Hydraulic lime and frost

[michael]

Is NHL3 hydraulic lime susceptible to frost damage once it has cured? I understand it takes about 5 to 6 hours to cure hard.

 

[biffvernon]

Oh it will still be susceptible to frost damage. It may feel hard after a few hourse buth there will still be a lot of free water in the mortar for a long time. Only part of the hardening process is the quick chemical reaction of the 'hydraulic' part of the lime. The same process of carbonation that occurs in hydrated lime will also occur in hydraulic lime. This will carry on for weeks or more. As the free water content diminishes so the frost damage recedes but think days rather than hours.

 

[MdB]

and days, weeks, months later, when it rains it will reabsorb some moisture which could then allow frost damage...

Think of lime mortar as being sacrificial requiring repair every generation or so (I believe - not really an expert). Better that the lime suffers rather than your stone or brick work.

 

[michael]

Do you think its a bit late in the year to consider any outside lime work then? Even though the days are either bright, sunny and a little cool or grey wet and humid, there are reports of early morning grass frost in a few places, however I'm on the South coast and I think the reported frost is more inland in the sticks but the nights here are still getting a little chilly.

Not sure whether to chance it or leave it until the spring. Its just a bit of render repair (original stucco render from late 19th century which I think they called Roman cement) Need to cut out and fill a few thinish cracks. Perhaps it might be better to temporarilly fill them with a modern flexible filler like Tetrion just for the winter rather than leaving them open to the elements and then tackle a proper lime repair in the spring. Ive also got a bit of pointing to deal with on an unrendered elevation of the building Any advice appreciated.It would be at least a couple of weeks before I could find the time to do anything anyway.

 

[Flyfisher]

I've got lots of bits of wall with missing render and other faults waiting for repair. I'm using breathable roofing felt to cover such areas and protect against the rain and coming winter until I get around to more permanent repairs in more clement weather. It certainly does a good job but, of course, it does look a bit messy - although that's not a big problem for us as the whole place looks a bit like a building site. Just a thought.

 

[skier-hughes]

Julie, my lime girl, says she'd point in frosty weather, as the frost would rarely attack the upright wall, covering it with hessian to be sure if it gets really cold. Totally freezing would be a different matter. Rain is the worst, as it just washes out what you are putting in!

 

[biffvernon]

We have this discussion every autumn. Unless you are somewhere very frost-prone, I'd be pretty relaxed about it. Particularly on a heated house, the weather would have to be extremely cold to get frost penetrating further far into your vulnerable mortar. It's been a few years since we've had a prolonged cold spell of sub-zero temeratures day and night.

 

[Inspector John]

I've placed one or two empty 45 gal oil drum with the tops cut out, holes drilled in the side near the bottom with some stone/old fire bricks etc (to retain the heat) placed on around the side and firewood just to keep the temperature up a little while rendering and re-lighting there after while theres frost or a risk of frost and maybe cover the render with polythene or bubble wrap

 

[BMcD]

My understanding is that the open structure of the lime when set, is such that when water within the render freezes, the ice crytals have room to expand. However, that said I wouldn't recommend laying on any render if the temperature is likely to drop below 5 degrees C within the following 72hrs.

 

[Tom]

Our last 5 quoins went in last weekend (the final outside work this year). Last night it dropped to 3.5 and we've 4 or 5 more nights of predicted tempertures below this (as low as 0). As the quoins are on North and East facing corners, I'm considering tacking some bubblewrap over them...just in case!!

 

[biffvernon]

Hard to get ice crystals to form above 0 degrees

 

[Tom]

Well, yes, but I'm erring on the side of caution. Like I said, these are on North and East facing walls and we're in quite an open position here. Plus, although the house is heated, it's only at around 16 degrees and the walls are 2-3 feet thick, so it's unlikely any heat will transfer to the outside of the corners.

 

[Jon Maine]

Julie, my lime girl, says she'd point in frosty weather, as the frost would rarely attack the upright wall, covering it with hessian to be sure if it gets really cold. Totally freezing would be a different matter. Rain is the worst, as it just washes out what you are putting in!

This is very much dependent on several variables, sheltered yes not a problem but every job has to be taken on its own merits as Biff says.