Pointing below the DPC

4 Aug 2007
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United Kingdom
I am a complete noobie in Diynot.com so please forgive me if I have made any errors.

I have a 1950's semi and the pointing below the DPC has been repointed at some time in the past. This repair has "blown" with some sections falling away. This prompted me to have a look at repointing the brickwork below the DPC (The pointing is OK above the DPC).

The repointing can be pulled away in most places with a tool so as to expose the original mortar. The original mortar looks very damp and very crumbly ( I can almost rake it out with my finger). I chose a head joint as a test section and was able to rake/push a small chisel right through to the cavity. I estimate that all the mortar is in a similar condition to the test section.

My question is, do I just rake out to 25mm and repoint over the crumbling mortar or do I need to look at getting all the mortar replaced. If I do need to just repoint it, do I use a cement:sand mix or a cement:lime:sand mix?
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the strength of any mortar depends on the hardness or porosity of the bricks.

the harder the brick the stronger the mortar.

experts say that a lime based mortar lends itself well to a softer bricked, victorian style house as it will allow the passage of water through the joints as well as the brick. this is so that it eases the effects that lead to spalling etc.

i would say though, a 3:1 cement mortar is a strong as you want to go.
if your using lime then the NHBC recommend a 1 to half to 4.5 mix cement lime sand
if theres no lime the a 1 to 3
if your using an "air entraining plasticiser" then 1 to 3.5

Hope that helps
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Hi folks,

Resurrecting this old thread. I, also am a n00b :)

My recently purchased (I know, I know!!) house is in Rugby, built around 1915 on clay.

I have recently dug out the area around the soil downpipe to discover from where I was getting a penetrating damp problem. Some mortar appeared to have been washed out of the bricks below the blue bricks due to a broken clay bend - meaning delicious effluent seeping under the floor. Judging by the rotten floor joist end - this has been leaking for quite some time! Yum yum.

Having dug down, out and replaced the soil pipe connections to the sewer I am faced with replacing the mortar in the joints underground before filling in.

My questions are as follows:

- What exactly should I use as a mortar mix?

I believe it will be lime based - the current stuff is coarse and yellowy in hue - contrasting with some crap repointing seemingly done in a fine grey cement. As I understand it, mixing cement in is perhaps undesireable?

- Should I pack it as far as possible into the brick gaps?

I cannot see how much has been flushed out.

- How long should I let it dry before filling in the hole?

Drying - ha - that'll be fun in this weather!

- Where is a good place to buy the mix ingredients?

Any help much appreciated!


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