Cement - with or without gravel?

rayonline_tm, Jan 30, 2:41pm
Hi all - I've been reading guides and their recommended ratios. Some just use cement and sand and others use a mixture with gravel.

Your suggestions? Is it without gravel provide a smoother finish?

The magnesium trowel provides a smoother finish than just using the steel one right and then later finish it off with the steel one? Just doing patch work but we found that at times when we use the steel one we get gaps in the cement or that we get stones or gravel on top of the cement.
annies3, Jan 30, 2:44pm
We have always used aggregate mixture of sand and gravel, the finish is dependent on the floating off which is done, ours is always fine.
hammer23, Jan 30, 2:51pm
4- 2- 1
Which is 4 of gravel,2 of cement,1 of sand and if you want a better finish add a bit of sand and cement to top level for an easier finish.
Of course if you go to say Placemakers they have it already mixed for,just add your own water like a packet cake mix.
tintop, Jan 30, 2:53pm
If you want concrete, use a mix of builders mix and cement. A mix ratio of about 5:1 is generally ok for most jobs, Be honest with the cement measure.

If you want plaster or mortar, use sand and cement,

In both cases excess water will lead to shrinkage and weaken the final strength.
rayonline_tm, Jan 30, 3:04pm
Cheers for that - any tips on getting a better finish. Yeah we used the 5:1 ratio builders mix at Placemakers and Portlands cement. We found when we used the steel trowel that there are gaps on the top and other times a stupid gravel sits on top of the cement. Does the magnesium trowel lifts the water up and make it easier? Then 3hrs later use the steel trowel over it again?
budgel, Jan 30, 3:32pm
Leaving gravel out will weaken the concrete.
Just use your bullfloat first to roughly smooth the concrete and work it up a bit and then come back with the steel float as soon as any surface water has disappeared, you should get enough fines on the top to get a good finish.
Once this point is reached, working the concrete with the metal float will bring the surface up to how you want it. Dont judge this by time, just the state of the mix as times can vary a lot in hot weather.

The concrete doesnt know what metal the float is made from, but if magnesium works for you, why not. Any small bits of gravel that come to the surface can be picked out before final finishing.

Once the finish has dried off a bit, keep it moist to stop it drying too quickly.
tintop, Jan 30, 6:14pm
Ok - the mix has to be mixed so that it is a uniform consistency, with enough added water so that it is workable and can be sloshed around a little to work it into corners, crevices etc. The the action of the float on the surface is to push the larger aggregate particles down and to allow the mortar to form a thin surface layer. This is the layer that forms the smooth surface.

A magnesium bull float is used because it is lighter and easier to manage than one of other materials.
stevo2, Jan 30, 7:09pm
I've always used a wooden or plastic float to start with and then finished it off with a steel float.
However i have been using a magnesium float instead of the wooden/plastic float on the last few jobs and it does seem to draw the slurry up just as well.
Use builders mix (a mix of aggregate and sand) for concrete or sand only for mortar or plaster.
Ratios are 5 or 6:1 cement for concrete or 3 or 4:1 for mortar.
rayonline_tm, Jan 30, 8:14pm
Thanks. Found they used a steel plasterer trowel. Trowel same as a float?
stevo2, Jan 30, 9:24pm
Basically yes.
Float is rectangular used for floating off concrete. Trowel is normally triangular although plasterers call their rectangular a trowel.
morrisjvan, Jan 31, 12:29am
use a wooden float once it is levelled off ,while it is still quite wet, then use the steel trowel when the surface water has gone.
rayonline_tm, Jan 31, 1:53am
Cheers :)

You think the timber frames is a must? I see how they level out the excess cement with a piece of timber by scrapping the excess off.
tezw1, Aug 9, 3:53pm
We use a straight edge to smooth out humps and hollows in the concrete just after it has been placed. On narrow areas a length of wood works fine, but is easier with 2 people. Side to side motion as you move it along so you don't drag the top of the concrete.
When trowelling off use a circular motion to bring up the 'cream' or fines then smooth off, a maganese float works well at this point to bring up the cream, then a steel trowel to smooth off. We use a trowel that is rounded at both ends so that the square corner doesn't bite in.