What classifies an invalid solid?

Hi, I just fired up hammer this morning to find the map I had been working on previously to be swiss-cheesed. By swiss-cheesed I mean about 40% of all my solids were A) not there, or B) cut to ribbons. This was supposedly due to an ‘invalid solid’ area; that I got upon launching hammer.

Since this was extremely annoying having had spent many an hour and most of the day on this map I was wondering what classifies an invalid solid? And If there is anyway to recover solids that were deemed invalid and turn them into ‘valid’ solids. My beef is that all vertices were snapped to the grid! D:

Invalid solids can be several things.

  1. A brush that’s concave.

Concave brushes are brushes that have verticies or faces that collapse in on itself. Think of a whole pie with a slice cut out of it, and it would be concave. If you require a concave object, use more than one brush.

  1. A brush that has coplanar faces.

Coplanar faces are faces that have more than one plane on them. This is usually caused when you have a face with more than 4 verticies that was vertex manipulated improperly. This problem can be solved by cutting the face into two or more triangles.

  1. Brush sides with no surface area.

If you use vertex manipulation to put two or more verticies of a brush in the same physical location without merging them, it will cause the compile tools to not work or complain, and end up with erratic results in-game.

  1. A brush with too many verticies or sides.

There’s a limit to the number of sides/verticies a brush can have. If you create a brush with too many sides through use of carve or the clip tool, it can cause erratic problems. I’m not totally sure what the maximum limit is, but you’d be best staying under 64 sides for brushes.

Whatever hammer wants to be Invalid.

Non-planar faces, vertices of the same face occupying the same position, concave overall shape, face with too many vertices.

Luckily most can be easily avoided if care is taken while using vertex manipulator. And don’t forget about the split face functionality of vertex manipulation. It helps you immensely when you have a non-planar face which is being triangulated in an undesired way.

Thanks everyone for taking time to answer my question.