Tile – Crack spanning several tiles

When I've done grout repair I've cleaned out the old grout, did some slight prodding to see if anything else was loose, made sure the area was bone dry and then got a small batch of grout from the local hardware store. You can probably buy a small tub of the premixed grout (unless you have colored grout then you're stuck buying a larger tub usually).

I just put it on as normal grout, slap it on, push it in, smooth it out a bit, let it dry and wipe off the excess. It'll take a little while to fade in but now it looks like it was part of the original tile job.

First, remember to lay your wood perpendicular to the floor joists. Laying it parallel can cause a waving effect which is unpleasant.

Next, find the longest, longest, straightest wall which is perpendicular to the joists. Measure out two feet from the wall all the way down the wall. Then find the best line down these marks, snap a chalk line, Measure back to the wall about 23 and 5/8 inches. Snap a this line. Line up your first run of floor against this line, tongue side out (nail through the tongue).

As for room to room, if they are really out of square with each other, try building a transition between rooms:

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This allows you to lay each room separately, allowing each room to be square.