Pointing ! What went wrong?

[KevMack]

Three years ago I did some pointing to a north facing above a conservatory. I recently had to get back up there to sort out a leak and then noticed that the pointing had failed. A thin layer had been pushed out at the front and then behind that it felt moist and quite soft. Ironically that’s why I replaced the old stuff. I seem to remember the mix was 4:1 sand to cement and I added some Wickes plasticiser/waterproofer. The only other thing that happened is it was late October and I did get caught by an early frost a couple of times. Was wondering if the cement was off. Any ideas as I don't want to repeat the error.



Many thanks in advance ...Kev.

 

[r896neo]

It sounds like frost damage, if you didn't protect it and it was frosty its a bit of a no brainer.
Frost damaged mortar doesn't ever harden properly. Rake out and re-do and don't fall into the same trap

 

[tomfe]

I've had problems with wickes plasticiser and waterproofer, not sure if I just had a doddgy batch but when I run out of my normal stuff I have to resort to this and it always feels a bit iffy. I should bin in really.

 

[^woody^]

Did you rake the joints out to a depth of 25mm?

With pointing, the face is always harder than the mortar beneath it. But there can be several reasons why the mortar could be soft, but frost damage would not tend to leave a hard face and soft mortar behind, but would all be soft.

It's very easy to use to much plasticiser in small pointing mixes, and even easier to have it poorly mixed. So more chance of bad mixing, than bad plasticiser.

 

[Doggit]

I've never come across a plasticiser and waterproofer combined, but whilst the plasticiser will make the mortar easier to work with, a waterproofer isn't really necessary for repointing. If the pointing has failed, then the mortar behind could be moist because the water running down the brick face is being directed behind the lose pointing.

Did you mix the plasticiser in with the mix, or in the gauging water first, and how deep did you rake out the old joints.

 

[Gerrydelasel]

Presumbly the old mortar is also cement mortar and not lime?

 

[KevMack]

Many thanks for the replies.
In response to some questions raised.
I think the old mortar was cement but not entirely sure. (would that make a difference?)
The mortar was raked out to 25mm.
The plasticiser/waterproofer was mixed in water beforehand at proportions calculated from figures on the back of the container.
Since I did this over several days each batch (hand-mixed) yet the entire wall is affected.
Out of interest ( Or becoming neurotic went and checked a little I'd done some years before. Still as hard as rock!

 

[Gerrydelasel]

I think the old mortar was cement but not entirely sure. (would that make a difference?)

Absolutely! How old is the building?

 

[KevMack]

It was a bungalow built in 1957. I'm now looking at using lime mortars instead when I redo it assuming the house doesn't collapse before the spring. Is that a better idea?

 

[Gerrydelasel]

Oh, 1957 is probably cement not lime. I guess that's not the source of your problem then.

 

[^woody^]

Is that a better idea?

No. Use cement

 

[theprinceofdarkness]

The plasticiser I use is a 3 % mix, so thats 150mL in a 5 L plastic container (two egg cupfuls or my gauge?).
Frank