dry stone walling in Portugal! help!

Hey Folks,

I just moved to Portugal the land of stone houses and stone walls!

Shame I don’t have any experience in this area and finding a Specialist so far as a foreigner hasn’t been fruitful, thought will keep on the look out.

I have a 6m dry stone wall behind my house which appears to be opening up on the corner, and it is just above my roof/bedroom!

One of the Portuguese neighbours visited and suggested I fix steel rods to some of the bigger stones and essentially brace the wall. I thought this was a good idea and something that I had already considered. I’m just not sure what thickness reo bar to use and what fixings, or if the idea is solid.

I have attached some pics let me know your thoughts.

Ta,
Rich

The visible face of that wall has issues with stone orientation, and really needs to be rebuilt to be durable for the long haul. It would help giving the best advice if we knew what size the stones are, and how tall the wall is. Do they look like any of them would be too heavy for you to pick up? From the grass in the foreground, I would guess that the largest stone at the lower left of the second and third photos is around 30 to 40 cm long.

Many of the joints between irregular stones are oriented along the slope of the hillside, which gives them little resistance to movement. They would be much stronger if the more or less horizontal joints "leaned back" down into the hillside, so that the upper one if greased would tend to slide back into the hill and not off the edge.

For temporary reinforcement, you may be able to use some rebar. I think I would bend the ends of pieces long enough to hook firmly around the biggest stones, using say 10 to 15 mm rebar depending on how big the stones actually are. The farther back the rear hook is the better it will hold. The big lower left stone looks to be in a stable position, and I would not try to hook to anything higher than that unless it is farther back into the hill. Do not hammer on rebar trying to seat it into crevices, or you may further destabilize the face of the wall.

I would suggest for the long term either gaining experience with dry stone walling technique or hiring someone good, or both, and (after building shelter/deflectors below to protect your roof from mishaps) taking down the unstable section of wall and rebuilding it properly.

I agree with Glens comments.
I have learned a bit about drystone walling and that vertical 'slot' in the wall looks wrong.
I have a few ideas;
- find out what is behind the wall
- watch a few videos
- clear the back away
- check or improve drainage if needed.
- dismantle the wall laying the stones out where you can see them all.
- think about creating a stone lifting apparatus to save your back

thanks for your comments folks . . .

The wall is actually massive, 5m tall and most of the stones too heavy to lift, the big one bottom left measures approx. 1m x 0.5m. Hence why I'm reluctant to take down and re-build, but I will keep a look out for stone wall specialists in the area . . .

Reason I thought to cement it up because at least i'll know then if it's on the move cos it will crack . . .

Ok, fair call.
With nothing in the photo to scale things I can see why I made a mistake of assuming it could be manhandled apart.
It certainly will call for expertise.
What part of Portugal are you in? I may be able to find somebody.
What is at the top, a road, a paved area because that may enable you to get help?
As a Civil Engineer, I can tell you there are mechanical solutions ground anchors, but I cannot tell you the cost.

Okay, so almost 3 times the dimensions (20 times the weight) as I was estimating. Yes, that is going to take some skilled workers and probably power equipment. I think it would take something like 20mm rebar to make tiebacks with hook ends to hold that. Ground anchors as John mentions would be a solution, and would require a professional engineer to plan.

We use rock anchors all the time where I work, but the added lines do not show how rock anchors are typically applied. They are bore into the rock vertically and then have a big square washer that goes over the end and cinches the rock up tight. They work amazingly well considering they are completely opposed to someone even thinking they would work since it is so counterintuitive. I will get some pictures today of how some at my job site.

Grady on Practical Engineering did a whole video on rock anchors and well worth watching on YouTube.

But in the application cited, its not really a Do It Yourself sort of thing because Iam not sure how a person would bore vertical holes without massive equipment to do the drilling. Pounding in rods by hand might jar the rocks loose and make it worse.

Here is how we reinforce rock that is crumbling. It’s kind of hard to see but the rods go straight into the rock and hold it together.

Perhaps look at this site
https://www.casteloconstruction.info/2015/12/22/just-arrived-in-central-portugal/
It details topics such as living and building in Portugal.
It is a company that carries out work, but runs a blog about a huge range of topics related to living there also.
https://www.casteloconstruction.info/2015/12/22/just-arrived-in-central-portugal/
Details repair of stone walls

I don't see rock anchors working because there is not rock behind to bind into just earth , unless I have misunderstood how they work.

I'm more inclined to dismantle the wall now I think it's going to be the safest and best long term solution.

Just you can't get machines up on the terrace above to dig out earth, a machine can only work from the bottom.

Perhaps a mechanical claw can lift each stone off from the top 🤷‍♂️

I will get some more photo's of the foundations and diff angles . . .

Glenn Herbert wrote:Okay, so almost 3 times the dimensions (20 times the weight) as I was estimating. Yes, that is going to take some skilled workers and probably power equipment. I think it would take something like 20mm rebar to make tiebacks with hook ends to hold that. Ground anchors as John mentions would be a solution, and would require a professional engineer to plan.

yeah i was looking at least 16mm, but will just hooking it round the ends of rocks be enough, i was thinking to drill holes and either cement bond the angled ends into the rock or use masonry bolts/big washers . . .

John C Daley wrote:Ok, fair call.
With nothing in the photo to scale things I can see why I made a mistake of assuming it could be manhandled apart.
It certainly will call for expertise.
What part of Portugal are you in? I may be able to find somebody.
What is at the top, a road, a paved area because that may enable you to get help?
As a Civil Engineer, I can tell you there are mechanical solutions ground anchors, but I cannot tell you the cost.

I'm near Sao Pedro do Sul buddy.

at the top is my neighbours land which is just abandoned/overgrown/earth, I'll take more pics.

My suggestion would be to anchor posts in the earth and use heavy wire to hold the rock against the "cliff".

This would be similar the gabion basket concept just one-sided instead of a basket.

I see you looked at the EXpat site I went to.
Did you get any leads from that?
I saw this https://www.silvercoastconstruction.com/

I don't think a wire fence would really keep the rocks where they are given their size, unless you spent a lot of money on really big and heavy posts and fence. A modest fence like that could slow the fall of rocks so that they wouldn't damage your house, until you can get the wall rebuilt. It would mostly keep falling rocks from bouncing out and hitting the roof, and funnel them straight down.

some more pics, with focus on the bottom corner which I think is the main problem area . . .
I'm thinking about a second 2m high stone retaining wall built in front of the corner and all around the side with cement in the gap, in addition to the reo bar bracing and filling the gap with bars/cement.

https://drive.google.com/drive/folders/1SVwWcXo24qJMo42KbiVKRVObH9BPWnnj?usp=share_link

With my limited knowledge of large stone walling and extensive knowledge of concrete, I doubt your suggestion is a good one.
One way to actually test things is to set up a 'movement' measuring device.
It could be the wall settles 200 yeras ago and now is stable.

If you have enough space at the bottom of the wall to build a substantial new wall, and can get new stones without difficulty, I think that would be a good solution.

It would be important to have the toe of a new 2 meter high wall at least 1 meter out from the toe of the unstable wall, and the face of the new wall sloping back at least 1 in 6 (or 1/3 of a meter), and all the new stonework bedded so that they want to slide back into the hill. I would carry the new wall up until it supports the unstable section, such that the exposed upper part of the old wall is not in danger of collapsing.

With that done, I don't think you would need to do anything else to the old wall aside from filling gaps to make it look better. This course of action would avoid the work and hazard of dismantling the old wall. Can you get new stone delivered to the bottom area and stockpiled with working space?

Glenn Herbert wrote:If you have enough space at the bottom of the wall to build a substantial new wall, and can get new stones without difficulty, I think that would be a good solution.

It would be important to have the toe of a new 2 meter high wall at least 1 meter out from the toe of the unstable wall, and the face of the new wall sloping back at least 1 in 6 (or 1/3 of a meter), and all the new stonework bedded so that they want to slide back into the hill. I would carry the new wall up until it supports the unstable section, such that the exposed upper part of the old wall is not in danger of collapsing.

With that done, I don't think you would need to do anything else to the old wall aside from filling gaps to make it look better. This course of action would avoid the work and hazard of dismantling the old wall. Can you get new stone delivered to the bottom area and stockpiled with working space?

Hey Glen, thanks for the response . . . I can get stones delivered to the toe of the old wall with still some working space . . .

My only issue is that bottom corner (front face of the wall not the side which runs into my Car Park), the terrace there is only a few metres wide behind the house so to come out 1m I'd be restricting access quite a bit, would mean never getting a small Tractor down there.

but might have to sacrifice that access for the safest solution 🤷‍♂️

From the Google pictures, it looks like the existing wall has a reasonable amount of batter (slope back of the face), and the unstable section starts a meter or more up from the flat. How much actual setback is there from the edge of the flat terrace to the wall face a meter or so up? I would measure the meter of new base thickness from that upper point, which may give you enough clearance for access on the terrace.

Glenn Herbert wrote:From the Google pictures, it looks like the existing wall has a reasonable amount of batter (slope back of the face), and the unstable section starts a meter or more up from the flat. How much actual setback is there from the edge of the flat terrace to the wall face a meter or so up? I would measure the meter of new base thickness from that upper point, which may give you enough clearance for access on the terrace.

Cool Glen I'm out of town atm but I'll get the measuring tape out as soon as I'm back Wed 👍🏼

Glenn Herbert wrote:From the Google pictures, it looks like the existing wall has a reasonable amount of batter (slope back of the face), and the unstable section starts a meter or more up from the flat. How much actual setback is there from the edge of the flat terrace to the wall face a meter or so up? I would measure the meter of new base thickness from that upper point, which may give you enough clearance for access on the terrace.

from the toe of the wall to the edge of the terrace (or just before the stones) it's about 2m currently so it would be reduced to 1m. So I'll never get a vehicle through there, but I think i'll have to sacrifice that luxury to reinforce this wall (and not rebuild it). I should still be able to get a walk behind tractor through at least.

Unless I look into steel retaining walls but no idea where to start. Though there is a really good metal recyclers nearby where i could get all kinds of steel frame . . .

I'm clearing the area today and hoping to order labour/materials this week to carry out the work. Will get a better night sleep once it's done!

It can be hard to tell how stable something like that is.  Could be quite stable and gonna sit like that for centuries, or it doesn't have long before it moves again.

A few of the stones in the middle appear to be going on halfway out, so I wouldn't want to stand near the bottom of that thing and start drilling.  Probably would be fine, and might not be.  Them stones are killers.

It seems a proper fix requires taking it apart from the top down and then rebuilding it.  Probably a lot less work to construct protection for your structure and keep your distance around heavy rainfall events.  

Hope it goes smoothly!

Is there some sort of net that could be installed across the front of the wall to hold things if they move?

I'm a drystone waller from Scotland, from the pictures you provided,  the wall needs stripped back to a solid part and rebuilt.A bodge repair will not last, pay me enough and I will fix it.

Rob, how do you define enough?

I agree that a bodge repair or anchors or nets will not permanently fix that wall, only delay disintegration. I do think that the visible face of the wall is solid enough that if well supported from below to say halfway from the terrace to the top, it would be stable for the forseeable future even though there are weak spots behind it. The definitively best solution would be to deconstruct the wall and rebuild it professionally; whether the time and expense to do that is worthwhile is up to the owner. The stone that is available as seen in the photos is not ideally shaped to serve in a retaining wall, but if carefully used  on a firm foundation could make a solid wall.

Hi ,how did you get on with the wall repair?