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Slate Roof Buying Guide

Records show the earliest use of slate as a roofing material was in North wales around 1300AD. It has ever since grown in popularity due to its aesthetics, durability and its ability to be consistent in its manufacturing process.

Traditionally, slate roofs were extremely expensive as they were split by hand, this was a time consuming process. So slates were originally only used on larger expensive structures such as Castles and Churches.

Spanish Quarries mastered the art of harvesting and splitting the slate more efficiently. Which allowed slates to be produced at a much higher volume at a much lower price. Making it affordable for everyday family homes, Even today Spanish slates make up approx 90% of sales in Europe.

This Slate Roof Buying Guide covers all main topics for you to fully understand the benefits of slate and how to use it.

Slate Roof Buying Guide -Look closely you can see “flakes” on the surface, these flakes are how the layers are built up through compression and time.

What is Slate?

Slate is a homogeneous metamorphic rock that originally was created from shale type sedimentary rock which is composed of volcanic ash or clay. 

Over time through metamorphic compression the rock develops perpindicular planes across its surface. These fine layers or grains as there known is what makes slate such a usable material.

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What is the manufacturing process of slate?

Slate is either excavated in a quarry (which is surface dug) or a mine  (completely underground and excavated).

We hand picked these slates purely down to there reliability, durability and the reputation of the Quarries they come from. 

Once large slabs are excavated they are taken to the mill where they are then processed further. They are inspected and each slab is destined for certain uses, much larger pieces are usually used for architectural purposes. Majority are used in roofing slates.

Slabs, Blocks & Books

Each slab goes through a manufacturing process where they use water cooled diamond tipped saws to cut the slabs. In to smaller more manageable pieces.  These are slightly bigger than the intended finished slate size, they are then called BLOCKS.

Blocks are then inspected for there grain quality and are graded. Each block will then be split by hand using a Bolster chisel and hammer along the grain length. This instantly separates layers of slate away from the block. The skilled tradesman aims each hit precisely the same width apart to try and create uniformity in thickness. These slates are then stacked and then described as BOOKS.

Books are then inspected further for uniformity and go through quality control.  They are then stacked into pallets and stored ready for transport.

Types of slate

Slate Roof Buying Guide- Natural Roofing Slate comes from many quarries around the world, such as:-

Welsh slate (wales, uk)

Welsh slate quarries are renowned for having the highest quality slate in the world. It’s durability rating is much higher than others and its strength is unique. Welsh slate is our most premium slate choice & our most favourite. We offer both Penrthyn (blue grey) also known as “Blue welsh” & Cwt Y Bugail (dark grey) slates. In both County and Celtic grades, Check them out here.

Spanish Slates (northern spain).

Spanish slates are the most affordable slates in todays market and that’s down to the huge volumes they can produce. The quality of Spanish slate is also extremely good and is our most popular slate. We offer three different types of Spanish slate:- LISO, CAFERSA & FERLOSA all unique slates, Check them out here.

Burlington Slate (Lancashire, UK)

Burlington Slate is hugely renowned in the UK for tradition and quality. Many of the country’s prestigious buildings are graced with this very slate. Available in both blue, grey and olive green. These slates are still produced in traditional, random and diminishing course format. Traditionally identified as part of Lancashire before a politicians pen “moved” the border to place them now in Cumbria. Check them out here.

Brazilian slate (Brazil)

Brazilian slate is formed Slightly differently to normal slate. It is formed using mudstone instead of traditional clay. The method of metamorphic compression is the same. The results produce a reliable good quality slate which is available in both Graphite grey and greyed green. We only supply the thicker 7-9mm slate due to it’s inherit brittleness, surface texture tends to be smooth & flat. Check them out here.

Chinese slates (china)

Chinese slates have fast become a widely available alternative to Spanish slates. We currently don’t supply Chinese slates.

Man Made roof tile /slate

All man made slates are composed using a fibre cement mixture combining of glass fibre and cement. Although they are renowned for there consistency and evenness they are not a natural roofing slate but a manufactured tile. Although a great alternative for low pitched roofs. On occasions we can source man made tiles upon request.

Slating a roof

Laying a slate roof properly takes allot of skill and preparation. We would always advise using a professional roofing company to install your slates.

However if your confident then there is nothing wrong with at least understanding the fundamentals of slating a roof. Slate Roof Buying Guide should at least help guide you through the basics.

Please watch the two videos below to give you a good introduction to how to install slates correctly.

STEPS 1-8 ON HOW TO SLATE A BASIC ROOF

First step

Is identifying what slate is suitable for your property. This isn’t just a case of picking a slate you like the look of! there are many factors that will affect this decision such as head lap, size of roof, location, pitch, size of slate and type of slate available.

Thankfully we have created our unique SLATE CALCULATOR TOOL which will work all this out for you including the quantity of slates you will need please bare in mind our calculator tool is designed for simplistic roofs. It doesn’t include items such as skylights, chimneys, eaves & valleys so you will need to calculate these separately and add them to the order. Give US a call if you need help with this we can easily do this for you OR send us a detailed drawing and we will calculate it for you.

Simply fill out the required data and choose which slate you want to use from the recommended list and place your order.

Step two

Now you know how many slates you need and what the head lap is. You can now calculate what the batten gauge needs to be, and there for calculate how many battens you need. Draw out a plan on paper of the complete roof with all the calculations and measurements drawn on.

Step three

Roll out the roofing membrane across the Rafters as the manufacturers instructions state and working your way from the bottom up making sure you have the membrane hanging over the bottom edge approx 50mm. Using 25mm clout nails tack the membrane in place  making sure your not pulling it too much and putting it under too much tension..

Step four

Prepare your slates by positioning a full length batten on top the membrane and do not fix it. Next place a slate on top of the batten and allow the slate to overhang over the lip of the roof and half way into the guttering approx 50mm (2″) making sure this gap is the same both sides. Make sure your slate holes are close to the centre of the batten now tack the batten down using the clout nails to hold it in place and do the same with the slate but don’t nail it down just tack it as you will need to remove the slate later.

Using a second batten slide it under your slate and up to the underside of the first batten. To cut your eaves slate place a full sized slate on to new batten and line the bottom of the slate with the bottom of the other slate so there horizontal and inline, the slate holes should be positioned centre of the new batten if not slightly move the batten so the holes line up centre. Mark a line across the slate where the top of the batten ends and cut the top of the slate off, this is called a eaves slate.

Step five

Now you have measured your eaves slate, you need to make sure the battens are laying true and straight to do this measure the distance from the lower batten to the edge of the roof and make sure its the same right across the roof edge. Repeat with the higher batten and nail the battens down permanently using 40mm galvanised nails.

Now place a third batten under the top lip of the full sized slate and position it so the slate edge sits half way up the batten. Place another slate on top of the other full sized slate making sure the holes now line up with the third batten, the slate should be off centre and sit half on half off the first slate (staggered). If the holes line up and the first slate edge is still on the batten then nail the batten in place making sure its level and straight .

What you now have is:-

  • eaves course
  • Starter course

Now you have created a double lap (standard practice in UK) and have set out your Batten gauge and Head lap. Based off the information we have provided you from the calculator.

Step 6 

Lay out your battens as instructed and nail them down, checking your measurements across the face to make sure your running straight.

Step 7,

Using the length of the roof divide this by the width of the slate to give you how many slates you need per row, using that figure now cut a rows worth of eaves slates. Nail them down on the first batten. Now place a row of full sized slates on top of the eaves slates making sure there staggered and not sat directly on top of each other see picture for clarity.

You will need to cut some slates vertically in half to create this staggered pattern or use slate and halves one per row, Nail the starter course of slates down. If you are slating a roof like in the example do not forget you will need to add a lead soaker every course and a layer of stepped lead running up the wall to create a protective waterproof layer.

Step 8

You are now ready to begin working your way up the roof continuously making sure your level across the roof (you will know if you run off course as the holes wont line up with the battens anymore so keep an eye on it). Once you reach the top of the roof depending on what you end to do we offer two different types of Ridges which you can use (see picture we used our CS CR2 mechanically dry fixed capped Clay ridge tileswe added end caps later.

Ridge tile installation

With this type of mechanically locked ridge tile you don’t need to add a seal of cement which reduces the overall weight factor) fixing the ridge tiles over the top to finish is easy. Double batten the ridge and hips so you have plenty of batten to screw in to and then using the two screws provided screw the ridge tile down, follow by the next ridge adding a bead of silicone between the joints for additional protection. Make sure at the end of your hips you add a Scroll HIP Iron.

Check out our YOUTUBE CHANNEL for customer videos of there slate roofs 

CLICK HERE

Cutting Slate

It’s important to remember to wear and use the correct Personal Protective Equipment and safety equipment such as goggles and correct breathing apparatus.

There are mainly two ways to cut slates, that’s using handheld traditional tools such as:-

  • Slate Cutter- handheld, cheap and easy to use.
  • Slater’s Axe & Bench Iron- suited for larger cutting projects.
  • Slate Guillotine- specialised tool for professional roofers

 

And there are mechanical tools that help speed the process up such as:-

 

  • Angle grinder with Diamond cutting disc.- more suited for thicker slates.
  • Circular saw with diamond cutting disc-suited for much larger projects such as large roofs with lots of hips and valleys.

All tools must be treated with respect and used methodically and slowly to achieve the best finish. If you do use the angle grinder its important to remember to recreate the riven edge by using a claw hammer and tapping upwards on the cut edge to allow flakes to be removed giving it a natural looking riven edge. 

 

To begin always score the slate on the backside to prevent damaging the face of the slate when cutting, mark a line so you can easily see where to cut.

Aim to follow the grain of the slate when cutting, starting from the thickest edge to begin with as this will minimise breakage. The easiest tool would be the hand held Slate cutters, these are the safety piece of equipment as well as being the cheapest tool. If you plan on only cutting a handful of slates this will work perfectly.