NHL 3.5 vs "unrated" NHL for small stone wall/foundation

[dobson156]

Hi,

I'd like to build a very small foundation for a large wood clad log store to ensure that it is off the ground and also level.

Everything else in the area is built from stone and lime mortar so I was just going to effectively built a short (<1ft) and level wall out of stone and sit the legs of the store on top of that.

I've done some research and I reckon NHL 3.5 is what I am after mixed with 2 parts sand.

I went to the local builders yard and they said they did have NHL but on inspection it didn't carry any sort of rating. Not 2, 3.5, 5... nothing. It did give instruction on the back of the 25kg bag saying it was suitable for walls and suggested 1 part lime, 1 part concrete, 2 parts sand.

What is this stuff, is it suitable? Googling suggests there are places near me that carry 3.5 but it is nearly 3x more expensive.

Any insight as to what this unrated Lime is would be very helpful. This foundation does not need to be perfect by any means. That said I'd like to get some experience using and handling "real" NHL as I can now for when I inevitably have to come on to bigger jobs which will require it use.

Thanks

 

[blup]

If you want rated 3.5 lime then pay 3 x over the price of unrated, I doubt it will make a difference for a low foundation strip for a log store.

Blup

 

[jeds]

The 'H' in NHL stands for 'hydraulic'. (natural hydraulic lime) I expect what you've seen in the builders merchant is hydrated lime, which is completely different stuff. Having said all that, as blub says above, I don't see the point in using NHL. Cement mortar would be a better option.

 

[dobson156]

Thanks Jeds, and you're absolutely right, whilst rushing around I didn't pay attention to Hydraulic vs Hydrated. It is of course Hydrated being sold.

I've done some further googling and can't quite get answer; when would you want to add hydrated lime to mortar? Does it have an impact on the final look of the mortar. As that's really what I am trying to match.

 

[stuart45]

Hydrated lime is a pure air lime, which only sets by carbonation. It's a bit weak for a foundation.

 

[dobson156]

Foundation is probably an overstatement. It's just small stone wall to level the ground for the log store and keep its timber feet off the ground.

Reason for thinking about lime is simply so it looks nice and fits in with the surrounding stone work as it will be on view.

 

[stuart45]

You could use a 1/1/6 mix, or a 1/1/5.

 

[jeds]

Hydrated lime is used as a plasticiser. I lived in Aussie for a while and they use it all the time over there. It helps keep the mortar from going off in hot weather. You could mix a bit in to lighten a mix but it won't set properly on its own. As stuart says, 1:1:5 or 6 would be ok.

 

[dobson156]

Thanks again. That answer everything I wanted to know.

TBH, I just had a look at another local building merchants website and they do a premix bag for cheap with hydrated lime in it. Just gonna go for that and call it good. like Blup said, I am sure it'll be fine.

 

[lostinthelight]

I don't know what grade of sand is in premix but I prefer courser sand for stone work . Building with stone can eat up the mortar so don't underestimate what you'll use.