Author Topic: Concrete vs Mortar vs Grout  (Read 11115 times)

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Offline n74tg

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Concrete vs Mortar vs Grout
« on: December 08, 2006, 06:41:22 PM »
I'm building my dry stack block walls.  I'm about ready to fill the cells that have rebar in them.  Some references say use grout, some say concrete, none say mortar.

Knowing that concrete is cement + water + sand + aggregate and
mortar is cement + water + sand + lime and
grout is cement + water + sand

Question is what function does lime play in mortar?  What would be wrong with using it to fill the cells in the block.
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Offline Amanda_931

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Re: Concrete vs Mortar vs Grout
« Reply #1 on: December 08, 2006, 06:49:38 PM »
Particularly if you had already started your hydrated lime soaking (Charmaine Taylor recommends Rubbermaidtm tubs--I sometimes have to bungee cord the tops down on them--but don't use an olive barrel, miserable to try to empty), a well-soaked lime/sand/sawdust mixture might make sense, give you a bit of insulation.

But you'd need some time--I've heard various lengths here, at least three or four days--when it wasn't going to freeze before it set up.

Offline n74tg

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Re: Concrete vs Mortar vs Grout
« Reply #2 on: December 08, 2006, 06:58:25 PM »
Amanda, I didn't understand your reply.  My block layers are not mortared together (dry stack wall), so what holds the wall together is the concrete/grout/mortar in the cells that have vertical rebar in them.

Maybe your "mixture" could be used in the non-rebared cells, but I need something to give strength in the cells that do have rebar in them.

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Offline jonsey/downunder

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Re: Concrete vs Mortar vs Grout
« Reply #3 on: December 09, 2006, 01:49:28 AM »
You would need to use the concrete mix for filling the blocks in your case. The term grout is probably a little misleading when used in this context. It would probably be a much more fluid concrete mix than normal with a finer chip. This would be used for pumping into the blocks, it flows better. Although lime can be and is some times used as a binder in mortar, it's main use is as a plasticizer. Lime mortar is also softer and weaker than the stone or brick which it bonds and is therefore able to accommodate slight movements caused by settlement or temperature changes without significant cracking. When used properly it would normally be mixed with the wet sand a few days before use. It is also fire retardant and was often used in chimney building. Although mortar has some stickablity, it has no real structural strength. It's main role is as a spacer for your brick/blocks or stone work. It is used to keep the bricks apart and to take up any inconsistency in size and shape.
« Last Edit: December 09, 2006, 03:23:11 AM by jonseyhay »
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Offline Amanda_931

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Re: Concrete vs Mortar vs Grout
« Reply #4 on: December 09, 2006, 08:44:30 AM »
Jonesey's probably right.

I mentioned the lime because a lime/sand (mortar or plaster) combination with added sawdust (also used as plaster or mortar) would add some insulation that plain concrete would not.

Would not add much if anything in the way of strength, but I figured you had the rebar and the dry stack coating (with lots of fiber, IIRC) for that.

And I'd have to search to find out how much sawdust--at a guess, halfway between the amounts of lime and sand for mortar.  Might take a good deal more, as it's not going to be subject to wear in your block cavities.

You can keep lime soaking for years (the Roman masons asserted that generations worked better, but they may have been trying to keep interlopers out of the business--some of their structures are still standing) but while it sets up, it does need to be protected from freezing.  

Rob Roy used the dry stack block for the buried parts of his first cordwood house.  Don't remember what he did with his cavities.

These days he's experimenting with (or maybe has switched to just using) the lime/sand/sawdust to mortar and insulate his logs.

Offline Deana

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Re: Concrete vs Mortar vs Grout
« Reply #5 on: December 09, 2006, 04:11:41 PM »
http://www.thenaturalhome.com/drystackblock.htm

"Dry stack concrete block technique uses surface bonding cement ("SBC") instead of mortar"
see last paragraph on the page for technical data sheet on quickcrete surface bonding cement

Offline n74tg

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Re: Concrete vs Mortar vs Grout
« Reply #6 on: December 09, 2006, 05:07:26 PM »
Deana - I will use SBC on the outside of the walls; this question was about what to put inside the cells that have vertical rebar inside them.  

Amanda - I hadn't thought about the added strength of the SBC in your post, so now I can see how you might suggest filling the cells with some insulating materials.

Thanks to all.
Tony
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Offline JRR

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Re: Concrete vs Mortar vs Grout
« Reply #7 on: December 10, 2006, 06:06:34 AM »
To steal a thread a wee bit:  Has anyone here used "perlite" to fill cement block cavities?

I read about how it is such a great insulator ... and so inexpensive!   And yet when I ask about it at the big-boxes, all I get is dumb looks.   Does the DIY'er actually have access to the (non-garden) stuff?

Offline glenn kangiser

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Re: Concrete vs Mortar vs Grout
« Reply #8 on: December 10, 2006, 08:09:06 AM »
I've read some on it - strength is low.  It or similar stuff can be used in light weight concrete.

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Re: Concrete vs Mortar vs Grout
« Reply #9 on: December 10, 2006, 08:52:47 AM »
The perlite might be a good idea to add insulation in the cavities that don't have rebar. But its probably not strong enough to trasmit stresses to the rebar if the rebar is to do its structural job.

Offline Amanda_931

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Re: Concrete vs Mortar vs Grout
« Reply #10 on: December 10, 2006, 03:22:51 PM »
Not sure if I mean perlite or vermiculite--both are expanded rock.

But one comes in open- and closed-cell varieties.  Gardners use the open-celled stuff.  Masons the other.  Because the gardners' quality soaks up water and never dries out, works for them, but not for anything you'd want to pick up as a block later.  So I was told by someone who really really should have known better.  Not me, this time.

Apparently specifically masonry supply places have the stuff to use, if you would want to make a lightweight earthen floor or insulate below an earth oven or rocket stove or.....

 

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