’re showing off.

MOCK-UPS

When you eventually go to pour the walls, you get only one chance to get them right, so it is always a good idea to make sure the architect and the client are completely on board with what the finished surface will look like. Is the board pattern what they expect? Does the surface provide the detail and the overall look and feel they envision?

The best way to answer those questions and get complete buy-in from everyone involved is with a mock-up. On this mock-up, we used both sides, model- ing a di erent board width and orientation on each one before settling on a horizontal scheme for this project.

When building a small, freestanding structure for the mock-up, you have to build a super-stout structure, adding many more kickers to hold the bottom and a tighter spacing of wales than you might oth- erwise use. This also applied to the walls we were building for this project with intermittent, free- standing sections. For each one, the formwork had to be built like a small fortress. The last thing you want is a blow-out of a form to shift position while placing the concrete.

FORMWORK

When we’re forming these walls, we need everyone to slow down. It takes two or sometimes three times longer to build these forms than it would using conventional concrete formwork.

We screw the formwork together to lock everything in place. Nails tend to loosen up a little and we don’t want any creep in the formwork under the weight of the concrete. Using screws also makes it easier to surgically strip our forms afterwards.

We also miter inside corners, and double- and triple-check that everything is plumb and straight. When building the formwork, you need to always be thinking about what the inside of those boards will telegraph into the concrete. Sloppy work will be immortalized in the concrete for all to see for evermore.

Of all the lumber species we have tried, we have found that Doug fir leaves the most beautiful grain pattern and one that both architects and clients seem to respond to without our having to sandblast or otherwise treat each board to accentuate the grain.

When we place the boards side by side, we join the edges with a bead of silicone. This helps keep the water in the mix and keeps the concrete from seeping out between individual boards.

When placing walls over a structural slab that will be used as a finished oor surface, as we did in the house shown in this article, we are careful to tape along the bottom of the wall. We want to prevent the wall concrete from bleeding out over the slab, and we also don’t want silicone on the slab, as this can disrupt the slab nish. You almost have to think like finish carpenters, which is a real shift from the usual process of forming and placing concrete.

Form ties are critical. We typically use berglass wall ties, even though the more common choice is a steel rod. However, when these are cut ush, the steel stands out against the concrete surface and will rust over time. The berglass ties we use (Super Ties by RJD Industries) are grey and blend in, becoming almost invisible once they are snapped-off  flush with the surface.

CONCRETE TIPS

We spec a 5-sack, 3,500-psi mix. This is a strong con- crete with a high cement ratio. You want that rich cement paste in there to pattern the wood. With this mix, we can run a 5-inch slump instead of the usual 4-inch slump so it will flow well and reduce the chance of honeycombing.

We usually get to the higher slump using plasticizers as an additive to the mix. A plasticizer allows you to keep the water content low, so you get a strong mix, without sacrificing workability.

On pour day, we pump the concrete through a steel wall pipe. You want to be able to reach all the way to the bottom of the form and place the concrete in lifts before pulling the pipe up and pouring another lift. Our crew places the concrete in 2-foot lifts, working all the way across the wall before moving on to the next lift.

Vibrating the concrete is probably the most crucial step. We use two guys with long vibrators that reach all the way to the bottom of the formwork. The trick is to be consistent, but you do not want to over-vibrate, as that will bring aggregate to the surface. To get the de- tail of the wood, you actually want a high percentage of cement paste at the surface, not aggregate. There is never a guarantee that you will avoid honeycombing, but we give it our utmost and have had good luck for the most part.

Board-form concrete walls mix well with glass and metal in modern house designs, such as this project Risinger built with Alterstudio Architecture of Austin, Texas (1). The grain and texture of the individual form boards telegraph in reverse onto the surface of the concrete (2). Since you get only one chance at the nal pour, Risinger typically builds a mock-up on site (3), allowing the architect to experiment and allowing Risinger to get complete buy-in from the architect and the client.

On this project, freestanding board-form wall sections required lots of staked kickers and wales to hold the formwork secure (4). The form builders had to think like finish carpenters, using blue tape to protect the finished slab (5) and mitering inside corners (6)

On the mock-up for this project, Risinger experimented with different form ties (7). Once snapped-off , a steel tie (8) is conspicuous compared with a berglass tie (9). Cutting berglass ties ush to the surface can be done quickly with minimal damage to the surrounding surface

How to Build A Foundation on Piles

Valerie Zapien

Transcribed Video Published November 4, 2016 on YouTube

For more information, go to source, www.MattRisinger.com

If you're planning a lakefront build, I'm going to show you how to do a steel pile foundation. Our company is just starting this beautiful new home here on Lake Austin.  We're working with Shiflett Group Architects and I want to talk to you about the foundation that we're doing for this very special lakefront house. As you can see, we've got a beautiful flat lot here and it drops onto Lake Austin. Beyond us, Lake Austin is a man-made constant level lake. We're right near downtown Austin and the beauty of that is we don't have to worry about the rising and falling water levels.  However, the downside of this property is we've got a water table that's just a few feet below my feet right now.  If I were to dig a hole right next to me here, about four feet deep, it would start filling up with water.   And the way that we deal with that on this particular lot is we're going to be using steel piles.   Anytime you build a foundation the first step is always going to be to get a geotechnical engineer out to do a core sample for you. And when he came in corded this lot, he drilled all the way down until we hit rock just a little over 50 feet deep. What we found was good soil the first couple feet and then very super soil from that water table all the way down until we got rock.  So, steel piles were the recommendation from the structural engineer.  Here, so let me talk about how this works.   When we get finished this is going to look like a very typical slab on grade foundation but the steel piles are really going to be doing the heavy lifting of supporting this foundation. Here's how we do those the steel piles.  They are put in by a pile contractor.  The first step on installing these steel piles is the drill about a 10-foot deep hole and that's going to give us a starter for these columns. Now these steel piles they come in about 30 foot length. There are three eighths inch wall steel and there about eight inches in diameter.   And before we start driving these we're going to well to cap, we don't want to have that column fill up with either water or mud. We want to keep that column free so we can fill it later with both rebar and concrete.   So, the first step after we drill that then is we're going to drop that first pipe in. And you'll notice when the forklift comes that first 30 feet goes down like nothing. All we're going to do is just press it down with the forklift. Now, I mentioned rock was 50 feet and depth and these columns come in 30 feet so once we're just a few feet out of the ground that first column, we have to bring another column.  And well these two sections a column together and then we can continue pushing that once we get to about the last five feet or so.  Before we hit rock, the forklift can't do it any further and that's where we need to bring in the pile driver.  In this case, we're using a crane supported piledriver which is going to drive that steel column all the way down until it hits refusal.   In this case, we hit rock between about 55 and 60 feet in depth and so now these steel pounds, once they hit rock and hit refusal each one of them can hold 300,000 pounds of bearing capacity.   Very, very impressive.   The engineer designs these in a very specific grid pattern so that our point loads from the house onto the slab are distributed to these piles and now in effect our house is floating above all that super miss below us.  Now, the steel piles are in place for both the house and the landscaping.   We're going to bring our concrete crew, Boothe Concrete, to be forming up the house slab and we're going to integrate the house's rebar into the steel piles.  We will come back in a couple weeks and we show you the progress.  

Ok, we're back it's been a couple weeks and as you can see the Boothe Concrete guys have done a fantastic job.   We're just a few days away from pouring the slab, but let me show you now that we're set how we've integrated this concrete slab in with those steel piles that we drove.   So, remember last time we drove those piles all the way down to bedrock and you'll notice those piles are at the bottom of our beams.  If you're not familiar with the reinforced concrete slab, you typically think of your slab thickness is just a few inches.   In fact, this will be a 5 inch thick slab but all the strength from the slab comes from the beams.   That's that grid pattern you're seeing.  It's deeper all the way through this foundation inside those beams.   We've got a rebar layer that's going to integrate into the concrete and stiffen the slab and give it strength.   And at the bottom of the beams, that's what that steel piles are going to be.   Before we got to this point, we filled those steel piles with concrete and then we've got rebar sticking out.   And that rebar is going to integrate into our slab rebar so that now we've got this grid pattern of beams.  At the bottom of those are piles and in fact, the entire concrete slab is going to sit on those piles.   Each one of those piles can bear 280,000 pounds of bearing so we've got several million pounds of bearing capacity on that steel.   Now that we're all set is a really impressive foundation. If you're not familiar with the yellow plastic, that's our vapor barrier. We're using 15 mil stego wrap here that's going to keep any moisture that's in the soil from getting into our concrete.  And now when we pour this next week, we'll cover it for a few days and then we'll be ready to move on.   You know you want to spend the time and the money on your foundation right because no matter what you do on top of your foundation, moves are going to have big problems with your house.   This is the best way to do it if you've got really bad soil.  I highly recommend you talk to your engineer, your builder, and/or your architect about whether steel piles might be an option for your property.

How to Create Board Formed Architectural Concrete Walls

Valerie Zapien

Published on Nov 6, 2013

It has texture, structure, and rugged beauty all at once! Architects love it, but it's not an easy detail to get right. Watch to see how my Concrete Craftsman do it right. I'll show how we formed these board formed concrete walls including tips on wall ties.

www.MattRisinger.com