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I need to affix my steel stringers to a concrete beam. Since the beam was poorly executed, it is not plumb.

top of steel stringer

On this piece I will weld some 5 mm thick plate on the backing, that will have holes for bolting in the concrete

I think that I will have to shim almost 12 mm on the top and 3 mm on the bottom.

What is the best way to so it?

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Steel shims if shimming steel and concrete - either with holes that you bolt through, or tack weld them in place. To the extent that you can use "fewer, thicker" shims rather than more thinner ones, do that. Paint, galvanizing, or "cold galvanizing" (zinc-loaded paint) may be advisable to limit/reduce rusting over time.

The other solution, though it's not usually referred to as "shimming" would be to use mortar/grout to correct the concrete beam surface for good bearing of the steel in correct orientation.

  • The mortar would be so thin that I don't think it would adhere nicely, this is why I'm looking for a shimming solution. Having shims to bolt thru would be troublesome, since I would drill the concrete with the stringer in place and bolt directly. But I could tack the shims in place. – Luiz Borges Apr 14 '15 at 15:08
  • Grout/mortar does not need to "adhere" in this application - consider that it's filling space and being compressed by the load - the steel shims don't adhere at all. There are also "epoxy grout" products sold for bedding machinery (bedding machinery might be a good subject to look at for what you can apply.) Removing some concrete from the high points before applying mortar/grout would be another way to approach it. Grouting fills the irregular space and spreads the load, where shims contact only the high points and concentrate the load unless they are between two dead flat surfaces. – Ecnerwal Apr 14 '15 at 15:20
  • If I understood correctly, I would install the stringer, and then pour grout beneath it to fill the voids. Right? If that is the case I could use even wood shims on the edges to support the stringer before I pour the grout – Luiz Borges Apr 14 '15 at 15:24
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    Yes, that's the basic idea - put it where it should be, and then grout it to keep it there. – Ecnerwal Apr 15 '15 at 0:46

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