Fence Post concrete mix

[Mattatooi]

I have 17x 8' @ 4x4" fence posts to install in garden. I will be digging out 2' of depth and using concrete. Can anyone tell me if the Postcrete type stuff is any good? And with the amount of posts I need would it be better to make my own concrete?

Now I am a complete newbie to making concrete so I am unsure what I actually need to make. I know I will probably be hiring a Cement mixer (£18 per day here). I have no idea how much materials I will need.

Also from removing patio I have got a heap of stones that was used under the patio base. Looks like 3/4" angluar stone? (think thats the name?);



Can I use these for mixing in to concrete? Or can I use these before I put concrete in so post is not on soil??

 

[Ian H]

The mixer would work out cheaper on 17 posts.

That stone will be ok mixed with sand, there will be a guide on the cement bags saying what mix of sand/stone/cement to mix.

 

[Tigercubrider]

It is well worth buying a post hole digger

You get deep holes with stable sides

http://www.toolstation.com/shop/Lan...&+Tools/sd3224/Draper+Post+Hole+Digger/p16835

 

[garash]

Hello, Usually it's three and one with Cement Mix. That's 3 Sand to one cement. You can add some of your stones yes, that will help. Don't despair - I am a 66 year old lady and I am going to project manage my own 60ft of fencing later on in the year. I had a good teacher in my first husband. However, Hubby number two will simply follow me and provide the muscle which I lack ! It is not Rocket science but obviously you need to take all your measurements into account. Good Luck ! Stones are good for drainage if put down hole on their own before you put the posts in.

 

[garash]

Sorry, also meant to say don't bother with Postcrete it will work out expensive and your own knock up will be better.

 

[alan333]

3 parts aggregate (stone chips), 2 parts course sand, 1 part cement. You can use your "heap of stones" as aggregate but they look quite small, so personally I'd mix some in with some aggregate in each batch rather than using them instead. You can also throw some quarter/half bricks etc in the hole along with your concrete if you wish, just make sure they're surrounded by concrete. The bigger the hole you dig the more concrete you'll need. You'll use somewhere between one third of a hundredweight and a full hunderweight per hole depending in how big they are. If your ground is soft then do bigger holes and more concrete, if the ground is hard you'll get away with smaller holes.
Note - the cement mix mentioned by garash above is for a cement mix, not a concrete mix, and isn't suitable for concreting fence posts.

Edit...on zooming in to your heap of stones they look big enough to replace the aggregate right enough.

 

[r896neo]

Just to clear up a few terms here,

Concrete is a mix of aggregate sand and cement.

General purpose mix for most applications is 3 stone 2 sand 1 cement.

Mortar is sand plus cement (no aggregate)

There are all different types of mortars depending on sand type and application.

5:1 plastering sand : Cement for rendering.

4:1 building sand to cement for bricklaying

6:1 sharp sand : Cement for laying flags etc.


As for your posts use up what you have got by making your own concrete or if you like you could simply bulk out your postcrete by adding a few shovels of stones in with each bag and mix it up dry then use it as normal postcrete.

 

[Doggit]

The 3/2/1 mix is standard to use for concrete, but if you're hiring a mixer, then that suggests you'll be going for a wet mix, but one trick I've learn on this site, is to use a damp mix instead of a wet one. Postcrete is great in that it'll go off in a few minutes, and you then set in the next post, and then drop in the panel. With a standard wet concrete, you have to support the posts over night whilst the mix goes off, but if you mix the agregate, and cement without any water, but with a slightly damp sand, then the post will hold straight, and the mix will go off on it's own (at least from what I've gathered). Now I don't know how long before you can fix the panels in, but you may want to investigate this method a bit more.

 

[Mattatooi]

Thanks all for the advice. In doing some reading I opted to just buy some postcrete type stuff. It is a bit more expensive, but it will be alot easier as it sets so fast.

Stones in picture are approx 3/4" on average. They were under the old concrete patio base, so pretty sure they are good for that. Going to put some in the bottom of the posts. I like the idea of mixing in some to the postcrete mix. This will help the bags go a bit longer I guess? What sorta ratio of stones to postcrete should i be mixing dry ? The stuff I got is - https://www.ribaproductselector.com/Docs/9/20759/external/COL820759.pdf - it says to add water first.

All being well going to be starting posts tomorrow.

 

[Doggit]

Check out Wickes for their multibag deals, and then decide, but would be much cheaper to make up the concrete because you've already got the aggregate.; But if you're going to add some aggregate, then I'd go 1/4 aggregate, to 3/4 postcrete, but you're going to have to mix it first, and then pour it in, but I wouldn't bother putting any in the bottom, as the water poured into the bottom of the holes will fill with postcrete, and negate the drainage trick of having stones under the post.

Postcrete will settle flat, so unless you're having the postcrete up at ground level, then you'll either need to add a bit of mortar on the top, sloping it upwards as it goes towards the post, or you need to coat the bottom of the post with bitumen to stop the earth soaking water into the post, and rotting it at ground level - I know they're supposed to be rot proof, but they're not.

 

[r896neo]

As I said you need to premix the stones and postcrete before putting it in the hole. Just throw 2 bags of postcrere into a barrow and then half a bag of stones and mix with a shovel briefly.

I wouldn't put loads of stone in, aim for roughly 3:1 postcrete to stones.

 

[London Mike 49]

This may be of interest; http://www.pavingexpert.com/concmix1.html

Mike

 

[Doggit]

2 bags of postcrere into a barrow and then half a bag of stones

Now that would make 4:1, but I'm more inclined to go with the 3:1 mix as you suggested later.

 

[r896neo]

Thanks Einstein, was just trying to show its not necessary to be super accurate.

 

[Doggit]

Sorry R896, having aspergers, I can get a bit literal at times, no offense meant; just trying to make sure we don't confuse the OP.