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What is Mortar?

posted by Bob Wednesday, January 12, 2011 at 4:34 PM

What is Mortar?

Mortar is a mixture of sand and cements that is most often used to build brick or block walls. In my July blog on cement and concrete I dealt exclusively with portland cement products and uses. I also promised that at a later date I would talk about the masonry world. For those of you on the edge of your seats since then, well today is your lucky day.

While portland cement concrete is certainly one of the most widely used building product in the world, masonry mortar is close behind. It is doubtful that you live or work in a building that doesn’t have mortar in it somewhere. The 3/8” gray line of material that separates the brick or block is mortar. Mortar is a very different animal than concrete. Concrete is designed to be used in thicker applications and to reach very high strengths. It achieves its durability through brute force. Mortar is also designed to be durable but achieves its goal through finesse. Its strengths are quite low compared with concrete and it is never used in thick applications. It is much creamier and more workable than concrete. If you play tennis, think of concrete as your most powerful serve when you are trying to smash the ball into or through your opponent so that they can’t return the serve. Then think of mortar as a very gently placed lob close to the net that gets your opponent leaning the wrong way with no chance of returning the ball. Both achieve the desired result of earning you a point. The point of this long winded analogy is to let you know that using concrete and mortar interchangeably will lead to disaster.

Mortar can be made in one of two ways. The older method is to take portland cement, add hydrated lime and mix with fine sand. The newer method is use masonry cement and fine sand. Masonry cement is simply a material made by most cement companies where they intergrind the portland with lime or other ingredients designed to produce high air content in a kiln. The results are the same. If you go to the store and buy a bag of mortar you will not be able to tell which method was used to make the masonry cement. There are some parts of the country where masonry cement is simply not available and you will only get portland/lime mortar. The good thing is that it doesn’t matter. In my thirty years of doing this type of work I have found that masons are the most determined group I have ever run into. Some will absolutely swear that you must use portland/lime while others insist masonry cement is the way to go. Just chalk it up to personal preference.

There are three things that make mortar very different from concrete. Mortar has lower strengths, must have the ability to retain water and have a high air content. There are three widely produced types of mortar. Types M, S and N. Type M will achieve a compressive strength of 2500 psi at 28 days. Type S will yield 1800 while Type N yields 750. By way of reference most general concrete is in the 4000 psi range but can go as high as 8000 psi for special applications. The easy way to remember the strengths is by spelling out the word MASON WORKS.

                                        M       A -----          O ----            W ----    O       R ----    K       S ----
                                                    2500                 1800                750                     350                   75

Types O and K are not made commercially and can only be used for non structural applications such as fixing old mortar that has fallen out.

Why not make mortar as strong as concrete? In America isn’t bigger better? Not with mortar. When you build a wall you want the block or brick to be the strongest part of the wall. When the wall shifts, and almost all do over time, the weakest part is going to break. If the brick or block were to break, then the fix would be building a new wall. If the mortar crumbles, provided you don’t let it go on for years, you simply need to repoint the wall (that means sticking mortar back in where the old mortar fell out). This is a simpler and more inexpensive fix. One important reason why masonry cement or a portland/lime blend works well in a mortar joint and straight portland does not is the high air content. Many walls are exposed to rain and water. In the winter many of these are in area where temperatures often dip below freezing. The mortar contains a certain amount of water. When water freezes it takes up more space than water. This means that it will expand and crack whatever is next to it. By intentionally putting lots of tiny air bubbles in the mortar, the expanded ice has somewhere to go without causing damage. Concrete generally has enough mass that this isn’t a problem.

I previously mentioned that mortar must also be able to retain water for a certain period of time. Most masons mix up enough mortar to be able to lay a good amount of brick or block without having to stop and mix more. If the mortar they mixed doesn’t retain its flowable nature for at least an hour the mason will simply add more water to bring it back to life. While this is a really bad idea, it is done in the field all of the time. The problem with this is that the strength of the mortar is designed around certain water to cement ratio. If the ratio is skewed, then so are you when the walls fail due to weak mortar.

So which mortar should I use? Commercial jobs will usually state which you are required to use. For none specification work, Type S is usually a safe bet and is what most of you would use on your projects. For those who have a quest to know more, the best general rule is that if the wall is non load bearing, such as a divider wall inside of a building, then Type N is sufficient. If the wall is below grade or carrying the load of the roof or several stories of brick or block use Type S. Type M is rarely called for and only used in certain large commercial projects.

Bob Schmidt
Product Manager
Sakrete of North America

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USER COMMENTS

what type of cement can i use for tuck pointing 1000 sq ft of brick wall. i like to use my hom made hand caulking gun. thank you
- peter
Wednesday, March 23, 2011 at 12:23 PM

Use the Mortar Mix Type N or S depending on the strengths you are looking for.
- slw
Monday, March 28, 2011 at 9:58 AM

Nice Blog.
- Ron Yatteau
Wednesday, March 30, 2011 at 8:42 PM

Thank you for the information, now I feel better educated to take decisions on when to use mortar vs. Portland.
- Jose Rosales
Wednesday, March 14, 2012 at 9:49 PM

You have a great sense of humor, and, write very well. Thanks for the information. I almost used Portland cement instead of mortar...thanks
- Suzanne
Saturday, July 14, 2012 at 2:36 PM

Would type S be appropriate for replacing the mortar that has fallen out of a field stone load-bearing wall in an old farmhouse? Is there a product that could then be applied like a plaster to this wall to produce a smooth wall surface?
- Mark
Sunday, October 21, 2012 at 10:14 AM

Mark, for a general repair on a load bearing wall the Type S could be used to fill in mortar that has fallen out. The Type S Mortar-Stucco can also be used as a stucco finish and is commonly used over concrete block or metal lath. Going over stone could be tricky though, if it is slick it could be difficult to bond to. The finished surface you are looking to apply on the stone would that be on the interior or exterior of the building?
Dean - Tech Service Team
Monday, October 22, 2012 at 4:46 PM

Hi Dean. I have the same question than Mark. In my case in in the basement. I want to do some stucco brick to replace what has being deteriorated around basement windows and then finish with a smooth finish inside the window cavity. I also want to do the same for the basement and there are also some lime stone walls that are decaying. So Do you think Mortar-Stucco would be appropriate? I also bought an addessive and drylock, but I do not know if I need it after all.
- Jose
Sunday, March 24, 2013 at 6:13 PM

Hi Jose, is it the mortar that is deteriorating or is the brick/stone deteriorating. If it is only the mortar then you should remove any loose mortar from the joints and you can repoint with a Type S since it appears to be below grade. If the repair is much larger than just repointing mortar and the wall is deteriorating then you may want to get someone to invesigate the area, especially being a structural issue.
Dean - Tech Service Team
Monday, March 25, 2013 at 5:15 PM

I am making stepping stones with detailed moasics tiles to be inset. When I use cement and press in the tiles, there is inevitably a bulge around the tile edge after the cement dries. It is enough of a level difference that water will collect and cause the tiles to pop off over time. Is mortar mix an appropriate substitute for a stepping stone (strength wise)? How else can I get a fine-grained finish to fill in the gaps? Thanks.
- Vicky
Friday, March 29, 2013 at 11:20 AM

Hi Vicky, mortars are not recommended for stepping stones/traffic surfaces. They don't have the strength or abrasion resistance as a concrete would. With mosaic tiles the joints are typically small, you may want to try a tile grout to fill in the joints between the tiles. Also when you place the mosaic tiles in the stepping stone you may want to strike off the cement that bulges from the outside of the tile so that there isn't any excess.
Dean - Tech Service Team
Tuesday, April 2, 2013 at 4:31 PM

Thank you for your response. I have tried tile grout before, but that layer seems to separate over time. Am I appyling it incorrectly? Also, I get water that rises to the top so that I can't even detect a bulge until the water evaporates. Am I mixing it too wet? Or am I placing the tiles too quickly after pouring the cement into a mold? Thanks.
- Vicky
Tuesday, April 2, 2013 at 9:38 PM

Are you using just cement in the mold? Or is it more of a sand mix that has cement and sand?
Dean - Tech Service Team
Wednesday, April 3, 2013 at 7:44 AM

Hello I was wondering if any one can help me find out what type of concrete to use so I can make a target for my son to shoot at with a 22 ( a little bunker). P.S. this will be in a safe location at a safe range.
- SPc. Brown
Wednesday, April 3, 2013 at 10:30 AM

Spc. Brown, here at Sakrete we don't have a concrete specifically for that use however you could try out any of our concretes to make that target. If it is just as support for the target then the Fast Setting Concrete Mix can be used to fill in around the support post.
Dean - Tech Service Team
Thursday, April 4, 2013 at 5:08 PM

Dean, My last round I used Sakrete Sand Mix.
- Vicky
Thursday, April 4, 2013 at 11:41 PM

Vicky, I would try to clean off any of the excess material around the tiles before it hardens as you lay them into the Sand Mix since water is collecting in those areas. If that doesn't work out then you may have to use a thin set mortar to adhere the mosaics to the Sand Mix stepping Stone and then grout between the tiles.
Dean - Tech Service Team
Friday, April 5, 2013 at 4:18 PM

i am involved with a major construction project and the AE is adament that a portland cement masonry mortar be used, and forbids masonry cement mortar in his specs. is there really a difference? if so, which is better? thanks.
- nat
Thursday, April 18, 2013 at 10:17 AM

Nat, the main difference between the two is the method in which they are manufactured. It's mainly personal preference, there are some masons that only use a portland/lime mix and some others that only use masonry cement mortars. Most commercial projects have either a portland/lime mortar or a masonry cement mortar spec'd and this seems to be one of those where only a portland/lime can be used.
- Nat
Thursday, April 18, 2013 at 4:44 PM

What would be best for Belgium block driveway curbing joints?
- Barry
Sunday, April 28, 2013 at 10:36 PM

My understanding is that mortar is sticky-er than cement, so as the strength goes up from type N to type S does the "stickyness" go down?
- Barry
Sunday, April 28, 2013 at 10:40 PM

Barry, for the driveway joints it would be best to use the Sakrete Sand Mix in the joints, it will have a much higher compressive strength and better abrasion resistance than a mortar.
Dean - Tech Service Team
Wednesday, May 1, 2013 at 3:05 PM

Barry, the Type S Mortar does have a higher compressive strength than the Type N Mortar however the "stickyness" won't decrease.
Dean - Tech Service Team
Wednesday, May 1, 2013 at 3:12 PM

Great article! :-) Two questions 1.) How much water is needed in mortar mixtures? 2.) My friend is planing on casting a slab on a grade. He plans to use a mix of 0.5:1:3 (water:cement:sand). This is more a mortar then a concrete element. I warned him aboth this due to lack of corase agregate. What are your opinions on this? I mean if I look at this mixing ratio he is clearly going to have an M type of mortar and maybe above wich will give him enough compressive strenght for slab on ground and would probably perform well, but hes completly missing the point here...
- James
Saturday, May 4, 2013 at 3:51 PM

James, with a 60lb bag of Sakrete Type S Mortar Mix you will add approximately 4 quarts of water. Typically concrete slabs vary from 4-6" in thickness. A general rule is that for any applications greater than 2" a coarse aggregate should be used in it. If the slab is going to be greater than 2 inches then a typical mix is 1:2:3. 1 part portland, 2 parts sand and 3 parts gravel. When going less than 2 inches a typical mix is 1 part portland to 3-4 parts of concrete sand or general purpose sand.
Dean - Tech Service Team
Monday, May 6, 2013 at 5:11 PM

Dean, Thank you very much for your answers :-) I want to ask you another thing. Slab on grade that will be cast will serve as a foundation for stone tile floor. Something like this: http://img145.imageshack.us/img145/3352/85695044.jpg Wich type of mortar would you use for this kind of work? Thank you very much.
- James
Tuesday, May 7, 2013 at 2:36 AM

James, the product to use as the mortar for that type of application would be the Sakrete Sand Mix. Since it is a horizontal application you don't want to use a Type N or Type S Mortar, those are used for vertical mortar applications.
Dean - Tech Service Team
Tuesday, May 7, 2013 at 9:00 AM

The pvc plastic pipes for a well were installed through brick wall, below grade. Should I fill the brick gap with mortar or cement? About two bricks knocked out. Am worried about termites in Virginia Beach
- sheila
Sunday, June 2, 2013 at 4:52 PM

Sheila, for those applications many times mortars are used however down the road it is likely to crack. To fill a small gap around the pvc pipe and the brick the better product to use is the Polyurethane Non Sag Sealant. It can be used for vertical applications and will not crack like a mortar will.
Dean - Tech Service Team
Monday, June 3, 2013 at 4:25 PM

What product should I use to fill brick size gap?
- Sheila
Tuesday, June 4, 2013 at 7:56 AM

Sheila, if the gap is that large you may want to try and fill in the area with a brick (mortar it in place) and then when that sets use the Polyurethane Non Sag Sealant around the pipe to seal it.
Dean - Tech Service Team
Tuesday, June 4, 2013 at 4:59 PM

Bob, thank you for your blogs... very informative. I have a garage slab about 50m2. I intend to tile the floor and have some M10 left over from building the house. Can I use the M10 to level the slab and raise it at the back so I have slope of 0.5% (help drainage when cleaning floor). The M10 would need to be feathered a bit, but as I am laying tile over the whole lot, it seems like this could work. Thoughts? Thanks, kkc.
- kkckkc
Tuesday, July 30, 2013 at 2:11 AM

Sorry Bob, I forgot to mention that for the tiling, I would of course use proper tiling glue/mortar - recommendations? Also do I need to wait for the M10 to cure or can I start laying tiles after a couple of days? Many thanks, kkckkc.
- kkckkc
Tuesday, July 30, 2013 at 4:05 AM

If you have areas that need to be feathered I wouldn't recommend using a product that will have large aggregate. Typically products that are used for featheredge applications only have a fine sand as the aggregate.
Dean - Tech Service Team
Wednesday, July 31, 2013 at 4:18 PM

thanks Dean, I have done the slope now using a combination of smooth M10 and 0-6mmm concrete. Will start tiling in about a week. Thanks for all the advice. regard, kkc
- kkckkc
Monday, August 5, 2013 at 4:42 AM

HEllo Dean I am setting a premade acrylic like shower pan on a concrete floor. the manufacturer says use "mortar cement". I want to use several small piles rather making a thin slab on concrete. What Sakrete product should I use for Mortar Cement and could I use Sand topping mix? I would like not much water and not much shrinkage. -tom
- Tom
Sunday, September 1, 2013 at 10:21 AM

Tom, for that application the Sakrete Sand Mix is the recommended product to use for shower pans. As you also stated, it is used at a dry pack consistency for your application, where some of the water is held out.
Dean - Tech Service Team
Tuesday, September 3, 2013 at 2:35 PM

Thanks for the recommendation. I appreciate your advice. I just want to clarify that I am putting down a shower pan and using the sand mix under it to provide support. I am not building a shower pan with a liner to later apply tile to. So, I should use the sand mix under the already made acrylic pan, right?
- Tom
Tuesday, September 3, 2013 at 5:53 PM

Hi Tom, yes the Sand Mix is the recommended product to use as support under the acrylic pan.
Dean - Tech Service Team
Wednesday, September 4, 2013 at 12:12 PM

Can Sakrete Sand Mix be used to make stepping stones?
- Paula
Tuesday, September 10, 2013 at 12:25 PM

Hi Paula, it depends on how thick the stepping stones will be, the Sand Mix is designed for 1/2" - 2" applications. If the molds are going to be in that range then you can use the Sand Mix.
Dean - Tech Service Team
Wednesday, September 11, 2013 at 8:14 AM

hi tom I've got a 100 year old log cabin with chinking between the logs. YOu can now buy "chinking" material that looks fake to me. I'm 99% sure my cabin was chinked with mortar and I'd like to maintain the original look. (I always thought it was concerete but it breaks away and falls out in chunks over time.) Do you know anything about this and if so which kind would you recommend? Do I need to take out the old mortar or can I just mortar next to or over the old stuff?
- Jim
Friday, October 25, 2013 at 5:34 AM

Jim, unfortunately we dont have any chinking material. There are specific materials used for chinking between logs. Our mortars are used for masonry purposes such as brick and block.
Dean - Tech Service Team
Friday, October 25, 2013 at 12:27 PM

Bob or Dean: Can you help clarify a point for me. I am repointing a 100yr old rubble fieldstone foundation that has original lime mortar in most of the wall, with more recently, portland cement based stucco applied in select areas by a previous owner to attempt to halt the old mortar crumbling and turning to sand. However, it didn't halt it, but in fact seems to have speeded up the degredation of the original mortar. While I agree that there is a lot of debate about the product to use, ie. lime based or portland cement based. The idea that is is personal preference seems wrong to me. There clearly is science and engineering that can describe the correct product. I've read many blogs and spent endless hours searching the internet for a robust answer and feel that the three articles that I share the links to below are the most technical sound. From this research I believe that use of a type s or type n portland based mortar mix to repoint an old field stone foundation will cause damange. It will not 'give' appropriately as the foundation moves and it will prevent the original remaining lime based mortar in the walls from being able to breathe and release water vapor - which would then cause additional failure of the original mortar. Most masons I've spoken to seem ignorant of this information and inform me that they always use type s mortar. To which point I ask if they have returned to that job site to inspect their work 10 years later. The original lime mortar has lasted over 100 years, one would think that the interior repointing should be able to last more than 5-10 years. Please correct me if I am wrong - but isn't a high lime content mortar mix essential when repoointing a wall that has an existing lime based mortar holding the wall intact? If you concur that one should match the new mortar chemistry with the existing wall - how do I know which product to select as yours seems to suggest it can be either lime based or masonry cement and I don't see any way to determine which it is on the bag. Your insight on this is really appreciated - Many thanks!
- Marcus
Wednesday, November 6, 2013 at 9:20 AM

Marcus you are correct. Using a Type S is not a good idea to repoint such an old structure, it will make the mortar stronger than the wall which isnt good. You want to make sure that with any repair, the material that is being used should be about the same strength as the original material. For this repointing project you would need a mortar in the 350 psi range also known as a Type O Mortar, Type S is 1800 psi and Type N is 750 psi. Sakrete unfortunately doesn't make a Type O Mortar however you could make your own mortar. A typical formula for that mortar would be one part portland, one part lime and 6 parts mason sand.
Dean - Tech Service Team
Wednesday, November 6, 2013 at 12:57 PM

Dean - thanks for the confirmation!
- Marcus
Wednesday, November 6, 2013 at 4:02 PM

Hi Dean, thanks for the article. I'm repointing a small patch (about 4'x3') of an exterior brick wall of a 100 year old all brick row house. The patch is on the front of the house, so not an adjoining wall. I'm curious if I can use the Sakrete Type S for this job, or if there's a more fitting product. I'm not concerned about color matching, as it'll be painted over, but I have read online that using a new mortar on an old home that probably used a lime mix initially may not be a good idea, and may lead to needing repointing in short time. If that's true, how long may it take to require a repointing? Dean, your insight on this would be much appreciated. Thanks!
- Adam
Saturday, November 16, 2013 at 12:06 PM

Adam, if the wall you are repairing is 100 years old using Type S Mortar wouldn't be recommended. It would be much better to make a custom mix like in the previous post. You can mix one part portland, one part lime and 6 parts mason sand to make a custom mix that would be similar to the existing mortar that is currently on that wall.
Dean - Tech Service Team
Tuesday, November 19, 2013 at 4:16 PM

Thanks, Dean
- Adam
Tuesday, November 19, 2013 at 4:41 PM

I'm planning on using mortar along the interface between a crawlspace floor and foundation wall. The purpose is to impede dampness (there is no water, just damp spots at the joint...). I will coat the applied mortar (and 4 inches of the foundation and floor) with a Xypex (crystaline sealant) slurry. What would be the best type of mortar to use?
- Chris
Tuesday, December 3, 2013 at 3:03 PM

Hi Chris, how large of an area are you planning on filling in? My only concern with this is that since they are two dissimilar substrates many times if a rigid material is placed between it could crack due to differences in movement. You see this quite often when concrete is poured directly up against a wall of a house, it will develop a small hairline crack.
Dean - Tech Service Team
Thursday, December 5, 2013 at 11:46 AM

I need to repair some missing mortar from bricks. One on edge of my front porch and one gap on chimney attached to house. I only need a small amount. What do you recommend I use.
- Carol
Friday, December 27, 2013 at 6:50 AM

Carol, when choosing which mortar to use you need to consider the age of the structure and how old the mortar is that was used. That can be difficult sometimes so a general rule is that anything older than 1920's you should use a historic pointing material and for newer construction a Type N or S will work. For your application if it's newer than the 20's the Type N Mortar will work well.
Dean - Tech Service Team
Friday, December 27, 2013 at 1:13 PM

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