The only issue that I can see possibly arising from building on bed rock would be water seepage under the first layer of earth bags, that can be stopped with a lime mortar between the rock and the first layer of bags.
Do you mean an exterior ring of mortar stopping water seeping in from the outside or a layer of mortar under all of the first layer of bags? i.e. the first layer of bags resting on mortar?
You will have no issues for strength, as Bryant spoke of, waterproofing the first layer is normal practise and you have commented that water drains away from the proposed site.
Sounds great, and I would love to see an image when possible
John Daley Bendigo, Australia
The Enemy of progress is the hope of a perfect plan
Hello. I'm looking at doing this also on 12 acres I purchased in southern Colorado. The building will be a glass studio and I plan to adapt it to a 12 x 20ish rock slab on the property, although I may go further out on the front (south facing slope) which drops off the slab but would give me more area for a earthship style integrated greenhouse. Can anyone point me to a better explanation on waterproofing the first layer? Also looking for best price on bags, I'm ready to order. Thanks!