Bolts on loose rock

Sometimes there's good crags to climb but you don't know wich is the limit of the bolts when the rock is as soft as in Cueva del Arenal, Spain. The routes' equippers noticed in their blog (in spanish) that some of the bolts meticulously placed went out due a very bad sandstone quality, luckily it happened on the very last ones meaning no ground-fall potential danger. Sandstone normaly has a compact layer outside and becomes softer inside. The glue bolts won't work if the rock is too loose. If you're bolting a route in sandstone and the bolt hole is always sandy better if you stop. Even if it is a 12mm rod with glue it won't work in the future.