Sunday, March 27, 2011

Board Formed Concrete Fail

So much has happened since I last wrote, I know it's been a while.  I had a post all lined up to boast to you about how we formed the huge concrete wall using panels constructed by affixing HardiPlank siding of varying heights to sheets of plywood. 
I was going to tell you how this best-of-both-worlds approach proposed by our concrete subcontractor would take advantage of the flatness of plywood and the wood grain texture of siding to give us the look of perfectly uniform board formed concrete.
It was going to be so great!  But, here's the rub.  It didn't work.  Like really really didn't work.  You see, HardiPlank is a product made of fiber*cement* and what sticks to cement better than cement?  Well, it turns out, nothing.

The concrete crew neglected to use form release oil, but several experts since have offered that even form release oil couldn't have prevented the disaster that resulted from all the HardiPlank forms being permanently and very stubbornly stuck to what is meant to be the single resounding architectural element of the entire project, our giant concrete front wall.
For those of you who aren't schooled on board-formed concrete, let's back up and I'll tell you how we got to this point.  Traditionally, concrete forms were built from framing lumber like 2x8s or 2x10s. The concrete is poured between the wood forms and when the boards are stripped off, there is a slight imprint from the wood texture. Some concrete slumps between the boards leaving horizontal lines at the seams too.  You see this look a lot in modern architecture.
Given  that our wall is 16' high, 25' long, and has an exposed steel beam that spans a 17' wide gap in the wall, it's crucial that the wall be very flat.  Lumber tends to warp and move, so the thought was to form with plywood for flatness and the add siding with the wood grain pattern for texture.
2 months and $25,000 later, we have reached a resolution.  It looks beautiful, it looks intentional, but I still cringe at how we got to this point.
The solution?  We soaked the wall, scored the siding, and took chippers and grinders to every inch, being careful to not damage the concrete underneath .  It was time consuming, labor intensive, and awful.  Then, we hired a sandblaster to blast off the fine layer that was left and smooth the texture.

The lesson?  If someone on your project claims to have invented a new wheel, ask a lot of questions.  Ask other people in the field, suppliers, vendors, and reps.  Go to the forums and ask people who do this all the time what potential trouble you might run into with a new process.  I love finding better ways to build, but I hope you all can learn from my mistake on this one.