bricklaying mortar

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sm_jamieson

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Aug 13, 2007, 5:08:25 AM8/13/07
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I have a tendency to use too much cement in the mix generally, and I
want to get this right before tackling the extension walls etc. I
think I do this because with a weaker mix, when the mortar has cured
in a couple of days, it seems quite weak if you scrape with a finger
nail etc. (no it's not drying out before curing)
Also, hydrated lime does not seem to be generally available at
builders merchants, so is it correct that most brickies would use
cement, sand and additive instead these days ? If so, what is the best
additive and typical proportions for brick laying mortar ?
Cheers,
Simon.

TMC

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Aug 13, 2007, 5:15:56 AM8/13/07
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"sm_jamieson" <sm_ja...@hotmail.com> wrote in message
news:1186996105....@o61g2000hsh.googlegroups.com...
When I did the mixing for the brickies for my last extension they insisted
on 16 sand to 3 cement with about the same Fairy liquid per 2 gallon bucket
of water as I would use for a sink of water when washing up

Tony


dg

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Aug 13, 2007, 6:21:16 AM8/13/07
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Internal blockwork should be between 6:1 and 10:1 - a weaker mix is
important to allow flexibility of the mortar and especially if using
aerated concrete blocks - as too strong a mix will cause the blocks to
crack as the wall moves.

With external brickwork, use a 3:1 mix up to DPC and a 5:1 for facing
bricks. The weathering protection of the mortar is done by pointing
and compacting the surface of the joint, and not by having a strong
mix.

Flexibility is important for domestic builds, and only high-rise and
engineering projects require more rigidity.

Whilst the 'official' line is to use proper air-entraining additive in
the mortar, detergent such as fairy liquid can be used with no
detriment above ground level. With normal building sand and a typical
'belle' size mixer, just a tiny squirt will be enough in the mixer
(about 1 teaspoon)


Andrew Gabriel

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Aug 13, 2007, 6:50:01 AM8/13/07
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In article <1186996105....@o61g2000hsh.googlegroups.com>,

sm_jamieson <sm_ja...@hotmail.com> writes:
> I have a tendency to use too much cement in the mix generally, and I
> want to get this right before tackling the extension walls etc. I
> think I do this because with a weaker mix, when the mortar has cured
> in a couple of days, it seems quite weak if you scrape with a finger
> nail etc. (no it's not drying out before curing)

Mortar takes weeks to reach final cure. You are being impatient.

> Also, hydrated lime does not seem to be generally available at
> builders merchants, so is it correct that most brickies would use
> cement, sand and additive instead these days ? If so, what is the best
> additive and typical proportions for brick laying mortar ?

You can buy plasticiser at most places which sell cement.
Many cements have it included anyway (it will say on the bag).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

tom.ha...@gmail.com

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Aug 13, 2007, 7:36:22 AM8/13/07
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On 13 Aug, 10:08, sm_jamieson <sm_jamie...@hotmail.com> wrote:

3:1 with any proprietary plasticiser (following the manufacturer's
instructions) seems popular below dpc. 6:1:1 (the extra "1" being
lime) is the most commonly used mortar by builders near me. I have
never come across a builders merchant that doesn't stock hydrated
lime. In fact it sounds a bit ridiculous to me. I prefer to use lime
as it's all too easy to make large percentage errors with small
quantities of plasticiser.

Sand is another issue. "Building" sand aka soft sand seems not to be
used much in my area. The preferred sand is known as "plastering" sand
and looks to me to be a mix of sharp:soft in about 60:40. I have asked
brickies and stonemasons why they use it, and a typical answer goes
something like "soft sand's too soft" or "sharp sand's too sharp".
When I mention that I have seen brickies using soft sand they are
usually disgusted.

The most important thing however is matching the mortar. To achieve
the colour I need, I have to buy "yellow" sand from a particular
builders merchant (which is a sharp/soft mix with a fair bit of grit)
and their brand of cement. The hydrated lime I can get from anywhere.

T

sm_jamieson

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Aug 13, 2007, 7:42:45 AM8/13/07
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Thanks, now I'm in a quandry about using lime or additive. Lime is a
pain - one more bag of stuff to buy. And anyone use lime under DPC ?
If I can really use detergent, and lots of brickies do, thats fine.
I can also mix in a bit of sharp sand for good measure.
Simon.

The Natural Philosopher

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Aug 13, 2007, 7:43:14 AM8/13/07
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sm_jamieson wrote:
> I have a tendency to use too much cement in the mix generally, and I
> want to get this right before tackling the extension walls etc. I
> think I do this because with a weaker mix, when the mortar has cured
> in a couple of days, it seems quite weak if you scrape with a finger
> nail etc. (no it's not drying out before curing)

Should be pretty much rock hard if you mixed it 'strong'

> Also, hydrated lime does not seem to be generally available at
> builders merchants,

Is at all mne.

> so is it correct that most brickies would use
> cement, sand and additive instead these days ?

Yes, cos lime is expensive and takes longer to set, and indeed never
does set quite in the way that cement does. If you want to lay ten
course of bricks in a day and come back the next morning and work
without fear of knocking it all down, you need cement, not lime.


If so, what is the best
> additive and typical proportions for brick laying mortar ?

I don't use additives except in winter. It would cvary fro 2:1
sand:cement for below ground work with non porous engineering bricks, to
about 4:1 for general sheltered above ground stuff,.or evem sandier if
its a scratch job and I don't care.
> Cheers,
> Simon.
>

tom.ha...@gmail.com

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Aug 13, 2007, 7:53:41 AM8/13/07
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On 13 Aug, 10:15, "TMC" <a...@anon.co.uk> wrote:
> "sm_jamieson" <sm_jamie...@hotmail.com> wrote in message

I believe the practice of adding fairy liquid is somewhat frowned upon
these days.

T

tom.ha...@gmail.com

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Aug 13, 2007, 7:57:01 AM8/13/07
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Is your extension going to match your house? Lime is not used under
dpc.

T

ma...@atics.co.uk

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Aug 13, 2007, 8:36:24 AM8/13/07
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On 13 Aug, 10:08, sm_jamieson <sm_jamie...@hotmail.com> wrote:

Dear Simon
Up until approximately 1900, most buildings were made with a lime
mortar. That is why London survived the Blitz as it is very flexible.
It operates by virtue of changing the hydroxide to carobonate using
CO2 in the air over a long period of time. Lime putty is obtained by
taking say chalk CaCO3 (calcium carbonate) which has been heated to
1000 degrees C to make it the oxide (quick iime) which was then
slaked to make the hydroxide (lime putty) which, after a period of
"gestation", in a lime pit was taken out as a gelatinous mess and
"knocked" up (by the "boy") to a plastic state (hence the expression)
before mixing with sand. The ratio is defined by the natural voids in
between the particles of the sand. It is usually 3 parts sand to one
part binder (be it lime or Portland cement).
Hydrated lime is (as far as I know) simply ground up calcium
hydroxide. See, for example,
http://www.castlecement.co.uk/new/documents/hydrated-lime_000.pdf
Therein you will see suggested ratios to use both below and above dpc.
I use lime putty for plasters where they were orginally lime and
cement for renders/plasters when it is orginally cement. You can find
advice on new build ratios and merits from an unbiased source by
looking up the BRE guidelines which have different ratios for
different areas of houses eg chimneys and below ground differ from
above the dpc and also according to the likely weather.
It all depends on what you are wanting it to do.
Personally, I ensure the total ratio of binder to sand is 3 to 1 for
building bricks above dpc and that is the classic 1:1:6 - The 1 of
lime and 1 of cement when added together forming a total that makes it
1:3.
Chris

sm_jamieson

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Aug 13, 2007, 9:16:21 AM8/13/07
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On 13 Aug, 10:08, sm_jamieson <sm_jamie...@hotmail.com> wrote:

Well, conclusion so far :-
Different brickies use different mixes. It must be sufficiently
flexible and more so than the blocks, so aerated blocks need a very
flexible mix (which makes the aircrete walls seem even more feeble to
me !).
And using additive instead of lime is very widespread.
If additive has the same effect as the lime, I may get a proper
additive and use that instead.

By the way, what is the actual important effect of the lime in a
cement/sand/lime mix ? If it just makes it easier to work, I don't
consider that important. But if, for example, it makes a strong yet
flexible mix, it may be very important for aircrete walls.

If there is no general consensus on these matters, it makes it
difficult for the DIYer who doesn't want to mess things up!

Cheers,
Simon.

Stuart Noble

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Aug 13, 2007, 9:32:21 AM8/13/07
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That is the question. Does a 50-50 mix give you the best, or the worst,
of both worlds?
Nobody talks about pozzolans much, but these were used extensively in
Victorian building to make lime mortar set. Small amounts of cement work
in the same way, but this is said to cancel out the benefits of lime. If
you can make any sense of it all, either here or in the other place to
which you will soon be re-directed, let us know.

meow...@care2.com

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Aug 13, 2007, 9:39:53 AM8/13/07
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You seem to be confusing cement mortar containing lime with lime
mortar. The 2 are quite different, and while lime mortar sets slowly,
cement mortar with added lime sets fast and hard. When used in cement
mortar the lime only adds workability, it does not bring the other
properties of lime mortar.

3:1 is the strongest mix, as stiffer mixes microcrack during cure. So
there is no mileage in using more cement than that.

Cement takes a month to cure fully, all mixes are weak a day or 2
later, but come back a week later and they've toughened up pretty
good.

Detergents weaken final mortar strength, but for domestic brickwork
this isnt too significant.

1:1:6 is a good gen purp brickwork mix, but plenty of other mixes also
work.


NT

sm_jamieson

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Aug 13, 2007, 9:43:18 AM8/13/07
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On 13 Aug, 14:32, Stuart Noble <stuart_nobleNOS...@ntlworld.com>
wrote:

Well, I guess, for a typical single storey extension, a few courses of
blue bricks, DPC, cavity wall of brick/aircrete, what are the most
common mixes used ? I guess a survey could be done.
The main thing that concerned me is the aircrete blocks cracking on
the inner skin, since these are so feeble anyway. I can't see a
brickie building 2 skins at the same time, using two piles of
mortar ...
Simon.

Andrew Gabriel

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Aug 13, 2007, 11:34:29 AM8/13/07
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In article <1187012393.7...@q75g2000hsh.googlegroups.com>,

meow...@care2.com writes:
>
> 1:1:6 is a good gen purp brickwork mix, but plenty of other mixes also
> work.

The 1:1 ratio lime to cement is important. Most other ratios
of lime to cement in either direction don't work and give a
poorer bond than was expected.

sm_jamieson

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Aug 13, 2007, 11:46:57 AM8/13/07
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So, are we saying all lime adds to cement/sand is workability ? What
does this really mean ? Why bother with the lime if it adds so
little ? I'm sure its more expensive than sand.

Simon.

dg

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Aug 13, 2007, 2:55:01 PM8/13/07
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> Simon.- Hide quoted text -
>
> - Show quoted text -

Back in the good old days, when the Clerk of Works ruled the site, you
could only build a maximum of 1m of wall per day, and the walls had to
go up evenly around the building to avoid differential loading of the
foundations. Also we could only build cavity walls in sections between
the tie wires (two block courses/six brick courses) and then the ties
had to be laid across the two skins - horizontal and at 90 degrees,
before proceeding with the next courses. And two mixers were needed
for the two different mortars

None of this one leaf up to lintel height and hanging the ties out
malarky

You are wrong with your impression of aerated blocks being feeble.
They are not.

Whatever the walling material, mortar should be weaker than the bricks/
blocks. So even concrete blocks can crack if a mortar is used which is
too strong.

And the question you should be asking yourself is ... should the
mortar keep the blocks together, or keep them apart? Answers on a
postcard please

dg

meow...@care2.com

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Aug 13, 2007, 6:40:25 PM8/13/07
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The workability's worth it for many jobs. Cement and sand alone just
doesnt behave well, extending work times in many cases.


NT

meow...@care2.com

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Aug 13, 2007, 6:47:15 PM8/13/07
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On 13 Aug, 14:32, Stuart Noble <stuart_nobleNOS...@ntlworld.com>
wrote:
> sm_jamieson wrote:
> > On 13 Aug, 10:08, sm_jamieson

> > cement/sand/lime mix ? If it just makes it easier

> That is the question. Does a 50-50 mix give you the best, or the worst,
> of both worlds?

Neither, its just cement mortar.

> Nobody talks about pozzolans much, but these were used extensively in
> Victorian building to make lime mortar set. Small amounts of cement work
> in the same way, but this is said to cancel out the benefits of lime.

Cement is pozzolanic, but has very different results on lime mortar to
other pozzolans.


> > If there is no general consensus on these matters, it makes it
> > difficult for the DIYer who doesn't want to mess things up!

au contraire, theres not good concensus because its hard to muck it
up. Whether you use 5:1, 7:1, 1:1:6 or even lime 3:1, with fairy
liquid, feb or nothing, your walls will get built and will stay there.


NT

ma...@atics.co.uk

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Aug 14, 2007, 3:31:54 AM8/14/07
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Dear Simon
The purpose of a PROPER functional lime in a mortar is to act as a
binder. it is an alternative to cement. As, quite correctly in a later
post, it is explained that the method of setting is chemically
different. Lime is slow (approx 0.4% air volume of CO2?) carbonation
of the hydroxide and cement sets quite quicky hence the later post
explaining how brick walls used to be built. Bagged lime is NOT an
effective binder. For good physical chemical reasons (platelet
formation) calcium hydroxide from bagged lime in a set mortar cannot
act as a binder. It acts as a plasticer and makes the mixture more
fluid. It has practically no setting strength. It effectively weakens
the mortar STRENGTH whilst maintaining filling the voids. IF you want
to use bagged lime as a mortar binder then you need to put it in a
plastic bin for several months or a year to form a "putty" which will
then have SOME binding strength. However, the best way of using lime
is with a proper lime putty NOT bagged lime. In your case, you are
only interested in the mortar. You can dispense with lime if you like
but I would not myself as it will be a better mortar with it.Penny
pinching at this stage is not worth it. Plasticisers "aerate" the
mortar with small bubbles of air to make it easier to lay and mix. I
would substitute that with lime myself!
Chris

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