Stabilizing Toilet

My bathroom floor is tile over concrete. The house is settling and the slab has a few cracks so I understand why the toilet is no longer steady. Its shifting caused a leak in the water riser tube so I tightened the hold down bolts in an attempt to stabilize it and broke off a piece of the flange. Now that I've installed a flange repair kit, how can I tell how much I can tighten before cracking the toilet base?
I put the toilet back down without a wax ring to observe the gap. In the front I can use nickels for shims but in the back the gap is about 50% bigger than that. Is thinset mortar the best material to use to support the toilet all around the base? How do I force it under the base and how much is needed? Is it best to put some sort of coating on the floor and toilet so I can remove the mortar more easily next time I have to take off the toilet?
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They make ribbed, stackable white plastic toilet shims specifically for this purpose. Don't use mortar. It'll hinder removal in the future.
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What in the tobes of hades prompted you to pick THINSET MORTAR as the possible repair material? It would make just as much sense to choose licorice whips or toenail fungus.
They make toilet shims for this. Probably on the rack at Home Depot right next to the toilet flange repair kit...
Then again, you did think that you were going to somehow draw the tolet, made of RIGID and FRAGILE vitreous china, down over an uneven floor... Takes a smart one to figure that out.
Do you know which end to put in the toilet to do your business?
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