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-   -   Bond strength of mortar??? (http://www.diychatroom.com/f19/bond-strength-mortar-46012/)

figs 06-05-2009 10:19 AM

Bond strength of mortar???
 
I am building an outdoor fireplace in Phoenix, Arizona using CMUs and type S mortar. Since it is the summer (temperatures about 100 to 110 degrees or more), I want to make sure that I am mixing the mortar to a consistency that will achieve maximum flexural bond strength.

For hot weather, what would be the proper consistency for mortar?

Should I be retempering the mortar?

How long is a batch of mortar good in such weather conditions?

Should I wet the CMU before construction?

Should I mist the CMU after construction?

Is there a method to field test the bond strength of the mortar, so I can be assured that the construction will last?

Should I cover the block (shield it from the sun) for a period of time after construction?

Thanks

Willie T 06-05-2009 10:35 AM

I am building a fireplace in Phoenix, Arizona using CMUs and type S mortar. Since it is the summer (temperatures about 100 to 110 degrees or more), I want to make sure that I am mixing the mortar to a consistency that will achieve maximum flexural bond strength.

For hot weather, what would be the proper consistency for mortar? You want the same consistancy as in any weather. It still has to support and level the blocks.

Should I be retempering the mortar? Never a great idea, but necessary sometimes to maintain workability.

How long is a batch of mortar good in such weather conditions? I wouldn't try for over an hour in such hot conditions.

Should I wet the CMU before construction? Always.

Should I mist the CMU after construction? If the sun is that bad, wouldn't hurt.

Is there a method to field test the bond strength of the mortar, so I can be assured that the construction will last? All I can say here is just mix it right.

Thanks

Yoyizit 06-05-2009 12:14 PM

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

Tscarborough 06-05-2009 02:06 PM

You can generally re-temper once with no issue, plus keep it shaken up on the board. Dip or spray your block before laying. There is no practical field test for bond strength other than a good kick. The main thing is that for your application, it is not that critical.

That article deals with compressive strength, not bond strength.

Yoyizit 06-05-2009 06:10 PM

Quote:

Originally Posted by Tscarborough (Post 283267)
That article deals with compressive strength, not bond strength.

Right you are
"The maximum adhesion strength of a mortar applied onto a substrate, which can be determined by shear or tensile strength test.
www.netweber.co.uk/header/help.html"

One requirement is
"Tensile strength= 0.1 to 0.2 MPa."
which is 15 to 30 psi, not all that high.

Tscarborough 06-05-2009 09:19 PM

Compressive and bond share a relationship, but it is not direct.

Yoyizit 06-06-2009 09:46 AM

Quote:

Originally Posted by Tscarborough (Post 283476)
Compressive and bond share a relationship, but it is not direct.

Unfortunately I couldn't get into the reports that this search
http://www.google.com/search?client=...UTF-8&oe=UTF-8
generated.

Tscarborough 06-06-2009 03:23 PM

As a rule, you will always want to use the weakest compressive strength mortar possible in context with the masonry units being laid, as that will provide the best flexural and bond strength. Mortar is not concrete, and the desired physical properties of each are very different.


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