I'm finally in the stage of installing my manufactured stone veneer to the poured concrete foundation wall. The walls are clean. A local mason told me I needed to apply a scratch coat to the wall before applying stone. So I did in one section, but to me it seems like the scratch coat is very brittle. I mixed up some mortar and applied a stone to it and it stuck fairly well, I also applied one to just the concrete wall which stuck good as well. Do I really need to apply a scratch coat? I'm afraid the scratch coat will not adhere well and start coming off, taking the stone with it.
If the walls are clean of any dirt, form release, contaminent, etc... there is no need for a scratch coat. As you suspect, it would only serve as a failure point and merely be redundant, with no benefit. I would highly recommend using a little bonding agent in the setting mud though.
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