Should someone go about creating a new spell, "Accelerated Erosion", how would and/or can the system work with it?

A sandblaster or such isn't going to blow right through a fortified bunker, but how would you handle that kind of small-but-inexorable erosion?

If you have the time to get through a fortified bunker with a sand blaster... well I can't possibly imagine a slower and noisier method of trying to get through one. You'd be better off grabbing a pick and getting to work.

I'd say that any erosion of that level is too small to mater in the time span of a normal game.

No. For fast damage, there already is the Wreck(Barrier) spell. For slow damage, who wants to sustain a spell for several days, with the risk of an adverse mage inspecting the building and tracking the spell back to you?

Should someone go about creating a new spell "accelerated erosion", I'd just ask why. I really don't see the use for it over some of the other options a mage has. If you need to handle erosion for some other reason, let the GM just wing it. This is an area where GM handwaving is appropriate, as you really don't need any dice rolls for something as insignificant as erosion.

We're playing Shadowrun, not Shadowrun: Landscapers.

Shhhh, don't give the devs ideas

But yeah, erosion of any significant kind to building materials would take years and that is only to cause a slightly notable indent maybe. The building will succumb to plants growing in the build long before it will succumb to any sort of erosion affects. Even with a sand blaster you're still looking at insane amounts of time to manage anything at all. (I mean you can sandblast a PVC pipe for hours with no real affect, and that stuff isn't very tough.)

I'll have to add "landscaper" to my list of future character concepts.

To be fair, he didn't say "Slightly Accelerated Erosion". I mean, given enough time, anything can be eroded - but that is a LOT of time. How much acceleration are you talking about? I'd rule out a literal acceleration of erosion as a workable spell because magic spells can't affect temporal phenomena (Limits of Sorcery sidebar, Street Magic p159), but I suppose you could just model it as an elemental (Earth, Air, or Water as appropriate, each a different spell) attack spell vs barriers.

I think there are easier means to accomplish this. Shape concrete and/or plysteel for example is a a great way to get through most buildings. I'm sure stuff like powerbolt could do it given enough time. I'm not real familiar with all the spells and whatnot, but isn't there some kind of wrecking ball type spell (Like punch or something?) that could work for this?

Making a specialty spell to get through walls and barriers and stuff might be kinda cool, but I don't think that erosion would be the best way to do it.

Perhaps the idea is to have a spell with the capability to do something to a barrier rating way too high for things like powerbolt to have any chance of touching. What if you really want to take down a fortress made of some crazy super hard state of the art metal?

I think the best idea would be a manipulation spell that convinced plants to grow like crazy and attack the barrier, or took a bunch of water from the air and then froze and unfroze it on the barrier, or something like that. Sand wouldn't do much against a material with a better hardness than quartz, which a high barrier rating may have. Also, there is precedent for a spell that heats things up over time until they catch on fire. So, perhaps the best bet would be a manipulation spell that you would have to sustain for several minutes to melt a barrier - but it would work on high barrier ratings just fine, as long as you could beat the OR. I have no idea how you would assign drain to something like that though, as it is way more useful than the combustion spell it is sort of derived from.

So a shape water and then a control weather spell to get freezing temperatures. Or any other spell to get the elemental effects you want. But there's really not a whole lot of reason to need an accelerated erosion spell in Shadowrun.

No, you want rapidly fluctuating temperatures: freezing, melting, freezing, melting...