Rapid drying cement

andygb

I have not used this before and wondered if it was OK to use on its own without ballast or sharp sand. The job in question is an upstairs window sill (below the wood) and involves a depth of 5CM width of 12CM and length of around 1.2 metres.
It is supposed to dry in around 30 minutes and will be ready to work on in around 4 hours. What sort of consistency should I be after (creamy porridge, with no lumps:D)?

DVardysShadow

Why do you need it to be rapid set? If you use it on its own, you will have a long brittle lump. which may go off too quickly for you to work it. Putting sand in, I am told, wil slow it down.

andygb

DVardysShadow wrote: »

Why do you need it to be rapid set? If you use it on its own, you will have a long brittle lump. which may go off too quickly for you to work it. Putting sand in, I am told, wil slow it down.

It was bought a while ago for another job, but it is sealed, so is still good. I wondered if it would be too brittle which is why I posted this question - I know nothing about cement or how to use it.
Will using sharp sand alter the characteristics of the cement - make it less brittle and therefore stronger?

keystone

Yes you must use some aggregate in it to bulk it up and give it strength. Sharp sand is fine for a rendering mix but really I'd be putting in some 10mm gravel as well for the volume you are talking about.

How long is a "while ago"? It can still go off and be useless even if its unopened. You might be better off with a bag of a DIY shed's ready mixed, just add water, concrete TBH.

Cheers

iamcornholio

You would be better off spending £4 on a tin of expanding foam

Anyway rapid hardening cement is just cement that hardens quicker. It is used exactly the same and needs to be mixed with sand just the same to a workable mix. 5cm is too big a depth for mortar and you will need to add some fine gravel to prevent cracking

andygb

keystone wrote: »

Yes you must use some aggregate in it to bulk it up and give it strength. Sharp sand is fine for a rendering mix but really I'd be putting in some 10mm gravel as well for the volume you are talking about.

How long is a "while ago"? It can still go off and be useless even if its unopened. You might be better off with a bag of a DIY shed's ready mixed, just add water, concrete TBH.

Cheers

Just nipped out and bought some ready mixed stuff, which seems to be the best route.
Cheers.

ormus

cement on its own is fairly brittle.
hence you use sand and or aggregate to make render/concrete. much stronger.
add rebar and its very very strong.

and yes it does go off after some months.