Page 1 of 1
Posted: Wed May 03, 2006 2:33 pm
by DavidL
Hi all,
I have some slabs to lay for a path and patio. I also have some old (1 year or more?) bags of cement. Is it OK to use this cement? I know it has a shelf life, but what is the effect of this on the curing of the cement?
I started to lay it on Monday (the first few slabs), and it's still not very hard, so I am wondering if this is a problem?
Also, just double checked the various pages and I realise I made a 6:1 mix, but the pages recommend 4:1. Goes to show I should have checked that first I guess. Shall I quickly rake out what's there before it sets too much?
Thanks for any help/advice!
David.
Posted: Wed May 03, 2006 4:59 pm
by Tony McC
The site-life for cement is usually taken to be 1 month. You could stretch that to 3 months if it's kept bone dry and frost-free, but at 12 months, it's f***ed!
Posted: Wed May 03, 2006 5:16 pm
by DavidL
I posted this question to a selfbuild forum as well, and one poster on that site is a chemist for Lafarge. He seems to think that the cement is fine so long as it has been kept dry.
It does need to be crumbled a bit, but again he thinks that is OK. If it is solid, then maybe not!!
Apparently the shelf life relates to the additives to prevent a high concentration of Chromium-VI. Beyond the shelf life they are no longer affective so you are at risk of contact Dermatitis if you play with the stuff.
What makes you say then that it will not be any good?? What has been your experience?? I think my main problem is that I made the mix too weak for the edging and pointing (I am just bedding them onto builders sand).
I'm not trying to be diffiuclt - just trying to undestand the conflicting opinions.
Thanks,
David.
Posted: Thu May 04, 2006 1:15 pm
by danensis
If the cement is still powdery, it can be used as a pozzolan to make roman cement, with lime putty and sand.
Posted: Thu May 04, 2006 1:45 pm
by Tony McC
If you could keep the cement unopened in a bone-dry atmosphere, I dare it would last for a lot longer, but if there is any water vapour in the air (and even today, with the sun cracking t'flags here at Borlochs Hall, the relative humidity is over 75%) the cement powder absorbs it, partially hydrates, and 'perishes' as we refer to it.
There's a whole world of difference between lab conditions and real life
Posted: Fri May 05, 2006 1:35 pm
by danensis
Notwithstanding what Tony says, if you are using cement as a pozzolan it doesn't matter how knackered it is as cement - indeed you can use fine brick dust, and the original pozzolan was volcanic ash. Them Romans knew a thing or two about building - how many of our structures will still be there in 2000 years time (nuclear power stations apart)?
Posted: Tue May 16, 2006 12:10 pm
by mouldmaker
DavidL wrote:Apparently the shelf life relates to the additives to prevent a high concentration of Chromium-VI. Beyond the shelf life they are no longer affective so you are at risk of contact Dermatitis if you play with the stuff.
In my experience, chemists are great in the lab, sod all good on site.
I'm concerned at your comments on dermatitis; this has nothing whatsoever to do with shelf life. You can get anything from contact dermatitis to burns serious enough to require amputation from cement.
Always read the instructions, wear the correct protective equipment etc and if in doubt you can download an appropriate advisory leaflet from the HSE.
Posted: Tue May 16, 2006 1:10 pm
by DavidL
I know what you mean - I have worked with people fresh out of academia that were perfectly qualified but didn't know diddly squat in real life. But this Chemist is in the process of building his own house so he has real world experience as well.
As I understood it the shelf life related to additives that would degrade over time. These additives are to prevent the higher levels of Chromium-VI which is believed to be the cause of Contact Dermatitis when people are touching cement. If you are susceptable to such things, then beware.
The chemist in question pointed out that if he had been susceptible he would be in trouble by now, having worked with the stuff long before such information and research had been done.
The chemist did however point out that these were his thoughts - not official ones!! He also pointed out that he would steer clear of wet cement and take adequate precautions at all times.
I believe this is true of so many things - how many people die from Lung cancer brought on by smoking at an early age, and how many live until they are 100?? If you have the cancerous genes, smoking will activate the cancer. The occasional night in a smokey atmosphere can be devastating if you are susceptible, while others are un-harmed. You pays your money, you take your choice.
As for the cement I put down - it has gone off just fine. The weaker mix took longer, but seems stable enough. I've used a stronger mix since.
I can see the point of the water absortion because some parts are hard and brittle. The middle however is fine Breaking it up with a shovel seems affective enough, and it mixes just fine. I am sure it is not perfect, but then again, it's only for a garden path. If it was for a more substantial application I would be concerned (walls, whole house...) but as it is I will finish off the bag and a bit I have left.
Posted: Fri May 26, 2006 12:50 am
by Gisburne
I have recent experience of using some really old bags of cement - well over a year old, maybe even pushing 2 years. They were kept in my shed, which is fairly dry but prone to ordinary humidity, and I went to kick the bags and they were rock hard. So I assumed they had gone off. But I opened the bags (might as well) and although I didn't exactly find fine powder, any lumps (plenty of em) that were in there did crumble in my fingers. I decided to use the cement for some concrete foundations for a small wall, but wouldn't trust it for bricklaying mortar. A vigorous mixing in a wheelbarrow (so that I could chop it all up with a shovel) and it was fine, set okay, solid as anything I've done before. Not to be recommended, but you can get away with it depending on what you want to do (nothing that holds up your house, just in case!), and the condition you find when you open the bags. Just my (limited) experience, which came about because I always seem to start jobs, buy too much stuff, then leave half unused in the shed!
Posted: Fri May 26, 2006 11:09 am
by DavidL
which came about because I always seem to start jobs, buy too much stuff, then leave half unused in the shed!
A man after my own heart.... :p
Posted: Fri May 26, 2006 5:23 pm
by TarmacLady
I'm the first in line to pinch a penny wherever I can, but unless I'm *very* mistaken about the price of cement (and just had a spin round a few merchants' sites to make sure) --
The cost of a new, fresh bag of cement is not worth the hassle of putting down something that's a bit dodgy and then having to tear it all out and start over, especially when looked at as a percentage of the total cost of the job...
If in doubt, throw it out!