Increasing stickiness of mortar

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Old 06-24-06, 09:05 PM
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Increasing stickiness of mortar

Working on my 2' high retaing CMU wall and facing with river rock(aprox 8"x8"x4") problem I'm having is my mix of 1:3 portalnd type S and sand isn't very "sticky". I'm wetting the stones and CMU with a spray bottle but having a hard time "buttering" the backs of the stones. I've thought about lime but what proportion. thanks
 
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Old 06-25-06, 03:12 AM
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1/2 lime, but when you say buttering the back of the stone, do you mean you are adhering the stone to the wall?
 
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Old 06-25-06, 07:14 AM
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Tscarb...yes adhering to the wall ie veneering.
 
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Old 06-25-06, 07:53 AM
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Too much sand, make it a 1:1 ratio.
 
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Old 06-25-06, 10:30 AM
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Frank, That would make a very poor mortar. It would probably be OK for a mud bed, but is totally unacceptable for any type of masonry, including stucco work. The most important characteristic of mortar is not compressive strength, it is bond strength. Plasticity, autogenous healing and low shrinkage are all other important aspects of mortar that using a 1-1 portland/san mix will be deficient in.

For adhering veneer stone, 1 to 1/2 to 3 is preferred. Mix it dryer than you would for laying CMU or brick; usually when people complain that they can't make the stones adhere, it is because they are making the mud too wet.
 
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Old 06-27-06, 05:22 PM
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I've always used 1 part type S and 2 parts sand.
 
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Old 06-27-06, 05:33 PM
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Still too much cement, Pilot Dane. Google "ASTM C-270", for proper proportioning, and "Lime mortar" for an even better explanation of why the current standards encourage too hard of a mortar.
 
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Old 06-27-06, 07:16 PM
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Increasing stickiness of mortar

Tscarborough is right about the mix.

For your application you do not need stregth.

The ASTM specifications state in the appendix that you should use the weakest mortar possible and still carry the load (which is almost nothing). The weaker mortars have a higher amount of lime, which gives you more workability, better bond and more watertightness. Adding lime to your Type S will help.

A better choice of mortar would have been Type N mortar(weaker yet) with some lime added.

Many prepackaged mortars are made using a cement combination of chemicals and fillers instead of portland cement and lime. This is sunstitution allowed within the specifications, but many people feel there is nothing as good as the traditional portland and lime (some previous codes recognized this, especially for uninspected masonry and in certain areas).

Dick
 
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Old 06-27-06, 08:45 PM
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Print out the ASTM C-270 and bring it out to show your wall. Maybe roll it up and smack the wall with it.
I belive people don't measure correctly, Everybody fills a shovel differantly. It is hard to tell if someone makes good mortar by an email. I think his mix is too sandy and needs to increase the amount of cement (glue) to hold the stones on the wall.
Frank
 
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Old 06-28-06, 03:38 AM
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Actually, what he was trying to do was stick dimensional stone to a wall as though it were cultured stone, which won't work no matter how you mix the mud.
 
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Old 06-28-06, 09:46 AM
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I thought it was a cultured stone he was working with. If not then he needs a proper footing in front of the wall and build like you would lay blocks.
 
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Old 06-29-06, 07:02 PM
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Guys, agreed...a 15 pound stone will not stick to a wall freely but...built up from a footer 6 inches beyond the CMU 2 high that i have built, somewhat attached to the wall that keeps the stone from falling forward is what i'm after. i'm not building 2 individual wythes with a space between, this will be essentially one solid wall 8 inches with CMU and roughly 4-6" of stone faced on the front, overall a 10-12" solid hunk of concrete with some larger aggregate (stones!) in place. man I didn't think this would be so difficult, i appreciate all of your comments but i think that there was some confusion on what i was trying to accomplish.....CMU wall to hold back the backfill...and real river rock to dress it up...fake stone would have been the easiest (Lick and stick) but I had access to free riverrock.. thanks all I'll post some pics when i'm done.
 
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Old 06-29-06, 07:08 PM
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You ARE building 2 wythes, the amount of space between means nothing. You have to lay the stone as you did the CMU and not try and adhere it to the CMU and then tuckpoint it. That is silly, and makes more work than it saves, plus tuckpointing it will not provide the full bed of mortar required. Why fight it? Do it right and save yourself time and effort.
 
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Old 06-29-06, 07:48 PM
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Well then if it is considered 2 wythes I would assume that weep holes are manditory ie water "could" get between the two wythes.
 
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Old 06-29-06, 08:20 PM
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Technically, yes. You have said you will have a solid cap, so it won't be critical, but it certainly won't hurt either.

If I were building the same wall, I would have either french drain behind the wall (ending at sunshine) or weeps that extended through both wythes.
 
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Old 06-30-06, 06:52 PM
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tscarborough is right about the drains, otherwise water presure will push it over, you have got good advice on how to do the wall its up to you if you want to do it right. Lay a bed of motar down and start laying the stone this is the easy way, lay it just like blocks butter the end and push it into place.
Frank
 
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Old 06-30-06, 07:57 PM
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So if I want 1.5" between the stones I use a dryer mix, right? A mix that would allow the mortar to "squeeze"out wont give me much of a space between the stones.
 
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