Anna Kettle wrote:
On Thu, 19 Jun 2008 19:12:58 GMT, "George"
wrote:

wrote in message
...
I've got a large North-facing house wall of soft Norfolk red bricks -
and a large number have spalled.

It's really an impractically large number to cut out and replace.

I've been trying to patch over them with lime mortar (lime putty,
sharp sand and red brick dust).

Mix is good consistency & sticky - but it still isn't bonding very
well to the bricks (which have been gone over roughly with a wire
brush, brushed down and then wetted).

So I'm thinking - maybe wet down with 10% pva solution?

Other suggestions?
Use this in the cement mix,as you have done wet the brick first.
http://tinyurl.com/6o3w92

You dont need to add plasticiser to lime putty, it _is_ a plasticiser

I suspect that your layer of mortar a bit thin. 6-10mm works best

Consolidate the mortar once it has picked up a bit (ie some of the
water has migrated into the brickwork leaving air voids)

Try painting the brick with limewash before plastering. It will soak
into the brick a bit so when the lime sets there will be a chemical
bond between the brick and the lime mortar

Try drilling a few holes in the brick to give added mechanical key.
Hoover out the holes, wet them, limewash them, then plaster

But whatever you do it is still patching and you will never get a good
colourmatch. Cutting out and replacing the bricks will look better :-)

I wouldnt add PVA, it impairs the breathability and so will tend to
make the spalling worse in the future


that depends on whether the PVA stops the water getting in,or getting out.

Below damp course, no. Above damp. well it may actually help
Anna