Teaching Concrete Counters in VT

It was great to be back up at Yestermorrow Vermont last weekend teaching a group of 12 students the art of concrete counter-tops.  The best class we have taught in recent years!  My biggest worry all weekend was forgetting to bring socks.  The weather was as beautiful as the group of students!  The projects had several challenges we were able to overcome through collaborative thinking.

The experience is always powerful no matter how many times I do this.  By lunch on the first day we had poured our first set of counters, and by days end had a full kitchen formed up and the math done for a weigh-out of materials Sunday morning.  Students seemed to have a serious focus and motivation to learn and build.  This combination allowed for a brighter side throughout the weekend, humor was crazy, we even came up with a business plan to market concrete balls of all applications…baseball fruit etc send us your money for a start-up ha ha.



May brings more concrete and CAD rendering

625 lbs of concrete will fill this form to create a custom shower piece.
RKM house kitchen rendering for Gourmet Magazine online.


First Concrete Vanity Sink Installed!

Just poured the RKM sink 2 today!  These images show part of the process in creating the form or “mold” the concrete is poured into.  Building the form for a sink is very technical and involves many steps.  First a plywood form (HDO) is fabricated.  It is made smaller than the final size to allow for the second step.  The basin and in this case backsplash and counter are wrapped in 1/8″ acrylic plexi, the outer shell with 1/16″ PETG.  The plexi is cut and then “welded” in place using a solvent.  The plexi seams are then shaved and chamfered using a block plane and razor blade.


The form then needs a drain knockout, and in this case a faucet knockout, both made of rigid insulation.  As the pieces are assembled (designed to separate once cast) they need silicon caulk on all seems and corners.  A “top hat” is built to hold the concrete  in vertical and hydrostatic pressure after pouring.  Next the form is blown out with compressed air to remove dust and particles, and sprayed with a release solvent.   The final step is the weighing out of concrete.  Stone Soup has experimented with various methods for water reduction, sealing, and color matching in the mix formula.

After all the time invested in preparation, over 20 hours on this, the actual pouring is/has to be quick.   In less than two hours you know if your planning worked.  Mixing the concrete, an experimental orange color in this case, takes under 45 minutes.   The form is then progressively filled, closing up each stage with the aforementioned “hatboxes”.  This is all done on a specially designed Vibe table.    After buttoning up the top of the  form a small celebration is in order, but don’t put your guard down, the top plates or “top hats” should be removed within the hour.  This is your chance to smooth out the underside of the sink to make for an easier install…will update on the removal or release from the plexi/plywood form.

Ray just installed the first of two concrete vanity sinks we are creating for the RKM house in Amherst.  This is located in the lavatory on the main floor off the living room/kitchen.  The second sink mold form is complete and ready to cast tomorrow!  It is going into the full bath between the bedrooms on the second level.   Color…bright orange.

RKM Concrete Vanity Sink

This vanity sink was a challenge to say the least.  In the works for a year now, the concept was drafted and calculated.  At this point it had to be fabricated.  Familiar with standard concrete countertops the 3d aspects of this eluded me.  After many months in the shop pondering the process I started to build the box in the shape of the sink from HDO plywood.  My expectations were simple at first not realizing the need to taper the sink box in all directions.  this taper helps drainage and deforming the box after casting.  Then the introduction of plastics became another necessity, a sheet of plexi-glass was in order.  Having worked with this material in the past I was not familiar with straight seem welds or chamfering the corners by hand, after several tests the material seemed to play nicely.  The form got built with PETG laminated outside walls and base surfaces for the to be tops of the back splash.  As the project continued I learned many factors that go into a sink with an integrated backsplash such as how to caulk the seams you can’t reach by hand.  Improvisation became key as I started the mixer using a formula I was not used to.  Extra forms, rebar modifications and advice were all administered during the 1 hour pour!  Soon after pulling the top-hat off the sink the 2% flow mix reared its ugly head.  A great agent to eliminate gas buildup, it didn’t trowel well for finishing.  Alas here are images of my first attempt of a integrated sink /backsplash/counter in concrete.  Taking the sink from the form is another story…

2300 lbs Countertop Pour

Had a great experience at Stone Soup Concrete today pouring 5 concrete countertops for a bar in Boston.  They were 2″ thick with knockouts for the tap tree and integrated drain-rails.  due to the thickness, cupping(not beer mugs but the counter) and the high usage we reinforced with two separate layers of 6 x 6″ remesh.  The pour took under 5 hours for the three of us.  It was great to be surrounded by experts.

Process showing the creation of a concrete integrated sink form. Welding the plexi was a learning curve. then shaved all smooth as i could, caulked the seems, meanwhile adding an overflow channel to meet the drain pipe.




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