How hard can it be? Rock wall repair

I need to fix our rock wall but have no idea where to start.  It engaged in a game of car vs wall last night,  i think it won by the sounds and the speed which the car ran away with something dragging behind, but a few rocks fell out in the process.  If I leave it damaged, future drivers will be lulled into a false sense of security that their car can win... anyway....

I don't know enough to learn how to fix it.  Hoping you can help.



(Not the same wall, but built about the same time in a similar style, probably by the same mason)

It's a retaining wall so most of it is some sort of cement.   On the outside, there are irregular rocks, most smaller than the size of a human head, all with one flat side for the outside of the wall.  There is lots of filler (cement?) between the rocks.  More filler than in the picture.  On top is a thin layer of different cement that has been worn away to show some gravel.  It all looks very rustic.

And because it already looks rustic and I still have the rocks that fell out of the holes, my imagination says I can buy a gallon of glue cement ready to go and put the rocks where they go, scrape away the stuff that squishes out.  Like laying bricks but less stressful.  

How does reality compare with my imagination?

What words do I need to feed into search to learn what I'm missing?

How does the weather (two or three more months of zero rainfall) influence it?  Is it like old time mortar where we have to water it each day for a week if there isn't enough air humidity?

Not sure if I will do the repair myself, just want to know how difficult it is and what's involved.  Depending on what I learn, maybe I'll try it.  Funny thing is, I got a good deal on masons trowels at the thrift shop that morning, so I feel like it's a sign I could try this new skill.

I should point out, the rock part of the wall seems to be decorative.  The real wall is hidden behind it and does all the work of keeping earth in place..  This is solid.  

The real/working wall looks built about the same time as the decorative elements as they join together, but looks like slightly different cement that is less pretty and doesn't crumble when playing chicken with stupid delivery drivers.  

Hi  you are in BC; do you get freeze/thaw?
If so, water b/t the retaining wall and the facer stones will push the facing stones off.
There might have been a cap to divert water from flowing down through?
I have limited experience but have seen it done poorly many times. cheers Douug

There are some nights that freeze in the winter, but it's not normally enough to damage cement or pottery. The wall is probably from the 1950s and has only minimal weather damage.

That thin layer of fancy cement (you can see a version of it in the photo, maybe a quarter inch thick) seems to protect as well as level the top.  All the pieces are there, so I'm hopeful it can be reattached as well as the rocks.

I tried playing with google and ducky in my spare time today and found my words are insufficient.   Rock wall repair gives drywall repair.  Stone wall repair gives brick repointing and dry stacking.  

All I learned is is my current batch of ducklings love this video best.

The basic rules of DIY stonemasonry are simple:

* Rocks have a way they want to lay. Your job is to find that and then place them that way. Don't try standing a big flat rock on its end unless you have a really good reason to.

* Running bond gives strength along the length of a wall. Headers give you starting and ending points, and stretchers keep the faces tied together. If you place smaller stones next to one another, try and have a larger one spanning them in the next course.

* Dry stack and experiment to make the best use of what's on hand. When you've got something that works, mark your rocks, take a photo or two, disassemble, then rebuild with mortar.

* Move slowly and deliberately, and get help if you need it with larger rocks. Use bigger ones lower down and smaller as you go up. A wall will get narrower as it gets taller. That's ok and it contributes to the stability of the structure.

In this particular case, all you really have to do is put things back together, but you may find the damage extends beyond the area where stuff fell out of place. You might achieve a better repair if you're willing to demolish a bigger volume to get any rocks that were knocked loose replaced firmly.

Is there a word I can take to the DIY store to ask about the 'glue' for the rock?  Is it just cement or mortar or???  

Is it the same as what the original wall was made with? Do I also have to buy rock or sand or other additives?

How does this compare with the stuff used to make lime (sp?) plaster?  

Am image of the4 damaged wall would help a lot, otherwise we are dealing with words alone.

Hey R,

mortar is a mix of aggregate (sand) and a binder (cement or lime) and water.
Plaster is a specific type of mortar.
So they're all very similar.

Modern adhesive cement has additives (glue?) to make it stick much more than regular mortar. Adhesive cement might come in a bucket ready to use, in a bag to just add water or as an additive (powder or liquid) that you add when making your cement mortar.

Your plan is to basically glue the stones back in place where they were? In that case you need an adhesive cement mortar, with some flexibility and very small aggregate (fine sand or no sand). "Adhesive cement for repairs" might help you as a word combination when talking to the store clerks.

But let me tell you that I don't know how well that's going to work. You would probably have a better chance of success by chiseling away some of the mortar in the places the stones fell out to make some room for a good coating of mortar (1/3" at least).

Best of luck!

Adhesive cement

Thank you!  This is going to be a big help.  

You would probably have a better chance of success by chiseling away some of the mortar in the places the stones fell out to make some room for a good coating of mortar (1/3" at least).

I was thinking this too.  Lucky the car impact loosened some (but not much) of the mortar around the dislodged rocks, so I was just going to clear away that and hope it made enough space.  I  could chip some away if needed.  See if the rock fits, find new smaller rocks if needed (it's the same type of rock that comes out of the ground here).  Hit stuff with back of mason hammer if needed to make it fit.  At least that was my idea.  I don't know if it's a good one.  But if memory serves, I need to make sure the old surface has texture so the new mortar can grab hold.  The rocks are inconsistent in how far out they stick out, thus the rustic look.  So there's about half an inch fudge room if I need it.  

It's up and down that needs to be more careful if I'm going to get the (can't think of the proper word) hat back on top or make a new one.  The mason took a lot of effort to make the top of the wall level.  I feel that is important somehow.

I'm glad to hear it only needs 1/3 inch mortar space to glue the stones back in.  I was worried it needed more gap.

Adhesive cement might come in a bucket ready to use, in a bag to just add water or as an additive (powder or liquid) that you add when making your cement mortar.

Is there a preference?   Part of me likes the idea of premixed putty ready to use like for plastering drywall.  But there is always a chance I might need to do this again in the future.  Would a bag of powder be worth the investment?   (Note to self, look up what the bag of stuff we used to repoint the chimney is called, but that was much smoother so probably not what's needed).

John C Daley wrote:Am image of the4 damaged wall would help a lot, otherwise we are dealing with words alone.

A photo of the damage is problematic right now.  But the construction is the same as the photo above (checking the records, they are installed at the same time by the same mason using the same techniques) but imagine one or more of the rocks fell out.  The thing the photo doesn't show is the rocks only go in a few inches and don't appear to be structural (no cross linking kind of thing like with a normal stone or brick wall).

Chicken foot is for scale.

You know you're a permie when...

r ranson wrote:Chicken foot is for scale.

You just made me laugh a lot.


As for premade or not I don't have a preference. I would check the price, premade is often ridiculously expensive.
My preference is not to use that stuff at all. It's smelly, sticky and probably not healthy in any way.

And yes, texture on the stone and the old layer of mortar is good.

Can I use regular mortar for stonework without the fancy glue?

I admit, most of my masonry knowledge is theoretical and from pre 1950.  The technology seems to have changed dramatically but the method looks basically the same.

You could try. If it's just a couple of stones you don't have much to loose.

Make the stones and the (textured) old mortar wet. Throw in some (cement or lime) mortar into the holes and press the stones in. If you're lucky it'll hold together.
If not you can still go down the "advanced ingredients" path.

A previous poster, B. wrote:

Hey R,

"mortar is a mix of aggregate (sand) and a binder (cement or lime) and water.
Plaster is a specific type of mortar.
So they're all very similar.

Modern adhesive cement has additives (glue?) to make it stick much more than regular mortar. Adhesive cement might come in a bucket ready to use, in a bag to just add water or as an additive (powder or liquid) that you add when making your cement mortar.

Your plan is to basically glue the stones back in place where they were? In that case you need an adhesive cement mortar, with some flexibility and very small aggregate (fine sand or no sand). "Adhesive cement for repairs" might help you as a word combination when talking to the store clerks.

But let me tell you that I don't know how well that's going to work. You would probably have a better chance of success by chiseling away some of the mortar in the places the stones fell out to make some room for a good coating of mortar (1/3" at least)."

This is all correct.  I want to emphasize that you really will want to chisel away or grind away (grinders are cheap but dangerous if you are not careful; you would need a masonry disk, not the disk it comes with) mortar still attached to the stone.  Wear safety goggles.  As for adhesive, you can use portland cement, premix mortar, or tile "mastic."  Assuming the original mortar was just regular mortar, that might make the most sense.  You will use it to 'glue' the rocks back into place, and then come back once it's hard and fixed to fill in the joint gaps.  You may need to use some nails or pieces of wood, or pens or pencils as spacers to hold the rocks so as to maintain bottom joint space.  You can gently pull these out about 12 hours later.  

Now, this is in an ideal situation where the rocks refit well and you mix the mortar to an optimal enough consistency to hold it in place while setting.  If this does not work and the rocks fall out, you can add lime to the mortar mix (new batch ; also you should only be mixing about a quart at a time for this).  This makes it "stickier."  

OR, you can just cheat and use some "fast grabbing" construction adhesive instead.  Liquid nails should work but there are weaker brands that actually grab better.  I recommend that approach.  All you are trying to do at this point is get the rocks replaced and affixed.  (You will grout later and that grout will also hold them into place.)  You would need to clean off the rock faces and make sure they are dry.  Put the fixative only in the wall opening/spaces and use a decent amount, but not so much that it is going to squeeze out of the joints.  IF you make a mess, just let it harden and chip/cut it out a day or so later.  If you try cleaning it while wet, you make smear it all over the other rocks, and then will need acetone or whatever the clean up solvent is...  Big pain in the rear.  Anyway once it hardens up and is holding the rocks into place, come back and grout the joints with mortar.  BTW you will need a jointing tool (Look up "OX Pro Brick Jointer" for EXAMPLE.   Select one that is about the same width as your existing joints.  YOu don't need this brand.   Just an example.  Might want to go to you tube to look at a video on brick and stone jointing)

Basically, rock and brick work are one of those things that are fundamentally simple but can be elevated to an art form.  Your project is actually pretty basic, so address it with confidence.  Write back if you need clarification.   FWIW, I have been doing this and concrete off and on for 40 years, and consider myself a competent amateur.  In my case this means I can and have done footers, walls, steps, slabs, etc. for myself and for pay, and successfully.  BUT make no mistake, the people who do this day in and day out for *years* are the true masters and artists.  Anytime you can watch one at work for a little while (ask for permission) do so.  You will always learn something.  It's like drywall... anyone can do it, but doing it fast and well is another art form.

Ok,  I looked at your pic closely and have a couple more comments.  First, get a "flat' not curved jointer for your tool.  You will want to have the joints be flatish or planar rather than curved - to match the existing joints.  Second, (this may be a bit tricky but the good news is that mortar is water soluble so you if you don't like the finished product, you can remove and redo it before it sets up hard.  So, no stress) if you want the repair to match the old work well, you will want to very gently brush it with a wire brush a day later when it is hard but the surface can still be abraded).  The idea is to get the surface to be more sandy looking than super smooth. This is to match the weathered look of the old mortar.   You can also get the same effect by spraying water on it with a hand operated sprayer (like a windex sprayer (with water)) spraying hard.  This will dissolve some of the cement/lime in the mortar, leaving more sand apparent on the surface.  If you look at the pic you can see see that this is what has happened over time.  One other thing.  Once your repair is done and hard, you can come back with a little brush and buttermilk and brush it on the new joint if you want to encourage new moss growth quickly.  This also works on ferrocement walls, for those of you who know about ferrocement.

Good luck!

I agree with a lot of what people have said -- there is good advice about chiseling away the old mortar, wetting the stone,  and even using constructive adhesive to hold the stones in place and using grout to "(re)point" <https://en.wikipedia.org/wiki/Repointing>.  All that said, it would also be helpful to take some pictures of the damage so that we can see what we are dealing with.  Sometimes there are details in the job that changes the advice.  This reminds me of a story when one of my best friends was in grad school and...  

One of the students in the lab asked, "I have my father's old farm truck, and I heard that it is a good idea to have all the fluids flushed every once in a while."  Basically, all the car heads in the room said, "yea, it will help clean everything out inside and things will run more efficiently," and they interjected various details.  Then one of them asked, how many miles does she have on her.  The answer was, "I think it is just over 400,000 miles."  Everyone in the room shouted at the same time: "DON'T TOUCH IT!!!"  You see, the truck was made back in the 70's when a good run on an engine was between 100K to 200K before requiring a rebuild. If it had 400K, that means it has run at least 2x the max life expectancy, and you really do not want to do *anything* different to it than had been done to it over the last 30 to 50 years.  At this point, half of what is holding the parts together are likely to be sludge and grime, and everything is worn together.  Running the cleaners through the engine is probably going to do more harm than good.  So keep up the unbelievable good work.  Any vehicle that has lasted that long has had a good maintenance schedule.  Now, a new vehicle (or an old vehicle with a new engine) will benefit from getting cleaned out every few years...

Anyway, back to my point about the wall...  There could be details in the wall that will change the advice, but yea, any wall that has stood the weather and test of time for 75 years, is well enough built that you are likely only going to need to put the rocks back in the same place, and then repoint them (or clean up the joints).

Do you know when the rock wall was made?

I have repointed a few rubblestone foundations in my day and have found the 'look' can be effected if you don't utilize the same time of mortar utilized when it was first built.

If aesthetics be damned, no need to worry. If you are trying to get everything to blend right and this is an older wall, you may want to look into making some lime mortar. I used somewhere around a 3 parts sand to 1 part hydraulic lime ratio for my house's foundation. The trick is to dry mix it and then slowly add water to get a workable consistency. Adding too much water can make a really sloppy job. Be sure to wear proper PPE when dealing with hydraulic lime as it can be caustic.

For rubblestone foundations (slightly off-topic I know), it is important to let them 'breath' as they will expand and contract with the seasonal conditions. If you put in cement, you run the risk of cracking stones as the cement won't expand/contract at the same rate.  

@Timothy, very good point.  If it is old enough, it may well be a lime based mortar instead of cement.  You do NOT want to mix the two! I have heard stories of buildings in the UK becoming permanently damaged by someone repointing brick/stone with cement mortar.  In fact, people working on old buildings in the UK have to go through a training course so they do not make that mistake.

I do not know how to test the difference for these mortars.  Anyone here know how, or can provide links to tests?

If the wall is the original dirt/hill/yard retainer and it was designed as such with a stone face for nicer looks, then the strength of that "mortar" may be one of several different versions.

From mr. Google -

There are several types of mortar, including Type M, S, N, and O, each with different strengths and applications.

When I rebuilt my 2-flue chimney, I opted for Type M, knowing I was going up 30 plus feet and thought I wanted it as strong as possible.

That choice has yet to be tested - maybe one of my grandkids will be cursing my name on the next rebuild!

I have also seen where folks build a stone wall with wooden casing surround, carefully placing stones in the form and them pouring regular concrete around the rocks, moving them just enough to embed them fully.

A hard bristle scrub brush is then used on day 2 to make the face of it pretty.

My point is - your old wall could be constructed in so many ways - you'll either need to do some real digging to ascertain it's original style, or just make it solid to repel any further intruders!

Good Luck, and if possible, give us a follow up on the completed project!