How to grade slates.

[epsilonGreedy]

I understand the first step with grading slates is to divide them onsite into 3 to 4 groups by thickness. Assuming that slate weight is proportional to thickness I was thinking of rigging up a simple balance scale to take the guesswork out of assessing each slate. Is this a crazy idea? What to the pro's do?

[Gus Potter]

If you have a good quality slate 3 piles are the most practical (Scotch slate are a bit harder to work with). Do it by eye and how the weight feels in your hand. Try a couple of hundred, stand back and have a look. You'll soon get the hang of it. The density of the slate varies as it's a natural material. Also, some edges will be thicker than others.

 

Once you get them up on the roof and start laying then if the odd one is kicking up just lay it to the side. Some will have say a thin edge, knobbly bit, so you can just trim these when you are up there say for a valley or at the verge where you may put a small tail or kick up to shed the water back into the roof.

 

If you have a lot of slates to do then you can rig up a hap - shelter. You may need to hole them so a holing machine is a great tool to have. I like the ones where you turn the handle like a drill rather than the ones that "punch". In winter a flask of tea or coffee, a radio and a bit of old insulation to keep your feet warm when standing at the holing machine.

 

 

[epsilonGreedy]

6 minutes ago, Gus Potter said:

If you have a good quality slate 3 piles are the most practical (Scotch slate are a bit harder to work with). Do it by eye and how the weight feels in your hand. Try a couple of hundred, stand back and have a look. You'll soon get the hang of it. The density of the slate varies as it's a natural material. Also, some edges will be thicker than others.

 

 

Ok I will try the by-eye-hand technique first. I might borrow Swmbo's cooking scale to grade the first 30 numerically then switch to hand.

 

9 minutes ago, Gus Potter said:

Once you get them up on the roof and start laying then if the odd one is kicking up just lay it to the side. Some will have say a thin edge, knobbly bit, so you can just trim these when you are up there say for a valley or at the verge where you may put a small tail or kick up to shed the water back into the roof.

 

 

Yup I have 8 hips in total plus 4 more for the garage so plenty of opportunity to assign rogue slates to awkward bits of the roof.

 

The idea of creating a kick with errant knobbly slates is an excellent tip, something I would have thought about having finished the job.

 

14 minutes ago, Gus Potter said:

If you have a lot of slates to do then you can rig up a hap - shelter. You may need to hole them so a holing machine is a great tool to have. I like the ones where you turn the handle like a drill rather than the ones that "punch". In winter a flask of tea or coffee, a radio and a bit of old insulation to keep your feet warm when standing at the holing machine.

 

 

3500 but the garage roof (1000 slates) is 8 months away. The slates are preholed about 5 mm further up the 500mm long slate than the "universal" hole position so I guess these means the batten gauge will be a touch tighter. It is a 30 degree pitch in a moderate weather exposure area.

[Gus Potter]

"The idea of creating a kick with errant knobbly slates is an excellent tip, something I would have thought about having finished the job."

 

Sorry, lack of clarity on my part. You cut the knobbly bit off (forming a half slate) as often the slate above will not sit right. As you go up the verge you'll have a half slate, full slate width etc. You can create the tilt you want by the detailing the verge flashing.