Attaching Titan Post Anchors to Blue Stone caps

by Dave
(Worcester, MA)

I'm building a pergola over a concrete paver patio,
but the retaining wall is field stone with blue stone caps.

What would be the best method of attaching the Titan Post Anchors to the blue stone?

Would TapCon screws work well in the stone?

Would lag bolts with lag shields work better?

Any other ideas?

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Dec 26, 2009
Anchoring into Blue Stone
by: Rich Bergman- Editor

Fastening to blue stone is a common question I get asked a lot. Here are my thoughts. Blue stone is not a particularly strong stone and it comes it varying thicknesses. So unless it is really thick - say 5" or 6" - I would usually suggest you have something underneath like concrete or something a screw can really hold onto.

The problem with relying on blue stone and some other stones that may be fairly thin - like 1"-2" is that you can split and crack the stone especially if you are close to the edge - like within say 2". At least that has been my experience.

So one way to avoid this is to drill a hole right through the stone. Make sure the hole is wide enough that the concrete screw can pass through easily. Then you want to be able to screw into the substrate below the stone. So a second drill hole has to be done that works with the Tapcon or whatever screw you use.

This means you probably need a fastener that is long enough to go through the blue stone and still have enough holding power into the substrate. I really like the GRK XL Caliburn concrete screws for that kind of a job. They are better than Tapcons in my opinion. But Tapcons will work also.

Now this is not to say that you won't be able to fasten right into the blue stone. It is just a cautionary piece of advice that you ought to test a scrap piece and see how it performs. But in general the thinner the stone and the closer to the edge the less reliable it is.

I wonder if someone knows the density of blue stone and can compare it to concrete because that would give you a good idea of the differences between the two materials.

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