Concrete mixing for pier

[Astrokev]

Hi All

I'm nearly ready to order materials to make my obsy footings and pier. Possibly a stupid question (I'm not afraid to ask stupid questions!) -

The mix I am planning on using is 1 cement : 4 ballast.  I'm probably going to be mixing at least some of the mix by hand, and want a quick and easy way of measuring the cement needed per "standard" bag of ballast (Wickes). How accurate does this ratio have to be? 

Thanks!

[triton1]

I generally use a nearly heaped shovel of cement to 4 heaped shovels of ballast.As long as all the mixes are the same shouldn't be a problem.l think it's 4 per bag.

[Jannis]

Personally i simply used a 5/10 liter bucket to measure. I don't think it's critical to get the ratio precisely (there are many different ratios anyway depending on your desired concrete strength), but i quickly found out that just counting shovels were no good.  I aimed for a ~B20 mix.

Remember to use as little water as possible. If you're measuring the water, don't pour it all in at once, leave a bit and add only if needed. When you think you are just about there with the water, adding just a few more drops can suddenly make it all too wet.

I also thought i would just mix everything in a bucket, but i was only able to blend one single 50L bucket before my arms were all tired, my 700W drill was running hot, and the mixing tool had made a crack in the bucket (it was a thick bucket designed for this). I then proceeded with a proper mixing machine and in the end i realized i would never have been able to finish with a bucket. I ended up with about 3 tons of concrete in the end
How much do you intend to mix?

[wxsatuser]

All I did was buy Wickes multipurpose concrete bags.
Back then they were 25kg but now 20kg, just mixed each one in a wheelbarrow and poured as needed.

I made mine quite wet so it's easy to push down pier tube to get rid of voids.
I mixed over 10 in about an hour, base was only 2foot square and pier pipe was brown sewage pipe.
The sewage pipe was put 3feet into the hole and quickly held with a bag of postcrete, as postcrete went off
I started mixing and pouring the multipurpose. Think overall it was about 1/3 of a ton.

I did exactly the same back in the early 90s when I mixed over a ton for my 40foot amateur radio mast.
Thats still in the ground and is still perfect to this day.

[Astrokev]

Thanks for the replies, this is really helpful.

 

Jannis - I'm estimating needing to mix just under 1 m3.  No idea what that is in weight, but sounds heavy ;-)

[estwing]

1:3:5 or 1:2:4 cement,sand and gravel

[wxsatuser]

1 hour ago, Astrokev said:

Thanks for the replies, this is really helpful.

 

Jannis - I'm estimating needing to mix just under 1 m3.  No idea what that is in weight, but sounds heavy ;-)

About 2400kg

Happy mixing.

[smudgeball]

5 hours ago, wxsatuser said:

About 2400kg

Happy mixing.

[Adam J]

On 08/07/2017 at 06:40, wxsatuser said:

All I did was buy Wickes multipurpose concrete bags.
Back then they were 25kg but now 20kg, just mixed each one in a wheelbarrow and poured as needed.

I made mine quite wet so it's easy to push down pier tube to get rid of voids.
I mixed over 10 in about an hour, base was only 2foot square and pier pipe was brown sewage pipe.
The sewage pipe was put 3feet into the hole and quickly held with a bag of postcrete, as postcrete went off
I started mixing and pouring the multipurpose. Think overall it was about 1/3 of a ton.

I did exactly the same back in the early 90s when I mixed over a ton for my 40foot amateur radio mast.
Thats still in the ground and is still perfect to this day.

I also tried this, but its playing with fire to try and pour the multi-purpose mix after the post mix I ended up with a crack between the two pours as the post mix had gone off before the applying the multimix it left the pier unstable and only held together by the form. I ended up digging it up and starting again. 

[RayD]

Have you considered Minimix or Mastamix? I had 1m3 to do and it took about 40 minutes all in for 2 of us barrowing it in from the front. They mix as it draws off the wagon so you have no waste and only pay for what you have. You select the mix at the time, and they will advise what mix is best for this application. 

Mine was about £200 all in and they loaned me the 2 barrows. I'd do it again definitely as by the time I'd factored in the cost of mixer hire it worked out cheaper.

Above all its a precise and well made mix and very unlikely to give you problems with bad patches.

Also it's worth investing £40 in a cheap electric poker which vibrates and takes out all the air pockets and really settles the pour. This also really reduces the likelihood of cracking.  

[pete_l]

A few things.

Concrete needs water to set properly. The water can soak away into the soil if the soil is dry. Try lining your hole with a polyethene sheet, just to retain the water in the mix.

You can also get retarders, that slow down the setting process.

Also in hot weather, you should ensure that the surface doesn't dry out. You should spray it occasionally - but not with force or you'll wash away the top surface.

[spillage]

It might be worth looking for a cement mixer second hand locally. You can buy it use and then sell it when finished. There is no rush and if you lose a few quid I'm sure it's not going to be as much as hiring one. Then a 6:1 mix of ballast and cement.

[wxsatuser]

2 hours ago, Adam J said:

I also tried this, but its playing with fire to try and pour the multi-purpose mix after the post mix I ended up with a crack between the two pours as the post mix had gone off before the applying the multimix it left the pier unstable and only held together by the form. I ended up digging it up and starting again. 

The Postcrete is only to hold the pipe vertical, it's in a hole in the the bottom of the main hole.
It has no bearing on the main mix.

Mine has been down 4 years now and still going strong.

[Astrokev]

Thanks everyone; some really good ideas, and plenty of food for thought. I'll be giving an update on final methods etc in my obsy build thread.

Kev

[ACross]

Mix ratios are important (1:2:4 is good) but most important is the amount of water you use, too wet and the mix will be *much* weaker.  Add only a small amount then increase slowly until the mix will stand in heaps with only moderate slump.

If you think all the mixing can be done in a day, hire a mixer. If not, buy one, wrap the legs in plastic to keep them clean, don't bash the barrel and then sell on flea-bay when you are finished with it.  I did this for an extension and actually sold it 2 years later for more than I originally paid for it. 

Oh, and never be tempted to use quick setting concrete or additives to accelerate the mix; you will have joint cracks and air gaps.

 

Anthony

[ACross]

Another tip:

Have a look at B&Q bags of ballast (Wickes and others do them also). This is pre-mixed sharp sand and shingle/stones and I used this with regular blue-circle cement for my pier (conc filled air vent duct, fitted with internal cable conduits) and frame foundations. I bought the weather-proof bags of cement and used a long blade knife to slice the bag of cement into two halves, then put half a bag to three bags ballast into the mixer.  It was surprising how quick the job was finished, mixing and pouring all done in about four hours.

As with all foundation designs, depth is better than width (unless you plan to use metal rebars).  My pier is 250mm diameter, 2.8m out of the ground and sits on a foundation that is approx 1m deep but only 400mm diameter.  Likewise the legs of the frame are on small 200mm dia pads that are approx 600mm deep.

[smudgeball]

Hi

I poured my pier footing today.

Was fortunate to have a work colleague with a cement mixer (and a van ! ) so it made the job a lot easier. Plus I was able to setup the mixer right next to the formwork for pouring.

I just went for the "ready mix" bags and made the best formwork that I could.

I'm please with the result.

Currently covered up ( I've sprayed it twice today and will do so again tomorrow morning).

Neil

[Erla]

It doesn't sound much, but 1m3 is a lot to mix by hand and especially so for inexperienced. Then there is a question of it setting in layers, as it is summer and while you mix one batch the other is already setting. I can't remember from the top of my head what the minimum order is, but some do smaller quantities. The price is something around £100 for a cubic meter, and some suppliers do "difficult access", which means they would just run a hose through wherever and pump it in, while you literally drink tea. Used this service a lot when doing construction projects in London. No wastage, fast, no mess. 

Just checked - some suppliers do one cubic meter.

[Jkulin]

Hi,

I just called Wolverhampton Concrete on 01902 504601 and they work on charging a minimum of 1m3, they need 24-48 hours notice and as long as the access is clear the lads will barrow it round to your garden and drop it into the hole, all for £185 Incl. VAT

They  will mix it whatever ratio you need on site.

Just got to wait for my pier to be made now and jobs a good'un!

[ollypenrice]

1 hour ago, Jkulin said:

Hi,

I just called Wolverhampton Concrete on 01902 504601 and they work on charging a minimum of 1m3, they need 24-48 hours notice and as long as the access is clear the lads will barrow it round to your garden and drop it into the hole, all for £185 Incl. VAT

They  will mix it whatever ratio you need on site.

Just got to wait for my pier to be made now and jobs a good'un!

That's a good deal. It was a lot more expensive per tonne to get a load brought up our small mountain!

Olly

[RayD]

1 hour ago, Jkulin said:

Hi,

I just called Wolverhampton Concrete on 01902 504601 and they work on charging a minimum of 1m3, they need 24-48 hours notice and as long as the access is clear the lads will barrow it round to your garden and drop it into the hole, all for £185 Incl. VAT

They  will mix it whatever ratio you need on site.

Just got to wait for my pier to be made now and jobs a good'un!

That's about the right place.  I did mine this way and it's worth every penny.  The mix is perfect and all done in less than an hour with no back breaking.

[Astrokev]

This sounds very tempting - I must research further. Thanks.

Kevin

[valefor]

This is the path i took on both my piers. http://m.skyatnightmagazine.com/feature/how-guide/how-build-back-garden-telescope-pier

Tho i went 70cm deep with my tube. Mine is a 150mm waste pipe too and i did a 3.1 ballast and cement mix. The first one went up 5 years ago and only came out because i moved. Took 4 men to get it out again. Lol

Dave

[sonneyboy]

Hi,  I poured mine last Sunday.  Wickes ballast 25kg (ish) bags) - its a guess as they dont mark the packaging - mixed 2.5 bags ballast per 12.5kg cement worked for me.  Was working alone so treated myself to the 12.5kg weatherproof bags of mastercrete cement rather than the hassle of splitting the 25kg bags, bought weatherproof as stored outside and no guarantee of when I was gonna start the job.  I figured the small bags would save me some valuable time on the day which I believe it did and was less messy.   I purchased a second-hand £65 quid cement mixer a month ago in preparation which takes the urgency out of hiring something and clock watching.  For base and pier (air gap separated) I used 90 bags of ballast, they took some carrying up my driveway and through the house i can tell you, that was the most gruelling aspect.  Bagged suited me as I had to carry it through my house, bulk would have saved some cash but not suited to my property (though how you save depends on your locality and nearby outlets).  I found 1 bag of ballast filled one 99p 14L builders bucket.  Once i was ready to mix it took hardly any time.  I'd certainly do it again this way...but not for a while!

Paul 

[spillage]

Due to obstacles in my garden I found I spent ages pacing around deciding where to put my pier. Then spent the whole time I was mixing and filling wondering if I had made a mistake in the planning. I am now just glad it there and there is where it will stay...