Board Formed Concrete – An Architect’s Guide

Board Formed Concrete – An Architect’s Guide


Hi, Eric here with thirty by forty design
workshop, today we’re going to be discussing board formed concrete which we’re using on
two large site retaining walls on our Squid Cove project here in Maine. So, we’ve just cast a small mock-up and in
the process I’ve learned quite a bit and I’m eager to share that with you. Now, we’re all likely familiar with poured
in place concrete. It’s one of the humblest of building materials
and it’s unique in that it begins as a highly plastic slurry and after it cures it becomes
its polar opposite – extremely hard and durable. And, aside from its inherent utility in foundations
and its weather-resistive properties, we can exploit this transformation from slurry to
sculpture in our architecture. Typically, concrete is poured into large,
panelized forms made of plywood or aluminum. This results – to varying degrees – in a relatively
smooth appearance. Yet even smooth forms will telegraph knots
and surface imperfections to the finished face of concrete walls once the forms are
stripped. Now, board forming is actually an old technique
that preceded the larger panelized systems commonly used today and it’s a method that
accentuates concrete’s plasticity. In lieu of plywood or metal panels, boards
comprise the container – or form – into which the concrete mix is poured. This results in a finished wall imparted with
the reverse impression of the face of these boards, including all the imperfections, the
knots, and the gaps. It’s this texture that we’re after when we
specify board formed concrete. It gives life to wall surfaces, subtly highlighting
the process of their making and for our project it also links it back to the other wood textures
we’re using and the surrounding wooded site. So concrete is composed of four elements:
water, cement, aggregate and sand. By altering the mix between these ingredients
we can control how the concrete will perform over its lifetime and in the specific environment
where we’re using it. For exterior walls we want a dense concrete
and a high quality paste. It’s the paste that predominates the color
of a concrete wall. So, we’re using a higher strength concrete
which means more cement paste. And to that we’re adding a super-plasticizer
technically known as a “high range water reducer.” This is an admixture that affects the cement
particles, which are normally attracted to each other and they tend to clump together
in the presence of water. A super-plasticizer binds to the cement particles
and in so doing, leaves space between them large enough for water molecules to enter. Now what this does is it allows the water
to hydrate the cement more efficiently. Hydration is the chemical reaction that causes
concrete to “cure” or harden. Superplasticizer allows us to use less water
– which makes for stronger concrete – and still maintains its workability which is typically
a problem when we use less water in the mix. It also ensures that the concrete will readily
flow into all the imperfections in the boards that make up our forms. The concrete mix is arguably the most important
part of our recipe. We want lots of texture so wood type and face
figure is important. For our project, we settled on a local spruce
– which was readily available, it was inexpensive and it was pretty easy to work with. Most board forms use softwoods like spruce,
pine, fir, or larch. Now, we did experiment with finishes to accentuate
the surface texture. We tried pressure washing, wire brushing,
sandblasting with walnut shells and finally with coal slag. For our test panel we also included regular
mill-finished, un-planed boards. And this is probably a good time to discuss
the necessity for sample panels, they’re just an absolute must and you only get one chance
to get the real thing cast properly and looking the way you intended. So Nate, our general contractor, built ours
as a 2-foot by 2-foot by 8-inch thick panel which was enough to test out the board textures
and a few different edge finishing techniques. Next, you’ll have to choose board orientation
and width. Now, these are fundamentally aesthetic decisions:
whether it’s vertical, horizontal, fixed or random width, broad or narrow but they can
be used to underscore a particular design vision. We chose a horizontal board which helps with
the site wall to gesture to the horizon which is helping us to reach out into the site. And we chose a fixed width board of 6-inches
which is a comfortable, human-scaled proportion. And 6-inches also allowed our coursing to
easily correlate with other elements of the architecture like the deck, our lighting and
the interior and exterior steps which we’ve designed which also relate back to the stepping
site. Vertical boards will tend to make elements
feel taller, while narrower board widths – regardless of orientation – will accentuate directionality
even more, making vertical orientations seem taller and horizontal ones seem longer. The more boards though the more expensive
the forming labor becomes so there’s a delicate balance to maintain there. To keep the concrete forms held together under
the immense weight and outward pressure of wet concrete the two sides of the form walls
must be tied together. Now, typically these form ties are made of
mild steel and the tips are broken off flush with the wall face after the wall is cast. In most cases this is fine, but mild steel
will rust and because our board formed walls are acting as aesthetic elements in our project
– site walls near a large deck and a gathering space we want them to look as good as possible. Complicating this decision was the fact that
we opted to use standard plywood forms for the outer shell of our forms. This was for ease of setup and bracing and
allowed us to line the forms with our wood boards. What this also meant was that we have to use
ties that worked with our concrete contractor’s standard forms. So, we priced out stainless steel ties, but
the added cost was significant and, as it turned out, was more than our client wanted
to spend. So, we’re planning to use the standard mild-steel
ties and then we’ll just come back and patch the holes after they’ve been broken off. Now, fiberglass rod ties are another option
if you’re not using a standard form. They aren’t expensive, they don’t rust, and
they’re actually quite unobtrusive, but we had a hard time sourcing them locally and
again, they didn’t work with our subcontractor’s forms so it really wasn’t a viable option
for us. Now is also the time to think about the corner
details. Our retaining walls are doubling as a seating
bench and a planter so the corners are becoming really important. Hard edges on concrete don’t perform well
over time as they tend to break and they sort of look terrible. So, our contractor Nate mocked-up a few different
options for us to consider and we settled on a small chamfer, which from a distance,
creates a shadow line that actually looks a lot like a hard-edged corner. We tried a true corner and a quarter-round
tooled edge as well but neither of those looked quite as nice as the small chamfer. After casting the sample panel and discussing
it with our client, we all agreed that the unaltered boards provided enough subtle texture
for our needs. And, this helped by reducing the extra labor
cost of blasting every one of the boards. There’s reinforcing: all concrete should have
reinforcing to prevent cracking and with that you’ll also need control joints per ACI requirements. Concrete will crack and control joints essentially
“control” where that cracking occurs keeping it contained rather than letting it spider-web
across a beautifully formed wall face. Especially long walls will require them and
you’ll have to plan for these in the forms as well. Now, there’s also things like planters, which
we’re using. You’ll have to form those and you’ll have
to reinforce them separately. There are bond-outs for integrated equipment
or devices, things like exterior lights, speakers, recesses, utility connections, drainage if
you’re using a planter that’s especially important. And finally, you might choose to embellish
the wall with any number of embedments – dates, patterns, emblems, things like that. That all needs to find its way into the formwork. Now for the concrete placement. Adding the superplasticizer will aid in the
workability of the concrete as it will tend to flow into voids readily. However, this doesn’t eliminate the need to
vibrate the concrete as it’s placed. But, you have to be careful not to over-vibrate
or over-consolidate or hit the rebar when vibrating as that will tend to bring the aggregate
to the surface and negate all the hard work of the previous steps. Vibrating keeps large voids or honeycombs
from forming in the wall which are not only unsightly, but they can impact the longevity
of a wall allowing water to pool and freeze and crack it over time. Also think about how you want to finish the
top surface. For us, we opted for a hand-troweled, smooth
finish. Because of the variables involved it’s hard
for me to say precisely what this will add to your project over a standard concrete wall. It will depend on height, thickness, job scope,
details, board size, ties; in short, all the things we just discussed. However, the more information you can provide
your concrete sub and the more experience they have in placing board-formed concrete
the better your final price will be. So you should come in prepared to discuss
the requirements and expect to work through the details together as you work to quantify
the added costs. So, to recap, the costs above and beyond a
standard poured-in-place wall are: boards and any prefinishing that you choose to do
to them sandblasting or whatever, extra labor to install the boarding, any special form
ties, stainless, fiberglass, superplasticizer, a higher strength concrete, any embedments
or specialty bond-outs and potentially more stripping time. Now, for our project’s budget all of this
was pretty manageable and the trade-off – we think – is priceless. I’ll be sure to update the video once the
actual site walls are poured and complete and you can leave any questions you have in
the comments.

49 Comments

  • minimal.5

    November 16, 2016

    omg thanks for the video.I learned a lot 🙂

    Reply
  • Jeremy James

    November 16, 2016

    educate me on rammed earth please

    Reply
  • Leneufcinqcergy

    November 17, 2016

    I love concrete!!!!! Thank you!!!!!

    Reply
  • Bailey

    November 17, 2016

    Thank you so much for your wonderfully informative video. I hope you receive ad revenue from these quality videos.

    Reply
  • LJ Lancaster

    November 17, 2016

    Love your videos mate. They are both informative and entertaining. I fell in love with board formed concrete every since I saw the Tea House by Archi-Union Architects on Arch Daily. The interesting geometries of the walls/stairwell they created was amazing. – LJ 😀

    Reply
  • MakeMeThinkAgain

    November 17, 2016

    Using slag or recycled concrete?

    Reply
  • alex urquidez

    November 17, 2016

    Really good video man, thanks for the information!
    Greetings from mexico

    Reply
  • hellonoko

    November 18, 2016

    Really enjoying your video, can you suggest any books on concrete, forming, architectural concrete?

    Reply
  • Evelyn Zuberbühler

    December 12, 2016

    I am really enjoying your videos and this is another interesting one. I was wondering if it was possible to use hempcrete for this type of project? Also, could a similar type of method be used on flooring?

    Reply
  • Karim

    January 4, 2017

    I've learned from your channel more than what I've learned in Architecture School

    Reply
  • Ashley Mcwatters

    January 6, 2017

    Enjoyed the video! We offer a fiberglass tie that would be perfect for your application! We also have a system that can work on standard form ply single waler applications. Check out our fiberglass concrete ties at:
    http://sigmadg.com/fiberglass-form-ties-for-concrete-forming.html

    Reply
  • Leneufcinqcergy

    January 24, 2017

    I have a question please. I am planning to build my own house but have conflicting design ideas I think. I am in love and have been for quite sometime with Shou Sugi Ban (before it was all the rage) but I also love concrete equally. I want to build a very simple rectangular structure with the exterior being completely wood and the interior being completely concrete (walls, floors & ceilings). Maybe using concrete veneers for the walls and ceilings to make it more doable. Does this make sense? Will it be overly jarring, look ridiculous. I want both but need some advice. What do you think please? P.S. I still haven't found suitable instructions online for building smooth walls from concrete for the DIYer homebuilder.

    Reply
  • David Luger

    January 29, 2017

    Beautiful designs and good vid. I would love to see what you would come up with designing a concrete monolithic dome home. They are super efficient and strong and functional but usually hard on the eyes.

    Reply
  • ConcreteLand

    February 6, 2017

    Sand is an aggregate. It's just finer.

    Reply
  • rutu patel

    February 10, 2017

    is there any way I can see your designs and finished projects … I've just been seeing your videos for the past 6 hrs , so informative n fun n inspiring .

    Reply
  • Islam Yunusov

    February 25, 2017

    Wow! What a 'quality' content! So pleasing and empowering> Thank you for what you do!

    Reply
  • J S

    March 15, 2017

    Wichita Zoo has some fantastic vertical board formed buildings. As a kid I always wondered how they were done. I was fascinated by how they seemed to so naturally come up out of the earth. So natural looking. I've never seen any other buildings like them. I'd love to see a house built in this style some day.

    Reply
  • Alexander Lavin

    March 30, 2017

    Thanks so much for the video. I've just stumbled headlong into a concrete house obsession and it's great to know there is outstanding work here in Northern New England. Thanks again–Ando would approve!

    Reply
  • salty roe

    April 2, 2017

    2 of the 4 elements are coarse aggregate (usually gravel) and fine aggregate (usually sand). Most concrete has reinforcing (usually steel). Both coarse and fine have been replaced by recycled materials, my favorite is crushed glass.

    Reply
  • Mauro Cerino

    May 7, 2017

    Hi Eric! i love this video. i'm learning a lot whit this little resumes that i can apply in my project classes and add it to my sources of resources.
    have you plan to do a list videos whit others materials? i'd love if you start with wood and steel, they are huge themes.

    Reply
  • Robert R

    May 19, 2017

    heres a tip. have you tried plastic tie rods? you can lubricate them and pull them out the next day. reusable also

    Reply
  • Kamilia Sghaier

    May 19, 2017

    Thank you so much for the video ! Our english class was happy to watch it!

    Reply
  • Gregg Parks

    May 22, 2017

    The video was very nicely presented.

    Reply
  • for real

    June 15, 2017

    30×40 Design Workshop…I love concrete homes. Any suggestions for a good prefab home manufacturer that services the deep south?

    Reply
  • las vegas life

    July 12, 2017

    So what did you decide to use on the wood texturing? Sandblasting? And would you use that technique again or use another method?

    Reply
  • Maxine Bannan

    July 19, 2017

    Greetings from New Zealand.
    Great to see your video and how you've explained the basic principle. The image you've used of the horizontal board entrance with the staircase to the right side is actually a home I built here in NZ.
    Soon I'll be uploading more information and instructional videos to You Tube also.
    Regards Ross Bannan (Bannan Construction Ltd)
    "Concreteologist"

    Reply
  • Mike Veltri

    August 7, 2017

    Excellent video, thank you! Any Scottsdale AZ contractors you would recommend?

    Reply
  • Arq. Gloria Guillén

    August 7, 2017

    Hello, thanx for sharing your info. Im planning to do a board form concrete wall, it measures 9.45 meters width and 11 meters tall, what distance should be between the control joints? And, have you known about a proyect that used plastic fence as an outer shell, instead of wood?

    Reply
  • neckarsulme

    August 22, 2017

    Looks awesome, but what about insulation and water penetration?

    Reply
  • archstudioRAM

    September 13, 2017

    Thank you

    Reply
  • drwestlund

    September 16, 2017

    Great video. Thank you for not wasting my time with a lot of nonsense and sticking to the point. I also love concrete and its many potential uses and possibilities. Rock on

    Reply
  • Trump 2020

    October 26, 2017

    deregulate housing and all industry so rent falls near 0

    Reply
  • 42oodles

    December 3, 2017

    update??

    Reply
  • Allagadan Design

    December 4, 2017

    I've been really frustrated with my architectural career for some time. But since I discovered your channel, You inspired me to believe once again. I lost my passion some years ago and now I am so fired up to make a fresh new start. Thank you sir. You deserve to be in the roster of great architects someday. You are an educator and a catalyst.

    Reply
  • Snipely

    January 2, 2018

    Very informative video. How are the boards treated so they release from the concrete? Is it possible to do a form against an existing wall to create a veneer?

    Reply
  • jose monteiro

    January 21, 2018

    Composite wall, concrete and mud

    Reply
  • Daniel Jonasson

    January 30, 2018

    As an alternative you can use the "cement-project" collection from Kerlite (I'm sure other manufacturers offer similar products). It's basically a huge (up to 118"x39") tile, which gives you the board formed concrete look but can be applied to most walls. I'm not really a big fan of using "fake" materials but it can come in handy at times.

    Reply
  • Walchand Chougule

    February 18, 2018

    Hey Eric, It is always a pleasure watching your videos, they are so well explained and in detail. So was this video.
    I am very much inspired by Tadao Ando's Work, as this Video was on Exposed Concrete, Can you give me some details what is his technique of Constructing/Designing Exposed concrete structures. That would really Help.

    Reply
  • Juani Carmona

    March 4, 2018

    Very useful information thank you!

    Reply
  • Jimbo Slice

    April 7, 2018

    At least 30% more

    Reply
  • Matthew Creary

    May 27, 2018

    💰

    Reply
  • akash rajput

    June 25, 2018

    What is the actual proportion of concrete mixer ? or which grade of concrete used in this exposed concrete wall ?

    Reply
  • Saacred Ranch

    February 4, 2019

    Aloha, thank you for the very informational video. One question, once a wall is done, can you reuse the boards for another wall? Mahalo

    Reply
  • futbolera

    February 22, 2019

    THANK YOU!

    Reply
  • Brian Breed

    February 26, 2019

    Excellent video. Very informative. Do most concrete companies know what the additive is that is added to the slurry. I’m an architect is colorado and want to try this process. I’m looking forward to it. Should pine work ?? Thanks a ton.

    Reply
  • mrpbright

    March 28, 2019

    Bar none the best cosmetically focused formed crete video. Loved the pace and content. I'm curious what you think about poured panel veneer over existing clockwork. Thanks for this video. Heading out to check out the rest of them.

    Reply
  • Maker Marx

    May 29, 2019

    TIP: for all you DIY guys out there – make molds for seats, stepping stones, blocks or a fire pit and cast your concrete and wood texture experiments in there. You end up with samples that are useful, functional and informative.

    Reply
  • Erick Meza

    June 14, 2019

    Does anyone know what the standard would be for insulation, if using this system as an exterior wall. Would one add a thin frame on the inside and insulate between the space? Please reach out if you have any idea. Thanks!!

    Reply
  • Igor Rech

    August 6, 2019

    is this the same thechniche that tadao ando uses? what is that 4 round things in his concrete? thanks

    Reply

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