Hi All,

I'm new to this group and thought I'd post a question (probably answered before so apologies, I can't find the answer).

I've decided to have a go at replacing my old shed which presently sits on a sloping concrete base that must have been laid by a drunk! Either that or one end of the base is slowly sinking (does this happen?)

the are of the existing base is approx 16ft by 10ft and slopes by about 3 inches across the 16ft side. My old shed sits at a funny angle and the door doesn't close properly as there is a large triangular void at the top of the door.

I want to create a 16 ft x 16 ft base in it's place to build a new workshop on, I'm reasonably proficient at DIY and have used concrete before (laying patios and fencing) but have never laid a concrete base.

The area behind the shed drops down about 2.5 ft, my plan was to run a spirit line level across from the highest corner and enclose the entire area with a retaining wall using dense 440mm blocks.

I would then chuck in a bit of hardcore and compress, followed by about 6in of ready mixed concrete and level off.

My question is, would I experience any problems with the new layer of concrete being quite thin as I approach the highest corner? The thickness is likely to be only a few mm thick.

The alternative is to take out all the existing concrete and level this (within a retaining wall) followed by a layer of concrete (6in) however this is likely to be quite a bit of hard work using a sledge hammer. My project is estimated to be around £2k so I'm hesitant to bump the cost up by hiring tools if I can get by without.

Also, if I was to take the second option, is there any merit in concreting over a reinforced steel grid, Or is this unnecessary?

Any advice would be gratefully received.

Kind regards
Damian

Damian Hemsworth wrote:
Hi All,

I'm new to this group and thought I'd post a question (probably answered before so apologies, I can't find the answer).

I've decided to have a go at replacing my old shed which presently sits on a sloping concrete base that must have been laid by a drunk! Either that or one end of the base is slowly sinking (does this happen?)

the are of the existing base is approx 16ft by 10ft and slopes by about 3 inches across the 16ft side. My old shed sits at a funny angle and the door doesn't close properly as there is a large triangular void at the top of the door.

I want to create a 16 ft x 16 ft base in it's place to build a new workshop on, I'm reasonably proficient at DIY and have used concrete before (laying patios and fencing) but have never laid a concrete base.

The area behind the shed drops down about 2.5 ft, my plan was to run a spirit line level across from the highest corner and enclose the entire area with a retaining wall using dense 440mm blocks.

I would then chuck in a bit of hardcore and compress, followed by about 6in of ready mixed concrete and level off.

My question is, would I experience any problems with the new layer of concrete being quite thin as I approach the highest corner? The thickness is likely to be only a few mm thick.

The alternative is to take out all the existing concrete and level this (within a retaining wall) followed by a layer of concrete (6in) however this is likely to be quite a bit of hard work using a sledge hammer. My project is estimated to be around £2k so I'm hesitant to bump the cost up by hiring tools if I can get by without.

Also, if I was to take the second option, is there any merit in concreting over a reinforced steel grid, Or is this unnecessary?

Any advice would be gratefully received.

Kind regards
Damian

First find out if the current base is moving either as a complete item
ie no cracks or just in a few places as indicated by cracks. No good
building over a shifting foundation.
Yes this can happen if for example under ground water flow (eg broken
drain) is washing away under the slab.

Assume all is sound or you have to dig it up in order to be sound, then
thin areas wont work. I'd say minimum 50mm extra at your highest point.
Maybe just remove a small amount of existing concrete in the upper corner.
Make up a cement and water slurry and put this down immediately prior to
pouring the concrete to get the best bond where it is likely to be a
thin layer.
Make sure the shed is raised off the new concrete to allow air flow all
around and under.
Standing the shed on concrete lintels is a lowish cost way of getting
bearers that won't rot or wick up and water. Put as much preservative on
the underside of the shed as it will take. "full lead" creosote is good
and still available if you look for it - Bird Brand in one good one.
Soak the shed in creosote too as much as it will take and then some
more. The smell soon goes and it will extend the life no end.

"Damian Hemsworth" wrote in message
...

Hi All,

I'm new to this group and thought I'd post a question (probably answered
before so apologies, I can't find the answer).

I've decided to have a go at replacing my old shed which presently sits on
a sloping concrete base that must have been laid by a drunk! Either that or
one end of the base is slowly sinking (does this happen?)

the are of the existing base is approx 16ft by 10ft and slopes by about 3
inches across the 16ft side. My old shed sits at a funny angle and the door
doesn't close properly as there is a large triangular void at the top of
the door.

I want to create a 16 ft x 16 ft base in it's place to build a new workshop
on, I'm reasonably proficient at DIY and have used concrete before (laying
patios and fencing) but have never laid a concrete base.

The area behind the shed drops down about 2.5 ft, my plan was to run a
spirit line level across from the highest corner and enclose the entire
area with a retaining wall using dense 440mm blocks.

I would then chuck in a bit of hardcore and compress, followed by about 6in
of ready mixed concrete and level off.

My question is, would I experience any problems with the new layer of
concrete being quite thin as I approach the highest corner? The thickness
is likely to be only a few mm thick.

The alternative is to take out all the existing concrete and level this
(within a retaining wall) followed by a layer of concrete (6in) however
this is likely to be quite a bit of hard work using a sledge hammer. My
project is estimated to be around £2k so I'm hesitant to bump the cost up
by hiring tools if I can get by without.

Also, if I was to take the second option, is there any merit in concreting
over a reinforced steel grid, Or is this unnecessary?

Any advice would be gratefully received.

Kind regards
Damian

Undermine the slab in one or two places to see what it's resting on.

If it has top soil under it, break up the slab, move rubble to one side,
excavate to sub-sol, make up back to level with the rubble and possibly
more, blind with sharp sand, lay a waterproof membrane and pour a new 100 mm
slab over it.

If the top soil has already been removed and it's on hard-core, just break
up the slab, blind with sharp sand, lay a waterproof membrane and pour a
new 100 mm slab.

Re-inforce the slab in either case with A142 mesh. Sound like your site
slopes. make sure that the slab is higher than the higher ground level to
stop water entering the new shed.

Andrew

On 25/06/15 11:20, Damian Hemsworth wrote:
Hi All,

I'm new to this group and thought I'd post a question (probably answered before so apologies, I can't find the answer).

I've decided to have a go at replacing my old shed which presently sits on a sloping concrete base that must have been laid by a drunk! Either that or one end of the base is slowly sinking (does this happen?)

the are of the existing base is approx 16ft by 10ft and slopes by about 3 inches across the 16ft side. My old shed sits at a funny angle and the door doesn't close properly as there is a large triangular void at the top of the door.

I want to create a 16 ft x 16 ft base in it's place to build a new workshop on, I'm reasonably proficient at DIY and have used concrete before (laying patios and fencing) but have never laid a concrete base.

The area behind the shed drops down about 2.5 ft, my plan was to run a spirit line level across from the highest corner and enclose the entire area with a retaining wall using dense 440mm blocks.

I would then chuck in a bit of hardcore and compress, followed by about 6in of ready mixed concrete and level off.

My question is, would I experience any problems with the new layer of concrete being quite thin as I approach the highest corner? The thickness is likely to be only a few mm thick.

The alternative is to take out all the existing concrete and level this (within a retaining wall) followed by a layer of concrete (6in) however this is likely to be quite a bit of hard work using a sledge hammer. My project is estimated to be around £2k so I'm hesitant to bump the cost up by hiring tools if I can get by without.

Also, if I was to take the second option, is there any merit in concreting over a reinforced steel grid, Or is this unnecessary?

Any advice would be gratefully received.

Kind regards
Damian


That much concrete is hard work.

Why not build an extra load wall 6ft off the end of the concrete, then:

Make a floor of 4x2" decking timber, using packing plates under them to
where the concrete is low (either metal shims or Wallbarn adjustable
pinths - very good these, I used them).

Floor that with 18mm ply (and maybe some celotex).

Build floorless shed onto that.


OK - your floor will be 5-6" high but it will save a lot of work. 4x2"
joists should span the 5.5ft gap between the end of the concrete and the
wall without much fuss.

Just an idea....

On Thursday, 25 June 2015 11:20:16 UTC+1, Damian Hemsworth wrote:
Hi All,

I'm new to this group and thought I'd post a question (probably answered before so apologies, I can't find the answer).

I've decided to have a go at replacing my old shed which presently sits on a sloping concrete base that must have been laid by a drunk! Either that or one end of the base is slowly sinking (does this happen?)

the are of the existing base is approx 16ft by 10ft and slopes by about 3 inches across the 16ft side. My old shed sits at a funny angle and the door doesn't close properly as there is a large triangular void at the top of the door.

I want to create a 16 ft x 16 ft base in it's place to build a new workshop on, I'm reasonably proficient at DIY and have used concrete before (laying patios and fencing) but have never laid a concrete base.

The area behind the shed drops down about 2.5 ft, my plan was to run a spirit line level across from the highest corner and enclose the entire area with a retaining wall using dense 440mm blocks.

I would then chuck in a bit of hardcore and compress, followed by about 6in of ready mixed concrete and level off.

My question is, would I experience any problems with the new layer of concrete being quite thin as I approach the highest corner? The thickness is likely to be only a few mm thick.

The alternative is to take out all the existing concrete and level this (within a retaining wall) followed by a layer of concrete (6in) however this is likely to be quite a bit of hard work using a sledge hammer. My project is estimated to be around £2k so I'm hesitant to bump the cost up by hiring tools if I can get by without.

Also, if I was to take the second option, is there any merit in concreting over a reinforced steel grid, Or is this unnecessary?

Any advice would be gratefully received.

Kind regards
Damian

If your old slab is subsiding it will most likely continue to subside, and likely break up. Either you can build on it using adjustable supports, or need to remove it and redo, digging further down this time.

No way is an inch thick concrete going to survive, even on top of the old slab.

If you want it to last long term the only real option is to remove the slab & go down further this time. You could avoid that work with a bodge job, but that's what it will be, who knows how long it'll survive for.

Wooden bases of course avoid all the hard work, but they always rot away. One other possibility is concrete piers. Dig deepish holes, fill with concrete and build from those, avoiding using the old slab for support.


NT

No way is an inch thick concrete going to survive, even on top of the
old slab.


I have proved to my own satisfaction with various projects that this is
fundamentally untrue. Such advice pre-dates SBR (and probably even PVA).

All I will say is that it might be wise to break up the base at the end
where at the moment you would end up with just a skim of concrete. In my
experience, such thin amounts get water in the join and with no real
strength or weight there, it just crumbles away down to the old concrete.
If you break it up on the thin end then I'd say this would work.


Brian

--
From the Sofa of Brian Gaff Reply address is active
"Damian Hemsworth" wrote in message
...
Hi All,

I'm new to this group and thought I'd post a question (probably answered
before so apologies, I can't find the answer).

I've decided to have a go at replacing my old shed which presently sits on a
sloping concrete base that must have been laid by a drunk! Either that or
one end of the base is slowly sinking (does this happen?)

the are of the existing base is approx 16ft by 10ft and slopes by about 3
inches across the 16ft side. My old shed sits at a funny angle and the door
doesn't close properly as there is a large triangular void at the top of the
door.

I want to create a 16 ft x 16 ft base in it's place to build a new workshop
on, I'm reasonably proficient at DIY and have used concrete before (laying
patios and fencing) but have never laid a concrete base.

The area behind the shed drops down about 2.5 ft, my plan was to run a
spirit line level across from the highest corner and enclose the entire area
with a retaining wall using dense 440mm blocks.

I would then chuck in a bit of hardcore and compress, followed by about 6in
of ready mixed concrete and level off.

My question is, would I experience any problems with the new layer of
concrete being quite thin as I approach the highest corner? The thickness is
likely to be only a few mm thick.

The alternative is to take out all the existing concrete and level this
(within a retaining wall) followed by a layer of concrete (6in) however this
is likely to be quite a bit of hard work using a sledge hammer. My project
is estimated to be around £2k so I'm hesitant to bump the cost up by hiring
tools if I can get by without.

Also, if I was to take the second option, is there any merit in concreting
over a reinforced steel grid, Or is this unnecessary?

Any advice would be gratefully received.

Kind regards
Damian

On Thursday, 25 June 2015 15:41:39 UTC+1, stuart noble wrote:
No way is an inch thick concrete going to survive, even on top of the
old slab.


I have proved to my own satisfaction with various projects that this is
fundamentally untrue. Such advice pre-dates SBR (and probably even PVA).

the op's going down to a few mm! Can you get that to work?


NT

On 25/06/2015 19:43, wrote:
On Thursday, 25 June 2015 15:41:39 UTC+1, stuart noble wrote:
No way is an inch thick concrete going to survive, even on top of the
old slab.


I have proved to my own satisfaction with various projects that this is
fundamentally untrue. Such advice pre-dates SBR (and probably even PVA).

the op's going down to a few mm! Can you get that to work?


NT


You can feather an SBR screed down to nothing. You may have to use
plasterers sand at the thin end but concrete should be ok at 25mm

On 25/06/15 19:43, wrote:
On Thursday, 25 June 2015 15:41:39 UTC+1, stuart noble wrote:
No way is an inch thick concrete going to survive, even on top of the
old slab.


I have proved to my own satisfaction with various projects that this is
fundamentally untrue. Such advice pre-dates SBR (and probably even PVA).

the op's going down to a few mm! Can you get that to work?


NT


Unless he puts a thick layer at the thin and and an even thicker layer
at the other?