Concrete mix to make ornamental block.
All manner of questions and solutions to problems and issues surrounding the subject of brickwork, blockwork and stonework

5 posts   •   Page 1 of 1
tonyjeffs
Apprentice
Apprentice
Posts: 5
Joined: Tue Jul 22, 2008 5:46 am

Concrete mix to make ornamental block.

by tonyjeffs » Tue Jul 22, 2008 8:18 am

Hi
I'm making some exposed aggregate concrete blocks to match and repair a 70 year old garden wall.

I'm not doing too badly getting there by trial and error.
-Using a 1-2-5 mix with a small amount of plasticiser seems best, but is grainy and doesn't flow, so it's not great to work with, and voids result if I'm not careful. Any suggestions on a better mix? Is it better relatively dry or should I keep it wetter to make it more workable and flowing?

I use a stiff brush after about 10 hours to brush the outside of the blocks , and then hose down to expose the aggregate finish. Does that technique and time seem about right, or is there a better way?

They arent very strong when I take them out of the formwork, but hopefully they'll acquire more strenght over a few days, or would a different mix be stronger?

I'm going to try adding a bit of soil (!) to the mix in the hope that they'll look a bit older. Might this work?

Thanks
Tony

Freeman
Apprentice
Apprentice
Posts: 18
Joined: Wed Jul 23, 2008 8:09 pm

by Freeman » Wed Jul 23, 2008 9:18 pm

Are you vibrating the mix once in the former? tapping the sides should be sufficient, this will help you to avoid the voids.

Once they are laid, paint them with watered down yoghurt, this speeds up the ageing process.

tonyjeffs
Apprentice
Apprentice
Posts: 5
Joined: Tue Jul 22, 2008 5:46 am

by tonyjeffs » Sun Aug 17, 2008 6:49 am

Thanks for tip. Sorry for delay - I lost track of the forum.

Your advice works well, and I seem at last to have got the knack. I've also gone for a wetter mix that'll flow a little.
I haven't got to the yoghurt part yet, though!


Tony

tonyjeffs
Apprentice
Apprentice
Posts: 5
Joined: Tue Jul 22, 2008 5:46 am

by tonyjeffs » Wed Sep 10, 2008 11:42 am

Freeman,
That tapping technique works really well. Y' can see the level in the mould drop slightly and occasionally the bubbles of air escaping.

I have another question - the variable unpredictable quality of my concrete.
Sometimes the blocks I make turn out good and strong, but my latest batch are pretty chalky, and I don't know why. After 24 hours of a 1:2:4 mix, they're still soft. I appreciate it takes days for concrete to cure properly, but I thought they ought to be stronger than that. I've started adding a bit more water so that it flows more easily into the mould- perhaps that's the problem -would it weaken the product? Or is it just the cooler weather slowing the process down? Perhaps if I add pva it might help?

THe blocks have a 1cm square lip at the front which overhangs the block below - this is the bit that needs to be strong, else it'll snap off.

Thanks

Tony

TheDoctor5
Posts: 1381
Joined: Tue Jan 20, 2009 9:17 am

by TheDoctor5 » Thu Jan 22, 2009 9:45 am

Last year 64% of the questions asked in our forum were answered within our DIY project pages at www.diydoctor.org.uk/projects.htm The project pages are now separated alphabetically and your answers are accompanied by diagrams and the ability to see, and buy, the tools and/or required to complete your project. Use our search box to look for your answer and save a great deal of time and money!

5 posts   •   Page 1 of 1
It is currently Fri Feb 23, 2024 11:53 am