Brendan,

This is unfortunately one of those questions that does not have a definitive answer. I am not aware of any formal guidance available.

There are of course practical limitations on pour sizes. If it is to be finished using a tamping board or a power float then the pour size must allow access from the sides without standing on the screed, and more importantly, the mesh.

The environment would also have a big effect, especially the amount of wind and sun around. For example, screeding the top deck of a car park in mid-summer would be very different to screeding a sheltered 1st floor when other floors exist above.

If the area is multi spanned, then joint positions become important. It is poor practice to have joints at intermediate supports as hogging moments would encourage cracks in the screed. Similarly it is not good practice to have joints at mid-span since this is where the screed is at its thinnest. In the other direction there are differing opinions. My own thoughts are that screed joints should not coincide with the joint between units, nor occur directly over a hollow core. This is however a matter of opinion rather than a factual aspect.

Mesh usually comes in standard sheets 2.4m x 4.8m. It is best to have joints close to the end of a sheet, whilst allowing the required overlap. If sheets project a long way beyond the edge formwork, then placing the screed often deflects the mesh downwards, causing the mesh outside the formwork to rise. This then causes problems on the next pour, so getting joints to fit mesh modules is worth considering.

If you have a question for Cliff, simply fill out the form below and submit it to Key2Concrete: