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  #81  
Old 01-27-2014, 07:40 PM
Apprentice
 
Join Date: Dec 2013
Location: Wisconsin
Posts: 120
Default Re: High Heat Mortar Primer

Quote:
Originally Posted by brickie in oz View Post
I have only ever used the pre mixed junk once, it was for a small patch up job and I didnt want to go to all the trouble of sourcing and mixing mortar.

In all my years of bricklaying maybe 30 I lost count, but more that 25, I have never struggled with mortar until I used pre mix.

What an abomination on man kind.
Brickie, pre mixed mortar is now the newest thing for masonry construction. Being a mason for 32 yrs. I have learned to live with it. It doesn't have anywhere the workable aspects of a sand pile, a skid each of lime and portland cement. For standard mortar for brickwork you could not beat 32 shovels of sand and a bag each of lime and cement. Hence type "n". Boy could a guy work with that mortar. Today's mortar that comes out of silos acts like grout, i.e. has not plasticity. Mortars have gotten stronger so now we need control joints in brick veneers ever 25 feet and at every corner. Old buildings in my area never had CJS because the mortar was meant to give a little bit. Just my 2 cents about today's mortars. So as far as making my own home brew for less money or buying something in a pail or bag that is premixed and costs a lot more you can figure which way I am going. You bet I will mix my own and make it so I can work with it. Just thought I would give some thought.
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  #82  
Old 11-08-2014, 04:07 PM
Serf
 
Join Date: Nov 2014
Location: WA, USA
Posts: 1
Default Re: High Heat Mortar Primer

On "oldie but goodie" topic.

1) I'm curious if the order of mixing the ingredients matters, and if so why? (I just want to learn a little more about the chemistry or physics or practicalities of it.)

I would have thought to mix the finest-grain ingredients together first (Portland cement, fireclay, and lime), and only after they are mixed then mix in sand. Sort of like sieving together the flour and baking-powder first, in a cake mix. But the list of ingredients (1:3:1:1, as in 1 part Portland cement, 3 parts sand, 1 part lime, 1 part fire clay) and what I've read elsewhere suggests mixing the sand and cement together first, and then adding the lime, and the fireclay last.

2) Sand: how "fine" is fine-grain? Let's talk mesh (size of grains). Is #50 fine enough? Is #80 better, or is it too fine? #120? The latter seems like powder, to me. It is available where I live down to #400 mesh, which is a very fine dust like kaolin powder; even finer particles are available for specialized purposes. ("Mesh" refers to the size of the opening the grains will fit through, when sieving.)

3) Also, how much water to add? This seems to be left out of the recipe mixes. Perhaps the various videos or pics tell this better than words, to get the right consistency. I used to think that the less water the better (within reason) for strength, as this is what I learned using Quikrete in driveways (non-refractory application, of course!) -- too much water weakens it. But some experimentation quickly revealed that too little water is also a problem in making refractory mortar, the mix never really adheres to itself, doesn't hydrate/cure enough or right, and is very weak and crumbly. (Even if one could form a ball that held together after pressing it in your hands, that wasn't wet enough -- it needed more water.) Like Goldilocks and porridge, I guess it has to be "just right": well-mixed, not to dry and not to wet.

If the order of mixing isn't important, would it help to mix the cement/lime/fireclay first, then (separately) add water to the sand and then mix the wet sand with the dry ingredients, to help spread the moisture around?

Just brainstorming, to learn from the pros on here. :-) Many thanks to those who really know, for sharing your insights here!)
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