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A thick epoxy question, not work related just rhetorical8/14
So this morning we got yet again another request from a designer regarding "epoxy river tables". I almost throw up in my mouth every time this happens, which is a lot. But Im really wondering about a few things.
Does anyone have any real long term data on the structural adhesive bond between 2.5" to 3" thick epoxy and wood? And even more so sap wood?
We have never done any of these for a multitude of reasons. The main one being that everyone sees them on the internet and pinterest and wants one until they find out the two live edge slabs to make a coffee table may be worth 150 bucks a piece (if they are cheap), and the epoxy is $100+ a gallon plus colorant and metal flake, and so on. And you've yet to calculate a wood or metal base, at which point they click-thru on the pinterest link and see the coffee table they were enamoured by is $2600.00 and the dining room or conference table is 12-15K.
Regardless of the price. These things have always gotten me wondering if anyone truly has any long term experience with the bond between 3" thick epoxy and a wood surface? You have the mechanical keyed connection between the epoxy and any negative profiles in the live edge of the material but I have seen epoxy on many occasions delaminate on thick applications creating a kind of cloudy pocket or bubble where it has detached from the substrate. I have always seen some of these river table deals that have pretty smooth/sanded live edge and wondered if over time the live edge wont pop completely free from the epoxy or just as bad show a bunch of separation between the epoxy and the wood through the clear pour?
Beyond all that you see a lot of massive tables that seem to rely structurally on the integrity of the entire top solely based on the adhesive and mechanical bond of the epoxy to the live edge? I have seen massive conference tables with post bases that if that epoxy connection fails, the entire table is going to peel apart at the center, chopping anyone off at the thighs who is sitting their drinking their caramel macchiato.
Im thankful that every inquiry has not gone forward but I know the day is going to come when one will.
A small table doesnt worry me but the large requests we get concern me. We can always turn the work away but just like the requests will continue to come, the chance is the request will come on a job where we will want to take the money and just trying to get ahead of the curve.
How thick is the epoxy coating? If you get good bonds from epoxy, it is worth approx 3000psi in shear.
We use it to bond crazy loaded hardware directly to fibreglass sailboat boat decks.
The key is for the substrate to be stable. 80 grit scratches are all you need for proper "keying".
I've wondered the same things. Besides the wood moving, polyester resin shrinks when it cures. That would make the bond even worse. I also can't imagine the resin will be so pristine after a year of people cleaning with the wrong product, or a slightly abrasive cloth. A nice wood slab will still be a good design in 10 years, a river table may not be.
My biggest concern for this type of construction is if the wood is air dried or kiln dried. I don't care if it's air dried for 50 years...its going to move and break all the bond lines. I could see possibly doing it with KD.
These are all the issues I have had as well. I know epoxy has tremendous bonding strength. We use it quite often. But I have just never been able to get my head around the subtleties of the differential movement between a 3" thick epoxy pour (even in multiple lifts) and a 3" thick slab.
Agree on the air dried vs. KD and also agree completely on the cleaning, wear and tear, issues. I have had the opportunity to see a few of the clear acrylic desk stations that you commonly see on the nightly news and since HDTV has come along its a bit more obvious to someone who looks, but TV can make a scratched up plexiglass table look far better than it does in person.
The fad issue aside its just been something Ive been concerned about. We have typically tried to lean people towards a gapped live edge with a custom tempered glass insert in the gap mainly for the maintenance and durability issue.
I often wonder whether those making these style of tables have any traditional experience in the nuances of jointing of large timbers.