Working with Hydraulic Lime below 5 degrees

[Tom]

Last night it dropped down to 3.9 degrees here (Lincolnshire). I'm almost done with the work outside (for this year, anyway!) and only have 4 quoins to fit, which are currently on order from the quarry. I'm hoping to have these within a couple of weeks. The mortar will be 3:1 Sand:Hydraulic Lime. Will it be ok to do this last bit of work? If I do it, should I try to cover the area with hessian (although that would be quite tricky) or would it make no difference? I'd be happy to leave this work until next year if it were possible but the area is load bearing (1/4 up on the corner of the the house) and the stone there at present is very weak. Any help would be gratefully received. Thanks.

Jaqy

 

[johnandrew]

Jaqy

The Victorian Farm on BBC2 showed the building of a pig sty in winter using lime mortar. They too were very concerned about the risk of frost damage. They covered the work with sheep skins overnight to protect it. I would suggest that covering your work to protect against frost would be very advisable.

The risk of failure might vary according to how hydraulic your mortar is and how much of a set you get before the temperature drops. Are you using NHL 2, 3.5, or 5? Or something else?

In summary, my suggestion would be to protect it, whatever mortar you are using. Better that than risk failure.

John

 

[Flyfisher]

Last winter I had some lime mortar fail during the frosts. It was standard 3:1 mix using hydrated lime. I didn't protect it from the frost.

BUT . . . I did the work in May :!:
It was the mortar applied underneath pantiles on the end of a roof, so not a structural issue, but it was certainly annoying.

Any suggestions why this should have happened?

 

[DaveBrigg]

Part of our render suffered frost damage last winter, and that was finished in August. However, it was part of a garden wall, so not affected by warmth from the house. There was also a little damage at the base of a wall of a room which is not usually heated. The base of the wall had the most moisture, as the wall dried from the top downwards. If your house is heated, that might make the difference. I would be tempted to go ahead anyway. If the lime suffers frost damage I imagine it will only be on the exposed edges, which could be repointed in the spring.

 

[biffvernon]

I don't see how the type of lime, hydrated or hydraulic, can make any difference. Frost damage occurs when free water in a mortar that has not yet set hard freezes, expanding and breaking the interlocking structure of growing calcium carbonate crystals. The temperature has to be below 0 degrees within the mortar for damage to occur so the slight ground frosts we get in the autumn probably won't matter.

 

[Gareth Hughes]

But I seem to recall from science lessons that the thermal expansion / contraction graph of water behaves slightly oddly at about plus 4 degrees?

 

[Flyfisher]

Is this an example where the breathability of lime mortar is a disadvantage? Lime work done in the summer must surely have set properly by winter and, I assume, would have dried out nicely. To be frost damaged it must, presumably, have absorbed sufficient water for the damage to occur.

I wasn't expecting to be repointing after just one year.

 

[Gareth Hughes]

Even so, better to sacrifice the pointing to the frost gods than the bricks...

 

[Flyfisher]

Yes, I've no problem with the principle, just the timescale. Who wants to re-point their failing mortar every year?

 

[Tom]

Thanks for all the replies. Answering some of the questions;

I'm using NHL 3.5

The house is heated but the walls are between 2 and 3 foot thick and these are quoins I'm talking about, so it's unlikely any heat will reach them at all. Plus, they're on a corner which faces North and West so they'll get very little in the way on any warm air / sun on them but will get all the cold wind at night.

I'm happy to fit them and cover with hessian until next year. Fortunately, they're all on top of each other rather than spread out up the wall, so it'll just be one lot of hessian. Next year, I can rake out any mortar which has failed. Hopefully, this will only be to a depth of 2 or 3 inches and the deeper stuff will be fine. If it all fails, I'll just have to take all the 4 out next year and redo. Not the end of the world, in the great scheme of things :roll:

Thanks for all the advice. If anyone can think of anything I haven't taken into account, please let me know. Thanks again.

Jaqy

 

[biffvernon]

But I seem to recall from science lessons that the thermal expansion / contraction graph of water behaves slightly oddly at about plus 4 degrees?

Yes water expands as it cools below 4 degrees (not by very much) but while it's liquid it doesn't do any harm. It can just ooze out. It's the growing ice crystals that have the power to break rock.