Flashing pointing keeps cracking

Bob49 · 18 Jan 2019

Hi,

Last Spring I repointed some lead flashing, some parts had cracked other bits had fallen out. Looking at it yesterday I see that it already has fine cracks in it and some tiny bits are missing.

I see two possible reasons for this, it doesn't look as though the lead is very tight around the joint, it seems to have mostly cracked where the mortar meets the lead. Perhaps this is normal.

Also it is above a uPVC window which has no external lintel so there is slight movement in the brickwork. While repointing, some of bricks in the course above were ever so slightly loose so I took great care to fill every part of the joint with mortar.

I don't think raking it all out and starting again will solve anything, unless I re-did all the lead work, which maybe beyond my ability.

So what about using something like Ever Build lead mate?

https://www.everbuild.co.uk/product/lead-mate-sealant/

But instead of raking out just put a bead over the existing mortar all the way along. It says it's permanently flexible.

Good idea or not?

Or get a proper roofer in?

Thanks,

Bob

palaceray · 18 Jan 2019

Leadmate is the awnser.

Rake out the cement and point the joint with leadmate.

Make sure the lead is securely wedged before pointing.

noseall · 19 Jan 2019

palaceray said:
Leadmate is the awnser.

Correct.

^woody^ · 19 Jan 2019

Doing it properly is the answer.

Rake out the joint to 25mm, dampen the joint, fill with a mortar that's not too strong, (5:1) and compress and tool the face nicely.

Assuming the lead is properly angled into the joint (the bend pre-formed at 90° and not bent into the joint whilst placed on the wall), is a good 15-20mm into the joint, and securely wedged.

Cracking mortar is caused by it being too strong, drying too quick, and being too thin.

catlad · 19 Jan 2019

Or point it with leadmate and forget about it.

^woody^ · 19 Jan 2019

Has anyone got any images of leadmate that shows a nice crisp, straight and even joint rather than a wavy up and down in and out series of blobs?

datarebal · 19 Jan 2019

I do somewhere. Into stone. I'll post it when I'm back in uk

datarebal · 19 Jan 2019

Where we do use it in some circumstances. If your brick is soft forget it and use nhl 3.5 mix
Full fill joints

Bob49 · 19 Jan 2019

^woody^ said:
Doing it properly is the answer.

Rake out the joint to 25mm, dampen the joint, fill with a mortar that's not too strong, (5:1) and compress and tool the face nicely.

Assuming the lead is properly angled into the joint (the bend pre-formed at 90° and not bent into the joint whilst placed on the wall), is a good 15-20mm into the joint, and securely wedged.

Cracking mortar is caused by it being too strong, drying too quick, and being too thin.

Thanks, I used a tub of Cementone general pupose mortar, doubt if that is too strong. I don't think the lead is properly angled into the joint. So it's either a roofer to redo the whole lot as I don't fancy doing that myself or just leave it and repoint again when bits fall out.

Or (complete bodge this) go over the pointing with something like Dow 791 Weatherproofing sealent in light grey using masking tape to get a good finish. This stuff smooths out very well, I read that leadmate is too sticky to smooth out nicely.

Bob

noseall · 20 Jan 2019

^woody^ said:
Has anyone got any images of leadmate that shows a nice crisp, straight and even joint rather than a wavy up and down in and out series of blobs?

Has anyone got any images of folk looking up at distant lead flashings and commenting how they should have used mortar instead of wavy leadmate.

Mine is always finished perfectly, by the way. I only apply the leadmate (on stepped flashings) to the lead then use mortar for the remainder of the rake-out.

Leadmate is much more temperature tolerant too.

^woody^ · 20 Jan 2019

noseall said:
Has anyone got any images of folk looking up at distant lead flashings and commenting how they should have used mortar instead of wavy leadmate

This is uncanny. Only last week I was out with my young apprentice on a survey, and whilst he was quick to notice the complete absence of a roof, my more experienced eye pointed out the poor application of leadmate.

23vc · 20 Jan 2019

I used mortar on mine, thought I’d do it on the hottest day of last year just to make it easier. A little bit has cracked, so leadmate should sort it, then the mortar and wavy lead mate combo should look great.
I didn’t go for lead mate originally as I’m tight.

diynot

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Flashing pointing keeps cracking

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