Pointed wall with NHL 3.5 - start over?

[GillesF]

Hi all

I'm new to this forum. 4 years ago, we purchased a house in Flanders dating back to 1895 and we are slowly renovating it.

I have recently started repointing of an old brick wall (inside) which is part of the garage because the old lime mortar had completely crumbled. Based on what I read online and what was easily available, I chose to repoint this with St-Astier NHL 3.5 with a 1 - 2.5 ratio. I have now finished 10m² of the 20m² wall and upon reading further and learning more about lime products I was told that NHL 3.5 is too strong and a non hydraulic lime should be used. Should I now start over? Although I like the repointing work but I dread to start raking out the new lime mortar again ...

Extra information: this is an old brick wall which is not part of the main building. It bears the load of the garage's flat roof. There are traces of damp at the bottom but this could still be the result of the work of the previous owner who had put styrofoam against the walls and thus removing breathability. This wall will eventually be covered with hemplime insulation. The outside of this wall will probably need repointing too but I don't know the state of it because this is located in the neighbour's garden.

Thanks!

 

[malcolm]

I would certainly not undo the work you have done.

I use NHL 3.5 everywhere though almost all of my work has been outside. The story I have read is that NHL3.5 is much harder than non-hydraulic lime, but I removed some bricks after a year and only the outer 1mm that had carbonated was hard. The rest was still quite soft and easy to remove from the bricks. In contrast some 300 year old foundation bricks had carbonated all the way through and I can't remove the mortar. I think the NHL is intended to increase the initial strength so you can build more bricks every day and has less to do with long term performance. It is less breathable but breathable enough for anything but the softest bricks.

Though I would be glad to be corrected as others on here have a lot more experience than me.

 

[a twig]

Similar to Malcolm in my experience - I wouldn’t worry and would just crack on with an NHL2 based mortar from now on, life’s too short to be repointing large wall sections in fat lime unless you really have to, particularly as the weather starts to turn.

Appreciate the above is not a purist point of view - but in my limited opinion all too easy to go down a conservation / heritage rabbit hole and let the perfect become the enemy of the good

 

[Lacan07]

Hi all

I'm new to this forum. 4 years ago, we purchased a house in Flanders dating back to 1895 and we are slowly renovating it.

I have recently started repointing of an old brick wall (inside) which is part of the garage because the old lime mortar had completely crumbled. Based on what I read online and what was easily available, I chose to repoint this with St-Astier NHL 3.5 with a 1 - 2.5 ratio. I have now finished 10m² of the 20m² wall and upon reading further and learning more about lime products I was told that NHL 3.5 is too strong and a non hydraulic lime should be used. Should I now start over? Although I like the repointing work but I dread to start raking out the new lime mortar again ...

Extra information: this is an old brick wall which is not part of the main building. It bears the load of the garage's flat roof. There are traces of damp at the bottom but this could still be the result of the work of the previous owner who had put styrofoam against the walls and thus removing breathability. This wall will eventually be covered with hemplime insulation. The outside of this wall will probably need repointing too but I don't know the state of it because this is located in the neighbour's garden.

Thanks!

Absolutely not!!

The fact is NHL lime is still the most specified lime product by architects, conservationists, etc, and St-Astier is considered a premium product. Its fair to say it is a relatively modern invention but you've only pointed a garage wall. There have been studies that suggest it can harden over time so a safer bet for interior and exterior work would be an NHL2, but the most important thing is its breathable. Its also quick setting and generally less fussy than lime putty.

If you want to try your hand a lime putty based mortar save it for the main house, work should take place between spring and summer.

 

[GillesF]

Hi all

Thanks for the feedback! Yes, I will continue using NHL for this wall and practice and then use a lime putty based mortar for the cellar and other parts of the main house. Unfortunately, it seems I cannot get Saint-Astier NHL 2 locally, only 3.5 or 5 so I will have to continue with the NHL 3.5.

 

[Stevers]

It may be an option to enfeeble the NHL 3.5 with hydrated lime to simulate NHL 2.0. Recently I did this for finish plaster coat, and only regretted not adding more hydrated lime for a fatter mixture. I just added the hydrated lime in powder form to the mix as you would lime to a cement lime mortar, whereas I think strictly speaking powdered hydrated lime should be made into a putty before use.
On balance I'd go with the straight NHL3.5 - less to go wrong, and no real downside.

 

[Lacan07]

It may be an option to enfeeble the NHL 3.5 with hydrated lime to simulate NHL 2.0. Recently I did this for finish plaster coat, and only regretted not adding more hydrated lime for a fatter mixture. I just added the hydrated lime in powder form to the mix as you would lime to a cement lime mortar, whereas I think strictly speaking powdered hydrated lime should be made into a putty before use.
On balance I'd go with the straight NHL3.5 - less to go wrong, and no real downside.

Yes, to do this it would be better to turn the hydrated lime into a putty first