Using Lime Mortar to repoint

[oxalto]

I am about to begin repointing my house in lime mortar. I have removed the cement which was previously used to repoint on top of the old lime mortar and will begin raking out where needed. The house is built in random uncoursed rubble limestone, in the normal manner with earth as the main mortar and lime mortar on the outer (and inner) face. I have 3 questions for the great sages of PPUK, please:

1. At what depth is it ok to stop raking out? (The loose old lime mortar comes out easily but then I could keep going further into soil until I hit the inside of the house, as it is all "loose")

2. Do I need to cover the new lime mortar with dampened hessien immediately, or only after it is green hard? I understand that I should dampen all the stonework prior to repointing, and then try to keep it from drying out too quickly.

3. Some of the pointing around the stones has become so loose that the odd stone has fallen out (some quite large). Is this mortar ok to use to reset the stones, or should I try to use an earth mix again? Ought I to build up the mortar in stages when resetting or can I use a 6 inch depth in one go?

I am using a coarse mix from the Old House Store which is a 3:1 mix - the website calls it "A plastering grade ready-mixed mortar containing a blend of the finest high quality well-graded sharp and soft sands with matured buxton lime putty. Used for plastering, rendering, bricklaying and pointing"

Thanks in advance for your help!

 

[MdB]

1. At what depth is it ok to stop raking out? (The loose old lime mortar comes out easily but then I could keep going further into soil until I hit the inside of the house, as it is all "loose")

I believe the recommended depth is the same as the width of the joint. I also hoover out anything that is lose enough to be sucked out. If it is that bad then it isn't doing anything useful so might as well be replaced.

2. Do I need to cover the new lime mortar with dampened hessien immediately, or only after it is green hard? I understand that I should dampen all the stonework prior to repointing, and then try to keep it from drying out too quickly.

You can't harm it by keeping it damp - it just won't set. I therefore keep on spraying as much as possible as soon as possible. A certain amount depends on the stone - our sandstone just sucks the moisture up whilst the granite I fitted to the hearth is still a bit damp though it hasn't been sprayed at all.

3. Some of the pointing around the stones has become so loose that the odd stone has fallen out (some quite large). Is this mortar ok to use to reset the stones, or should I try to use an earth mix again? Ought I to build up the mortar in stages when resetting or can I use a 6 inch depth in one go?

Only the odd stone? Lucky you.
My understanding is that putty based mortar is fine for repair type work but you want something stronger (NHL 3.5 for example) for structures that need greater strength such as chimneys. If you put a large depth of mortar into the wall, it will take a very long time to reach full strength as the deeper stuff won't carbonate for many years. However this isn't necessarily a bad thing as it will act as a spacer fine (which is its main job) and if the wall cracks, the uncarbonated lime will be exposed and then carbonate. This is the self repairing function of lime that you may of heard of. Personally, I've used putty based lime to repair large sections of my wall on the grounds that I didn't have easy access to NHL, the repairs didn't need great structural strength but mainly because lime mortar of any description would be far stronger than the soil/cob mortar and voids that were there before.


My fireplace part way through renovation.

My fireplace once complete.

 

[oxalto]

Thanks for the tips Mdb - your fireplace looks to be a similar construction to my house so i'll follow your lead and reset the stones in lime mortar. You make a very good point about it being stronger than the earth mix!

I'll try to keep to mortar as moist as possible then. Any idea how long it is likely to be before it is green hard if used externally in the current warmish/dryish conditions? How long ought I to keep the dampened hessien on for?

Do you literally hoover out your joints by the way?! This mightn't be too easy externally and I'd have a full bag in seconds! Someone else suggested hosing them out - any thoughts?

 

[MdB]

I'll try to keep to mortar as moist as possible then. Any idea how long it is likely to be before it is green hard if used externally in the current warmish/dryish conditions? How long ought I to keep the dampened hessien on for?

I'm not sure, I've only done a bit of external pointing and I didn't have the option of using sacking as it would have been in the way of the builders who were rebuilding the wall next to the bit I did. I tried to spray it as often as possible but it probably could have done with more. Our walls are so porous the wall was often dry 30 seconds after you stopped spraying.

Do you literally hoover out your joints by the way?! This mightn't be too easy externally and I'd have a full bag in seconds! Someone else suggested hosing them out - any thoughts?

Yep, I did though it did cause the odd raised eyebrow from neighbours when I was up the scaffold tower. I uses an old Dyson with the filters removed. Being bagless, it was easy to empty which was needed lots of times - sometimes every 5 minutes. The Dyson did well as it took a lot of punishment. It finally gave up the ghost with a worn out motor bearing - most likely due to the removed filters as they protect the motor.

I now have a Henry which is ok but uses bags so would get expensive to do the same job and it isn't as easy to dispose of the collected dirt/dust.

I definitely wouldn't use a hose. This will very quickly erode mud/cob which is in good nick and also soften the rest. An air compressor might be an idea though - not that I've tried it.

 

[Flyfisher]

I now have a Henry which is ok but uses bags so would get expensive to do the same job and it isn't as easy to dispose of the collected dirt/dust.

I use a Henry for 'building' jobs but I don't bother with a bag, which makes it very easy to empty - just undo two clips, lift off the motor unit together with the fabric filter, remove the hose and carry the lower half to the dustbin/skip for emptying.

Perhaps not using a bag will reduce poor Henry's working life, but he shows no signs of failure so far. The fabric filter seems to do a pretty good job of keeping the dirt out of the motor unit, so maybe a bag isn't strictly necessary.

 

[MdB]

The fabric filter seems to do a pretty good job of keeping the dirt out of the motor unit, so maybe a bag isn't strictly necessary.

This will reduce performance / motor life in the long term and our Henry is a bit too new to do this to yet. Once it is a bit older, I guess we will probably go bagless too.

 

[CliffordPope]

I'd be cautious of using a hoover. My cottage walls appear to have been made with random sized stones set in mud. This has now dried to a powder, which is retained by the pointing, inside and out. Raking out a joint releases a trickle of soil.
Hoovering it would probably suck out the entire wall. In cases where long decay had exposed empty fissures several feet deep I made a feeble attempt to ram in fresh mortar with a broom handle, but it is a hopeless task.
The main purpose of the pointing seems to be to stop water getting in, and prevent soil running out. It doesn't need any encouragement with raking.

 

[MdB]

I'd be cautious of using a hoover. My cottage walls appear to have been made with random sized stones set in mud. This has now dried to a powder, which is retained by the pointing, inside and out. Raking out a joint releases a trickle of soil.
Hoovering it would probably suck out the entire wall. In cases where long decay had exposed empty fissures several feet deep I made a feeble attempt to ram in fresh mortar with a broom handle, but it is a hopeless task.
The main purpose of the pointing seems to be to stop water getting in, and prevent soil running out. It doesn't need any encouragement with raking.

I guess it depends on the state of your soil. Where ours is taking weight, it is hard packed and takes effort to remove it - the hoover / dyson / henry doesn't touch it so it isn't a problem. If your soil is very lose though, as you say, you don't want to suck it all out.

I too filled in deep cracks where I could with a ram rod but you are right, I can't imagine it improved things a great deal as I believe the centre of our walls is just rock and void with very little mud/soil holding it together.

 

[oxalto]

Thanks for all the advice everyone. I'll try to rake back to sound earth where it is to be found and go easy where the soil has become powdery.

Of course Restoration Home has just told me that my walls are poorly constructed and about to fall down with the weight of a heavy roof on top. This seems a shame since in some places the stone was put around an earlier timber frame structure to keep it from falling down.

I was relieved, though, when the same tv prog deemed uncoursed random rubble most suitable for a farmhouse. I'd better start removing the dressed stone Georgian areas then....

 

[Feltwell]

I use a Henry for 'building' jobs but I don't bother with a bag, which makes it very easy to empty - just undo two clips, lift off the motor unit together with the fabric filter, remove the hose and carry the lower half to the dustbin/skip for emptying.

Perhaps not using a bag will reduce poor Henry's working life, but he shows no signs of failure so far. The fabric filter seems to do a pretty good job of keeping the dirt out of the motor unit, so maybe a bag isn't strictly necessary.

I have an ancient, metal bodied "Henry" - in fact it's from before they gave them the name! My parents got it at some point in the 1980's, and it wasn't new then. It's never been used with bags, and has always been used for those jobs that might wreck the "good" vacuum that's used for the "normal" cleaning of the house.

It's a great bit of kit, not the most powerful but very reliable despite the abuse! The only downside of no bags is that when emptying it you tend to get covered in a fair bit of the dust, especially when banging the worst of the dust out of the fabric filter. It also always emits a good blast of dust from the motor vent when it's first switched on after having been emptied.

Dysons often die as few people ever wash out the motor filter, which is supposed to be done every 6 months. The incoming air cools the motor, with a clogged filter it overheats and eventually fails. Cleaning the filter out is very easy but not as easy as forgetting to do it! I'm guilty of this, mine was only saved recently by the thermal trip switch cutting in before the motor failed. The filter was clogged with plaster dust, I've heard before that Dysons do not appreciate being used on plaster dust

 

[FamilyWiggs]

A bagged vacuum cleaner can be made almost bagless, by unsealing the bottom of the paper bag.

When in use, the bottom can be folded over a couple of times and held with a spring clip or similar. This is then removed to aid emptying, before resealing and re-using the bag.

I do this for dirty dusty building jobs with an old Vax, because otherwise the motor filter gets totally clogged or you are spending a fortune on paper bags.

It seems to work.

I wouldn't however advocate the Yorkshire method, of washing the paper bag to get further uses out of it! 8)

 

[Flyfisher]

The only downside of no bags is that . . . . . It also always emits a good blast of dust from the motor vent when it's first switched on after having been emptied.

Yes, more dust will be expelled through the vacuum cleaner exhaust. My solution to this was to buy an eight metre flexible hose, which allows me to put the main unit outside the room in question, preferably outside the house completely. This works particularly well when cleaning up confined spaces such as attics.

 

[AMc]

Dysons often die as few people ever wash out the motor filter, which is supposed to be done every 6 months. The incoming air cools the motor, with a clogged filter it overheats and eventually fails. Cleaning the filter out is very easy but not as easy as forgetting to do it! I'm guilty of this, mine was only saved recently by the thermal trip switch cutting in before the motor failed. The filter was clogged with plaster dust, I've heard before that Dysons do not appreciate being used on plaster dust

I used to regularly trip the thermal switch on our DC02 because the filters would clog - leaving it to cool for an hour and rinsing the filters brought it back to life. I wouldn't recommend it but you can accelerate the drying of the washed filters by putting them on the motor exhaust side I did rinse them fairly regularly but my house has been so full of building dust, for so long it's not surprising that it used to need more cleaning than the manual suggested.

After the best part of a decade I've just replaced the DC02 when the front of the case crackled into bits from bumped into the end of the bed. The remains went in 15 minutes on Freegle to someone who wanted the motor and tools as spares. Dyson have just discontinued spares for the DC01 and DC02 15 years after they introduced them :shock:

My new DC32 "animal" from their eBay outlet has a warning in the instructions about only using it to clean up "small amounts of flour, brick or plaster dust". I did wonder if that was the filters or the fact that powders like flour in air can explode.
The DC32 has a "turbo brush head" which is do powerful it managed to strip the colour off an old IKEA synthetic rug :shock: :shock: :shock: it really is monstrously strong.

 

[Roger H]

To flush out dust filled joints, a drill on its side (minus the bit) pushed out a fair blast of air. Goggles and mask are recommended.