Today I had a chance to put my research on screeding into practice.
The screed thickness varies from 75mm - 25mm due to the unevenness of the old concrete slab.
Taking advice from an old post I went with
2 part granite chippings
2 part sharp sand
1 part cement
My 1st mixer load was quite dry. The way I would describe it, taking a handful of the mix you could form a concrete snowball, if that makes sense.
Now the problem I found was getting an acceptable finish with this mix. As I tampered it down I expected the surface to smooth as the 'fat' moved to the surface.
This didn't happen and I was left with a grainy gritty finish.
I decided to change the mix and add more water.
1 part granite chippings
3 part sharp sand
1 part cement
With more of the finer aggregate and more water I got my 'fat' and was able to trowel a smooth finish.
Have I compromised the integrity of the screed by making these changes?
Also, using a shovel as my measure of the sand,chippings and cement, I found a slight problem.
The chippings tended to form a small pile on the shovel, where as the sand a large pile. I suspect by weight they would have been roughly the same as the chippings are far denser, but by volume I was getting a more sand than chippings.
The screed thickness varies from 75mm - 25mm due to the unevenness of the old concrete slab.
Taking advice from an old post I went with
2 part granite chippings
2 part sharp sand
1 part cement
My 1st mixer load was quite dry. The way I would describe it, taking a handful of the mix you could form a concrete snowball, if that makes sense.
Now the problem I found was getting an acceptable finish with this mix. As I tampered it down I expected the surface to smooth as the 'fat' moved to the surface.
This didn't happen and I was left with a grainy gritty finish.
I decided to change the mix and add more water.
1 part granite chippings
3 part sharp sand
1 part cement
With more of the finer aggregate and more water I got my 'fat' and was able to trowel a smooth finish.
Have I compromised the integrity of the screed by making these changes?
Also, using a shovel as my measure of the sand,chippings and cement, I found a slight problem.
The chippings tended to form a small pile on the shovel, where as the sand a large pile. I suspect by weight they would have been roughly the same as the chippings are far denser, but by volume I was getting a more sand than chippings.