Grout vs Mortar in reinforced masonry
Grout vs Mortar in reinforced masonry
(OP)
I am looking for an article that a contractor (he is bright, but not an engineer) could read to give the reasons why it is important to make sure that grout is used to fill the cells of reinforced masonry rather than the cells being simply packed with mortar. He tells me that mortar is used for this purpose all the time and he has never seen a problem with it. He says that without evidence of problems, it will be a hard sell to make sure his subs use grout the right way. Does anyone know of something that I can show him that shows the actual in-use effects in a wall built this way?
I have plenty of small articles showing the importance of vibrating the grout to make sure it fills all voids, but nothing to show that replacing the grout with mortar has had adverse effects on strength or durability.
I have plenty of small articles showing the importance of vibrating the grout to make sure it fills all voids, but nothing to show that replacing the grout with mortar has had adverse effects on strength or durability.






RE: Grout vs Mortar in reinforced masonry
RE: Grout vs Mortar in reinforced masonry
RE: Grout vs Mortar in reinforced masonry
Refer the "well meaning" contractor to the National Concrete Masonry Association TEK Note series (ncma.org).
Just pick any state and member to get access to the TEK Note series. The TEK notes (over 100) are written in a manner that is understandable by all and contain the specific code and material standards.
TEK 9-4A gives a good discussion on materials, specifications and the properties of grout.
TEK 3-2A gives a good discussion on the proper construction of fully and partially grouted masonry.
It sound like the contractor has just seen a lot of small projects and not enough of the correct materials, which have been used for many years.
Dick
RE: Grout vs Mortar in reinforced masonry
RE: Grout vs Mortar in reinforced masonry
The masonry won't qualify as STRUCTURAL MASONRY unless F'M is met and usually by Unit Stength design. The mortar, probably "S" won't by definition cover this. So... now the contractor is taking the project in the direction where Unit Strengths must be met by field testing in order for code to be met. Now the contractor has to feel comfortable enough that his mortar will meet grout spec by field testing(probably 2000 psi for f'm=1500psi which is the most typical).
The reality of the situation is that you might shoot yourself in the foot trying to get the masons to change their practice. I've seen a bunch of times where grout-as-you-go masons just can't deal with pumped grout and you would have a better product if you just let them mortar it in. Some masons will try to skip bond-beams in inconvenient locations for scaffolding or too near another bond beam when truck grout comes. That is just one example of many possibilities.
In my experience, (this may raise some eyebrows) the mason should have no issue with working in a batch of site grout every couple of courses by mixing portland cement in lieu of mortar cement or masonry cement. With a good mix (use the damn measuring box!) and occasional grout compression test specimen, you should get above 3000psi and feel comfortable justifying F'm.
RE: Grout vs Mortar in reinforced masonry
RE: Grout vs Mortar in reinforced masonry
By all means avoid getting highter strength masonry by using high strength grout and/or mortar. It is far more economical, safer and easier to justify and test by using higher strength masonry units. This puts the higher stregth material at the out fibers of the section and eliminates the errors of using an average strength. - CMUs can also be tested before they are in place, resulting in increased reliability, which is a luxury you do not have with many other materials like concrete.
The reason for using grout and NOT mortar is because of specifications! - It is as clear as that.
Mortar is designed to be workable with a trowel, not to "fill" voids. Grout also makes the constructability of the wall more reliable because of the ability to fill all the voids and the proven lower in-place shrinkage.
RE: Grout vs Mortar in reinforced masonry
http://www.lime.org/BLG/Biggs.pdf
RE: Grout vs Mortar in reinforced masonry
I'm assuming the mortar mix is a 3:1 sand to cement mix (mortar cement or masonry cement). I think that's a safe assumption because that is the easiest (and i think cheapest) to do. switching the masonry/mortar cement bag to a bag of Portland makes Fine Grout per Table 2103.10 of the IBC, not concrete. ok, so it's still concrete... But it's not hi-test.
If i'm wrong,... that's my landlord's problem.
RE: Grout vs Mortar in reinforced masonry
I've never heard that concrete should not be used for grout and I've seen a lot of masonry constructed with 3,000 psi for grout.
ASTM C476 specifies that portland cement is an acceptable cementitious material. The only other requirements in C476 is the cement to aggregate ratio, and a minimum compressive strength of 2,000 psi.
If that is the case, then what exactly is the problem with using 3,000 psi concrete as grout?
RE: Grout vs Mortar in reinforced masonry
The block are probably there and they probably do meet the specifications since it is not enonomical to make anything as weak as the ASTM C90 specs.
The spec you referred to (IBC 2103.10) is for "Ceramic tile Mortar Composition" and not for structural grout to fill the cells of block. It applies to grout for ceramic tile floors, ceilings and walls. All must contain hdrated lime.
The applicable core filling grout standard is IBC 2103.12 for both fine and coarse grout. Both of these types of grout refer to either portland or blended cements and to the option addition of a small percentage of lime. The slump requiremetn for proper plcement is much different.
If the mortar meeting the proportions of ASTM C470 can meet all the gradation and physical requirements of ASTM C476 for grout, it could be used if verified in advance by testing the raw materials used and is reformulated by adding water and also meeting the compressive strength requirements of the grout with require different sampling, procedures and performance. - In short, the mortar is not adequate and that is why there are two different standards.
If you look at the appendix if ASTM C270 for mortar, you find that the most important factor in the selection of mortar is workability, since the strength is really secondary. This section recommends using the weakest mortar possible to carry the load since other factor can be more important. Grout on the other hand, is intended to have the ability to fully fill all voids and bond the block/steel together. - Grout and moratr are two different material designed to perform two different purposes. The only thing in common is cement, aggregate and water, after that there are many different materials with the same raw material but with different compositions and different end properties.
It is just the best and easiest to follow the material standards and placement methods and schedules.
RE: Grout vs Mortar in reinforced masonry
RE: Grout vs Mortar in reinforced masonry
I have never seen the word "snot" in a construction specification/description or a placement procedure. Usually, grout is vibrated or "puddled"(in the case of low lifts). - Certainly, the people that routinely build load bearing high-rise structures do not have that word in their engineering vocanulary.
It is intended that the excess placement water necessary in the grout is absorbed by the masonry units. Even the ASTM grout testing procedures recognize this and use a grout "prism" sampling/curing procedure in the ASTM C1019 method to simiulate this.
Grout is not just wet concrete.
RE: Grout vs Mortar in reinforced masonry
Examples
"You would have to weld the snot out of it."
"Tighten the bolt with the DTI until it snots"
and
"...concrete can snot up in the cells..."
RE: Grout vs Mortar in reinforced masonry
that's it for me quoting code on the web. i'll catch up with yall in 2009. We're still saving up for Windows Vista or was it Civil3D, i'm not sure anymore.
"If it ain't broke, sell an update."
-dsg
RE: Grout vs Mortar in reinforced masonry
Besides the fact that it doesn't meet the masonry code definition of grout as is being re-iterated in this thread over and over, I understand that it doesn't bond to the units as well as grout.
I can only guess as for the reason why it doesn't bond-- It may have to do with the flowability being a lot less than grout so it does not get sucked into the pores of the units like grout does. Or, the amount of moisture that is available is sucked out of the concrete directly adjacent to the units and this concrete does not fully hydrate, thus causing a weak interface.
I don't really know, I just remember my concrete/masonry professor telling me to never allow this substitution particularly because it does not bond to the units. And contractors have come to me and wanted to substitute concrete for grout before also, and I got the impression they did this often-but I did not allow it.
RE: Grout vs Mortar in reinforced masonry
Thanks for the comments. But what I'm having a hard time with is that concrete DOES meet the masonry code definition of grout unless I'm missing something (which is entirely possible).
ACI 530-02 Specification section 2.2 states "...provide grout that conforms to the requirements of ASTM C476."
ASTM C476-02 section 3.1.1.1 gives portland cement as an acceptable cementitious material and Table 1 (Grout Proportions by Volume) lists the following proportions for fine grout (coarse grout similar):
Portland Cement or Blended Cement = 1 part
Hydrated Lime or Lime Putty = 0 to 1/10 part
Fine Aggregate = 2 1/4 to 3 parts (+/-)
Now, assuming the aggregates meet ASTM A404 and the slump is the same, I don't see where the problem is from a code perspective. Any additional thoughts or input would be appreciated.
RE: Grout vs Mortar in reinforced masonry
My appologies, I was referring to my 2006 IBC code. The older table was about 2 pages earlier.
Heynewp -
You are right about the moisture transfer. Because of the aggregate gradation and fines in mortar, the moisture does not get absorbed into into the masonry usit and is tied up in the hydration process.
With grout, and the amount of aggregates that have a lower area per volume, the water is available for absorption, which tends to compact/late consolidate the grout. That is the reason for the requirement for re-consolidation and "topping off" of the grout well after the actual placement. The saturated masonry units provide an ideal curing condition for the grout.
dick
RE: Grout vs Mortar in reinforced masonry
RE: Grout vs Mortar in reinforced masonry
i guessing that bumping the slump way up on a concrete mix would push the w/c ratio out of wack and i'm guessing would induce unwanted shrinkage since it would pull away from the cmu. with grout, it becomes "unified" for lack of a better term with the cmu. in other words, i envision the concrete and cmu not being "one".
as for replacing grout with mortar, it's not correct and should be rejected completely. i'm certain i can find a place where that is also specifically stated.
even if it's not specifically stated for those idiot contractors, the architect/engineer should reject their arguement on the grounds that the plans, specs and submittals are very specific on the use for each material. to hell with spending valuable time trying to convince them. they haven't read the first word in the codes so tell them to find where it says that they can substitute one for the other. if they produce something out of the codes, then review it and draw your own conclusion. if you're not sure about a contractor's misinterpretation, the reject it until they provide conclusive evidence.
i also happen to agree with concretemasonry comments.
RE: Grout vs Mortar in reinforced masonry
http://www.maconline.org/tech/materials/grout.html
http://www.cement.org/masonry/mortar.asp
h
I had a really good article xeroxed (several times over - pre-internet age) that was called something like "Mortar is Not Grout". Will try to find it.
RE: Grout vs Mortar in reinforced masonry
RE: Grout vs Mortar in reinforced masonry
RE: Grout vs Mortar in reinforced masonry
To quote from the article, "There have been no reported incidences in the literature of failures attributed to mortar being used in lieu of grout."
This is exactly what the contractor was referring to. He made it sound like the building inspectors don't concern themselves with this because there have been no failures.
By the way, concretemasonry, you are correct in that the contractor is typically involved in smaller projects. He has seen masonry go up this way for many years before he started acting as GC for these projects - he says it is hard to argue with years of past experience if there have never been problems with the way things have been done...
RE: Grout vs Mortar in reinforced masonry
This answered my question. In summary, grout and concrete have the same materials. However, the only way to get an adequate slump is by using a superplasticizer. Once the cmu absorbs some of the water the w/c ratio is too low which is obviously a bad thing. It makes sense now.
Thanks to all for the input.
As to the original question I would never permit mortar to be used for grout. The simple answer to the contractor's request is that it does not meet code.
RE: Grout vs Mortar in reinforced masonry
Acting as Amicus Forum here is a prima facia example of mortar mix/concrete used to fill cement block in building that has survived
5 major hurricanes while everything around it was blown or washed away. The building was condemned the day it was completed due to numerous supposedly code violations, the block reinforcement being a major one. The connections for the 4'or 5' sections of rebar used to reinforce the block are 2' lengths of pipe that were epoxied together while building. Terry, the owner builder used an innovative way to work with the epoxy. He slipped the tube over the existing rebar and plugged the pipe where the base resin wouldn't leak and as he added rebar he coated it with the hardener and by twisting it while inserting it into the pipe he mixed the two. He used locally produced mortar mix to fill the block.
The building built in the early 70's has been involved in numerous attempts to have it demolished and take over the prime beach front property it sits on.
The last attempt was prior to Hurricane Ivan where a local engineering firm submitted a report saying that the building couldn't withstand a wind greater than a whale fart and wave higher than one that could be kicked up by a 3 yr old. Hurricane Ivan hit and every building cited in the report as being able to sustain almost anything that could be thrown at it disappeared into piles of rubble. Not one of those structures survived.
The first comment after any storm hits Pensacola Beach is Tiffany's still standing.
This is after Hurricane Dennis
http:/
This is just beore Hurricane Ivan hit. It looked the same after the storm except most of the red paint was gone.
http://
RE: Grout vs Mortar in reinforced masonry
i'm not buying into the concept that the block wall could absorb hydration water from grout. Convenience water, absolutely, but not hydration water. a 0" slump mix still has its hydration water. it would seem to me that the chemical water demand is stronger than the capilliary pull. i'm having trouble imagining breaking open a grouted cell and finding dusty unhydrated cement around the edges.
Side-story below (as if there was a point before to this)
i just remembered about this one job i worked on where the masonry sub (of the Non-Bozo variety) begged the SE of Record to use a mortar mix interchangeably for mortar and grout. The mix they would put in the hopper was 6 ft3 of sand, 1 bag of Type "S" Masonry Cement, and 1 bag of Portland Cement. (1 bag = 1 cubic foot). this was how they liked to work and had many different bldgs to show as examples. i personally thought it was a harsh mix with crappy workability on the mortar side, but they liked it and could make it work for the joints. Grout mixes had more water. As part of the deal, there was field testing of the mortar and grout as components thrown in. (Just Say NO to
Prism Testing! Nooooobody wants to do it, HAH!!)
RE: Grout vs Mortar in reinforced masonry
It's good that that little shack is still standing. The owner's two brothers unfortunately had lost their stick-built and straw-built houses in prior windstorms. I'm also relieved to see that BarBQ is not on the menu. That would be too sad.
-dsg