pre mixed lime mortar ?

[Ollie78]

I am refurbishing some big sash windows in a church at the moment and on some of them fairly large amounts of mortar have fallen out from between the outside of the boxes and the stone.
My normal process to tackle this is to expanding foam in the back of the gap and then use a pre mixed cement mortar to point in the remaining gap.
However, because this is a stone place built in the 1800`s I suspect I should be using a lime based mortar. Some various repairs have been done with different colours of cement before, they don`t look right at all and some have cracked away where the cement was too hard.

So, is there a lime based product where I can "just add water" similar to a pre mixed cement mortar ? Or even a wet mix in tubs/bags like the drywall adhesive comes in sometimes?
Mainly because I will only be needing half a bucket at a time and am not experienced enough with the stuff to get the mix right etc.

Cheers
Ollie

 

[Blackswanwood]

Yes - it’s called hot lime mortar and you can buy it in tubs ready to use.

 

[Blackswanwood]

Ollie - another thought - there is a product called Gunlime which is a lime mortar made specifically for use with a pointing gun.

 

[Jake]

There are dry pre-mixed hydraulic limes, Lime Green is the brand I recall off the top of my head but there are many others. There are also tubs of trad lime putty based mortars. Have a look at Conserv / Mike Wye / Masons Mortar or the like, there are a bunch of suppliers. But for just a bit the shipping is going to be costly. The mixes are not complicated, sharpish sand and the lime component, volume based.

It's getting very late in the year to be applying lime putty type mortars, although it's very mild so you might get away with it. A hydraulic lime might be a better idea but the purists will say otherwise.

 

[Ollie78]

Thanks for this, its easier to find once you know the name of it.
Just looked at some of the hot lime mortar and it says it takes a year to cure! . This seems a bit insane but I am assuming it will "dry" quicker than that.

A bit worrying about the lateness of the year as @Jake has said I am assuming this is mainly a temperature problem.

A bit more detail on the job the windows are between 2.5m and 3m tall and sit against nicely faced stone external reveals (probably the wrong name for them)
On the second window I started,basically all the previous pointing fell out as I was getting the sashes out with some careful violence, the gap varies from 5mm to about 20mm and as deep as 100mm but I will back fill with foam.
I am replacing the cills and bedding them on a hybrid polymer sealant. If the gap was small I would seal it with this as well but not at that size.

I have just discovered burnt sand trowel mastic which looks like it might work but is also hidiously expensive at £42 for 10litres (there are 10 of these windows). Any views on this stuff?

Will the hydraulic lime mortar be a better bet over the hot lime ? not really sure what to do now.

 

[Jake]

Lime putty sets by a very slow reaction with atmospheric CO2. Hydraulic lime will set by reacting with the water in the mix.

The "proper" old fashioned way is to wait until Spring, as then lime putty will have a good run of months to at least cure on the surface.

Personally, If I was doing your job at this time of year I'd use NHL. What stone is it?

 

[Ollie78]

Lime putty sets by a very slow reaction with atmospheric CO2. Hydraulic lime will set by reacting with the water in the mix.

The "proper" old fashioned way is to wait until Spring, as then lime putty will have a good run of months to at least cure on the surface.

Personally, If I was doing your job at this time of year I'd use NHL. What stone is it?

I think its a sandstone of some sort, will take a picture tomorrow, waiting till spring not ideal due to scaffolding etc.

 

[johnnyb]

Burnt sand mastic is just linseed and dry sand. In the appropriate colour its perfect for pointing stonework around timber windows. But were talking a fillet. Like you'd use putty size. Bigger bits need something else. Contact a few companies with pics for the best way/ materials.

 

[pgrbff]

Speak to Masons Mortar in Scotland. I would not use hot lime or putty lime mortar, (fat lime), especialy at this time of year. It would need to be monitored for days or even weeks, keeping off the wind, sun and cold, usualy using damp hessian. If you buy premixed hydraulic mortar it can, depending on the brand, be treated like cement mortar. I suspect they add lots of additives as it is much easier to use than bagged hydraulic lime mixed with sand.
I fit all my windows with NHL 3.5 premixed hydraulic lime mortar. Needs keeping damp, above 5C for 3-5 days, but will start setting within hours rather than days for fat lime mortar.
Burnt sand mastic is used instead of silicon to. Form a final fillet on the outside.
I use Vimark here in Italy, very easy to use, instructions are also in English so may be available in the UK.
When I lived in Ireland I would buy St Astier lime and mix it with sharp sand but it was far more difficult to look after.

 

[Ollie78]

Thanks for the advice so far everyone.
Here is a couple of pics of the windows in question if it sheds any further light on it.

The stone arch bit.

The gap in question

Closeup of gap

The stuff that fell out of the gap

 

[Doug71]

I've used the lime mortar in tubs before, think I got it from here https://www.womersleys.co.uk/ looks like they even sell it on Amazon now. They do a stone repair mix which looks interesting.

I know this will offend some but a builder I know has a mix he uses to imitate lime mortar if needed which is something like 4:2:1:1 which I think is 4 building sand, 2 grit sand, 1 lime (builders/hydrated) and 1 cement (mix of grey and white depending on colour needed).

I used burnt sand mastic around my own windows and some of it fell out (probably operator error). I often use Everbuild Trowel Mastic which is like a modern version of the burnt sand but I find easier to use and seems to stay in place better!

 

[Old.bodger]

On the subject of cement….
I understand a small inclusion of Prompt cement
https://masonsmortar.co.uk/shop/natural-cement/prompt-natural-cement/#
Gives an authentic colour and a ‘false’ set to assist at this time of the year. I think you need citric acid to adjust the setting time of the Prompt………interesting stuff !

 

[Homers double]

I’ve recently had a conversation with Rose of Jericho who are based near to Dorchester, depending where in Wiltshire you are it may be worth a visit.
They are extremely helpful and can do colour matching of lime mortar

https://roseofjericho.co.uk/shop/

 

[Jake]

Thanks for the advice so far everyone.
Here is a couple of pics of the windows in question if it sheds any further light on it.


Closeup of gap


The stuff that fell out of the gap
View attachment 191931

That's lime mortar for sure and as you say the stone looks like a sandstone or something, but anyway not a pretty impervious granite etc, I wouldn't use a cement mortar against that. Give those merchants and call and those photos, see what they advise. Premix NHL2 or 3 maybe, I'd guess.

 

[Ollie78]

That's lime mortar for sure and as you say the stone looks like a sandstone or something, but anyway not a pretty impervious granite etc, I wouldn't use a cement mortar against that. Give those merchants and call and those photos, see what they advise. Premix NHL2 or 3 maybe, I'd guess.

Thanks for all the information. I will give them a call tomorrow and see what they suggest.

 

[Ollie78]

A small update for future reference.
After contacting a couple of suppliers one suggested nhl 2.5 lime mortar but apparently this will need 56 days under hessian so is really no good as I cannot cover them easily and need to take the scaffolding down as well.
The other option suggested was Womersly ironstone pre mixed mortar, they made no mention of covering it for ages but do say it must be kept moist for a few days and above 5 degrees. So I will probably end up trying that one out.

 

[pgrbff]

2.5 would only be needed with very friable stone or brick, 3.5 is the most common. As youare using it in small amounts around a window I am sure you will be fine. Use a pointing gun if you have one, damp down the stone before application, a small spray bottle like bath or kitchen cleaner is fine. As it sets up keep misting it. Cover well if it's cold, less than 5C, or very windy. It could still be soft the next day, I don't know the product, you should be able to mist and brush off with a paint brush to clean up the surrounding stone the next day.

 

[Stuart Moffat]

Is it a listed building?
Is it a Church of England church?
If the latter then the process for building control is essentially delegated, and the answer to your question would be proposed by the church’s appointed architect, and then approved by an appointed person that covers the whole diocese. Bureaucratic but having had to deal with poor inappropriate stonework repairs on our village church then if the answer to either question is yes, make sure the church follows the process I would suggest.

 

[Ollie78]

Is it a listed building?
Is it a Church of England church?
If the latter then the process for building control is essentially delegated, and the answer to your question would be proposed by the church’s appointed architect, and then approved by an appointed person that covers the whole diocese. Bureaucratic but having had to deal with poor inappropriate stonework repairs on our village church then if the answer to either question is yes, make sure the church follows the process I would suggest.

It was a methodist church but now a home. They are living in another part of the building and only now sorting out the main church bit.
It is in a conservation area, not sure what grade of listing. I am just fixing the windows.

 

[Stuart Moffat]

Ollie if it’s in a conservation area and not listed, you can ignore everything I said!
Stuart