Grout vs Mortar in reinforced masonry 3

[enginerding]

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.

 

[msucog]

i'm certain that concrete is stated to not be used as a substitute for grout. i don't know where but i know it's there somewhere. i'll do some digging for the sake of having it on hand next time i see something like this in the field.

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.

 

[MattJM]

To more directly answer your question about an article, simply search google.:

http://www.maconline.org/tech/materials/grout.html

http://www.cement.org/masonry/mortar.asp

http://www.astm.org/SNEWS/DECEMBER_2006/p_melander_dec06.html

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.

 

[MikeE55]

Getting back to the original question of what to tell a contractor who wants to use mortar instead of grout, I have found it is effective to point them to IBC 2006 section 2105 on Quality Assurance. I interpret 2105.2.2 (and subsequent paragraphs) as stating you either use grout to fill masonry cells, or the strength of the masonry must be proven using the prism test method. Why would anyone want to use mortar if it triggers a whole additional level of testing? It is much simpler to just use 2000 psi grout conforming to ASTM C476.

 

[miecz]

Concrete can not be used for grout. The main property of grout is it's ability to be poured without segregation. This is ensured by the proper mix and slump. Concrete cannot be poured without segregating.

 

[enginerding]

haynewp's second post in this thread is an article that seems to suggest that current research is showing that it could be OK to substitute "soupy" mortar for grout. The article states that more research is required, and currently the building codes and project specs call for a difference between mortar and grout, but it seems my contractor friend may be correct...

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...

 

[MarcbSE]

Sorry to all for branching the thread, but just to close the side discusion I found the following article "What is Grout" at

http://www.maconline.org/tech/materials/grout/whatisgrout/whatisgrout.html

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.

 

[unclesyd]

I agree that everything needs to meet the current codes and standards. This is not an attempt to advocate anything other than the correct one. This is a little relief.

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://photos.pensacolanewsjournal.com/_dennis/dennis_0711_3_cs/photo1.shtml

This is just beore Hurricane Ivan hit. It looked the same after the storm except most of the red paint was gone.

http://photos.pensacolanewsjournal.com/_ivan/gallery_ivan091404/photo10.shtml

 

[DarthSoilsGuy]

i wouldn't want to be on a job with super-p in the grout mix with the masons i've met. Retarders sure, but not super-p. the super-p would be used up before they start the pour. I don't know about the masons you people know. But, the ones i know are always trying to wrap the last course(s) of block or finish out a bond beam (where are those d@## embed plates) while the truck is sitting there spinning. If you give the bozos i know a super-p grout mix, you'll be sitting there watching them "wet-set" the lap in their verts with a sledgehammer. (oops, didn't have time to shake-shake the rebar)

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!!)

 

[DarthSoilsGuy]

just looked at those photos unclesyd posted

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