concrete skills - making ornamental block

[tonyjeffs]

I'm making some ornamental blocks to repair a garden wall. They have a sloping front face with exposed stone chippings. I have just about got the knack of making them - 1-3-6 mix cement sand aggregate. Leave them to set overnight, brush and wash gently to expose stone.

The remaining problem I'm having is the colour. For the original

1930's wall the concrete is a sort of grey-beige colour. My new blocks are sparkling white, including the ones I made a year ago.

I suppose I could start adding dye, but wondered if the answer is more in the mix I'm using. Maybe I'm not accurate.

Any thoughts on improving what I'm doing.

Thanks

Tony

[dom]

Sand colour and cement type both influence the results - but if you want a yellowish tint go for a mortar dye.

[Bruce]

Your choice of sand has the biggest effect on the result. However, matching a 70-year old concrete block with a newly made concrete block is almost impossible, because the 1930s blocks will have weathered to expose some of the aggregate in the original concrete.

Why not try to obtain some matching 1930s blocks from demolition or possibly an architectural salvage yard?

Otherwise, consider replacing the 1930s blocks with new ones so they all match.

[tonyjeffs]

Here is a pic of my efforts compared to the original. The latest looks better, but I guessed the sand and it isn't very strong.

[tonyjeffs]

Here is a pic of my efforts compared to the original. The latest looks better, but I guessed the sand and it isn't very strong.

[Rod]

long after making it are you judging the strength? As I understand it, concrete-based products can take a long time to fully harden - from memory 21 days is often used as a guide for ordinary concrete. Make sure it is does not dry out fully for at least a few days.

The other devil in such products is using the wrong amount of water - too much or too little. (Funny how they always seem to be wading through very liquid concrete on the Grand Designs of this world. :-) )

The next devil is thorough mixing. Most of the minor works I DIY at home have plenty of strength but that is in spite of crap mixing. I know very well that thoroughness is vital to achieve maximum strength.

Finally, do you do anything to shake the mould? I am thinking that a good vibration might help. Maybe even poking and/or nudging it with an SDS chisel?

I am impressed that you are putting in such effort to get it right.

[tonyjeffs]

...I think a touch of madness explains that one! The satisfaction is in solving the puzzle rather than fixing the wall.

The tips are all good. I'll take them on board and do a bit of trial and error. I'll find some cans so I can gauge my mix more accurately. Water's tricky - dry mix is strong, but doesn't fill the mould so easily.

I'm checking the strength after about 24 hours.But I'll leave them laying around for a day or two after that. Mixing is good - half size B&Q cement mixer.

For the vibration aspect, I thought maybe I could stand the setting blocks on top of the washing machine while t Mrs J does the washing, but she wasn't happy with the idea'. A vibrating platform would be better'n a chizel as theres a polysterine spacer in the middle and not much room to prod, but a chizel will help. Maybe I can rig else up to vibrate it. Maybe a wooden platform resting on the lawnmower. I'll give it some thought.

Thanks for v helpful ideas.

Tony

[Steve Walker]

You could try accelerated aging. Soak the cured blocks overnight in a bucket containing some coffee or teabags, a lump of rusty metal, some plant fertiliser and a bit of milk or sugar (not intentionally a recipe for builder's tea-break, just coincidence). You'd get a staining effect, but you'd also get rapid colonisation by microbes, lichen etc. Just a mad idea....

[Bruce]

I would use a partial cement replacement with 30% to 50% PFA (pulverised fuel ash) replacing 30% to 50% of the cement. That will give a greyer rather than whiter appearance. It will give a slightly lower strength but a much more durable block.

The darker colour of the 1930s block is partly due to things that are growing on the surface. I cannot recall what they are called, but I have successfully encouraged their growth on a new retaining wall that abutted an older one by painting the new concrete with diluted organic live yoghurt (unpasteurised). 70% yoghurt, 30% water. If your local water supply is chlorinated, use mineral water. Spa still mineral water (in the red capped bottle) is best for this.

Wait for at least 6-8 weeks before you do it.

I think the combination of a greyer block and the live yoghurt should do the trick. If it doesn't work, I offer a 100% refund of the price you paid for this advice. Or you can easily scrub it off while hosing it down. ;-)

And no, none of this is a joke, however funny it might sound. ;-)

[meow2222]

strength of any concrete mix after 24 hrs is going to be extremely low. Test them after a sensible time, a few days at a bare minimum.

One idea not yet mentioned is to add subsoil, IIRC upto 1/3 as much as the sand. Needs good mixing though.

NT

[Man at B&Q]

Or cowshit, diluted and painted on.

MBQ

[tonyjeffs]

Thanks everyone. I'll do a few experiments with the accelerated ageing ideas. I tried just painting wet soil on one. I'll see how that goes. Yoghurt and butter sounds good too. No cows in the area though.

It takes a long time to produce each block, - clean up and prepare the mould is most of the work. I'd like to produce a cou[;e of hundred, so i need to speed up my technique.

Tony "Making blocks in the hot sun I fought the law and the law won Today I got another ...six done I fought the law and the law won.....