Mortar for Roof Verge

[malcolm]

What type of mortar would you use for a roof verge?

My new roof is in slate or peg tile (depending on which side of the roof you are looking at) and the tiles now extend around 50mm past the gable with a cement board under cloak. On the old roof the verge mortar had clearly been repaired many times due to cracking and falling out. The repairs were largely in cement and would have needed repairing again had we not lifted and replaced the tiles/slates.

I would have thought a relatively soft lime mix would better resist cracking if that is the problem more than erosion. NHL 3.5 with course sharp sand maybe. The roofer has agreed to use whatever mix I specify in lue of guarantee, or will do it in whatever readymix they normally use (presumably 4:1 sand cement).

Also any tips on bedding ridge tiles? I'm tempted to let them do what they do for the ridge tiles as it doesn't really matter if the mix cracks.

He is a decent roofer. I'm quite pleased with his welded leading, but might be stuck in the modern age a little with his cements.

 

[Zebra]

I am no expert on these things but a few years ago I was in a similar boat as you are now - a good roofer, willing to let me specify materials, but not familiar with anything other than cement in his normal line of work - and I didn't think I had enough experience to specify roofing materials so I let him do what he would normally do, and it was done in cement. It's a timber framed house, and yes, the ridge has cracked. The verges haven't. If I was making the choice again, I'd get him to use an NHL mortar, perhaps 2 soft sand, 1 sharp to 1 NHL 3.5, which is the mix I used for pointing. Just sharp is very difficult to use, the soft sand makes it a bit stickier.

 

[88v8]

When I built my garage roof, in complete ignorance of how a roof should be/normally is built, I laid all the tiles and then pointed the verge.
Wrong....
The correct way is to bed the verges as one goes, not to be trying to poke mortar in after the event. But by the time three roofers had ben to look at the pointing job (which with the broken leg I didn't know I had would be rather difficult), made their excuses and left, I did some research and realised I had made a booboo. With the verges all nailed down, no way was I going to strip it, so....

Onto the batten ends I screwed stainless mesh, scrunched into each batten space, having first nailed loops of fibreglass tape along the batten ends to prevent the mortar from retreating into the roof - as you know, it must be compacted, not just poked in. This all gave something for the mortar to sit against and grip.

Then I used some NHL 5, as the verges are obviously exposed to the weather, plus sharp.
I used Tradlym sharp, the grain size is good. I think random sharp from t'local builders' merchant has its place, but on a job I never want to do again, it needed to be the right stuff.
The mix was sharp x 6, St Astier NHL 5 x 1 and NHL 3.5 x 1, so 3:1 overall.

With a hand sprayer, I wetted the verges and undercloak as I went, so I was never pointing into a dry space. Where the voids were larger, I poked in bits of (wetted) stone to take up space and minimise shrinkage.
I wiped off the tile edges with a piece of old sacking as I went.
When it was part set, I attacked it vigorously with the churn brush. The St Astier has quite a quick set. One has to time it right for churning, as you know.

Perhaps not ideal, as compared to a fully built-up verge, but I can look out of the window as I write, and feel not unhappy with the result.

For the ridge, given that the roof timbers are new and will inevitably shrink, I used the same 3:1 mix but with NHL 3.5 only, as I wanted more flexibility and the NHL 5.0 sets rather hard.

If someone unfamiliar with lime work is doing the job, the key differences I think are the remorseless wetting and the compaction. Also, not doing the job in direct sun, and keeping it damp a couple of days while it goes off. I did the work in the autumn, not by any miracle of planning, I may say.

Ivor

A few weeks ago... [invisible image]

 

[DJH]

Very neat leadwork but maybe not correct in that with slate, plain/peg tiles soakers should be used rather than a cover flashing over the top of the roof covering. As it is (unless there are soakers fitted underneath and we can't see them) there is a risk of water travelling under the lead and into the structure. This could be exacerbated with rain under strong wind conditions blown under the flashing. Wind could, and will swirl around the chimney with a risk of it lifting the lead and leaving the roof abutment to the chimney open to the elements...

Soakers are the way to go really for a good job... 8)

Doug

 

[malcolm]

That's a good point about soakers Doug. Isn't it a pain having to know every single detail about how things should be done (or worse, how things were done when people built things properly). There aren't any soakers. Only the permeable roof felt underneath turned up at the chimney.

I reckon the chances of getting a roofer to bed the verge tiles in as they go these days is pretty slim Ivor. Did you get advice on the lime mix or if the mix from your own experience? I think lime is the way to go as cracking seems to be a much greater problem than erosion.

 

[88v8]

I'd like to tell you that the mix is a time-hallowed recipe handed down from useterwos, but I made it up as I couldn't get any definite steer from Trad Lime.

Regardless of mix however, if one ends up with an uncompacted frill of mortar I can't see it lasting so well.

On our previous house the south verge was rebuilt as the supports had rotted and the cement had cracked. I recall the builder taking it all apart and bedding it, although that didn't prevent it from cracking again when the new timbers dried.
Substantially though, that verge was still OK when we sold 30 years later, and the verges of our 1991 extension which I am sure was all cement, were perfect as I recall, hmmm.

Must say however, on my own job, it would have been infinitely easier if I had done the work in a proper sequence, ie bedded the verge as I went and then laid the top few courses and bedded the ridge across, then worked back down. What I did involved far too much clambering over tiles already laid, with consequent breakages. Also I didn't lap sufficiently given the 30 degree slope, so thank goodness for the Roofshield that some kind person on here flagged up, I reckon that will save my bacon in years to come. Never mind, it looks pictureskew which is what matters.

Anyway, back to your verge... if your roofer has never used lime before, is it possible to give him some practice elsewhere before he starts on your roof?Perhaps some brickwork or something that needs doing, where he can get used to the wetting and compacting? Alarming thought, having a chap learning on one's roof.

Ivor

 

[malcolm]

I like your garage by the way, and the Peugeot 205 - I have it's arch rival the Renault 5.

The roofer pointed the leading in my lime mix but didn't listen to what I said about how to use it. I should imagine he wouldn't do a great job of the roof and verge in lime. Almost tempted just to leave him to his stuff. The roof can't be worse than it was before.

I notice some bags of readymix cement outside with "for roofing" marked on the bags. For some reason they are a 3:1 mix. I'm surprised they don't at least use a 4:1 mix which might crack a little less.

 

[88v8]

It's hard getting people to diverge from their usual ways.
One is inclined to give up.
Or DIY, which can be better.
Or not.

Had a 5GT turbo from 1986-91, and another from 91 to 99. Company cars. Those were the days.
Then a 205 GTI 1.9 which was on the whole a better car but less memorable.
Now the most basic 205 which was my father's and has 23,000 on the clock.

The base model 5 seems to have pretty well vanished. Seems by accident or design Peugeot got the rustproofing right and Renault didn't.

Ivor

 

[malcolm]

I've been working on the Renault 5 today instead of the house. Mine is a Mk1 version from 1983 and while rust in difficult to repair areas was a common problem I suspect most died from neglect because they are such a pain to work on.

I don't let other people work on my cars as I know I won't be happy with the work. I wouldn't let anyone work on the house either, but it is so labour intensive it will take a few people all summer to sort out the exterior. I might let the roofer use his cement mix on the verges, but I'll make sure the other chimney gets some soakers.