Flashing mortar mix?

[AMc]

Some of the mortar holding the flashing over my vinery has failed and the lead has moved. The mortar looks very white to my eye and I suspect has far too much lime to sand.
They're coming at short notice, tomorrow morning (Wednesday 9th Oct) to rake out the failed section, refix the lead and repoint. Having dissuaded them from "using a bit of cement for strength" :roll:
To my surprise they've asked me what the mortar mix should be as none of the builders coming were involved in the job though they both work for the same firm.

Checking the original schedule the RICS surveyor specifed NHL 2 mixed 1:2 with sharp sand for all brick and mortar work.

As all that is available locally is Castle NHL 3.5, I'm suggesting a 1:3 mix unless anyone knows better?

Any prompt replies would be gratefully received

 

[plasticpigeon]

When I've used sharp sand from a builders merchant the mortar has come out the colour of the lime, ie very pale grey/white even at 3:1 mix. I think it is the fines in a sand that give the mortar colour. Umm, I think 3:1 is pretty standard, but there are proper builders on here that actually know what they're talking abut!

 

[stuart45]

Normally when lead flashing comes adrift it's because the joints were not raked out deep enough and the lead wedges were not put in properly.
A friend of mine who does a lot of lead work usually goes deeper than the inch that many do.

 

[88v8]

And/or the flashing may be too long in one run.

Ivor

 

[AMc]

Flashing has slipped but not come away from the wall. Still plenty of lead in the wall. This run is no longer than the others on the same bit of vinery roof, so I doubt that's the issue.
The wedges aren't obvious which is already a point to investigate once we can get to it - access over a 4.5m glass slope is a problem.

Thanks for the thoughts.

I'd still like to check the mix is right at 1 part NHL 3.5 to 3 parts sharp?

(2nd edit) there was definitely something wrong with the original mix. I had the same sharp sand through the build - most of which is beige but this is brilliant white and very, very hard. It may not be the whole issue, but it's certainly a contributing factor.

 

[88v8]

I don't know any better as to the mix, but if they're not accustomed to working with lime, make sure they know to damp the wall before repointing.

Ivor

 

[AMc]

Thanks for that

 

[andrew gayton]

most mortar will fall from the bed joint in a flashing. Thats why calder was invented.

 

[AMc]

most mortar will fall from the bed joint in a flashing. Thats why calder was invented.

I'm sorry I don't understand what you mean? I have similar mortar on flashing all over the roof old and recently renewed. Just this section has eased.

According to the builders the previous work had too few wedges (was 2 now 7) and the mortar hadn't been pushed all the way into the joint.
A double wammy of weakness which caused this particular section to loosen. There was still plenty of lead in the wall and there is no indication of water damage behind it.

They've added extra wedges, wetted the joint and repointed with 1:2:1 NHL3.5:Sharp:Builders soft to get it more workable. They've also repointed a couple of other sections done in this poor mix as getting to the problem was the bulk of the work.

 

[andrew gayton]

In my experience, properly set lead rolls / wedges will keep the lead flashing in place (if laid in max 1500mm bays) although mortar will generally fail due to a disparity in the 'substrate' (brick v lead) and thermal movement (despite reduced bay sizes). Calder - lead coloured lead pointing sealant - if applied skillfully - stays in place and certainly less visually intrusive than mortar.

 

[AMc]

Calder - lead coloured lead pointing sealant - if applied skillfully - stays in place and certainly less visually intrusive than mortar.

Google gave me nothing for Calder If the new repair doesn't stick I'll have a look at alternatives but (fingers crossed) it will be OK.

 

[andrew gayton]

http://www.plumbcenter.co.uk/en/drainage/lead-flashing/calder-tube-lead-sheet-sealant-310-ml-69907

 

[stuart45]

It's worth putting some patination oil on the new lead to avoid the chance of white stains down the roof.

 

[AMc]

Thanks but no new lead, just repositioned what was there and added more wedges.
We used patination oil the first time around which worked very well - no stains. Shame it only came in a gallon tub and we used a teacup full

 

[andrew gayton]

you can get patination oil in litre tins!

 

[AMc]

Not where I bought it, when I bought it - it was only a tenner or so and I gave it to the roofer

 

[DJH]

Hello. I've just picked up on this topic. As a new member I am browsing through as many topics as I can and am really enjoying myself.

My particular interest is lead work and I know I'm a bit late joining in this conversation but I thought I could help in some way. Firstly, as some one has said, the mortar joints for flashings should be raked out a minimum of at least 1 1/2" inches. 2" would be ideal. With wider joints in ashlar the ideal method is to turn up the back edge of the flashing forming an upstand, set it into the joint and then drill, plug and fix with a non ferrous screw and washer about 500 mm apart. The joint can then be pointed in with mortar.
A good tip is to put in a separating membrane of building paper on the lead. This will achieve two things. It will lessen the chance of mortar being smeared on the new lead and, if trimmed neatly, will allow some expansion and contraction movement in the lead without pulling the mortar out or cracking it.

The use of rolled up and flattened wedge shape strips of lead is a tried and tested method of fixing lead into stone and brickwork joints. The downside of this method is that if the wedges are driven in too enthusiastically there's a risk of spalling the face from soft bricks and stones and if they aren't driven in far enough they show when the mortar joint is pointed. There is a new product on the market ( which I have no interest in!) which is a clever little stainless steel clip which is just pushed into the joint without any problem.

With a standard brick joint a fillet of polysulphide mastic applied to the back of the joint when the lead is fitted will act as a barrier to any water which soaks in through the subsequent mortar pointing. This mastic is sold by builders merchants as Lead Pointing Mastic. Never, never use silicone mastic for leadwork, especially the one that smells like vinegar as it contains ascetic acid (or something like that!) which attacks lead.

I hope this might be of use to you.

 

[Moo]

Is your Lead Pointing Mastic the same stuff as Calder?
If it isn't, can you give us some idea of the relative merits of the two products?
(I need to know, because the builder has just done the flashing on the new roof on our little bay, and I want to make sure that the next stage is done right).

 

[DJH]

Yes, it is Moo. I'm a bit reluctant to name products but Calders are an excellent company. They used to be Cooksons at one time. BLM (British Lead Mills) is another good company and they also have a mastic which is just as good. At one time they used to supply a sand coloured mastic but I think they discontinued it. I remember buying up their stock many years ago. Still got some tubes and as it happens I wanted some today but all of them have gone off.

 

[DJH]

Patination Oil has been around for some time now and is a very good product, It is intended for use on newly installed leadwork to prevent rainwater from carbonating the surface of lead before natural patination had taken place. This carbonating is witnessed by white marks and stains caused by runoff of rainwater and patination oil is a must to be applied to lead before any rain and certainly at the end of the day. This runoff can mark other materials, slate roofs especially are prone to this staining and it's the devils own job to get it off.

I found when applying the oil it's best to maintain up and down strokes with a cloth which has oil on it and and using it without turning the cloth allowing it to become black which in turn helps to maintain an even colour on the lead. Another important thing to do is to lift the free edge of the lead and apply oil to a good four inches or so up the underside. This helps prevent staining from water that is trapped under the lead by capillary action and then dribbles down the roof long after it's stopped raining and the roof has dried out just waiting for some white stain to come along!

Patination Oil is designed to degrade over time in ultra violet light from the sun (when it shines that is!!) when the lead will adopt it's silvery grey look so the more coats you put on the longer it will take to weather off. Another thing to watch out for is taking care not to allow the oil to come into contact with bituminous felt underlay as it melts it!!

There are water based patination fluids that are a bit kinder to the environment and are much more pleasant to use.

I'm just offering these tips as I've used them in the past and hope may be of help.