Hello,

Last Friday I mixed up some concrete. Each mix was about 1/3 bag cement
(35k bags) with aggregate and water with a splash of washing up liquid.
All seemed well, but the last load was well into darkness so I was
working by security light with lots of shadow.

The final load was the top inch or three of the footings, so I levelled and
tamped it and covered it up for the night. It stayed covered for a few
days to protect from sun, but when I looked it was soft enough to push my
finger in!

The top few inches are affected, lower down seems solid, so :
1 What went wrong ?
2 Can I scrape the soft stuff off and simply replace with another batch,
perhaps overlapping the solid stuff sideways?

John

--
John Mulrooney
NOTE Email address IS correct but might not be checked for a while.

If you think you can - you can.

On Sep 9, 8:10*pm, JTM wrote:
Hello,

Last Friday I mixed up some concrete. *Each mix was about 1/3 bag cement
(35k bags) with aggregate and water with a splash of washing up liquid.
All seemed well, but the last load was well into darkness so I was
working by security light with lots of shadow.

The final load was the top inch or three of the footings, so I levelled and
tamped it and covered it up for the night. *It stayed covered for a few
days to protect from sun, but when I looked it was soft enough to push my
finger in!

The top few inches are affected, lower down seems solid, so :
1 What went wrong ?
2 Can I scrape the soft stuff off and simply replace with another batch,
perhaps overlapping the solid stuff sideways?

John

--
*John Mulrooney
NOTE Email address IS correct but might not be checked for a while.

If you think you can - you can.

You DO NOT add washing up liquid to concrete. Cement could be old or
to weaker mix. Looks like a complete dig out, as footing foundation
should be poured in one.

JTM wrote:
Hello,

Last Friday I mixed up some concrete. Each mix was about 1/3 bag cement
(35k bags) with aggregate and water with a splash of washing up liquid.
All seemed well, but the last load was well into darkness so I was
working by security light with lots of shadow.

The final load was the top inch or three of the footings, so I levelled and
tamped it and covered it up for the night. It stayed covered for a few
days to protect from sun, but when I looked it was soft enough to push my
finger in!

The top few inches are affected, lower down seems solid, so :
1 What went wrong ?

it dried out.

2 Can I scrape the soft stuff off and simply replace with another batch,
perhaps overlapping the solid stuff sideways?


No: water it.

John

JTM wrote:
Hello,

Last Friday I mixed up some concrete. Each mix was about 1/3 bag
cement (35k bags) with aggregate and water with a splash of washing
up liquid. All seemed well, but the last load was well into darkness
so I was
working by security light with lots of shadow.

A basic structural concrete mix should be 1:2:4 (1 part cement, 2 parts sand
and 4 parts Chipping's) with only sufficient water added to allow the
concrete to be properly worked [1] (I have not given an amount for water
figure the wetness of the sand will alter that amount) - do *NOT* add
"washing up liquid).

The final load was the top inch or three of the footings, so I
levelled and tamped it and covered it up for the night. It stayed
covered for a few days to protect from sun, but when I looked it was
soft enough to push my finger in!

Footings should always be poured in on session - and not added to at a later
date as the 'old' and 'new' pour will not adhere to each other.

The top few inches are affected, lower down seems solid, so :
1 What went wrong ?
2 Can I scrape the soft stuff off and simply replace with another
batch, perhaps overlapping the solid stuff sideways?


What are the footings for?

If it's for a new building or suchlike, then it would be advisable to take
the lot out and start anew - laying in one continuous pour.

If it's simply for a garden wall, single brick garage or small shed, then
remove the to 'soft' bit and start the brickwork/blockwork from the top of
the 'solid' concrete.

If it's for any thing else - let the group know, so that the proper advice
can be given.

NOTE: That the advice given is general, and *will* alter for specific
concrete use.

[1] Too much or too little water will dramatically weaken the concrete,
as will certain additives.


Cash

Cash wrote:
JTM wrote:
Hello,

Last Friday I mixed up some concrete. Each mix was about 1/3 bag
cement (35k bags) with aggregate and water with a splash of washing
up liquid. All seemed well, but the last load was well into darkness
so I was
working by security light with lots of shadow.

A basic structural concrete mix should be 1:2:4 (1 part cement, 2
parts sand and 4 parts Chipping's) with only sufficient water added
to allow the concrete to be properly worked [1] (I have not given an
amount for water figure the wetness of the sand will alter that
amount) - do *NOT* add "washing up liquid).



Erratum

Please note that the above paragraph should have read:

A basic structural concrete mix should be 1:2:4 (1 part cement, 2 parts sand
and 4 parts chipping's) with only sufficient water added to allow the
concrete to be properly worked [1]. Note that I have not given a specific
amount for the water figure, as the moisture in the sand can and will alter
that amount) - do NOT add"washing up liquid).


Sorry for that :-)

Cash

Cash coughed up some electrons that declared:

JTM wrote:
Hello,

Last Friday I mixed up some concrete. Each mix was about 1/3 bag
cement (35k bags) with aggregate and water with a splash of washing
up liquid. All seemed well, but the last load was well into darkness
so I was
working by security light with lots of shadow.

A basic structural concrete mix should be 1:2:4 (1 part cement, 2 parts
sand and 4 parts Chipping's) with only sufficient water added to allow the
concrete to be properly worked [1] (I have not given an amount for water
figure the wetness of the sand will alter that amount) - do *NOT* add
"washing up liquid).

The final load was the top inch or three of the footings, so I
levelled and tamped it and covered it up for the night. It stayed
covered for a few days to protect from sun, but when I looked it was
soft enough to push my finger in!

Footings should always be poured in on session - and not added to at a
later date as the 'old' and 'new' pour will not adhere to each other.

The top few inches are affected, lower down seems solid, so :
1 What went wrong ?
2 Can I scrape the soft stuff off and simply replace with another
batch, perhaps overlapping the solid stuff sideways?


What are the footings for?

If it's for a new building or suchlike, then it would be advisable to take
the lot out and start anew - laying in one continuous pour.

If it's simply for a garden wall, single brick garage or small shed, then
remove the to 'soft' bit and start the brickwork/blockwork from the top of
the 'solid' concrete.

If it's for any thing else - let the group know, so that the proper advice
can be given.

NOTE: That the advice given is general, and *will* alter for specific
concrete use.

[1] Too much or too little water will dramatically weaken the concrete,
as will certain additives.


Cash

I had a friable surface on a concrete slab due to excess water in the mix.
It's solid further down (I had "dammed" a section out around a rising pipe,
so I removed the dam and checked). I soaked the top in PVA. Not bothered
here as it's only a 3m2 slab for a shower room and it's 4" thick.

As mentioned, it all depends on what the application is - JTM?

Cheers

Tim

In article , Cash
wrote:
Cash wrote:
JTM wrote:
Hello,

[snip]



Erratum

Please note that the above paragraph should have read:

A basic structural concrete mix should be 1:2:4 (1 part cement, 2 parts
sand and 4 parts chipping's) with only sufficient water added to allow
the concrete to be properly worked [1]. Note that I have not given a
specific amount for the water figure, as the moisture in the sand can
and will alter that amount) - do NOT add"washing up liquid).


Sorry for that :-)
Thank you, everyone, for the replies.

The project was a late start on a pizza oven mentioned in threads earlier
in the year. About 1.5m sq and the solid bit seems to be about 3 - 4
inches thick, reinforced with 10mm rebar.

Regards

John

--
John Mulrooney
NOTE Email address IS correct but might not be checked for a while.

Glass, china and reputations are easily cracked, but never well mended.

Kipper at sea wrote:
On Sep 9, 8:10 pm, JTM wrote:
Hello,

Last Friday I mixed up some concrete. Each mix was about 1/3 bag cement
(35k bags) with aggregate and water with a splash of washing up liquid.
All seemed well, but the last load was well into darkness so I was
working by security light with lots of shadow.

The final load was the top inch or three of the footings, so I levelled and
tamped it and covered it up for the night. It stayed covered for a few
days to protect from sun, but when I looked it was soft enough to push my
finger in!

The top few inches are affected, lower down seems solid, so :
1 What went wrong ?
2 Can I scrape the soft stuff off and simply replace with another batch,
perhaps overlapping the solid stuff sideways?

John

--
John Mulrooney
NOTE Email address IS correct but might not be checked for a while.

If you think you can - you can.

You DO NOT add washing up liquid to concrete. Cement could be old or
to weaker mix. Looks like a complete dig out, as footing foundation
should be poured in one.

Eh? Haven't I seen BCOs inspecting the footings at the halfway point?

Anyway, he HAS added washing up liquid, as I do, for the simple reason
that it dramatically reduces the amount of water required. Plasticisers
perform the same function except that the dosage is easier to measure
accurately, and they don't foam if you overdo it a little.

As NP says, try re-wetting it before doing anything more drastic.

On 10 Sep, 10:27, Stuart Noble wrote:
Kipper at sea wrote:
On Sep 9, 8:10 pm, JTM wrote:
Hello,

Last Friday I mixed up some concrete. *Each mix was about 1/3 bag cement
(35k bags) with aggregate and water with a splash of washing up liquid..
All seemed well, but the last load was well into darkness so I was
working by security light with lots of shadow.

The final load was the top inch or three of the footings, so I levelled and
tamped it and covered it up for the night. *It stayed covered for a few
days to protect from sun, but when I looked it was soft enough to push my
finger in!

The top few inches are affected, lower down seems solid, so :
1 What went wrong ?
2 Can I scrape the soft stuff off and simply replace with another batch,
perhaps overlapping the solid stuff sideways?

John

--
*John Mulrooney
NOTE Email address IS correct but might not be checked for a while.

If you think you can - you can.

You DO NOT add washing up liquid to concrete. Cement could be old or
to weaker mix. Looks like a complete dig out, as footing foundation
should be poured in one.

Eh? Haven't I seen BCOs inspecting the footings at the halfway point?

Anyway, he HAS added washing up liquid, as I do, for the simple reason
that it dramatically reduces the amount of water required. Plasticisers
perform the same function except that the dosage is easier to measure
accurately, and they don't foam if you overdo it a little.

As NP says, try re-wetting it before doing anything more drastic.

And plasticisers don't weaken he concrete or mortar like washing up
liquid does.

T

On 10 Sep, 08:00, JTM wrote:
In article , Cash

wrote:
Cash wrote:
JTM wrote:
Hello,

[snip]

Erratum
Please note that the above paragraph should have read:
A basic structural concrete mix should be 1:2:4 (1 part cement, 2 parts
sand and 4 parts chipping's) with only sufficient water added to allow
the concrete to be properly worked [1]. * Note that I have not given a
specific amount for the water figure, as the moisture in the sand can
and will alter that amount) - do NOT add"washing up liquid).
Sorry for that :-)

Thank you, everyone, for the replies.

The project was a late start on a pizza oven mentioned in threads earlier
in the year. *About 1.5m sq and the solid bit seems to be about 3 - 4
inches thick, reinforced with 10mm rebar.

Regards

John

--
*John Mulrooney
NOTE Email address IS correct but might not be checked for a while.

Glass, china and reputations are easily cracked, but never well mended.

I'd just leave it, as it will probably harden eventually. You could
have put too much washing up liquid in...

I always use 1:6 cement to ballast (pre mixed aggregate) and have
never had a problem. I have often got the ratios wrong, added too much
water, failed to cover in frosty conditions, etc. The concrete has
always gone off (sometimes slowly), but then I have never added
washing up liquid!

Let me guess - you were using fairy concentrated liquid and gave a
generous squirt?

T

Recyclist wrote:
On 10 Sep, 10:27, Stuart Noble wrote:
Kipper at sea wrote:
On Sep 9, 8:10 pm, JTM wrote:
Hello,
Last Friday I mixed up some concrete. Each mix was about 1/3 bag cement
(35k bags) with aggregate and water with a splash of washing up liquid.
All seemed well, but the last load was well into darkness so I was
working by security light with lots of shadow.
The final load was the top inch or three of the footings, so I levelled and
tamped it and covered it up for the night. It stayed covered for a few
days to protect from sun, but when I looked it was soft enough to push my
finger in!
The top few inches are affected, lower down seems solid, so :
1 What went wrong ?
2 Can I scrape the soft stuff off and simply replace with another batch,
perhaps overlapping the solid stuff sideways?
John
--
John Mulrooney
NOTE Email address IS correct but might not be checked for a while.
If you think you can - you can.
You DO NOT add washing up liquid to concrete. Cement could be old or
to weaker mix. Looks like a complete dig out, as footing foundation
should be poured in one.
Eh? Haven't I seen BCOs inspecting the footings at the halfway point?

Anyway, he HAS added washing up liquid, as I do, for the simple reason
that it dramatically reduces the amount of water required. Plasticisers
perform the same function except that the dosage is easier to measure
accurately, and they don't foam if you overdo it a little.

As NP says, try re-wetting it before doing anything more drastic.

And plasticisers don't weaken he concrete or mortar like washing up
liquid does.

T
Depends how much you use. An excess of either isn't desirable.
Plasticisers are usually very small salts (lignosulphonates?), heavily
diluted for easier measuring. Fairy is a surfactant with a foaming
problem that makes it more difficult to handle. The purpose of both is
to get between the particles, which water alone isn't very good at. I'd
go with a plasticiser for anything serious, but a squirt of Fairy is
fine for odd jobs IME.

Recyclist wrote:
On 10 Sep, 10:27, Stuart Noble wrote:
Kipper at sea wrote:
On Sep 9, 8:10 pm, JTM wrote:
Hello,
Last Friday I mixed up some concrete. Each mix was about 1/3 bag cement
(35k bags) with aggregate and water with a splash of washing up liquid.
All seemed well, but the last load was well into darkness so I was
working by security light with lots of shadow.
The final load was the top inch or three of the footings, so I levelled and
tamped it and covered it up for the night. It stayed covered for a few
days to protect from sun, but when I looked it was soft enough to push my
finger in!
The top few inches are affected, lower down seems solid, so :
1 What went wrong ?
2 Can I scrape the soft stuff off and simply replace with another batch,
perhaps overlapping the solid stuff sideways?
John
--
John Mulrooney
NOTE Email address IS correct but might not be checked for a while.
If you think you can - you can.
You DO NOT add washing up liquid to concrete. Cement could be old or
to weaker mix. Looks like a complete dig out, as footing foundation
should be poured in one.
Eh? Haven't I seen BCOs inspecting the footings at the halfway point?

Anyway, he HAS added washing up liquid, as I do, for the simple reason
that it dramatically reduces the amount of water required. Plasticisers
perform the same function except that the dosage is easier to measure
accurately, and they don't foam if you overdo it a little.

As NP says, try re-wetting it before doing anything more drastic.

And plasticisers don't weaken he concrete or mortar like washing up
liquid does.

T
Footings are mainly under compression, and if you have any rebar at the
base, completely under compression.

There really is no need to worry. All a footing is, is a way to
distribute a high force at the base of a wall over a larger area,
sufficiently far below ground to avoid surface movement due to humidity
changes etc. and using a structure that is inherently free of voids
where it contacts the subsoil - i.e. poured concrete.


And to provide a levelish base to begin laying block or brick.

If the loose top persists, scrape it off and lay a layer of blocks on
their sides to make up the difference, but unless the mixture was so
watery that the sand came to the top while the cement sunk - and if that
was the case. you didn't have enough cement anyway - it will be good enough.

Block houses really stay up because the weight of the blocks above stops
them sliding about. Mortar is almost unecessesary.

As long as the footings are relatively solid, a crumby top is no big deal.

In article
,
Recyclist wrote:

Let me guess - you were using fairy concentrated liquid and gave a
generous squirt?

Well it leaves my hands soft as my face ;-)

John, just off to buy another 1/4 meter pre-mixed aggregate.

Ta

--
John Mulrooney
NOTE Email address IS correct but might not be checked for a while.

There are 3 types of people: those who are numerate and those who aren't.