Broken Nines, Hairline Cracks, and Th... Log Out | Topics | Search
Moderators | Register | Edit Profile

Slate Roof Central Message Board » Slate Roofs » Broken Nines, Hairline Cracks, and Thin Slates « Previous Next »

Author Message
Top of pagePrevious messageNext messageBottom of page Link to this message

Daniel Ernst
Posted on Sunday, February 06, 2005 - 12:16 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Hello all!

I'm halfway up the north roof, getting into the groove of this slate installation. But I sometimes think I should have apprenticed with a slater for a season . . .

I am installing random width, 18" Vermont Royal Purple slates. The distribution is fairly good, with widths ranging from 9" - 14" for the main roofing field. The 9" and 12" make up the majority, the remainder 10", 11", and 14" (I guess 13" is taboo?).

There are more broken slates than I expected. I've been sorting the slates before taking them up - heavies, mediums, and lights (thinking a flatter roof is going to be less troublesome). While doing this I also give them a rap with the meaty part of my hand, to determine if they are sound. To date I'm seeing ~ 6% breakage rate. Quite a few are coming out of the 9" width. Perhaps this is because there is less mass to withstand punching / shipping?

Some slates ring true, appear to be solid, but show hairline cracks on the face (not both sides). The cracks are almost imperceptible, except when wet and drying, the hairline cracks are the last to dry out - and the telltale line appears. Is this a concern? Will these fail sooner than other slates?

Slate thickness. I have a pile of "light" slates that I am holding for the last few courses. However, some of these are very thin - a consistent 1/8" across the entire face. Should I install these, or set them aside? I saw this question elsewhere on the forum, but never a definitive answer . . .

I ordered 10% on top of the required number of squares - for rejects, replacements, and stores. I'm hoping it's enough. Perhaps I am being too picky? But then again, the last thing I need is to have multiple slates cracking and falling over the first few years of service.

Joe - Having never worked on a slate roof before, it feels as if the system is very fragile. One voice in my head is telling me, "Hey, this slate you are nailing down is going to outlast your great grandchildren, do it well!" The other voice is saying, "Look at this stuff, you are installing a maintenance nightmere."

Is it just that the installation is a stress test for the slates? That after that, they rest in peace?

Walter - Your roof scaffolding straps are doing the job very nicely. I laid down 2 squares yesterday, felt like I was flying high. Though some days I spend half my time just getting ready (setting up the scaffolding, chalking lines, sorting slates, hauling them up). Argh!

Apologies for the rambling post. Thanks for listening!

Regards,
Daniel
Top of pagePrevious messageNext messageBottom of page Link to this message

Walter Musson
Posted on Sunday, February 06, 2005 - 09:18 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Daniel,
All that prep time actually saves you time during the laying process.The sorting,setting brackets and planks,chalking lines,etc. gives you moments to reflect on things you may have overlooked,that if caught prior to doing the next phase will be beneficial.It's not a rapid pace endeavor as you can see.
You have seen I'm sure to not get your brackets too far apart vertically up the roof.The more you can step or jump from plank to plank up the roof will generate less foot traffic to the Purples.You already have mixed feelings about their capacity to have a long life.With care and finesse and being selective in how they lay adjacent to one another as well as the lay to the course above,you will have a long term roof.
The small cracks are not uncommon in those types of slates.Frustrating but not the cause of their immediate demise.The ones I call "wafers" those too thin to lay except possibly at the ridge,but if you have enough stock then don't install them.
Daniel,a 2 square day is quite impressive for someone just starting out.You should be pleased with your performance,and hopefully taking pictures to share with us all.
Keep up the good work and don't get "bummed" by the prep,you have no tender.
Best regards,
Top of pagePrevious messageNext messageBottom of page Link to this message

Joe Jenkins
Posted on Monday, February 07, 2005 - 08:15 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Ditto.
Top of pagePrevious messageNext messageBottom of page Link to this message

Stephen J Taran Jr.
Posted on Monday, February 07, 2005 - 10:05 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Daniel,
Being on both the quarry end and the roofing end I have had experience with a bit of everything. Some of the cracks could be surface flakes that did not come off when trimmed you can try peeling them away and a thin little piece might come off these are fine to use. but Royal purple can also be heavy on "blind joints" depending on the beds in the quarry. If these are blind joints they will break and should not be used You can tell by breaking one on the crack and if it breaks clean with a smooth edge and you might even see some white shiny flakes than this is a blind joint. Which is a part of nature in the slate.
Also 2 squares in a day thats great Let me know when we can hire you on.LOL.
Top of pagePrevious messageNext messageBottom of page Link to this message

Daniel Ernst
Posted on Tuesday, February 08, 2005 - 12:00 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Thanks for the responses, reassurances.

My work background is in pharmaceutical manufacturing. Upon finding a single defect we would sometimes reject the entire lot of product (overkill, but safety first).

I am also used to dealing with lumber yards. When I order lumber, I can expect that all boards will be servicable - some better than others, but all in reasonable condition. The lumber can be sorted, based on purpose (rafter, header, rim joist, etc.). In this sense, I understand the need to grade the slates.

But ordering material with a 6% reject rate has me stepping backward. I am learning that slate requires a different perspective . . .

I am struggling with where the damage took place. The slates appear integral on the pallet, but upon handling and inspection, show a fairly frequent number of cracks. The slates were shipped on an "Air-Ride" flatbed (pneumatically balanced suspension) - so I doubt Interstate traffic caused much stress. This takes me back to the cutting and punching process. But I don't know enough about the process to judge that either.

My hope is that my on-site inspection and handling will weed out the defective slates. My worry is that they should have been found earlier, but were not (and could the very same thing happen after installed on my roof?!).

I know others have expressed concerns about slate quality, and the need to account for breakage . . . but I am hardheaded . . . and learning firsthand is usually the only way to make it stick.

Walter - I have the roof scaffolding set close enough that I can easily move between the rows.
By the time I reach the top I'll have five rows of planks (for the 21' roof field). I may have been able to get away with four, but took the conservative route. I have yet to step on any installed slate - as I wouldn't forgive myself making the job more difficult by having to replace newly installed slates - ahhh!

Stephen - Several times I've come across what I thought were hairline cracks - only to discover that they are thin lines of a different colored stone - usually green - almost like a vein. Is this the cleavage plane, or the blind joint you describe? I have not been able to break the slates along this line, even with considerable thumping, using my palm. Whenever I find a hairline crack, I am probing as you suggested, to find the extent or depth.

Examining the samples we received I had noticed that the purple was of a much coarser texture and cut - say compared to the semi-weathering sea green. Now that I've worked through several pallets, the texture of the purple slate is very apparent - not always having a clean cut, veins, knots, etc. But viewed installed, they take on a very different character . . . a pleasing appearance. This is good, as long as they do not prove troublesome in the future. ;)

Regards,
Daniel
Top of pagePrevious messageNext messageBottom of page Link to this message

Tony EriePA
Posted on Tuesday, February 08, 2005 - 09:28 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Dan-
I recently got a batch of non-weathering and semi-weathering sea green, clear black, and purple from a Vermont quarry. Of the three colors, the purple appears the softest and easiest to cut with a cutter. I suspect that the purple slate may have a higher carbonate content and are likely less metamorphosed than the balck and the sea green which are much harder ... in fact, cutting or punching a hole in the clear black slate is pretty hard work. Its degree of metamorphism and initial mineral content likely gives it this characteristic. And overall, I think that of the three colors I got, the purple was most susceptible to damage, but my damage rate was less than 2-3%. Also, hairline cracks in the purple can be altered by groundwater or oxidation so there can be a color change to green in the crack, which makes them easier to see.
Tony F
Top of pagePrevious messageNext messageBottom of page Link to this message

Stephen J Taran
Posted on Wednesday, February 09, 2005 - 12:07 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Daniel,
I have been in the slate quarrys my whole life and I have never seen cracks oxidize. I have seen flint or slips color and crumble after 60 or so years on a roof. Slate is not metal. If the lines are different colors it very will can be flint lines. or it could be a vein of green running into the purple. Yes bad slate should be pulled out by the quarrys but what people do not realize with roofing slate they get what they pay for. For example. Unfortunatley when one quarry is say $50 a square less than another the quality can suffer. Than there are alot of brokers who buy from the cheapeast quarry possible and once again quality. When we do a roof I always order 10% extra but it is for cutting loss. If you end up with alot of bad slate at the end Contact the quarry and see what they say. slate is not cheap.

You can Visit our website and under slate information you will see manufacturing roofing slate there are several pictures showing how it is made. WWW.VTSLATEROOFERS.com

Add Your Message Here
Post:
Username: Posting Information:
This is a private posting area. Only registered users and moderators may post messages here.
Password:
Options: Enable HTML code in message
Automatically activate URLs in message
Action:

Topics | Last Day | Last Week | Tree View | Search | User List | Help/Instructions | Program Credits Administration