I need to dig and fill holes for 12 concrete fence posts - slotted ones to
take fence panels.

General guidance is they should be 2' deep.
Homebase 'how to' brochure suggests 1' * 1' by 2' hole for a 4" post.
This seems generally O.K. apart from the issue that if the concrete post is
on the boundary then the concrete filling will go 4" into the neighbouring
garden. Please tell me if I am barking up the wrong tree.

That would be (allowing for the 4" post in the middle) about 8" * 8" * 2' ~
..8 cubic feet of concrete per hole.
No! The hole is 2' * 1' * 1' = 2 cu ft.
The post is .33' * .33' * 2' = .2 cu ft
The remaining hole is therefore 1.8 cu ft.
[Damn - spotted this part way through.]
Mmm.. http://www.calculator.net/concrete-calculator.html does not have a
calculator for square holes with square posts within.
Tried to frig it - 2 * 3 * 0.3 should equal 1.8.
Used 2' * 3' * 4" but it rounds up to 2 cu ft (or down to 1.5 cu ft if you
go down to 3"). Damn again.
Suck it and see gets 2' * 1' * 11" to give me 1.83 cu feet
12 off it gives me 22 cu ft or 0.623 cu m.
In built (dodgy) calculator says 12 * 1.8 = 21.6 cu ft
Web converter says this is 0.648 cu m and 22 cu ft is 0.66 cu m.
Conclusion - web concrete calculator is doing rounding all over the place
and telling porkies (on a small scale).
Also, my head hurts and I need a drink.

The calculator suggests that this volume is equal to 48.4 * 60lb bags (but
of what?).
Postfix seems to come in 20kg bags (44lb bags?).

This is all rough approximation, but this suggests that you would need more
than one bag of postfix per hole (approximately 4).
[Unless, of course, the quick setting concrete doubles its dry volume when
mixed with water.]

Assuming 48 bags at £5 per bag this would be £240 for the pre mixed fast
setting stuff.
If I have under estimated the number of bags required each extra bag adds £5
to the total.

Surely I could mix 2/3 cubic metre of concrete, including hiring a mixer,
for much less than this?

http://www.benchmarkbuildingsupplies...calculator.htm gives me, for 2/3
cu metre of 1.2.4 ratio:
211kgs cement
396kgs sand
729kgs gravel

From the Travis Perkins Trademate web site:

8 * 25kg bags cement at £6.50 a bag is £52.
balast bulk bag (at least 855kg) is £62.50
mixer £11.50 for the week (HSS special offer)

This gives £126 but I am aware that I am slightly under (sand + gravel above
= 1135kg).
In fact, if the 'one ton' bag is only 855kg then I could be looking at a bag
and a half.
[Hang on - aren't the bags supposed to be one cubic metre? In which case one
bag will be fine (unless ballast shrinks by more than 1/3 when you add
cement and water). However in that case there is something screwy about the
weights from the on line calculator!]

I do note that postfix is £7.30 a bag at TP so I may achieve better prices
elsewhere, although TP were the cheapest for the concrete posts.

All this is looking like scarily large numbers!
Do I really need a full metric ton of ballast and 8 bags of cement to secure
12 concrete posts?
I nearly finished this post once then had to go through again doubling all
the quantities when I spotted my initial sizing mistake.

Has anyone else done a similar exercise of building a fence with concrete
posts who can reassure me that I am not wildly out with my calculation?

Help!

Dave R

David WE Roberts wrote:
I need to dig and fill holes for 12 concrete fence posts - slotted
ones to take fence panels.

General guidance is they should be 2' deep.
Homebase 'how to' brochure suggests 1' * 1' by 2' hole for a 4" post.
This seems generally O.K. apart from the issue that if the concrete
post is on the boundary then the concrete filling will go 4" into the
neighbouring garden. Please tell me if I am barking up the wrong tree.

Whoa there!

Far too complicated. 12 posts, do yourself a big favour & invest £20 in one
of these http://www.wickes.co.uk/Post-Hole-Digger/invt/501584 sell it on
FleaBay afterwards or hire it out to neighbours.

Nice neat round hole about 8" diameter x however deep - I'd agree on 2'.

I bag of Postcrete/Postfix per post generally, if the hole goes a bit bigger
due to lumps of rock, roots then 1.5 bags per post.

Couple of tips. Never assume fence panels are actually 1.8m wide - they
vary +/- as much as 3/4". Concrete fence posts are 'kin heavy, get them in
the right place first time - you need a helper.


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

"The Medway Handyman" wrote in message
news
David WE Roberts wrote:
I need to dig and fill holes for 12 concrete fence posts - slotted
ones to take fence panels.

General guidance is they should be 2' deep.
Homebase 'how to' brochure suggests 1' * 1' by 2' hole for a 4" post.
This seems generally O.K. apart from the issue that if the concrete
post is on the boundary then the concrete filling will go 4" into the
neighbouring garden. Please tell me if I am barking up the wrong tree.

Whoa there!

Far too complicated. 12 posts, do yourself a big favour & invest £20 in
one of these http://www.wickes.co.uk/Post-Hole-Digger/invt/501584 sell it
on FleaBay afterwards or hire it out to neighbours.

Nice neat round hole about 8" diameter x however deep - I'd agree on 2'.

I bag of Postcrete/Postfix per post generally, if the hole goes a bit
bigger due to lumps of rock, roots then 1.5 bags per post.

Couple of tips. Never assume fence panels are actually 1.8m wide - they
vary +/- as much as 3/4". Concrete fence posts are 'kin heavy, get them
in the right place first time - you need a helper.

O.K. - round holes are probably easier than square ones and I am already
eyeing up a couple of similar hole diggers.

I am a bit concerned about the amount of concrete around the post - the soil
here is quite sandy and I want this fence to be rock solid and to last for
50 years+ (working from the fence at our previous house which was still
going strong in the concrete post department after over 20 years, with just
the occasional fence panel replacement).

One of the concrete posts for our existing fence (bolt through, not slotted)
is leaning over but it seems to have 4" of concrete on one side only. This
suggests that 2" of concrete all round might do better. Question is, would
3" or 4" be even better or just overkill?
Perhaps 9" or 10" diameter holes?

I think I will have to go for regular 1.8m spacing as I need to be able to
replace fence panels as required - I think I will have to select the panels
to fit, or if not possible then pad narrow ones out with an extra strip of
wood.

Postfix is £3.99 a bag this Friday and Saturday at HomeBase if you 'bulk
buy' 4 or more bags (just read the 15% off flyer) so I may go for that.

Reduced my plan to 11 posts and a 'U' bracket for the panel which meets the
house rear wall (no space between the soil pipes for a concrete post). 20
bags of Postfix might be about right. I will also check with Travis Perkins
as they seem to do 2 sizes of bag.

I was planning to pick the posts up with one hand and toss them into the
hole, but you are probably right ;-)
Will have a test lift with my good lady and see if we can shift one together
or if I need to start waving beer tokens about.

Thanks very much for the advice.

Dave R

David WE Roberts wrote:
"The Medway Handyman" wrote in
message news
David WE Roberts wrote:
I need to dig and fill holes for 12 concrete fence posts - slotted
ones to take fence panels.

General guidance is they should be 2' deep.
Homebase 'how to' brochure suggests 1' * 1' by 2' hole for a 4"
post. This seems generally O.K. apart from the issue that if the
concrete post is on the boundary then the concrete filling will go
4" into the neighbouring garden. Please tell me if I am barking up
the wrong tree.

Whoa there!

Far too complicated. 12 posts, do yourself a big favour & invest
£20 in one of these
http://www.wickes.co.uk/Post-Hole-Digger/invt/501584 sell it on
FleaBay afterwards or hire it out to neighbours. Nice neat round hole
about 8" diameter x however deep - I'd agree on
2'. I bag of Postcrete/Postfix per post generally, if the hole goes a bit
bigger due to lumps of rock, roots then 1.5 bags per post.

Couple of tips. Never assume fence panels are actually 1.8m wide -
they vary +/- as much as 3/4". Concrete fence posts are 'kin heavy,
get them in the right place first time - you need a helper.

O.K. - round holes are probably easier than square ones and I am
already eyeing up a couple of similar hole diggers.

Well worth the money.

I am a bit concerned about the amount of concrete around the post -
the soil here is quite sandy and I want this fence to be rock solid
and to last for 50 years+ (working from the fence at our previous
house which was still going strong in the concrete post department
after over 20 years, with just the occasional fence panel
replacement).

Are you using concrete gravel boards?

One of the concrete posts for our existing fence (bolt through, not
slotted) is leaning over but it seems to have 4" of concrete on one
side only. This suggests that 2" of concrete all round might do
better. Question is, would 3" or 4" be even better or just overkill?
Perhaps 9" or 10" diameter holes?

Needs to go al round. Nothing wrong with bigger holes, you can do that with
the post hole digger.

I think I will have to go for regular 1.8m spacing as I need to be
able to replace fence panels as required - I think I will have to
select the panels to fit, or if not possible then pad narrow ones out
with an extra strip of wood.

No, what I'm saying is don't space the post at exactly 1.8m. If you space
at exactly 1.8 & have a 1.82 panel its a problem. Measure all the panels &
space for the widest one, you can then pad any narrow ones. Oh - and never
assume a panel is square.


Postfix is £3.99 a bag this Friday and Saturday at HomeBase if you
'bulk buy' 4 or more bags (just read the 15% off flyer) so I may go
for that.

Good price that.


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

"The Medway Handyman" wrote in message
m...
David WE Roberts wrote:
"The Medway Handyman" wrote in
message news
snip
Are you using concrete gravel boards?

Yes - and I was wondering last night if we would be able to get these in
after the posts had been set, or if they needed to be fitted before the next
post was concreted in.
If I go for 9' posts (to allow the 6" gravel board and 6' fence panel to sit
below the top of the post) then unless you can wiggle them in we would have
to lift this gravel board 7' in the air.
[O.K. for me at 6' tall, but perhaps not for my beautiful assistant.]
On the other hand if we lay down the gravel board before finally concreting
in the post we have the issue of getting the concrete in past the gravel
board on one side.
We could raise the gravel board a bit on bricks or wood, then lower it when
the concrete is in.
Won't really know what works until we fit the second post!
At least the gravel board will help with the spacing.

snip

I think I will have to go for regular 1.8m spacing as I need to be
able to replace fence panels as required - I think I will have to
select the panels to fit, or if not possible then pad narrow ones out
with an extra strip of wood.

No, what I'm saying is don't space the post at exactly 1.8m. If you
space at exactly 1.8 & have a 1.82 panel its a problem. Measure all the
panels & space for the widest one, you can then pad any narrow ones. Oh -
and never assume a panel is square.

I may just space for slightly over 1.8m and measure any panels we buy to
make sure we don't get any that are vastly outside spec.
If I space out too much I may end up having to pad out most panels.
In my previous place I suspect they spaced the posts to fit the original
panels as they were not consistent and the undersize panels were a b*gger to
replace.
I will need a little 'wiggle room' to allow for expansion of the wood when
wet.



snip
Dave - The Medway Handyman
www.medwayhandyman.co.uk


Thanks again for your advice.

Dave R

"David WE Roberts" wrote in message
...

"The Medway Handyman" wrote in message
m...
David WE Roberts wrote:
"The Medway Handyman" wrote in
message news
snip
Are you using concrete gravel boards?

Yes - and I was wondering last night if we would be able to get these in
after the posts had been set, or if they needed to be fitted before the
next post was concreted in.
If I go for 9' posts (to allow the 6" gravel board and 6' fence panel to
sit below the top of the post) then unless you can wiggle them in we would
have to lift this gravel board 7' in the air.
[O.K. for me at 6' tall, but perhaps not for my beautiful assistant.]
On the other hand if we lay down the gravel board before finally
concreting in the post we have the issue of getting the concrete in past
the gravel board on one side.

If you use a dry mix you can just shovel it in and poke it down with a stick
without having to worry about the gravel board being there.

You don't need concrete anyway, telegraph poles are shoved in a hole dug
with a post hole digger and then back filled without concrete (in most
cases). They don't fall over very often.

The best way under normal circumstances is to remove the minimum of material
needed to get the post in the ground as disturbed ground is what gives under
load.

(If digging holes was the best way to support something they wouldn't use
pile drivers

David WE Roberts wrote:
"The Medway Handyman" wrote in
message m...
David WE Roberts wrote:
"The Medway Handyman" wrote in
message news
snip
Are you using concrete gravel boards?

Yes - and I was wondering last night if we would be able to get these
in after the posts had been set, or if they needed to be fitted
before the next post was concreted in.

Yes.First post, gravel board, second post etc.

If I go for 9' posts (to allow the 6" gravel board and 6' fence panel
to sit below the top of the post) then unless you can wiggle them in
we would have to lift this gravel board 7' in the air.

You don't want to do that, trust me :-)

Why not go for 1' gravel boards & 5' panels? That way you can stay with 8'
posts.

[O.K. for me at 6' tall, but perhaps not for my beautiful assistant.]
On the other hand if we lay down the gravel board before finally
concreting in the post we have the issue of getting the concrete in
past the gravel board on one side.

Not a problem with Postfix/crete. You pour it in dry & then add water.

We could raise the gravel board a bit on bricks or wood, then lower
it when the concrete is in.
Won't really know what works until we fit the second post!
At least the gravel board will help with the spacing.



--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

"The Medway Handyman" wrote in message
om...
David WE Roberts wrote:
"The Medway Handyman" wrote in
message m...
David WE Roberts wrote:
"The Medway Handyman" wrote in
message news
snip
snip
Why not go for 1' gravel boards & 5' panels? That way you can stay with
8' posts.
snip

Looking to go to the full 2 metres (6' 6") fence height - so 6' panel and 6"
gravel board.