To Cover or Not to Cover...

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To Cover or Not to Cover...

Postby Staneheid » Sat Mar 14, 2009 1:51 pm

Hello all on the shiney new site; vastly improved methinks :D


Currently working on a well buckled and battered old farm dyke round a wood on a precipitous slope (great fun!!!) near sunny Galashiels and although there's plenty of half decent building stones, throughs and copes there aren't enough covers. I've been trying to get round this by putting the covers I have on then building up to their height with smaller flat stones where possible in between to cover the hearting to stop the water getting in. Is this accecptable or should I tell the farmer to haul ass and find me some decent covers?

Also, I've been reading the btcv guide on how to build on slopes which tells you to work up the slope to stop stones slipping, roping your covers etc. I haven't started the really steep section. Any tips, pointers or things to avoid doing would be much appreciated.







when n doubt, dyke it!
over the dyke and quiet
through mottled gate,
passing badgers sleeping
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Re: To Cover or Not to Cover...

Postby Tracey B » Tue Mar 17, 2009 9:12 pm

Hi there. Seeing as you haven't been exactly overwhelmed by the volume of responses to your post, thought I would get the ball rolling at least. Are you refering to cover bands? If yes, they are not realy a necessity structurally speaking. Only a tiny minority of walls in my neck of the woods have them, I think they are more of a regional variation. Don't worry too much about completely 'covering' the heart in the top course of the wall with flat stones, as long as the copes have good contact with the face stones on both sides you will be laughing all the way to payday.
As to walling on steep slopes, if you are reading BTCV, who am I to try and add my advice to those words of wisdom? Just one thing, only work very short stints, get those frames real close together. If you have any more specific (ie less general ) queries do come back to the Forum.
Where are you Sean and Donald?
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Re: To Cover or Not to Cover...

Postby Staneheid » Wed Mar 18, 2009 8:09 pm

Hi Tracey,

It really has turned into a bit of a ghost forum, all we need now is some tumble weed!!

As you can imagine, I've figured it out for myself using a few coverbands and adjusting the width of the top of the wall to suit my copes. I actutally just finnished today and it looked pretty sweet. I got paid too more to the point! The farmer said there's only another 52 fields to do... :shock:

Nice weather down your end?
over the dyke and quiet
through mottled gate,
passing badgers sleeping
there
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Re: To Cover or Not to Cover...

Postby Tracey B » Wed Mar 18, 2009 10:52 pm

Well there have been 65 views of this post, so there must be somebody out there. (Unless of course it was the same one person who has viewed it 65 times)?
Weather.....fantastic. Lambs in the field, daffodils flowering, its payback time for being out in that horrendous winter. Life is good.
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Re: To Cover or Not to Cover...

Postby stonewaller » Wed Mar 18, 2009 11:18 pm

Sorry to be so slow, Donald and I have been "battering" our heads agains the wall of NOSspeak (National occuptional standards I mentioned elsewhere). Taking up every spare moment literally. Have been meaning to reply to this one but now I've missed the boat. Re tumbleweed I did suggest that DSWA emailed all registered users as I thought many mightnot realise we're back. If its this bad now imagine what it'll be like when the evenings get longer. The stunning response to my batter post hasn't exactly filled me with enthusiasm...

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Re: To Cover or Not to Cover...

Postby Tracey B » Thu Mar 19, 2009 5:31 pm

Welcome back Sean. Please could we hear your thoughts on the cover band theory? How important are they to structural integrity? I think we should be told.
Reckon noone replied to the question about batter being reclassified as the word plumb because it is so obviously ridiculous. Batter describes the angle which diverges from plumb which means exactly vertical. How the one word, plumb, could serve to mean two entirely different things defeats me utterly. This is majorly important because the batter is the butter on the bread of us stonepeople's lives and work. Please don't mess with it, powers that be. (Its also traditional and if it aint broken why fix it).
Now thats what you CALL a rant.
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Re: To Cover or Not to Cover...

Postby stonedyker@talk21.com » Thu Mar 19, 2009 7:48 pm

There is no doubt that coverbands can add substantially to the strength of a drystone wall.

If there are no or very few coverbands it is especially important that the top course of stones are laid length in to the centre, to make sure the copes have enough 'bite' on the double and fully perform the functions of bridging the double, adding, strength and height.

Do covers keep the interior of the wall dry? Often they do - but I think this is a secondary function, especially in areas of hard stone such as basalt and granite.

A tightly built drystone wall will keep most of the wet out of the centre and the copes and covers will add to the waterproofing. I wonder if the assertion that covers keep the interior dry is a hangover from masonry walling, where capstones and copes must be properly placed to ensure that no water washes out or freezes the mortar.
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Re: To Cover or Not to Cover...

Postby Tracey B » Thu Mar 19, 2009 8:17 pm

Well Alleluiah, we got ourselves a bouncing baby Discussion. Don't let it die you walling paramedics out there.
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Re: To Cover or Not to Cover...

Postby stonewaller » Thu Mar 19, 2009 8:44 pm

I was literally about to reply to Tracey, had to do some more NOS stuff first, only to find Nick stealing my thunder, or reading my mind.

I should like to add that don't use covers as an excuse not to lay the last course well in. There is always the danger with covers as with continuos bands of throughs (I hope to launch a thread on these soon) that the stones under the covers will settle unevenly and some will potentially work loose. In this repect it can be argued that good flat copes that cross the wall, fit snugly, and therefore grip the levelling course fully are better as they lead to a more even distibution of weight. It is important to remember that copes do not only hold the top together, keep water out, and gain height - they also act to place a load on the top of the wall which (if even) helps deflect the line of force within the wall away from the face. Walls can only all down when this line of force extends outside of the face. There's a good article in "Stonechat 10" which should be online in due course (I'll try to get it finished and let everyone know when its up and running). In this respect there are likely to be many instances where covers play an important role in ensuring an even distibution of force to the wall below, provided they sit evenly on the levelling. Food for thought

Stonechats 13 & 14 have a couple of articles on coping which can also be found in the Books bit of my website, I don't deal with covers per se because we don't really get them in North Wales. However I do note a method of rubble coping (Masterclass - coping2) which I employ where a sort of cover is formed before the rubble cope is set on top of this. Then if the rubble is displaced the top of the wall is still held together.

Will that do?
Any more questions??

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Re: To Cover or Not to Cover...

Postby stonedyker@talk21.com » Thu Mar 19, 2009 9:07 pm

Hi Sean,
It occurs to me that covers are especially useful in wide topped walls, those over 14 inches. On really narow tops they could add to instability.

I like the point on rubble coping. With good covers and one good copestone every couple of feet quite a solid cope can be built up with really rubbish stone.

Just and idea for fundraising - how about binding up these Stonchats and selling them as a set? Put me down for one. I know they can be downloaded and printed off but my printer suffers from operator error.

Nick
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Re: To Cover or Not to Cover...

Postby david perry » Fri Mar 20, 2009 7:27 pm

In terms of keeping the rain out I really do think this is a little old wives tale.

In terms of a drystone wall I can see no real reason for keeping water out. I've never seen damage to a wall that was obviously caused by freezing water in a wall. There's too much free space anyway for that to happen.

Some of those wallers north of the border with more severe winters perhaps could verify this, if I'm correct.
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Re: To Cover or Not to Cover...

Postby stonewaller » Fri Mar 20, 2009 10:58 pm

Essentially I agree, never taken down a wall that's been wet inside even when its raining its still dusty until exposed.

However the free space idea doesn't really apply. If water does get into a wall what would cause a problem is water sitting between two stones say on a slightly dished surface. As this freezes and expands it will work on the other stone because it has temendous power.
Water expands in volume roughly 9% when freezing and will create a pressure of up 3625 psi (25MPa) if prevented from expanding when the temperature falls below freezing point (Chaplin, 2007. Retrieved January 28, 2007, from Explanation of the Density Anomalies of Water (D1-D19) Web site: http://www.lsbu.ac.uk/water/explan2.html. See article on Vermont walls by B Post, Stonechat 11).

If this freezes and thaws this small rocking would work on any faults, potentially causing a stone to be displaced. Even water between a wedge and a stone could work. There are also interesting implications if stones are not set level. In essence the freezing will displace a stone perpendicular to its 'bed' whatever angle that is but when it thaws the stone will drop vertically, in effect moving slightly.

Doesn't take much to have an effect, just as root heave is small but potentially (and almost inevitably) disastrous over a period of years.

More likely to be a problem in Vermont than here. I have something nagging in my mind about snow getting into Scottish walls. If it comes to me I'll post it, assuming stonedyker doesn't get in first.

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Re: To Cover or Not to Cover...

Postby stonedyker@talk21.com » Fri Mar 20, 2009 11:29 pm

Sean,
The two things which keep coming up with North American stonework are the effects of frost heave and seismic activity.

Neither occur to any great effect in the UK. I don't know what the European experience is. Perhaps someone can give some insight into how Alpine or Finnish walls are affected by frosts.

My understanding is that the frost causes the ground to heave, thus lifting and lowering and weakening the whole structure, more so than individual stones. I have not read the Article in Stonechat 11 so am open to challenge.

I would advocate that a well founded, tightly hearted wall will suffer infinitely small damage from frost anywhere in the UK.

I have worked on head dykes at 2000 feet which have suffered damage from snow. Snow drifts piling up on one side can put a lot of pressure on the stonework. Even this damage can be quickly put right, for example if copes are regularly checked. Perhaps the melting snow causes a lot of water to be around the foundation and if there is a tendancy for the found to slip on a slope it is more likely to do so in wet conditions.

A good dyke filled with snow should not move but, if during the process of thaw the pressure on one side acts with the frozen snow forced between the stones inside, I can see the greater chance of failure resulting.

The argument is probably academic. The beauty of drystone is that the work is completely reversible and repairable. In the summer the hill shepherd's job was to walk the dykes and attend to any repairs. A stitch in time saves ten.

Rabbits and badgers probably cause more damage than weather.

Nick
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Re: To Cover or Not to Cover...

Postby stonewaller » Fri Mar 20, 2009 11:53 pm

Vtrue

seismic activity.... end of a house I was living in fell down following the quake of 1982 in north wales. Although it took 5 years (bulged immediately after quake. Lots of field walls were damaged reportedly.

The gist of the Vermont article was about frost heave. I`ll email you a copy.

I agree frost heave within walls is not likely to be much of a concern abecause of amount of frost and lack of damp in wall, I was more on about the fact that the amount of space is not really a concern (beyond that most water will drain) it was more about how freezing would work if it did, so to speak.

Still thinking about snow, beyond problem of snow ploughs on narrow roads which was one thing.

badgers, rabbits, moles and haggii, haggisses or something.

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Re: To Cover or Not to Cover...

Postby Tracey B » Sat Mar 21, 2009 11:33 am

Well Sean, thats an article I am looking forward to reading.....'the effects of the haggis on dry stone walls-a case study'.
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