Hi Guys
The Sunday before last I laid the concrete pad for my growing on pond. It still hasn't cured properly. I can make grooves in it with a screwdriver and underneath the surface it looks more like damp sand than a concrete colour.
What I think has happened is that insufficient cement was added to the mix. Unfortunately I was not involved in the mixing; I was at the distribution and tamping end of the operation. I have two questions;
The weather has been cold and humid (90%). Is it possible that it could still cure?
If the cement content is too low is there anything I can do to rectify the situation without breaking it all up. Someone has suggested that I could make a cement and water slurry which can be spread and absorbed into the pad - I have my misgivings.
Anyone had any similar experiences and managed to avoid hiring a kangyo as a final solution?
Extremely p****d off.
Jon W
Uncured Concrete
Moderators: B.Scott, vippymini, Gazza, Manky Sanke
Hi Jon, What gauge did You knock the mix up at. At this time of year it takes a month of Sundays for anything to go off as there is so much moisture in the air.
Was the concrete knocked up as a wet mix? If so this would explain the very grey softish top to the base. This is simply that the fat in the cement as settled on top. As it always does. To be honest I would`nt get to worried just yet.
Did You lay a membrane under the concrete? As this will also stop the moisture from being drawn out into the ground below.
If I remember correctly back to My days at college. The setting stages of cement are reaction starts within 45 mins and second set is within 12 to 14 hours. This then leaves the concrete in what is known as a green state. At this time of year I would say that it will take upto atleast 28 days before Your concrete is going to be anywhere near cured. Try and get some heat to it. This will speed the processe.
For You not to be getting a setting reaction from The cement, It would of had to be a very weak mix, by this I mean something like a 12 and 1 mix even this will still go hard. Just not very strong.
If there is a problem with the base and the mix was to weak or even Your cement was faulty. Then there is simply nothing to do, other than rip it up and start again.Sorry
Justin
Was the concrete knocked up as a wet mix? If so this would explain the very grey softish top to the base. This is simply that the fat in the cement as settled on top. As it always does. To be honest I would`nt get to worried just yet.
Did You lay a membrane under the concrete? As this will also stop the moisture from being drawn out into the ground below.
If I remember correctly back to My days at college. The setting stages of cement are reaction starts within 45 mins and second set is within 12 to 14 hours. This then leaves the concrete in what is known as a green state. At this time of year I would say that it will take upto atleast 28 days before Your concrete is going to be anywhere near cured. Try and get some heat to it. This will speed the processe.
For You not to be getting a setting reaction from The cement, It would of had to be a very weak mix, by this I mean something like a 12 and 1 mix even this will still go hard. Just not very strong.
If there is a problem with the base and the mix was to weak or even Your cement was faulty. Then there is simply nothing to do, other than rip it up and start again.Sorry
Justin
Hi Justin
The concrete was mixed pretty wet. There is no membrane underneath it because it was laid on an existing concrete floor (12" thick) and it is encased with a perimeter of pre-laid concrete blocks. Funnily enough in desperation I have had a heater running in the shed today to see if this makes any difference - only problem is that relative to the size of the shed the heater is rather small.
I know the cement is okay because I have used the same batch for other purposes. I can't believe the mix was as weak as 1:12 but I suppose it is a possibility - I was unable to supervise the actual mixing which took place in the adjacent farmyard.
Well at least you have given me some hope. I was going to wait until this weekend before making a decision about whether to start hacking it up.
I'll leave it at least another week.
Thanks very much.
Jon
The concrete was mixed pretty wet. There is no membrane underneath it because it was laid on an existing concrete floor (12" thick) and it is encased with a perimeter of pre-laid concrete blocks. Funnily enough in desperation I have had a heater running in the shed today to see if this makes any difference - only problem is that relative to the size of the shed the heater is rather small.
I know the cement is okay because I have used the same batch for other purposes. I can't believe the mix was as weak as 1:12 but I suppose it is a possibility - I was unable to supervise the actual mixing which took place in the adjacent farmyard.
Well at least you have given me some hope. I was going to wait until this weekend before making a decision about whether to start hacking it up.
I'll leave it at least another week.
Thanks very much.
Jon
Hi Jon the fact That You have laid this base on a concrtete base will slow things down a little as well. I wouldnt touch things for atleast 28 days so a month.
I laid a concrete base on a pond I am building at the moment over a month ago, and You can still clearly see it is still along way from being cured.
I think its just down to the time of year mate.
Justin
I laid a concrete base on a pond I am building at the moment over a month ago, and You can still clearly see it is still along way from being cured.
I think its just down to the time of year mate.
Justin
Hi Justin
Although I've read a fair bit about it, the impression was that it generally only takes 3 days to cure. However this is my first foray into the mystic arts of building or using concrete so I have absolutely no practical experience whatsoever. I had no idea that the temperature, humidity and porosity of the substrate could have such a marked effect on curing time.
I've just been out for a look. I've had the heater on for about 7 hours and it does seem to have improved things slightly. Hopefully this is an indication that it will cure given more time and heat.
You can see what I've done so far on my thread "Jon's growing on pond build" which is a few down from this one.
I'm using this to determine whether I can develop the skills to build a main pond next year.
Regards
Jon
Although I've read a fair bit about it, the impression was that it generally only takes 3 days to cure. However this is my first foray into the mystic arts of building or using concrete so I have absolutely no practical experience whatsoever. I had no idea that the temperature, humidity and porosity of the substrate could have such a marked effect on curing time.
I've just been out for a look. I've had the heater on for about 7 hours and it does seem to have improved things slightly. Hopefully this is an indication that it will cure given more time and heat.
You can see what I've done so far on my thread "Jon's growing on pond build" which is a few down from this one.
I'm using this to determine whether I can develop the skills to build a main pond next year.
Regards
Jon
Hi Jon
I think that as long as it is firm enough to stand on (as well compacted sand would be) and has dried out properly, once it's fibreglassed it will be OK in your tank - the strength is already in the 12" concrete substrate.
Whatever the outcome of this attempt, you now know how important it is to check the correct mix is used for the concrete on your main pond!
Good luck
Bob
I think that as long as it is firm enough to stand on (as well compacted sand would be) and has dried out properly, once it's fibreglassed it will be OK in your tank - the strength is already in the 12" concrete substrate.
Whatever the outcome of this attempt, you now know how important it is to check the correct mix is used for the concrete on your main pond!
Good luck
Bob
Hi Bob
It was one of those situations where I was offered help. They guys helping had a fair amount of concreting experience so although I felt the mix wasn't quite right (too wet) I deferred on the grounds that they probably knew more than I did. Also, if I'd attempted it on my own it would have taken at least 8 hours continuous work.
If I do another build (even another small indoor pond) I think I will go for ready mix.
Cheers
Jon
It was one of those situations where I was offered help. They guys helping had a fair amount of concreting experience so although I felt the mix wasn't quite right (too wet) I deferred on the grounds that they probably knew more than I did. Also, if I'd attempted it on my own it would have taken at least 8 hours continuous work.
If I do another build (even another small indoor pond) I think I will go for ready mix.
Cheers
Jon
Jon go for one of the machines that mix the amount you want. I had 8 cu M back in September cost me ₤715.00 not bad for Kent prices 
We poured it by the wheel barrow load and had 4 of us, 2 wheeling, 2 troweling. Took 50 min's but went off in a couple of hours. May be an option for you next time?
Jules
We poured it by the wheel barrow load and had 4 of us, 2 wheeling, 2 troweling. Took 50 min's but went off in a couple of hours. May be an option for you next time?Jules
Hi Jules
Absolutely! I was only doing 1.5 cubic metres so I thought it would be fine to try mix my own. I'd been warned that round my way it isn't economic to order small amounts - you end up paying more for stuff you don't use. If I was doing anything larger I would definitely use ready mix.
Cheers
Jon
Absolutely! I was only doing 1.5 cubic metres so I thought it would be fine to try mix my own. I'd been warned that round my way it isn't economic to order small amounts - you end up paying more for stuff you don't use. If I was doing anything larger I would definitely use ready mix.
Cheers
Jon
Hi Justin
One thing you could say about it was that it was wet!. In fact I could probably have done with flippers rather than wellies. I thought I read somewhere that if it is too wet that the result can end up weaker? My worry is that it was so wet that the cement has been washed out of the mix.
To facilitate drying out I have rigged up a plastic tarpaulin as a tent over the pad with an electric heater in the middle. Open at both ends for ventilation. I figured that if I have got a problem that at least I will know a bit quicker and be able to start hacking up quicker. I'd originally planned to have the whole thing up and running before Xmas.
Cheers
Jon
One thing you could say about it was that it was wet!. In fact I could probably have done with flippers rather than wellies. I thought I read somewhere that if it is too wet that the result can end up weaker? My worry is that it was so wet that the cement has been washed out of the mix.
To facilitate drying out I have rigged up a plastic tarpaulin as a tent over the pad with an electric heater in the middle. Open at both ends for ventilation. I figured that if I have got a problem that at least I will know a bit quicker and be able to start hacking up quicker. I'd originally planned to have the whole thing up and running before Xmas.
Cheers
Jon
Hi Guys
After three weeks it appears that the concrete hasn't cured. I've dug a few exploratory holes and the consistency for the top 3 inches is that of hard compacted sand. Further down it is a little more solid.
Does anyone agree that I'm doing to have to dig the whole effing lot up because if I chisel down to the solid areas and re-lay more concrete that there won't be sufficient structural integrity to take the weight of the pond?
Cheers
Jon
After three weeks it appears that the concrete hasn't cured. I've dug a few exploratory holes and the consistency for the top 3 inches is that of hard compacted sand. Further down it is a little more solid.
Does anyone agree that I'm doing to have to dig the whole effing lot up because if I chisel down to the solid areas and re-lay more concrete that there won't be sufficient structural integrity to take the weight of the pond?
Cheers
Jon
Hi Jon
Did you have a heavy frost that night and that the slab got frozen if that’s the case it will never set and will be useless
With concrete there is a chemical reaction that take place the lime that’s in it heats up to sets the concrete
Also if the ballast is frozen the same thing can happen
Did you have a heavy frost that night and that the slab got frozen if that’s the case it will never set and will be useless
With concrete there is a chemical reaction that take place the lime that’s in it heats up to sets the concrete
Also if the ballast is frozen the same thing can happen
Hi Mak and fisheman
I thought we were using about a 4-5:1 mix, but when the guy doing the mixing was finished I discovered that over half the cement hadn't been used so it was more like 12:1. Also rather than the mix being too dry, at one point I was walking around in about 6 inches of water!
Minimum temperature during the first night was about 9C - I stuck a temperature sensor out there all night to check.
Unfortunately I deferred to others who I thought had more experience of mixing concrete.
I've dug a big hole in it and discovered at just above the level of the reinforcement mesh that it has set - so I've got the worst of both worlds. I guess it will be almost impossible to salvage the bottom drain and pipework as a result.
Cheers
Jon
I thought we were using about a 4-5:1 mix, but when the guy doing the mixing was finished I discovered that over half the cement hadn't been used so it was more like 12:1. Also rather than the mix being too dry, at one point I was walking around in about 6 inches of water!
Minimum temperature during the first night was about 9C - I stuck a temperature sensor out there all night to check.
Unfortunately I deferred to others who I thought had more experience of mixing concrete.
I've dug a big hole in it and discovered at just above the level of the reinforcement mesh that it has set - so I've got the worst of both worlds. I guess it will be almost impossible to salvage the bottom drain and pipework as a result.
Cheers
Jon