lime render


N

Nick Brooks

Hi

I need to patch an area of render that I believe is lime based. What's
the best way to go about it?

My local builders merchant has both hydraulic and hydrated lime.

How much sand will I need to add?

Will I need to add hair or is that only for internal plasters?

TIA

Nick Brooks
 
Ad

Advertisements

A

Andrew Gabriel

If the good stuff is quite hard then it will likely be a mix of lime
cement and sand probably 1:1:6. If it is pale and soft (what colour sand
is it?) it will be sand and lime, something like 4 or 5 to 1.

No hair is use these days. I'm not sure what hydraulic lime is. There is
quick lime = calcium oxide (not used in building as it is dangerous. I
have an idea it is used on playing fields to mark out pitches) and
slaked lime = calcium hydroxide -which is a lot safer.
There's a kind of calcium cycle (he says, trying to remember
'O' level Chemistry)...

You start by mining the chalk/limestone, Calcium Carbonate.

Heat Calcium Carbonate to make Calcium Oxide and drive off Carbon dioxide.
This is Quicklime (or old name, Burnt Lime), a rather nasty substance.

Add Calcium Oxide to water to form Calcium Hydroxide (and
enough heat to boil the water instantly if you're not careful).
This is Hydrated Lime or Slaked Lime.
This is what you use in Lime mortars, plasters, and renders.
(I'm not sure what the difference is between Hydrated Lime and
Hydraulic lime -- I suspect they are chemically the same, but
one is dryed out and the other is in liquid/paste form due to
excess water.)

Calcium Hydroxide absorbs carbon dioxide from the air and turns back
into chalk -- this is the lime mortar setting process, and that's
why it doesn't set in a couple of hours;-).

This brings you back to what you started with, chalk, except it's now
carefully shaped to fit round all your bricks ;-)
 
P

Peter Taylor

A couple of comments on your message Andrew:
There's a kind of calcium cycle (he says, trying to remember
'O' level Chemistry)...
It's called the carbon cycle.

You start by mining the chalk/limestone, Calcium Carbonate.

Heat Calcium Carbonate to make Calcium Oxide and drive off Carbon dioxide.
This is Quicklime (or old name, Burnt Lime), a rather nasty substance.

Add Calcium Oxide to water to form Calcium Hydroxide (and
enough heat to boil the water instantly if you're not careful).
This is Hydrated Lime or Slaked Lime.
This is what you use in Lime mortars, plasters, and renders.
Slaked lime kept covered in water, preventing contact with CO2, is the basic
ingredient of traditional lime putty sold in tubs and used for mortars,
plastering and rendering etc and has a very slow setting rate. Hydrated lime is
a fine powder sold in bags like cement. You're right, it is chemically the same
as slaked lime, but it has been heated again to dry it out and crushed and
sieved to make a fine dry powder. This is used mainly in proportion with cement
and sand to make gauged mortar for bricklaying and rendering, and gives greater
workability, plasticity than plain cement mortar, and lightens its colour.
Hydrated lime can be soaked, stirred and filtered again to make lime putty, but
it's a long process and the result is less pure, so that it sets more quickly.
(I'm not sure what the difference is between Hydrated Lime and
Hydraulic lime -- I suspect they are chemically the same, but
one is dryed out and the other is in liquid/paste form due to
excess water.)
Hydraulic Lime is also sold in powder form. But it has substances called
pozzolans added to the lime, which cause it to set quickly, sometimes very
quickly, like Plaster of Paris. Pozzolans include things like brick dust or
fuel ash. Hydraulic lime gets its name because, unlike lime putty, it will set
under water. The Romans discovered this this and used hydraulic lime to build
aquaducts.

Anna will be along soon and will probably find something wrong with what I've
said! I'm sure she'll have something to say to Mike about hair not being used
in plaster any more. :eek:)

Peter
 
A

Andrew

Nick Brooks said:
Hi

I need to patch an area of render that I believe is lime based. What's
the best way to go about it?

My local builders merchant has both hydraulic and hydrated lime.

How much sand will I need to add?

Will I need to add hair or is that only for internal plasters?

TIA

Nick Brooks
I found http://www.mikewye.co.uk/ to be quite informative. I haven't
tried putting any of it into practice yet as I haven't got the correct
round tuit for the job.

MBQ
 
P

Peter Taylor

Andrew wrote
I haven't got the correct round tuit for the job.
LOL. And I haven't visited that little village Upper Ladder for a long time
now!
 
G

G&M

Nick Brooks said:
Hi

I need to patch an area of render that I believe is lime based. What's
the best way to go about it?

My local builders merchant has both hydraulic and hydrated lime.
That's a good mechant. A few have one and most have neither. If the
render is painted, use the hydraulic outside as it sets quicker. Otherwise
you will need to slak the lime, then mix about 1:4 or 5 with the correct
colour sharp sand.
Will I need to add hair
No
 
Ad

Advertisements

A

Anna Kettle

Anna will be along soon and will probably find something wrong with what
I've said!
No complaints what you said looks sound to me :) I will just add that
what you use depends on what surface you are working onto. If its
rigid like brick or block then hydraulic is OK and is especially good
outdoors cos it is more weather resistant. If its a flexible surface
like lath then don't use hydraulic its too hard and brittle & will
crack so if you can't get readymade lime putty then make your own with
hydrated lime.
How much sand will I need to add?
3 sharpish sand : 1 lime putty or if you use hydraulic then read the
bag.
I'm sure she'll have something to say to Mike about hair not being
used in plaster any more. :eek:)
Quite right too! Hair is still used to give tensile strength. That is
not necessary for rigid surfaces like brick & block but it is
important to add plenty of hair for work onto lath & suchlike. Any
strong fibre will give the tensile strength eg hemp, straw but hair is
preferred if you want a good finish and hair from a white horse is the
most invisible.

Anna


~~ Anna Kettle, Suffolk, England
|""""| ~ Plaster conservation and lime plaster repair
/ ^^ \ // Freehand modelling in lime: overmantels, pargeting etc
|____| www.kettlenet.co.uk 01359 230642
 
P

Peter Taylor

Anna Kettle wrote
Quite right too! Hair is still used to give tensile strength. That is
not necessary for rigid surfaces like brick & block but it is
important to add plenty of hair for work onto lath & suchlike. Any
strong fibre will give the tensile strength eg hemp, straw but hair is
preferred if you want a good finish and hair from a white horse is the
most invisible.
Out of interest Anne, would you be happy to use synthetic reinforcing fibres (as
used in concrete mixes and screeds) instead of hair? This is the sort of thing
I mean: http://www.kaposplast.hu/english/politon.html

Peter
 
A

Anna Kettle

Out of interest Anne, would you be happy to use synthetic reinforcing fibres (as
used in concrete mixes and screeds) instead of hair? This is the sort of thing
I mean: http://www.kaposplast.hu/english/politon.html
I can't see anything wrong with synthetic fibre and it has the
advantage that it doesn't rot so the mortar can be mixed up way in
advance. I'm not planning to start using synthetic fibre myself cos
lots of my work is on old buildings so I try to keep as close to the
original materials as possible

Anna

~~ Anna Kettle, Suffolk, England
|""""| ~ Plaster conservation and lime plaster repair
/ ^^ \ // Freehand modelling in lime: overmantels, pargeting etc
|____| www.kettlenet.co.uk 01359 230642
 
Ad

Advertisements

T

The Natural Philosopher

Anna said:
No complaints what you said looks sound to me :) I will just add that
what you use depends on what surface you are working onto. If its
rigid like brick or block then hydraulic is OK and is especially good
outdoors cos it is more weather resistant. If its a flexible surface
like lath then don't use hydraulic its too hard and brittle & will
crack so if you can't get readymade lime putty then make your own with
hydrated lime.




3 sharpish sand : 1 lime putty or if you use hydraulic then read the
bag.




Quite right too! Hair is still used to give tensile strength. That is
not necessary for rigid surfaces like brick & block but it is
important to add plenty of hair for work onto lath & suchlike. Any
strong fibre will give the tensile strength eg hemp, straw but hair is
preferred if you want a good finish and hair from a white horse is the
most invisible.
Or go modern and buy some glass cloth or chopped strand mat :D
 

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.

Ask a Question

Similar Threads

lime rendering onto plaster 4
Lime Render Over Wood? 3
Internal rendering/Plastering with Sand/Cement/Lime Mix 9
render 3
rendering 3
Rendering 3
lime mortar 2
LIME PASTE 2

Top