Also, in my search to see if this topic had been discussed already, I came across this thread including a comment of my own that made me laugh:

In my experience, using plexiglas for formwork gives you a surface that is too glass-like, not baby-ass enough.

Donna, that was very common on older homes, where they used the form boards as roof sheathing, or sometimes wall sheathing. Board-forming concrete is slow and expensive, of course; standard aluminum or plywood forms are a much faster system. But I agree that board-forming looks great. Last year my brother worked on a project with two 20-foot tall board-formed concrete fireplaces. Pretty dramatic--especially the one that had a form blow out when the pour was almost complete, inside a partially finished, multi-million dollar home.

There is no way you could do any surface planing, though--the concrete residue would quickly ruin even the toughest planer blades. You could run them through a wire brush surfacer but then you would lose any aesthetic benefit of having been form boards. There are various form-release agents but I have used vegetable oil with reasonable success. If the boards are rough-sawn there will be some splinters left in the pour no matter what you do. 

Once contaminated with concrete / cement, wood becomes unusable for anything but structure and will destroy tooling on contact. Many contractors use release agents ranging from organic products to old motor oil, so watch out for that. A better option for reuse would be wax.

The only way I can see this working is if the wood is cut / milled to finish size prior to the pour (placing additional demands on form construction) at which point further processing is not required and the cruddy finish would be maintained.

This would require not just careful planning but also careful labor. While masons in general are pretty rough, concrete guys are worse.

Nice idea, serious uphill battle.

Not exactly the same thing but I designed a community garden that used shipping pallet boards to make raised planter beds. The wood naturally will turn grey in the sun, maybe a possibility to remake the form-work into a landscape feature.

Over and OUT

Peter N

Donna, are you doing exposed architectural finishes for concrete surfaces? If so, GC is more likely going to end up proprietary formliners that are not even wood. Nonpermiable materials are preferred over wood, which will not only soak in moisture, but also any chemical admixtures used. Chemical admixtures are inert when they bond with concrete mixes. But when they are soaked in wood they could be anything form harmless, to  irritants, to being toxic. All of them require skin and eye protection when applying. 

In any case I would not recommend their reuse for interior finishes. 

Thank you everyone for responses! Obviously this will take some samples and experimentation! We are working with a contractor who is close friends with the client, so asking for some specialty work around this fireplace won't be an issue. 

I did some research on contractor forums and they've all said basically what you all have said too. The idea of chemical off-gassing from form release agents is scary, so I could re-use the wood outside (like in a garden bench or wall) or at least use vegetable oil instead of something more toxic.

Miles, I do like the idea of cutting the wood to the size I want beforehand, then using it unworked after it's removed from the pour. On the other hand, I'm now especially in love with the idea of using a board in the concrete to form a void, then removing the board and cutting it into supports that fit perpendicularly back into its own void to support a shelf or something.

Wood Guy I'd be ok with losing the concrete remnants in the wood by wire brushing the hell out of them - that would even give the surface a nice texture. I just like the idea of being able to say "The wood here was was the same wood that was used to form the concrete wall that now supports it."  

And Rusty! I will be cautious with what admixtures are allowed!  Steven Ward knows someone who worked on WHY's Speed Museum project which supposedly has beautiful concrete. I'll check with him, too.

I should add I'm also thinking about the reuse of wood formwork by Eastern European Jewish carpenters in the 17th Century, as documented by Szymon Zajczyk in the book Wooden Synagogues.

None of them survive now. Hundreds of beautiful synagogues, early examples of reuse, burned down by the Nazis.

I like thinking of architecture as using materials thoughtfully.

i was going to chime in but i think everything i wanted to say has been said already! so i'll just hang out and wait for pictures.

Go, D!

https://alliedworks.com/projec...

Donna, 

Here are a few examples

http://www.metropolismag.com/a...

In olden days (before plywood) they often used second quality wood as a sub-floor, usually nailed at a 45 degree angle to the joists. Be hard to show off unless you took your guests to the basement.

Formwork usually get reused over and over and over so there is the cost of that to consider.

Well, since this helpful and pleasant thread is now first page again I'll update everyone that sadly this project did not go through; the investment in the existing house in the existing neighborhood was considered too high for return on investment. Owners, who are still good friends and lovely people,  bought a new house entirely. Insert shrug emoji here.

Onward!

I seem to remember this project reused the wood from the shuttered concrete elsewhere in the building, but i see no mention of it in the description. Nice finish though nonetheless.

http://panterhudspith.com/project/lincoln/