Making dry tamped cast stone looks deceptively easy. You can do it in your garage. Some do. A mixer, sand, cement, a mold and a tamper (wood rod and hammer will do). You can easily make keystone or address blocks that cost a few dollars but sell for $ 25-$50.
So Why Not?
The cosmetic appearance tells you nothing about the quality. Will it leach out white efflorescence? Will it stain the wall below? Will it fall apart with freeze thaw cycles? Will it delaminate due to improper tamping techniques?
All of these are very common problems with poorly made dry tamp. They even plague experienced manufacturers.
Here are examples:
This coping has so much absorption that it is leaking through to the flashing and staining the wall below with salts of efflorescence and probably unhydrated cement.
This experieced producer tried to drytamp the red face mix but add wetcast to the back so that structural embeds (weld plates) could be inserted into the wet mix for attachment to the bridge structure. If you look closely at the left panel you can even see the tamper tracks . Every panel on this bridge has delaminated.
This 1200# cornice piece has a cold joint and the beginnings of delamination that could cause failure from freeze/thaw if it was in a cold climate. Fortunately it is in Florida. The producer tried to turnover pieces that were far too large and heavy. The delamination was caused by a minute bending of the piece when it was turned over but the rebar in the nose of the ogee profile did not flex. One third of the hundreds of pieces on this bank failed in transit. The job delay to remake these resulted in a 1.5 million dollar lawsuit on a job worth only $250.000.
These sills were drytamped with a #4 bar too close to the surface. They are also too long at 88" to be turned over without flexing. The flexing creates a void where water can collect-freeeze, cause rusting and exfoliation of the rebar and destruction of the piece. EVERY piece on this job failed within 5 years.
My fees are far cheaper than the cost to you and your reputation of mistakes like these.
I am available on short notice to provide unbiased evaluations of "problem" cast stone installations. These problems usually consist of premature judgements of quality/color/patching before the job is complete.
