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.


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