Reinforcing in concrete slab raft?
David WE Roberts
As usual, every time I think I have something sorted someone else throws up
questions.
I am (weather permitting) soon to be laying a concrete raft 7.8m * 3.5m
100mm deep with 200mm depth around the edge to form footings for a single
block single storey wall.
I was going to lay it just as a concrete slab, as the interior will not have
much weight on it (unlike a garage floor).
One of the Builders Merchants suggested that a slab that big should really
have some reinforcement.
O.K. - 4 sheets of reinforcing mesh @ �16 a pop (+VAT) isn't a massive extra
cost but is it necessary?
The sheet in stock (Travis Perkins and Jewsons) is "Steel Fabric A142M 3.6m
* 2.0m".
The steel used looks pretty puny - not like the reinforcing steel we used
when I was a lad when the wire was as thick as a pencil.
Will a single layer of this stuff make a massive difference to the
structural strength of a raft?
Is 100mm thick enough (judging by the small floor from a previous shed I had
to break up, this thickness can be pretty tough).
TIA
Dave R
Harry Bloomfield
> Workshop question again:
>
> As usual, every time I think I have something sorted someone else throws up
> questions.
>
> I am (weather permitting) soon to be laying a concrete raft 7.8m * 3.5m 100mm
> deep with 200mm depth around the edge to form footings for a single block
> single storey wall.
>
> I was going to lay it just as a concrete slab, as the interior will not have
> much weight on it (unlike a garage floor).
>
> One of the Builders Merchants suggested that a slab that big should really
> have some reinforcement.
>
>
> The sheet in stock (Travis Perkins and Jewsons) is "Steel Fabric A142M 3.6m *
> 2.0m".
>
> The steel used looks pretty puny - not like the reinforcing steel we used
> when I was a lad when the wire was as thick as a pencil.
> Will a single layer of this stuff make a massive difference to the structural
> strength of a raft?
>
> Is 100mm thick enough (judging by the small floor from a previous shed I had
> to break up, this thickness can be pretty tough).
I would suggest 4" might be a bit thin, for that area, but it depends
on the sub soil. Yes rebar will make a lot of difference, but I would
suggest not that much if only 2mm thick. I would suggest 3/8".
--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk
Archie
"David WE Roberts" <nos...@talk21.com> wrote in message
news:7rjh5j...@mid.individual.net...
Another question. Have you considered putting in insulation under the raft
to help keep your feet warm?
David WE Roberts
"Archie" <Arc...@nospam.com> wrote in message
news:Dl05n.43161$9A6....@newsfe07.ams2...
Not for an unheated workshop/store at the bottom of the garden.
If I decide to have a 'person friendly' area later I can always add
insulation above the floor.
TMC
Would the panel recommend a dpm?
regards
Tony
Tim Watts
> Would the panel recommend a dpm?
>
> regards
>
> Tony
Yes (we me anyway).
Pros: the floor stays dry reducing the rust potential to your stored
items.
Tiny Cons: The price of a bit of heavy guage plastic DPM and a bit of
(10mm) blinding sand over the ground or hardcore to prevent the DPM
getting ripped to bits while you pour the concrete.
Big cons: None.
My inclination would be to size the pad such that the pad is a little
higher than the ground and that the shed wall cladding can be hung over
the side slightly - this will prevent ground runoff rainwater from
getting into the shed. At least don't make the pad vastly too big and
flat at the same time.
--
Tim Watts
Managers, politicians and environmentalists: Nature's carbon buffer.
David WE Roberts
"Tim Watts" <t...@dionic.net> wrote in message
news:hj25g5$a20$1...@news.eternal-september.org...
> On Mon, 18 Jan 2010 17:11:57 +0000, "TMC" <an...@nowhere.co.uk> wibbled:
>
>> Would the panel recommend a dpm?
>>
>> regards
>>
>> Tony
>
> Yes (we me anyway).
>
> Pros: the floor stays dry reducing the rust potential to your stored
> items.
>
> Tiny Cons: The price of a bit of heavy guage plastic DPM and a bit of
> (10mm) blinding sand over the ground or hardcore to prevent the DPM
> getting ripped to bits while you pour the concrete.
>
> Big cons: None.
>
> My inclination would be to size the pad such that the pad is a little
> higher than the ground and that the shed wall cladding can be hung over
> the side slightly - this will prevent ground runoff rainwater from
> getting into the shed. At least don't make the pad vastly too big and
> flat at the same time.
Sorry - full story to be found in previous posts.
Plan is to put down 100mm MOT, blinding sand if required and a DPM before
laying the concrete raft.
Also intended to match the concrete block wall to the edge of the raft to
hopefully avoid a lip which chucks water under the wall.
No external cladding planned - ATM it is just dense concrete block which
will be pointed and painted. DPM layer in the block wall to reduce rising
damp.
Did consider rendering but again ATM can't be arsed.
Sloping metal roof (will be insulated between rafters)
Inside of walls lined at some point with insulation and board (I have a
saved previous post from Andy Dingley about dry lining a shed).
I have a wood burning stove and may install it at some point for occasional
heating.
Designed to be under 30sqm internal floor area and of mainly inflammable
materials to avoid involvement with planning and building regs.
I had to suspend work just before Christmas when the weather went bad.
Tim Watts
wibbled:
> "Tim Watts" <t...@dionic.net> wrote in message
> news:hj25g5$a20$1...@news.eternal-september.org...
>> On Mon, 18 Jan 2010 17:11:57 +0000, "TMC" <an...@nowhere.co.uk> wibbled:
>>
>>> Would the panel recommend a dpm?
>>>
>>> regards
>>>
>>> Tony
>>
>> Yes (we me anyway).
>>
>> Pros: the floor stays dry reducing the rust potential to your stored
>> items.
>>
>> Tiny Cons: The price of a bit of heavy guage plastic DPM and a bit of
>> (10mm) blinding sand over the ground or hardcore to prevent the DPM
>> getting ripped to bits while you pour the concrete.
>>
>> Big cons: None.
>>
>> My inclination would be to size the pad such that the pad is a little
>> higher than the ground and that the shed wall cladding can be hung over
>> the side slightly - this will prevent ground runoff rainwater from
>> getting into the shed. At least don't make the pad vastly too big and
>> flat at the same time.
>
>
> Sorry - full story to be found in previous posts.
>
Sorry - didn't check.
> Plan is to put down 100mm MOT, blinding sand if required and a DPM
> before laying the concrete raft.
> Also intended to match the concrete block wall to the edge of the raft
> to hopefully avoid a lip which chucks water under the wall. No external
> cladding planned - ATM it is just dense concrete block which will be
> pointed and painted.
Sounds excellent :) Good luck.
> DPM layer in the block wall to reduce rising damp.
> Did consider rendering but again ATM can't be arsed. Sloping metal roof
> (will be insulated between rafters) Inside of walls lined at some point
> with insulation and board (I have a saved previous post from Andy
> Dingley about dry lining a shed). I have a wood burning stove and may
> install it at some point for occasional heating.
>
> Designed to be under 30sqm internal floor area and of mainly inflammable
> materials to avoid involvement with planning and building regs.
>
> I had to suspend work just before Christmas when the weather went bad.
Cool. Piccies please (even if it's not all done!) :)
David WE Roberts
> Cool. Piccies please (even if it's not all done!) :)
You into mud, then?
That's all there is at the moment.
I will try and record progress as I go along and post the pictures. :-)
Steve Walker
And just a general question while everyone is talking about slabs - the
usual construction for conservatories appears to be MOT, sand, DPM,
insulation, concrete, screed. Now when they widened the motorway around
here, they actually built it on polystyrene blocks to spread the load and I
have since read that it can be used under slabs, straight on the ground,
with no MOT or sand, so why is this construction never mentioned?
SteveW
js.b1
- Services pipe (hockey stick is ok)
- Design so any future cladding overhangs to avoids splashback/runback
- Price out glass fibre flakes v rebar, any rebar is better than none
- Insulation on the inside re ceiling, walls & floor
When you put insulation on the outside (above the ceiling, outside the
walls under cladding, below the concrete raft) you are creating a
thermal mass. That works fine IF you have sufficient kW inside
continually to actually heat that thermal mass up (which by tonnage of
blocks takes quite some time).
When you put insulation on the inside of floors, ceiling & walls you
have minimal thermal mass (open the door and the heat is gone), but it
takes seconds to get warm and re-heat so warm again. For any
occasionally heated room that is ideal.
A dehumidifier might actually give enough background heating and keep
things dry. X-Dry are a silica gel based device which will outperform
conventional units at low temperatures and provides heating. Stick on
an energy meter for a year if you want to balance dryness v heating.
David WE Roberts
"Steve Walker" <st...@theend.demon.co.uk> wrote in message
news:1otcke24hp15m.1...@40tude.net...
<snip>
>> Another question. Have you considered putting in insulation under the
>> raft
>> to help keep your feet warm?
>
> And just a general question while everyone is talking about slabs - the
> usual construction for conservatories appears to be MOT, sand, DPM,
> insulation, concrete, screed. Now when they widened the motorway around
> here, they actually built it on polystyrene blocks to spread the load and
> I
> have since read that it can be used under slabs, straight on the ground,
> with no MOT or sand, so why is this construction never mentioned?
>
> SteveW
Do you have any references for this?
Obviously of interest.
js.b1
> > built it on polystyrene blocks to spread the load
Spread the load...
I wonder if that is to change the impact profile from heavy goods.
Essentially change the short duration high peak impulse into a long
duration low peak impulse?
Tony Bryer
> The sheet in stock (Travis Perkins and Jewsons) is "Steel Fabric
> A142M 3.6m * 2.0m".
>
> The steel used looks pretty puny - not like the reinforcing steel
> we used when I was a lad when the wire was as thick as a pencil.
> Will a single layer of this stuff make a massive difference to the
> structural strength of a raft?
A142 is 142mm2 of steel per m width. As you surmise, it won't add a
huge amount of strength to the slab. What it does do in slabs is to
distribute concentrated loads (e.g. wheel loads in car parks) and
may stop cracking.
If you do incorporate it, be sure to space it so that there is 50mm
concrete cover. If less, it may rust and that will cause problems.
--
Tony Bryer, Greentram: 'Software to build on' Melbourne, Australia
www.superbeam.co.uk www.superbeam.com www.greentram.com
Les Desser
<nos...@talk21.com> Mon, 18 Jan 2010 16:39:15 writes
>I am (weather permitting) soon to be laying a concrete raft 7.8m * 3.5m
>100mm deep with 200mm depth around the edge to form footings for a
>single block single storey wall.
>
>I was going to lay it just as a concrete slab, as the interior will not
>have much weight on it (unlike a garage floor).
>
>One of the Builders Merchants suggested that a slab that big should
>really have some reinforcement.
You refer to it as a "raft" while you then talk about "footings".
As I understand it, a raft is there to spread the edge loads over the
whole area.
If there is no reinforcement then there is no raft. The weight of the
walls on the outside edge will just crack the "footings" off the rest.
The purpose of the steel is to stop the concrete cracking under tension.
In this case the steel would have to be laid near the top rather than
the middle or the bottom of the concrete. It may also need to be turned
down round the edges.
I have been involved in two raft structures so know the principles
involved, but have no idea as to the maths involved.
--
Les Desser
(The Reply-to address IS valid)
The Medway Handyman
> Workshop question again:
>
> As usual, every time I think I have something sorted someone else
> throws up questions.
>
> I am (weather permitting) soon to be laying a concrete raft 7.8m *
> 3.5m 100mm deep with 200mm depth around the edge to form footings for
> a single block single storey wall.
>
> I was going to lay it just as a concrete slab, as the interior will
> not have much weight on it (unlike a garage floor).
>
> One of the Builders Merchants suggested that a slab that big should
> really have some reinforcement.
Only experience I have is the damage to concrete at the bottom of a set of
stairs leading to a beer cellar. Kegs of beer seem to 'miss' the big rubber
mat & have hit the slabs at the bottom.
First attempt to make good was a concrete paving slab, destroyed on first
subsequent impact.
Second attempt was to use 'heavy duty' concrete mix. Lasted nearly 3 weeks.
Keg of Fosters destroyed it.
Final solution - same mix with 6mm ish rebar. Seems completely
indestructible after 4 months & numerous impacts.
I don't know what this proves exactly, but rebar seems to add an incredible
amount of strength to concrete.
--
Dave - The Medway Handyman
www.medwayhandyman.co.uk
The Natural Philosopher
> David WE Roberts was thinking very hard :
>> Workshop question again:
>>
>> As usual, every time I think I have something sorted someone else
>> throws up questions.
>>
>> I am (weather permitting) soon to be laying a concrete raft 7.8m *
>> 3.5m 100mm deep with 200mm depth around the edge to form footings for
>> a single block single storey wall.
>>
>> I was going to lay it just as a concrete slab, as the interior will
>> not have much weight on it (unlike a garage floor).
>>
>> One of the Builders Merchants suggested that a slab that big should
>> really have some reinforcement.
>>
>>
>> The sheet in stock (Travis Perkins and Jewsons) is "Steel Fabric A142M
>> 3.6m * 2.0m".
>>
>> The steel used looks pretty puny - not like the reinforcing steel we
>> used when I was a lad when the wire was as thick as a pencil.
>> Will a single layer of this stuff make a massive difference to the
>> structural strength of a raft?
>>
>> Is 100mm thick enough (judging by the small floor from a previous shed
>> I had to break up, this thickness can be pretty tough).
>
> I would suggest 4" might be a bit thin, for that area, but it depends on
> the sub soil. Yes rebar will make a lot of difference, but I would
> suggest not that much if only 2mm thick. I would suggest 3/8".
>
Anothther thing worth doing - remember if its clay, it will eventually
dry out a bit under the floor and subside -- is to put plenty of
hardcore and possibly high density polystyrene down as insulation under
it, that will take a bit of movement.
They don't call em concrete rafts for nowt, you know.
The aim is to have a solid base which may settle a bit, but wont twist
or crack.
The Natural Philosopher
> regards
>
> Tony
>
David WE Roberts
"Les Desser" <News...@dessergroup.com> wrote in message
news:gt4zCQXN...@dessergr0up.invalid...
From my reading so far there are 'raft foundations' which are for use on
very poor ground where as you say the point load of a wall or column is
spread over a large area and reinforcement is used to ensure that the load
is spread without trying to bend the raft like a banana.
Here the anticipated load is not large and the ground is reasonably good, so
'raft foundations' would not be called for.
I use the term 'raft' for a concrete floor which is deeper round the edge to
provide extra support directly under the walls.
My intention is to pour in one piece, instead of pouring footings below
ground, building up the base of the wall, then pouring a floor slab in the
centre (as is the general practice for larger/spankier/habitable buildings).
I an not expecting the raft to be needed to support the walls - it is
'footings and floor' all poured in one go as a simple solution to a
shed/workshop base.
Cheers
Dave R
Dave Osborne
>
> From my reading so far there are 'raft foundations' which are for use
> on very poor ground where as you say the point load of a wall or column
> is spread over a large area and reinforcement is used to ensure that the
> load is spread without trying to bend the raft like a banana.
>
> Here the anticipated load is not large and the ground is reasonably
> good, so 'raft foundations' would not be called for.
>
> I use the term 'raft' for a concrete floor which is deeper round the
> edge to provide extra support directly under the walls.
With respect, you are getting your ideas slightly confused.
Firstly, be careful about thinking of primary cast in place concrete as
a floor. In many cases its primary purpose is not to *be* a floor at all
and the fact that it is flat and level is a happy coincidence.
Secondly, almost any form of "foundation" you use (other than a simple
slab for a wooden shed) is going to be deeper round the edges than it is
in the centre, so using the term "raft" for this idea is inappropriate
as well as incorrect.
A raft is a foundation which is designed so that the loading of the
building is spread over a large area. The deeper edges (aka lip, apron
or keel) act in two ways. Firstly, they provide additional structural
strength where the main loading is (i.e. the external walls are built on
the edges), but secondly they provide a lip which stops the raft from
sliding over the underlying ground (sliding as in slipping, as in the
whole building moves without collapsing, possibly as a result of a minor
landslide or mining subsidence).
I am not a civil or structural engineer, but I would have thought that a
raft foundation is almost always going to be reinforced with steel mesh
sheets. It is also likely that there may be a requirement for rebar in
the apron as well, depending on whether the apron is contributing to the
structural integrity or not.
> I an not expecting the raft to be needed to support the walls - it is
> 'footings and floor' all poured in one go as a simple solution to a
> shed/workshop base.
>
As far as I am aware, normally, if you had strip foundations and then
in-filled the enclosed area to make a "floor", you would make make the
infill out of weaker concrete than the foundations, so that any movement
in the infill would not affect the integrity of the foundations. So
effectively, if you do decide to cast foundations and infill at the same
time, then you will be building a de facto raft which will need to be
reinforced to ensure its own structural integrity.
Finally, as Tony Bryer said, you need 50mm cover all round for
reinforcing mesh to prevent corrosion of the steel.
I recommend you read this website:
particularly these pages:
http://www.pavingexpert.com/concrete.htm
and
Tim Watts
wibbled:
> Workshop question again:
Might be worth standing back a bit now. Lots of replies about major
structural rafts etc.
How heavy is this all likely to be? Will the wall blocks be lightweight
(eg celcon) or concrete? What's the roof - timber+felt or tiled or metal?
At one extreme, if it were a wooden "shed", you could quite frankly stand
it on paving slabs laid on a bit of sand onto well compacted earth and
it's unlikely to go anywhere. And if it did, the timber wouldn't care
that much within limits.
At the other extreme, if there is a lot of load on the walls and the
ground is crap and liable to move or wash away, you could go for a trench
of concrete for the wall base and a separate floating floor slab.
It sounds like looking at conservatory build guides might be useful, and
cut the floor slab down a notch or two. The size and load of the walls
are likely to be in a similar range and it is the walls you want to
ensure integrity. The floor cracking a bit over time will not be as
serious if you under engineer it, compared to walls going.
David WE Roberts
> How heavy is this all likely to be? Will the wall blocks be lightweight
> (eg celcon) or concrete? What's the roof - timber+felt or tiled or metal?
Mostly answered already near the top of the thread.
Heavy concrete block - for painting. Not the rice crispies version for
rendering. Unless this makes a major difference to the requirements for the
base.
Metal roof, on rafters, insulation between rafters.
The ground is good - nice and flat and not clay.
My build seems to be in something of a gap between different standard
solutions.
It is not a wooden shed on a simple flat concrete base.
It is closer to a garage, but doesn't need the extra strength in the floor
to support a heavy vehicle moving in and out on a regular basis.
The design shown at http://www.pavingexpert.com/images/concrete/xs150gb.gif
for a keeled raft slab seems a little over the top - a big leap forward from
a simple slab.
http://www.pavingexpert.com does not give me a definitive answer. It shows a
simple slab for a prefabricated concrete garage (less strength than I am
aiming for) or the picture above for a brick built garage (more strength
than I am aiming for).
My current feeling is that it might be sensible to add a layer of
reinforcing sheet because the extra cost is not massive.
It would sit in the middle of the 100mm slab - 50mm above and below. All I
need to locate now is a supply of 50mm spacers.
I don't feel inclined to add the T20 bars as well.
I am going to ring Building Control for advice - although I will not need
approval the regulations are usually sensible.
Cheers
Dave R
John Rumm
> One of the Builders Merchants suggested that a slab that big should
> really have some reinforcement.
>
> O.K. - 4 sheets of reinforcing mesh @ �16 a pop (+VAT) isn't a massive
> extra cost but is it necessary?
>
> The sheet in stock (Travis Perkins and Jewsons) is "Steel Fabric A142M
> 3.6m * 2.0m".
Reading:
http://www.pavingexpert.com/reinfrc1.htm
it says: "A142 mesh is often used in 100mm thick light-use slabs such as
paths, driveways and garage bases"
So that seems to be ideal for this application.
> The steel used looks pretty puny - not like the reinforcing steel we
> used when I was a lad when the wire was as thick as a pencil.
> Will a single layer of this stuff make a massive difference to the
> structural strength of a raft?
yup.
> Is 100mm thick enough (judging by the small floor from a previous shed I
> had to break up, this thickness can be pretty tough).
Sounds ok.
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/
Steve Walker
I've checked into it and according to Vencel's (Jablite's) website: "Heavy
structures, such as road embankments, can impose unacceptably high loading
on the underlying soils. Lightweight Fillmaster blocks reduce the pressure
on soils."
I was already pretty sure this was the case, as I seemed to remember that
when the M60 was widened, the local papers referred to the construction
method being one that is regularly used in Norway for constructing roads
over poor ground.
SteveW
Steve Walker
I can't find the original reference (I will try again), but I have found
reference on Vencel's (Jablite's) website of using it for "hardcore
replacement," where they show it still being placed on sand and a DPM, but
without any other preparation.
I'm actually looking at options for a conservatory base at the moment as it
happens and I've been considering whether to dig out properly or to use a
DPM and Jablite (possibly with sand) directly over the existing patio -
it's been there for decades and isn't really expected to move now. Two of
the three dwarf walls would be positioned just off the existing flags and
the third just means lifting a row to dig its foundation. I'll probably do
it properly, though, even if it means digging out the area to avoid raising
it too high.
SteveW
tony sayer
thus
>On 19 Jan,
>
>> I've checked into it and according to Vencel's (Jablite's) website: "Heavy
>> structures, such as road embankments, can impose unacceptably high loading
>> on the underlying soils. Lightweight Fillmaster blocks reduce the pressure
>> on soils."
>>
>> I was already pretty sure this was the case, as I seemed to remember that
>> when the M60 was widened, the local papers referred to the construction
>> method being one that is regularly used in Norway for constructing roads
>> over poor ground.
>>
>in use) has woolen bales as foundations, presumably for similar reasons (clay
>soil).
>
Wasn't the railway line across chat moss near Manchester done the same
sort of way?...
--
Tony Sayer
Neil
>> structures, such as road embankments, can impose unacceptably high loading
>> on the underlying soils. Lightweight Fillmaster blocks reduce the pressure
>> on soils."
>>
>> I was already pretty sure this was the case, as I seemed to remember that
>> when the M60 was widened, the local papers referred to the construction
>> method being one that is regularly used in Norway for constructing roads
>> over poor ground.
>>
> in use) has woolen bales as foundations, presumably for similar reasons (clay
> soil).
>
Leasowe Lighthouse in/on the Wirral is supposedly built on bales of
cotton, based on the same principle - shame a ship had to founder and
sink to give the foundations mind you... No details on a quick Google
but it isn't the sort of thing you can mis-remember from school is it?
Les Desser
Handyman <davi...@no-spam-blueyonder.co.uk> Tue, 19 Jan 2010 00:26:01
writes
>Final solution - same mix with 6mm ish rebar. Seems completely
>indestructible after 4 months & numerous impacts.
>
>I don't know what this proves exactly, but rebar seems to add an
>incredible amount of strength to concrete.
Concrete is *very* weak under tension.
Any concrete is going to be subject to tension forces must be
reinforced.
When a heavy weight hits the concrete with enough force to deform it,
the opposite face is subject to tension and will very easily crack.
Do it a few more times and ...
Les Desser
<nos...@talk21.com> Tue, 19 Jan 2010 16:55:54 writes
>My current feeling is that it might be sensible to add a layer of
>reinforcing sheet because the extra cost is not massive.
>It would sit in the middle of the 100mm slab - 50mm above and below.
From my limited experience in these matters I would say that is the
worst place to put it. It will add very little to the strength of the
slap, other than to keep it together in the event of it cracking.
The reinforcement has to go in the part of the concrete that is subject
to expansion forces. So on a slap that is supporting walls, the steel
has to go in the upper half.
Dave Osborne
Except that conventional wisdom says that you need 50mm cover all round
to prevent the steel corroding. So the only place to put it in a 100mm
slab is in the middle...
js.b1
helped Haiti.
House built on a hillside of clay & numerous springs, concrete raft
with extensive rebar tubes in the keel & mesh across. The land behind
rises appreciably, so there is a degree of frost-heave at play. In the
worst 1980s winter the frost heave would lift 3x2 paving like an
earthquake fault pattern, jamming a garage door which normally had
0.75in clearance. In the recent winter the second night we hit -13oC
the frost heave actually creased the L-angle above the garage door
(the door is 250lbs T&G wood) and tore upwards a heavyweight bolt
striker like foil. 2009 had saturated the ground quite effectively.
On both occasions (1984? 2009) around 1am the big 11m steel beam which
spans the rear rang like a bell and simultaneously the ground floor
juddered. I suspect frost heave causes it to shunt slightly, a
neighbours garage floor which was just poured without rebar cracked &
shifted from frost heave this winter leaving a raised section. The
strip foundations did have rebar and were unaffected (indeed probably
interacted with the floor.
Hit a thin paving slab, the reverse is in tension and thus breaks.
Rebar makes all the difference.
If you are doing a conservatory, worth designing in a heat pump (B&Q
Airforce to Ebay) - you can use it to cool in summer, but also heat in
winter very effectively. Ideal for when the conservatory becomes a
utility room :-)
The Natural Philosopher
Les Desser
<Dave...@SPAMymail.com> Thu, 21 Jan 2010 00:20:58 writes
>> The reinforcement has to go in the part of the concrete that is
>>subject to expansion forces. So on a slap that is supporting walls,
>>the steel has to go in the upper half.
>
Sorry - correction: read "tension" in place of "expansion" above.
>Except that conventional wisdom says that you need 50mm cover all round
>to prevent the steel corroding. So the only place to put it in a 100mm
>slab is in the middle...
1. Then it has to be made thicker - if the steel has to go in the bottom
half
2. In this case I think it needs to go into the top half where there
should be no water penetration.
Harry Bloomfield
> Wasn't the railway line across chat moss near Manchester done the same
> sort of way?...
Yes, I remember something of the sort.
--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk
Grimly Curmudgeon
drugs began to take hold. I remember tony sayer <to...@bancom.co.uk>
saying something like:
>>It is reputed that the local railway viaduct (constructed 1849-51 and still
>>in use) has woolen bales as foundations, presumably for similar reasons (clay
>>soil).
>>
>Wasn't the railway line across chat moss near Manchester done the same
>sort of way?...
It's been done in many places - long before the railway came, too.
Appin
from Grimly Curmudgeon <grimly...@REMOVEgmail.com> contains these words:
The idea of the woollen bales was to let the embankment consolidate and
knit together. The wool would eventually rot, but by that time the
embankment would be knitted together enough to distrbute the load.
Bishop weed and similar plants were planted on embankments to start the
binding process.