Mesh in floor screed when layer over 2 foundations.

[rssteve]

I'm about to screed a block and beam floor. One end of the beams sits on the existing strip foundation for half. Then the other half sits on a need piled foundation. I'm worried if there is ever any movement it may cracked the screed which I intend to lay tiles on. I have got the screed with the fibers. Is it worth me chucking a sheet of 4mm galv mesh across this area in the hope it will stay any cracking.

 

[rssteve]

This is the area where he new and old foundations meet.

 

[noseall]

Differential movement will be very difficult to mitigate but every little helps.

Are those 7n dense concrete blocks between the beams? They look like aerated blocks.

 

[rssteve]

As long as it won't make matters worse having the metal in.

Yes they are celcons which are suitable for use in block and beam floors. Much easier to carry and slightly better insulated.

 

[^woody^]

With beams if there is any movement of one end, the floor will move as one, not as part, so there would be no cracking of the screed. Thats not to say that the screed is not at risk of cracking for other reasons though - such as debonding from thermalites due to their greater thermal movement.

Fibres control shrinkage [cracking] only, and are not a reinforcement to prevent movement cracking.

 

[tomfe]

They look like aerated blocks.

You have to make sure the transverse strength of the block is suitable for b&b some 7n blocks are not suitable for b&b (I think that's more down to not being tested rather than the strength).
If you have a break through between different floors, the original and the b&b, then you'll get movement there.

 

[rssteve]

It's not opposite ends of the beams which are on different foundations, it's some of the beams on the same ends. In the photo the new thermilite wall beams are supported on piles where as the beams directly next to it are support on the existing wall.

In that case I will add mesh to the whole floor. The existing floor is wood and will be carpeted so no screed joint there.

Got 150mm celotex laid across the top don't think it will be an issue in think the future with regards to blocks not supporting the weight. Not had any cracking yet with blocks being stacked ontop.