Repairing cracked roof edge mortar

[agg1000]

Hi,

I'm looking for advice on repairing the edging mortar on a slate roof. I've attached a couple of photos below to illustrate the problem. It is the edging between the roof slates and a granite gable end wall. The roof is 12 years old. The mortar has cracked along its full length allowing water ingress to the garage below. Aside from the cracks, the majority of the mortar is still sound, and may be difficult to remove without damaging/displacing the slates.

If possible I intend to fill the cracks and seal the gaps. I would then probably coat the entire point with a waterproof seal.

Could anyone suggest a product that may be suitable for this application? A flowable grout perhaps?

Cheers.

 

[catlad]

You don't finish that detail with mortar for the very reason it has failed so quickly. You need to use lead.

 

[agg1000]

Ok. Appreciate the response but I'm looking for info on how to repair the joint. I have no experience of roof detailing or repairs. What would a lead joint detail be like?

 

[Will..]

Like catlad says if you just patch with mortar you WILL get more problems over time. A full lead cap and flashing over the parapet is the way to go.

 

[vinn]

Difficulties with parapets always seems to mean lots of further problems. Any difficulty any parapet.
Each slate at the end of each course of slates needs to have a hidden soaker with a 75mm upstand.
The upstand is protected by the cover flashing coming down and over from above.
The cover flashing can be fixed after cutting slots with a diamond angle grinder blade.
Your present abutment flashing is a failed fillet of sand and cement.

This means that besides the above work mentioned by others it will be necessary to lift all the slates that abut the parapet.
Whats happening with any other parapets on your roof?
Do you have gutters on that roof slope?

 

[vinn]

Slightly to one side: I've fixed 1800mm lengths of treated hard metal capping that clip on to either side of the parapet. Sometimes these had to be custom made but mostly they come off the google shelf.

 

[agg1000]

Thanks for this. If I understand you correctly the detail should look something like the sketch below.
Does the lead need any kind of secure fixing, or does its own self weight hold it in place. Its not a particularly steep pitch on the roof.
I haven't done any research into this yet, but lead sounds expensive to me! Are there alternative plastic products?

There are gutters at the bottom of the roof, but they don't extend to the parapet.

The cracking is occurring on the similar detail at the other end of the house.

 

[catlad]

Your drawing looks good to me, If you look at the lead sheet manual online it will give you a lot of information on how to use lead in construction.

 

[vinn]

No, thats not it. You are half way there with the dwg. The soaker upstand doesn't go into a recess, it remains free and the cover flashing is typically separate from the capping. The cover flashing might be stepped or a strip length.

See p. 29-30 in the manual at: jamestownmetals.co.uk, or calderlead.co.uk at least you will get a better idea.