External lime repointing, build up depth?

[TheRoost]

We're going to be doing some patch pointing soon, using NHL 3.5, the worst bits are the horizontal joints just above ground level, where the old mortar has eroded to a full brick depth in places (i.e. 4.5" )

Some of the online guides for repointing say that deep joints should be built up in layers, with four days between coats! what I can't find anywhere is how deep each layer should be as a maximum, one suggests 10mm layers but that would take forever!

For normal area's of repointing where raking out is needed, would you apply the mortar in one layer, e.g. 25mm deep? so would it be reasonable to build up deep joints in 25mm layers, or could you go more?

Thanks.

Andy

 

[plasticpigeon]

I see no reason why it can't be done in one go, that is how it is done when the bricks are laid!!! The 10 mm or 1/2 " thickness guidance I've seen is for rendering or plastering whee there is a huge area for loss of moisture and a much larger risk of cracking on the surface.

 

[TheForge]

I've pointed much deeper recesses than that in one go. I can see two sides to the argument though. If you put lime in too thick, especially if it's putty, then it's unlikely to fully carbonate to the full depth. If it's NHL though I can't see it making any difference and by building up layers I would suggest you are just creating fault lines for failure.

 

[noj]

It's may be more a question of frost protection if you're doing it late in the year?

 

[TheRoost]

I see no reason why it can't be done in one go, that is how it is done when the bricks are laid!!!

Thanks, why didn't I think of that! Too much reading and not much brain engagement from me

I guess the guides I read are not specific to hydraulic lime, maybe the layering is suggested for lime putty.

Hopefully I should be finished before any frost but will protect with plastic sheeting anyway.

 

[Zebra]

I did my chimney in one go, in NHL3.5, three years ago, and it's been fine. I never read that in all my research on the subject, that you ought to do it in layers.

 

[Keithj]

With NHL, I can see no benefit in layering it - and a few reasons not to.

WIth plain lime putty, it won't reach full carbonated strength for a while if it's in the middle of a thick area. I remember the excavations at London Wall yonks ago, when they unearthed some Roman wall and found that the lime in the middle hadn't carbonated fully, 2000 years on. Or was that a folk myth?