nhl 3.5 not setting?

[robgil]

its in a mix with coarse sand 3 sand / 1 lime and its setting to the hardness of a hob nob. it crumbles to dust in between my fingers.
possible causes anyone? is there any kind of process of elimination i can go through to make sure im doing nothing wrong and to eliminate a bad or already carbonised bag?
The bag of lime was bought a few weeks a go and used straight away.
ive been using it for pointing and the conditions are damp , its been on there for around 5 days now.
even the stuff that has been left over on my mixing board has dried like a farleys rusk.

 

[MdB]

Lime isn't cement. You need to work on different time scales and remember that it is many time weaker.

I believe that NHL strength is measured after 28 days with full strength not being reached for years.

 

[Schoolmarm]

It shouldn't be crumbly like a hob nob though. Sounds like it has failed Rob.

 

[Ushy M]

Agree with Schoolmarm Rob, it does sound as if it's failed. We used NHL 3.5 for our external pointing work using the same sand:lime ratio and by the following day it had achieved a reasonable set. Odd though, as it sounds as if the lime you're using is reasonably fresh. Our last lot of pointing was done using lime that had sat in bags by the fireplace for 18 months. We tested the pH and found it still had good alkalinity - I've actually just been out to check and it's looking fine.

 

[robgil]

it is odd guys , the last lot i used dried within a few days and set rock hard.
is the 3 to 1 weight or volume? ive been measuring volume.

 

[Schoolmarm]

The bag could have been hanging about in the store for ages I suppose.

And Biff always says volume.


If it has dried super quick before a chemical set or carbonation takes place that wouldn't help either. Was it a high suction background? And did you wet it a long time in advance and then again before starting?

 

[skier-hughes]

volume.
Ours dried quite quickly to a firmness which we kept moist for quite some time, days, or maybe a week with light sprayings on a regular basis.

 

[christianb]

Did you moisten the background before applying it?

 

[robgil]

it went onto bricks , they were really wet , they are part of a plinth. ive been washing the timbers above so they were quite damp.
what are the ideal conditions? i have just been to check again and it is still quite damp still but the really dry bits crumble like a digestive.

 

[skier-hughes]

there shouldn't be any really dry bits.

 

[Schoolmarm]

I think the lime has already carbonated so the sand has stayed sandy.

 

[robgil]

so if i leave a couple of litres of mortar out in the open in a room on a wooden board for a few days , no heating , just sat there , after 3 or four days it should dry to the consistency of a digestive?
its just that any mortar i have mixed previously has dried far harder than this in less time , i suppose it could be down to the environment around it , it is a bit damper this time around.

 

[Schoolmarm]

:lol: :lol: See my post above yours, I think that bag of lime has gone off and left you with a sandy weak consistency.

 

[skier-hughes]

I think so to Marm!

 

[Schoolmarm]

8)


It hasn't " mortarified" :lol:

 

[lime&listed]

Hi there,
Thought I'd add a comment to the post. To introduce myself I am a historic building consultant, two years into restoring my own 17th century stone cottage in Benson, South Oxfordshire. I also work for the Old House Store at their new shop in Woodstock. We recently had a customer using our castle nhl3.5 lime who had a setting problem. It turned out he had his mix the wrong way round with 30% sharp 70% soft sand in a 3:1 sand/lime mix. A number of the conservation builders I know tend to use 70% sharp to 30% soft sand down to a 50/50 mix. Just wondered what sand you were using as this can affect the setting time?
Rob

 

[biffvernon]

Welcome to the forum, Rob.

I can't see that the proportions of 'soft' and 'sharp' sand can make any difference to how quickly the lime goes hard. I always use sand I dig up and it goes through a garden sieve for most purposes and the other garden sieve for finer work.

NHL should work in the same way as hydrated plus an additional chemical set when the hydraulic component reacts with the water. Robgil, you did use it as a dry powder and not try making a putty of course? Yeah, ok, silly question. Yes, measure the 3:1 by volume, but again this is not critical and the lime should go hard whatever the ratio - even neat lime.

 

[jamest]

Hi there,

I thought I might add something to this thread too (I've followed some of the stories on this forum with great interest over the last year or two).

Anyway, I can describe my experience with NHL2 and 3.5 mortar that I've been using recently for pointing, bricklaying and some other things around the house. If you let the stuff dry on the board or in an open container then it dries to the consistency of a Farley's rusk. I found that it can do the same thing in the joints under a couple of conditions.If the mix is a little bit too sloppy for pointing (but maybe OK for laying bricks with), then it’s hard to work with and you can end up pressing it into the joints too hard and/or often to get it to stay in. This seems to squeeze water out of it and/or bring the sand to the surface (or something), if this happens it can dry brittle and crumbly. If the mix is very dry, then it can end up not compacted enough in the joints and if there are any voids behind the surface layer then it can dry like it does on the board (like a rusk). I find that making sure it’s pushed in firmly to begin with (without squeezing it in) and then beating the crap out of it with a churn brush after an hour or two gets good results.

That's about all I can offer!

J

 

[robgil]

thanks for all the advice guys , its still not dry! it was crumbling because it was still damp , the dry stuff must have dried out too fast but the stuff on the wall is still damp.
there was a lot of water there from when i washed down the beams above bit i didn't think it would take this long to dry out.