What would be the cause and effect of a crack in brand new homes basement floor.
The concrete was poured back in late August.
There is now a crack that runs app. 10ft from a side wall towards the front of the house.

All concrete cracks. There are measures that can be taken to minimize the effects of cracking, and in a basement floor, the common measure is to embed wire mesh in the concrete.

The mesh does not STOP the cracking. What it does is in effect trade one big crack for hundreds of microscopic cracks. The resulting cracks are so small as to be practically invisible, and therefore harmless. (Loose fiber is sometimes used in the concrete as an acceptable substitute for mesh)

Possible causes of YOUR crack are:
1. The absence of wire mesh or fiber.
2. Improper placement of mesh.
3. Improper mix of concrete.
4. Improper curing of concrete.
5. Improper preparation of the subgrade.
6. Unusual soil conditions beneath the floor.

The effect of the crack is difficult to assess without seeing it. Effects could range from nothing at all to the entrance of radon gas, insects and other vermin, and/or water.

What is the width of the crack? (a hairline, or a measurable width such as an eighth of an inch or more)

Is there any vertical displacement from one side of the crack to the other? (in other words, has your floor settled or heaved)

Is your floor a rectangle, or is it L-shaped? What are the dimensions of the floor, approximately? Try to describe the crack in more detail; exactly where does it begin, what direction does it take, and where does it end? Is it wider at one end than the other? Is it parallel with one of the walls, or does it run at an angle?

The cure can also range from nothing to many things, depending on the crack. I would wait a year from when the floor was poured and see what develops. The crack may not change, or it may become wider or longer, or both. More cracks may develop, or they may not.

Measure and mark the extent of the crack, and keep records, measuring periodically, such as monthly. Measure the width as carefully as you can. Mark the length on the floor and note any progression of the crack. Watch for new cracks and make the same measurements.

Armed with those records, and continued descriptions of the crack, try us again next August, and we will try to assess your situation.

This message has been edited. Last edited by: Richard Hetzel,

Thank you for the quick response.
Should I have the builder fiil and seal the crack? We have not moved into house.

It's hard to say at this point. A lot depends on how the crack behaves, how wide it is, etc. The best method you have available to determine the best course of action is to monitor the crack over a period of time, keeping records as I suggested.

It is very possible that the crack means nothing, but without answers to all the questions I posed, it is difficult to comment any further.

My under construction home has developed a crack from one side of the house to the other. It starts on the back wall and runs diagonal for about 5 feet (about 1/2"). It then runs straight the rest of the way across the house (about 30') about a 1/8th to 1/16th wide.

What would cause this problem and what would the best fix be?

See the second post in this thread. Same questions. Without answers, it is not possible to comment intelligently. the best way to deal with cracks is to monitor them over a period of time (months) and see how they behave. Keep detailed records. Rfere to the questions in the second post.