# Recommendations for salting on flagstone walk with mortar joints



## Lawn Lad (Feb 4, 2002)

I have a commerical customer who had a new walk installed two years ago (sandstone with mortar joints set on 4" of concrete). The customer fired the last guy (who installed the walk) because they used too much de-icer. So we were aware of their concerns coming into this season.

It's a high maintenance account - 7 days a week. 1" trigger with shoveling, plowing, deicing lot/walks. 

We used Magic Salt and used it sparingly. The mortar joints have popped out. 

Is there any way to treat this type of walk without this happening? Seeing as how I doubt they'll accept this is par for the course. 

Any suggestions?

Also - two spots for the curbs that were replaced in their lot have deteriorated. Broke off in chunks and it also looks like just general decay. The rest of the curbing is fine - it must be 20 yrs old plus. Just the patches are falling apart. Is this because of the salt? Or more likely the mix that was used?


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## Chuck Smith (Dec 30, 1999)

Lad,

I doubt the mortar popping out is due only to the use of de-icer. It is very common on flagstone walks for the mortar to pop out for a number of reasons.

1. De-icer- ANY de-icer, because it causes a freeze thaw cycle.

2. Mortar doesn't stick well to flagstones (in my experience, the stones are too "smooth" compared to bricks for instance)

3. Running a snowblower on flagstones can cause enough vibration to loosen them.

4. Too much sand in the mortar mix will make it weak to begin with.

The only flagstone walk I ever saw with all the stones solidly in place, was at a friend's house. The stones were there for 20 years, and never had any de-icer on them or a snowblower. The mortar "grout" was only 1/2" wide. The stones were random rectangles. Even at this house, some of the mortar had popped out over the years and was replaced, but most of it is original. The walk is also pitched quite a bit, so moisture does not sit on it and freeze over and over. The walk is raised above the turf about 2", again, so water does not run onto the walk.

Something to remember is that the stone and concrete / mortar are two (or three) different materials, that expand and contract according to temperature at different rates. This does not help matters.

~Chuck


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## Rob (May 15, 2001)

Kind of off topic, but was interested in Chucks reasons for the mortar popping..
Do you think that it would be worthwhile or feasible to have this type of walkway heated ? I know that a bunch of municipal buildings have their walks and stairs heated to prevent the accumulation of snow as well as ice. The ones I have seen were always concrete, but I was wondering if it is possible to have it done to other types of walks.


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## paul soccodato (Nov 9, 2002)

The freeze/thaw cycle is what kills the joints & bedding.
Cement is porous, and allows moisture to penetrate. Then it freeze's and explode's the joint's.

Applying de-icers will only speed this up.

I tell all my clients that i do either patio's, walks, steps, or snowplowing, that the best thing for deicing them is sunlight. But it still happen's

You can also add "hydro" (calcium), to the mix, to make the mortar waterproof.

You can also seal the surface, to prevent moisture from penetrating.


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## Jerre Heyer (Mar 19, 2002)

Rob, Several types of heat pads and options for under walkway heating. Can be expensive though.

As for de icer there are several citrus based products that have been used with fair sucess on walkways in the area. No tracking and wont cause the breakdown of the concrete/mortar.

As Chuck the wise one has pointed out though. The freeze-thaw will cause havoc with walkways. 
Drainage below is very important . This was a long winter with deep freeze throught out the Lake Erie region as well as alot of the country. This drives the frost level deeper into the ground and makes the problem worse.

Good luck trying to settle the account.

p.s. As for the patches. If they are coming off in a big chunk the joint wasn't prepped correctly. It may need drilled and roded as well as acid cleaned before repouring. If it is crumbling off the mix was probably bad..... Just my experience from laying it down.

Jerre


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## Lawn Lad (Feb 4, 2002)

Thanks all for the replies. Part of the problem with sandstone is that it fluctuates in temperature a lot quicker, or this particular slap doesn't hold ground temperature. So we'll often get frost on it a lot quicker and with a dusting of snow it will be covered while surrounding walks may melt off requiring de-icer. Since we have to have the walks cleared by 6:30 am every day, sunlight doesn't do us much good in this case since there are many seniors walking in for Mass at 7:00 am. 

Jerre - you mentioned a citrus de-icer that has worked with some success. What are the product names? But if the real problem comes from the heaving from the freeze/thaw, then wouldn't the citrus similarly cause the same problem we're having now?


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## Jerre Heyer (Mar 19, 2002)

Lawn lad, Will get the info for you on the citrus. I get it from A.M. Lenoard. There on the web.

Freeze thaw will still cause the lifting and the walk may need additional drainage to help this problem from being aggrivated.

We have used the citrus because it can be put down before the storm and helps keep the build up of snow down requiring less use after the storm and reduces clean up time.

Jerre


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## snowfighterG (Feb 18, 2003)

*citrus deicer?*

Hey Jerre I never heard of a citrus deicer and we have the similar problems here with 46 townhouses that have limestone steps on them. We use pottassium chloride it's less damaging but it still beats them up pretty good especially the mortar joints.Can you give me the website for the citrus deicer. Where do you buy it from... where you are? What kind of experience have you had with it as far as damage goes?

Gino


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## Jerre Heyer (Mar 19, 2002)

Gino, I bought if from A.M. Leonard co. Was looking for the product name again and in the current catalog it wasn't listed. It was the summer catalog. I'll have to pull the data out of my files and post it. You may want to check the Leonard website and do a search.

We noticed less tracking and little damage. None that we can really atrribute to the deicer.

Jerre


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## Jerre Heyer (Mar 19, 2002)

Heres the juice.....Product is called Bare Ground. Sold in gallons from A.M. Leonard co. Also available from the company direct in concentrate. Hope this helps Jerre


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## Lawn Lad (Feb 4, 2002)

The walk in question abuts a curb next to the parking lot - a 90' stretch. The entire mortar joint has popped out between the curb and walk. Obviously the walk and curb move at two different rates with the freeze/thaw cycle. 

Rather than use mortar - has anyone used "caulk" in this type of joint? I'm thinking about the type of caulk that you see in parking decks or in between sections of concrete roadway. Would caulk work? How about on the rest of the sidewalk... would caulk be the way to go for the other joints? 

What type of de-icer would have to be used? Parking deck de-icing requires Potassium is it? Why is this? 

I heard someone mention "chloride" free de-icers. What is it about the choloride chemistry that causes problems? What are the alternatives to sodium and calcium chlorides?


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## Jay Kosack (Jan 2, 2002)

You may want to try Potassium Acetate. It is non-chloride and environmentally friendly.


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## Jerre Heyer (Mar 19, 2002)

Lawn Lad,

Calk will work but remember it will stick to the pavers and the curb and with too much movement may hold the pavers up or down along the edge and may cause breakage. Silicone (s.p.) will probably give the most flexability. I think I would look into some of the rope type fillers that will allow them to move independantly. Good luck sounds like you've got a tough customer there to work with.

Jerre


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## Alan (Mar 2, 2000)

Just a couple thoughts on this thread. 

I think the most "benign" deicer available might be CMA (Calcium Magnesium Acetate), if you are looking for a dry product. It can also be mixed as a brine and applied in liquid form. This is a chloride free material.

On the subject of freeze/thaw cycles I'm not so sure it is the result of the physical change from liquid to solid and back that causes the damage. Water is at its' most dense at something like 33° F. As temperature drops below that point water starts to expand again. In a normal scenario water is absorbed into the structure of an object and then freezes. In the case of a mortar joint the mortar is quite porous and absorbs water readily. As the water expands with falling temperatures it cannot be forced form the pores of the mortar and transfer back to the air as it is now a solid. The expansion of the solid water (ice) fractures the chemical bonds within the mortar and you see the resulting damage. In warm weather there is the same expansion of trapped water but since it remains liquid it can be forced out of the mortar and evaporate, causing no damage. 

As for a sealant in place of the mortar, the best bet would be a two part urethane. That stuff is hell to mix and place, but it works. It needs to be put on a clean substrate, preferably with a primer applied first. The joint should not be more than (working from memory here) half as deep as it is wide and the material should not be applied more than 1/4" thick. In deeper joints you use a "backer rod", a closed cell foam cord to prevent the sealant from ending up too thick. Some grades are pourable while others are used in a reloadable caulking gun. The thicker types need to be worked into the joint to be sure it is pressed tightly against the sides of the joint.


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## Chuck Smith (Dec 30, 1999)

> _Originally posted by Lawn Lad _
> *The walk in question abuts a curb next to the parking lot - a 90' stretch. The entire mortar joint has popped out between the curb and walk. *


Well, it seems to me that is a problem in itself. I have never seen a sidewalk without an expansion joint where the walk meets the curb. A mortar joint would not be used abutting a curb.

I know the curb in front of where I park my wife's car rises at least an inch every winter. The sidewalk stays put. There is an expansion joint in between the two. The pavement of the parking lot is not cracked or damaged, and neither is the sidewalk, or curb. There is no way mortar, or any type of caulk will hold up when the curb wants to rise 1 inch+ while the walk stays put.

Ditto on Alan's comments. CMA is expensive compared to other deicers, but in your situation, I feel that there should not be a mortar joint at the curb.

A common caulk used here is Phenoseal. It comes in grey, and even has a concrete texture. It is often used to caulk where a sidewalk meets a building, but even then, it is applied over an expansion joint. Remember a curb can have a footing as deep as 18". Those flagstones are sitting on a 4" base IMO.

Before applying any caulk, be sure to clean the concrete with Muratic Acid per the instructions on the container. It will "etch" the concrete helping the primer adhere.

~Chuck


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## BRL (Dec 21, 1999)

Chuck has it right. There should absolutely be an expansion joint there, then the mortar can start. Putting caulk there is a much more expensive replacement for using expansion joints, or it would simply be a cosmetic temporary repair of the problem vs a permanent solution. I would recommend to the client; saw cutting the moratar where it meets the curb (rent a walk behind unit for nice easy accurate cut for that length), install an expansion joint there, repair mortar joints & flag stone where needed, then use "concrete" caulk to seal the bordering area if needed. That would be at the least. If there is really only a 4" base for that walk I would suggest for more permanent & better results, reinstall that walk with the correct amount of base material (8"-12") to help further reduce the walk movement.


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## KenP (Oct 4, 2002)

There 's a lot of good info here, so I thought I'd chime in. I'm no expert, but I did a few years with a civil engineering firm doing inspections on roads, sidewalks, curbs, yada yada yada. There's many different thoughts out there about monolithic pours, expansion material, what and where to use it. 

I was never a big fan of monolithic pours, I feel that the different depths of the concrete make for unequal shifting during the freeze/thaw cycles making it crack sooner at the location of where the joint should have been placed. That said, I too feel a simple saw cut would suit this project the best. I would also use a caulk to seal the joint, phenoseal works great in the home remodeling and it's my choice for the everyday kitchens, baths etc that I do. 
I'm not sure of the idea to use it in a concrete joint. In all probability it would work fine. The product I've found by being a pool owner and having an expansion joint problem is Vulkem sealant. The stuff works great. It comes in the 30oz dispenser. and stays somewhat pliable. It worked wonders around my pool. I now use it on all the concrete cracks around my house. It comes in grey and I think white. You may want to practice a little before starting your joint to get the hang of the flow. It can be messy (take my word). 

In regards to your ice melting problems. We have several high maitence properties that have flagstone walks, patios, paths etc. The product we've been using for three years now with no visible damage is called MAG Flakes. It's a mix of three or four melting agents and it works really well. Two down sides are the cost, which we pass onto the customer (if they want it they get it). The other is it tastes really bad when it gets in your mouth. I'd be happy to get you more information, if you'd like otherwise good luck


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## s-10racing (Jan 19, 2002)

hello, little late to reply , but anyway. i have been in masonry trade for over 15 years& when i install sidewalks or patios, i tell them not to use any ice melting products unless the manufacter is standing behind product not to cause damage. salt based product does destroy masonry of all kinds. i tell them to use either sand or kitty litter , no it does not melt ice but they will not slip.... i have had so many people over years that had concrete surface pop & joints pop & brick surface pop , after spreading salt product on surfaces, i do go back to a certain extent to help , but where do you draw line, i pride myself on quality work, & will do what it takes to do it right. but you cant make every one happy. there are suposed to be expansion joints to stop cracks, but any sidewalk or patio will rise & fall because of freeze & thaw & it will crack 99% of the time .masonry is like a sponge it absorbs water ,the only way to stop water from being absorbed is to water proof & in my dealings with waterproofers they become slippery. its a catch 22, you need to have guide line saying you are not responsable , they are getting what they asked for, in contract from start, good luck , matt artymenko


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## Got Grass? (Feb 18, 2001)

It does sound as if it was a bad mix, simply because of the curb patches breaking apart.

From what I hear flagstone is one of if not the worst material to treat. A water proofer sounds good providing no water is allowed to sit underneath & pop them up, I know they make additives to sealants to provide more traction. Caulk may be a great choice as it's quite flexible. Heating the walk may be the best choice providing it is installed properly so it heats every little inch not to allow freezing. I would consider a mix of the suggestions posted here... Do NOT use salt...


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