Anchors for slate over concrete
We need some advice on the best anchors to use for attaching railings. The base is 1/4″-3/8″ slate set on concrete with mortar, so the total thickness over the concrete slab is 1/2″-3/4″. The slab is 3″-4″ thick.
I’m concerned that expanding-type anchors will stress the slate and cause cracks. If I use tapcon concrete screws, do I need a clearance hole through the slate slightly larger than the hole in the concrete slab?
Thanks in advance!
My guess would be that you are right about the expansion anchors, because they have to go through the slate to reach the concrete, and that means that both materials will be subject to the "expansion"
sounds like you're onto something with the tapcon anchors, and making the hole slightly larger may help...
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My experience is that you want to always anchor to the structrure, not the finish.
So, in this case, it'd be better to leave out some slate, and make up the anchors for the rails to the concrete and #### the slate to the rail.
Less elegent, for sure, but a more secure railing.
You can do the same thing without taking out the slate.Either start by over cutting the slate first or after you do the mounting hole chip out enough of the slate for a clearance hold.Epoxy allthread in the hole then add wahsers or lock nuts so that the base is just clear of the slate.
Drilling a hole for a pin with a concrete core drill is the way to go. You'll get a nice clean hole big enough for a large enough pin to be solid. Secure the pin in with either epoxy or non-shrinking machinery grout.
The hole must be quite dry for the epoxy to bond.