Hydrated and Hydraulic Lime Renders, without cement

[larry]

Hello,

I think I have done enough research to have answered my own question but I want to check I'm not going mad.

Renderer is coming Monday to start work on rendering our solid wall house.

We decided we'd go with a lime render for flexibility and breathability. The old sand cement render caused problems.

We had a long chat with the renderer about this and agreed that we'd use lime.

Today we've had a delivery from the builders merchants with two tonne bags of plastering sand and quite a few bags of Hanson Hydrated lime. 

On the TDS this specifically states "As hydrated lime is non-hydraulic, it is not suitable for use in mortars and renders without a Portland cement being present".

We've agreed - no cement. So I spoke to him and asked if there'd been a mixup as I was expecting hydraulic lime. 

He indicated no, it's the stuff he's used many times before, and would mix hydrated lime with sand to form the render. He's done this several times before.

What I read online tells me that if this will set it will take ages to set, and either he needs to add cement (which I don't want) or we need to use a hydraulic lime render.

My current plan is to try to find somewhere that supplies NHL and get this Monday and present as a fait accomplai (which might be harder than I anticipate)

My question is, am I missing something - is a hydrated lime render mixed with sand, no cement, something that  is acceptable in any world? Will it set? Will it last?

 

Thank for advice as ever

 

PS  - why do these sorts of things always seem to happen?? Finding myself in the 'well I'm not a real tradesperson but I'm sure this can't be right' is becoming an uncomfortably familiar feeling 

[nod]

Ask him if you can see some of his previous jobs 

Sand lime is fine under cover 

But it’s normal to mix it 6 sand 1 lime 1 cement for external work 

[jayc89]

What are you rendering onto? Cavity or a solid brick wall?

 

NHL, hydrated lime, has typically been used as it's very much like cement in how you work with it, however more recently studies have suggested that it can actually cure stronger than cement, so hot lime mixes/lime putty are now recommended for solid walls. On cavity walls, breathability really doesn't matter. 

 

Hydrated lime is typically used as a plasticiser, but in theory it can be used to make lime putty too, but it takes a long time. 

 

 

[larry]

15 minutes ago, jayc89 said:

What are you rendering onto? Cavity or a solid brick wall?

 

Solid brick. Pretty soft bricks though many of which are spalled. 

 

16 minutes ago, jayc89 said:

NHL, hydrated lime, has typically been used as it's very much like cement in how you work with it, however more recently studies have suggested that it can actually cure stronger than cement, so hot lime mixes/lime putty are now recommended for solid walls. On cavity walls, breathability really doesn't matter. 

 

Hydrated lime is typically used as a plasticiser, but in theory it can be used to make lime putty too, but it takes a long time. 

 

 

This is interesting. I don't think he's planning to make a putty from it though.

Re curing strength, presumably is that why you'd use e.g. NHL 2 not 3.5 on a soft wall? 

 

1 hour ago, nod said:

Ask him if you can see some of his previous jobs 

Sand lime is fine under cover 

But it’s normal to mix it 6 sand 1 lime 1 cement for external work 

Nod, thanks. Yes, 6:1:1 is what is listed on the TDS. Having been told multiple times to avoid cement, and having our previous s&c render fail, this is what I want to avoid. 

 

What happens to "sand lime" if not under cover! In a fairly dry part of country if it makes a difference.

Could it be done as a base coat with an NHL top coat or is that mixing apples and oranges?

 

Pics from previous jobs look OK. 

 

[jayc89]

7 minutes ago, larry said:

Solid brick. Pretty soft bricks though many of which are spalled. 

 

This is interesting. I don't think he's planning to make a putty from it though.

Re curing strength, presumably is that why you'd use e.g. NHL 2 not 3.5 on a soft wall? 

 

Nod, thanks. Yes, 6:1:1 is what is listed on the TDS. Having been told multiple times to avoid cement, and having our previous s&c render fail, this is what I want to avoid. 

 

What happens to "sand lime" if not under cover! In a fairly dry part of country if it makes a difference.

Could it be done as a base coat with an NHL top coat or is that mixing apples and oranges?

 

Pics from previous jobs look OK. 

 

 

It depends on the manufacturer. There's no real standards when it comes to NHL, so one NHL 2 might be entirely different to another NHL 2. 

If it was me, given you say the bricks are pretty soft, I'd be using a lime putty based render, rather than NHL. There's a couple of Facebook groups that are really useful when it comes to older properties; "Traditional and Listed Building Advice" and "Your Old House UK - Repair and Conservation" I've learned a lots from both. 

[nod]

32 minutes ago, larry said:

Solid brick. Pretty soft bricks though many of which are spalled. 

 

This is interesting. I don't think he's planning to make a putty from it though.

Re curing strength, presumably is that why you'd use e.g. NHL 2 not 3.5 on a soft wall? 

 

Nod, thanks. Yes, 6:1:1 is what is listed on the TDS. Having been told multiple times to avoid cement, and having our previous s&c render fail, this is what I want to avoid. 

 

What happens to "sand lime" if not under cover! In a fairly dry part of country if it makes a difference.

Could it be done as a base coat with an NHL top coat or is that mixing apples and oranges?

 

Pics from previous jobs look OK. 

 

Sand lime acts like a sponge and will never set 

 

many years ago when was an apprentice Sand lime and putty lime was what we used at collage 

We would plaster walls and the following we knock it off the wall and chuck it back in the mixer and reuse Week after week 

 

Even a spade of cement will help bind it together 

[jayc89]

18 minutes ago, nod said:

Sand lime acts like a sponge and will never set 

 

many years ago when was an apprentice Sand lime and putty lime was what we used at collage 

We would plaster walls and the following we knock it off the wall and chuck it back in the mixer and reuse Week after week 

 

Even a spade of cement will help bind it together 

doesn’t that depend on the carbonation process?

[jfb]

8 hours ago, nod said:

Sand lime acts like a sponge and will never set 

 

many years ago when was an apprentice Sand lime and putty lime was what we used at collage 

We would plaster walls and the following we knock it off the wall and chuck it back in the mixer and reuse Week after week 

 

Even a spade of cement will help bind it together 

By sand lime do you mean sand and NHL ? 
If so, it’s simply not true that it won’t set. If it’s cold and damp it can take a

while to set but in conditions like this it will set much faster. 
 

to the OP. I would contend that the builder has never actually used a lime render and be worried about presenting him with hydraulic lime to get on with. It’s not actually much harder than sand/cement rendering but takes a bit more care as it needs to be kept damp after application (getting the hose out and spraying the walls every day for a few days). also unlike with cement render you don’t really want to apply the finish coat the day after the scratch coat so would have a to wait a few days (depending on how much it has gone of). Probably a reason why builders like using cement, they can move on to the next job quicker.

 

can’t speak to putty as I haven’t really used it for rendering. But if you go for NHL I would use 3.5 not 2.

what sand have you got? You say you have plastering sand - not all is the same. Is it very fine or does it have some sharpness to it? (I’d want it not to be too fine)

 

[nod]

14 minutes ago, jfb said:

By sand lime do you mean sand and NHL ? 
If so, it’s simply not true that it won’t set. If it’s cold and damp it can take a

while to set but in conditions like this it will set much faster. 
 

to the OP. I would contend that the builder has never actually used a lime render and be worried about presenting him with hydraulic lime to get on with. It’s not actually much harder than sand/cement rendering but takes a bit more care as it needs to be kept damp after application (getting the hose out and spraying the walls every day for a few days). also unlike with cement render you don’t really want to apply the finish coat the day after the scratch coat so would have a to wait a few days (depending on how much it has gone of). Probably a reason why builders like using cement, they can move on to the next job quicker.

 

can’t speak to putty as I haven’t really used it for rendering. But if you go for NHL I would use 3.5 not 2.

what sand have you got? You say you have plastering sand - not all is the same. Is it very fine or does it have some sharpness to it? (I’d want it not to be too fine)

Sand lime doesn’t set 

If you take an old wall down that’s built with sand lime 

You can lift each brick off without any effort and simply dust the bricks off

Ive year’s experience with this stuff 

Pasting and copying paragraphs from google doesn’t really give the full picture Also If the bricks are soft and have had render stripped off them I would be fixing a steel mesh prior to starting Regardless of what I was putting on 

You probably won’t find that bit of advise on Google But I’ve redone dozens of properties that have been re rendered less than five years 

 

[larry]

42 minutes ago, jfb said:

By sand lime do you mean sand and NHL ? 
If so, it’s simply not true that it won’t set. If it’s cold and damp it can take a

while to set but in conditions like this it will set much faster. 
 

 

I think @nod was referring to hydrated lime + sand without cement. 

 

42 minutes ago, jfb said:

to the OP. I would contend that the builder has never actually used a lime render and be worried about presenting him with hydraulic lime to get on with. It’s not actually much harder than sand/cement rendering but takes a bit more care as it needs to be kept damp after application (getting the hose out and spraying the walls every day for a few days). also unlike with cement render you don’t really want to apply the finish coat the day after the scratch coat so would have a to wait a few days (depending on how much it has gone of). Probably a reason why builders like using cement, they can move on to the next job quicker.

 

Thank you. The same thought had crossed my mind also. Pragmatically, though, I think I'm using this chap. Scaffolding is going up literally as I type and I think he can render, which frankly is more than I can do. 

Remember though he was anticipating putting this up without cement and had implied that this would take a longer time than with cement, so the 'it takes a bit longer' I think might be fine. 

The additional care is perhaps something I can help with also e.g. happy to keep it wet. 

 

42 minutes ago, jfb said:

 

can’t speak to putty as I haven’t really used it for rendering. But if you go for NHL I would use 3.5 not 2.

what sand have you got? You say you have plastering sand - not all is the same. Is it very fine or does it have some sharpness to it? (I’d want it not to be too fine)

 

 

There are clearly a few different views both here and only as to the merits of putty vs NHL, though it sounds like both are 'accepted' approaches. 

Sand wise - no idea - just plastering sand from builder's merchants. How can I tell if it's too fine?

 

I guess I'm left with a bit of confusion though  - don't use hydrated lime + sand as it won't set at all, vs. it will set eventually, by carbonation,; don't use NHL as it's too strong so use lime putty (which also will set by carbonation)  vs NHL is fine (as I can say both seem to be approaches that you can find a legitimate source for). Which makes me think if there is a logic to using non-hydraulic hydrated lime  + sand only....  the information gap I have is how this would behave differently to lime putty (also non hydraulic lime) in practice.

 

Goodness before the internet I would haven't even queried this and we'd have just been done with it. Makes me think, are there houses out there where people have had hydrated lime + sand only and actually it has set/been completely fine.

 

Thanks for bearing with me and helping me unpick my logic!

[SteamyTea]

Here we go again.

Breathability.

It is taken on trust that lime based renders breath, and cement based renders don't.

Can anyone evidence this, I have been looking for years, the data is scarce to say the least.

What you need is a number in SI which is kg.m.m^-2.d^-1, that is the unit for vapour permeability.

Unfortunately most people in the industry do not stick to the SI system (why I have no idea as for most there is only 4 units to remember)

Thankfully there is this table to help people out.

 

 I have found this, which is about rammed earth, but it does mention lime. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8123846/

Trouble is, it does not specify what the concrete mix type was, or the lime mix type.

But it does show how the testing is done.

 

 

 

 

[larry]

1 minute ago, SteamyTea said:

Here we go again.

Breathability.

It is taken on trust that lime based renders breath, and cement based renders don't.

Can anyone evidence this, I have been looking for years, the data is scarce to say the least.

What you need is a number in SI which is kg.m.m^-2.d^-1, that is the unit for vapour permeability.

Unfortunately most people in the industry do not stick to the SI system (why I have no idea as for most there is only 4 units to remember)

Thankfully there is this table to help people out.

 

 I have found this, which is about rammed earth, but it does mention lime. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8123846/

Trouble is, it does not specify what the concrete mix type was, or the lime mix type.

But it does show how the testing is done.

 

 

 

 

Thanks @SteamyTea. I'm with you. From my own reading I think you are right that cement does not render (sorry) the plaster unbreathable. However the other properties of lime (flexibility and hygroscopicity) have been highlighted to me as also desirable. The cracks in our old cement render certainly convince me that the flexibility is desirable. I also suspect the standard masonry paint the last owner piled over the top didn't help. 

 

maybe then a hydrated lime + sand render that never sets will offer the ultimate in flexibility!!

 

I'll look at that paper 🙂

[ToughButterCup]

8 minutes ago, larry said:

.... I also suspect the standard masonry paint the last owner piled over the top didn't help. ...

 

Interesting comment. For us, your comment come just in time.

What rouses your suspicion, and - let's assume your suspicion is correct - which paint (or type of paint) would you suggest?

Is there such a thing as breathable paint ?  

 

 

PS

Apologies: I've asked a question I could have answered for myself

Here's a list of external, breathable paints

https://ggle.io/5uX3

 

Thank you @larry very  much indeed for raising the issue. Helped me avoid  a possible error.

Edited June 17, 2023 by ToughButterCup

[SteamyTea]

4 minutes ago, larry said:

However

Yes, I think the problem with all renders, and then secondary coatings is really the problem, and that is before the real issues of what is causing the vapours to permutate though the walls is addressed.

 

Do people who are about to lime render still coat a wall with PVA? Or a similar adhesive.

How much difference to compressive and tensile strength does the type of sand or 'grit' make?

What about thermal expansion, are there much differences for the same amount of sand in the mixes?  A wall in the sun can get quite hot, even if the air temperature is not excessive.

 

[ToughButterCup]

8 minutes ago, SteamyTea said:

.... A wall in the sun can get quite hot, even if the air temperature is not excessive.

 

An interesting thought:

We have a partially shaded 'Winter Garden' that has just been rendered. With all this sun and the recent render, we've been looking at the wall more than normal (glad not to see the blocks any more) - and realised that one area of the wall (2m sq?) gets full sun in the afternoon. We have embedded that thin pink plastic grid stuff (forgotten the trade name) in the render to help absorb movement in it. But didn't think at all about temperature variation within the same area of wall...... 

 

Probably overthinking it as usual. 

[larry]

19 minutes ago, ToughButterCup said:

 

Interesting comment. For us, your comment come just in time.

What rouses your suspicion, and - let's assume your suspicion is correct - which paint (or type of paint) would you suggest?

Is there such a thing as breathable paint ?  

 

 

PS

Apologies: I've asked a question I could have answered for myself

Here's a list of external, breathable paints

https://ggle.io/5uX3

 

Thank you @larry very  much indeed for raising the issue. Helped me avoid  a possible error.

 

I've used Tikkurilla paints internally who publish SD values and are reasonably priced.

 

Yes, I'd you look at Google steet view for my house in 2009 it is brown unpainted sand/cement, which I reckon was possibly nearly 100 years old. In 2016ish it was painted with homebase masonry paint (I know this as owner left the spare tub in the shed). In 2022 we then had penetrating damp with lots of cracks on render and spalled bricks underneath. 

 

[larry]

18 minutes ago, SteamyTea said:

 

Do people who are about to lime render still coat a wall with PVA? Or a similar adhesive.

 

I think this is also a key observation. Might as well put a layer of cling film on the wall....

[jayc89]

I have a gable end wall that was pointed with cement at some point. The majority of bricks below 1m have spalled. The rest of the house is pointed in lime and those bricks are fine. Pretty conclusive to me. 
 

Lime render needs a harling coat, bit like a slurry, which acts as the key. Shouldn’t be using anything like PVA.

[SteamyTea]

4 minutes ago, jayc89 said:

I have a gable end wall that was pointed with cement at some point. The majority of bricks below 1m have spalled. The rest of the house is pointed in lime and those bricks are fine. Pretty conclusive to me. 

Purely from a science perspective it is not conclusive at all.

Find 1001 walls that have the same starting conditions and see what the results are.  Then calculate the confidence interval.

13 minutes ago, larry said:

Might as well put a layer of cling film on the wall

Yes, I am not sure how it affects everything.  I get the impression it is used to keep the dust and grit in place until the first coat is on.

@nod, do you know?

[jayc89]

16 minutes ago, SteamyTea said:

Purely from a science perspective it is not conclusive at all.

Find 1001 walls that have the same starting conditions and see what the results are.  Then calculate the confidence interval.

Yes, I am not sure how it affects everything.  I get the impression it is used to keep the dust and grit in place until the first coat is on.

@nod, do you know?

I can literally turn the corner to where it‘s lime mortar and the bricks are fine. I’m about to have the cement raked out and repointed in lime so I guess we’ll see. 

[nod]

24 minutes ago, SteamyTea said:

Purely from a science perspective it is not conclusive at all.

Find 1001 walls that have the same starting conditions and see what the results are.  Then calculate the confidence interval.

Yes, I am not sure how it affects everything.  I get the impression it is used to keep the dust and grit in place until the first coat is on.

@nod, do you know?

Yes I do know 

Probably a lot more than google 

NO you don’t seal But you will need to mesh 

 

As contractor I’m using lime renders on a monthly basis You can’t cut corners 

[jfb]

Please don’t use hydrated lime and sand - it won’t set. I would definitely use NHL 3.5 not hydrated/cement myself. 

ratio 3:1 sand:lime

if your chap is fine to take a bit of time to do it should be fine. 

[jayc89]

12 minutes ago, jfb said:

Please don’t use hydrated lime and sand - it won’t set. I would definitely use NHL 3.5 not hydrated/cement myself. 

ratio 3:1 sand:lime

if your chap is fine to take a bit of time to do it should be fine. 

I direct mix of hydrated lime and sand won’t set, no. It’s often used as a practice mortar for that reason.

 

But it can be made into a putty which will 

 

[SteamyTea]

23 minutes ago, nod said:

you don’t seal But you will need to mesh 

Do you mean that expanded metal sheet stuff that is nailed to the walls?

[nod]

15 minutes ago, SteamyTea said:

Do you mean that expanded metal sheet stuff that is nailed to the walls?

I do 2.4 x600 sheets We normally plug and screw Stainless steel screws and 40 mil washers 

More often than not the render has pulled the faces of the brick off 

Some companies choose to grind the joints out prior to us starting 

This does the same job Just gives something for the render to key to 

I don’t even quote for re renders 

without the above being done 

 

If you put mesh on you will never get any issues 

We guarantee all our renders for five years No quibble 

So we have to be belt and braces