Mortar mix for roof verge!

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KevMack

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Hi there,
Four years ago I replaced about about two metres of roof verge which I have to say is still as solid as a rock. As a complete novice the first website I visited (diy-extra co uk) suggest 4:1 sharp sand to cement. That's the mix I used as I assumed, in my naivety, the mix had been sorted by now.
I'm now about to do the rest and have now seen lots of variables on the mix 3:1 sand/cement etc. Can anyone think of a good reason why I shouldn’t use the original successful mix!
I might add that the gap between tile and roof is quite large.
Thanks in advance for suggestions etc...!

Kev
 
Hi Vinn,

Thanks for the reply. Just out of interest what works for you!

Thanks...Kev
 
Sharp sand is largely unworkable (too friable) on its own. We usually mix a strong building sand and cement mix and add a shovel or two of sharp sand to prevent drying out shrinkage/cracking.
 
We use 4:1 for a verge consisting of 'Cooks' building sand and cement. We also add a splash of mortar plasticizer to the water (not too much, the instructions are on the bottle). Don't add fairy liquid, it's for your dishes.
 
Yes basically to add to the above, the bigger the largest aggregate in the mix, the less cement you need and the less likely shrinkage is (cracking).
Using less water also reduces shrinkage. Using too much cement increases cracking.
Filling bigger gaps causes more total shrinkage. Just make sure you put a wide enough bed.
 
Never use building sand on its own in the mix, as it is too soft for roof work. At least 1/3 of the sand should be sharp sand.
 
Sorry just to be clearer since you mentioned the gap is quite big, depending what big is, where that happens at hips and ridges due to tile profiles being wiggly, usually they insert slivers of tile in the wider gaps to avoid having a giant block of wet mortar.
 
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