How far do crimson/corruption biomes spread? [duplicate]

Question

I've completely rebuilt my base in a Forest Biome from the ground up since the release of the 1.2 update. And when my base was the same as in my old world, and most of the npc's were there (except the hardmode npc's), I thought it was time to activate hardmode.

The first thing I noticed is that I couldn't place any of the new npc's in my house because it was corrupt. Apperently this was because the crimson was under my house going from top to down. So I needed to move my house to another Forest Biome. But the Crimson is spreading really fast!

But how long will it take before the Crimson will have corrupted every green bit of my world? Or should I just place a block of stone to stop it? Is there even a way to stop it? I could always build it in the ice biome. But I find the constant visible falling snow annyoing. I already tried the obvious: purification powder. But the Crimson is just keep coming back!

What would you do?

Edit

Once I've made a new world, this time in a floating island (so no form of biomes will reach it), and was transfering some of my items (including NPC room furniture), I saw what was wrong all this time: I forgot to place a few walls! I don't know if this was causing the This house is invalid error. But at least this was a possible reason.

Thanks for all the suggestions and sorry for wasting your time. Have an Ale on me!

Answer 1

Crimson and Hallow will spread through your world like wildfire, underground and all through your map, including snow biomes.

Your best bet is to pick up as much of the unique biomes as you can to store in your pocket, and start building preservation biomes in the sky, preferably above Hallow to avoid having your preserves corrupted. This will run the risk of having frequent Wyvern attacks but... well, that's the risk you run when you go into Hardmode.

My real suggetion to you though is to start over on a new world, maybe even with a new, ungeared character, and NOT go directly for Hardmode right off the bat. With all the changes that have been made to the pre-hardmode world, it's worth exploring before taking on the WOF.

Answer 2

The Clentaminator, along with Green Solution can be used to purify it. However, these are sold by the Steampunker, who only appears in hardmode (the condition for selling individual solutions varies; the Green Solution only appears when no other solution is being sold).

You have other options. Firstly, you can build upward. The corruption rating of a home counts all corrupted tiles in a 45-tile radius. Moving upwards dramatically reduces the odds of that being an issue. If you go up high enough you will be outside of the Biome. There's no need to worry about making your homes accessible from the land; if someone moves in you can just save + quit and reload and they'll be in the home.

Secondly, activating hard mode of course spawns Hallowed and Corruption (or Crimson, in your case). Hallowed does not prevent homes from being suitable, fwiw, so if you can build that way you will also be safe.