#11  
Old 09-28-2010, 11:19 AM
GianniFocaccia's Avatar
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Default Re: Help with homebrew mortar

Eric,
Thanks for sharing your experience. I was leery of saturating the brick but felt compelled to lightly spray them. Amid the ambient heat and the heat of the bricks, the spray disappeared into the brick as if it wasn't there. My first adjustment was to make the mud a little wetter and found that if I tapped the bricks togethere with a rubber hammer, a better bond was achieved. Yes, the mud squirted out somewhat but it was so hot that it began to harden in a matter of minutes and actually made it easy to wipe off.

I am relieved to hear Tom say that the moisture/bonding ideal is a moving target. I will dip the bricks briefly and let the water run off/soak in. I am going to try mixing a higher silica sand (70%)/mortar sand(30%) because it is so sticky and smoother to work with, as well as going with two mortars simultaneously (silica sand only for the smaller inside of the soldier gap and see what happens. I'm not keen on tapering my soldiers just to get a smaller joint.

BTW - I weenied out and didn't work yesterday. I worked sunday (101F) and that was hot enough.

John
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  #12  
Old 09-28-2010, 11:29 AM
Master Builder
 
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Default Re: Help with homebrew mortar

Hi John....you didn't mention lime and fire clay but I assume you are using them as part of your homebrew? I basically followed the standard 3 sand / 1 portland / 1 lime / 1 fireclay mix ratio.
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  #13  
Old 09-28-2010, 12:07 PM
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Default Re: Help with homebrew mortar

You're right George, I'm using the classic recipe: 1 portland, 3 sand, 1 lime, 1 fireclay. It's kinda fun tinkering around with the ratios of regular and fine sand.
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  #14  
Old 09-28-2010, 03:14 PM
eprante's Avatar
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Default Re: Help with homebrew mortar

John,
just keep a bucket of water and a grout sponge in arms reach and wipe down the joints after you tap the bricks. You end up with a little gray haze on the bricks but that cleans up with muriatic acid easily.

Tscar,
Either you did a great job on your first brick laying project, or are really bad at making straight lines. We all appreciate your knowledge and advice.
Eric
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  #15  
Old 10-18-2010, 06:07 PM
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Default Re: Help with homebrew mortar

If the mortar does shrink and pulls away from the brick, is there a way to re-fill the thin gap created? Assuming the mortar has dried/cured...

Not that it happened to me or anything :-)

(OK, actually, my curing fire did cause the mortar and bricks directly above the fire to separate. Thus was entirely my fault. I set the brick with enough mortar to hold them in place, then filled the rest of the space a day later with a rather wet mix (HeatStop50) so it would better fill the space.)

I don't think I waited long enough before applying heat.
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  #16  
Old 10-18-2010, 06:23 PM
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Default Re: Help with homebrew mortar

Unfortunately no. If you want to repair it, you have to grind out the joint.
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  #17  
Old 10-19-2010, 09:51 AM
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Default Re: Help with homebrew mortar

One thing that I have noticed that does not get discussed here (Forno Bravo) is how to finish a mortar joint. I think a lot of peoples' issues with cracks, especially the ones before curing fires begin are a result of not tooling the mortar joint. Especially with the high shrinkage rate that Clay Mortars have it is critical that a joint be tooled.

A tool that every one who builds one of these ovens should have is a half round brick jointer (supper cheap tool) and do a quick search for how and why you tool a mortar joint on google. I think this will take care of a lot of cracking issues.

Also as someone who does a considerable volume of masonry work, I am in 100% agreement with Tscar, that the least amount of water that can be applied to a firebrick before mortaring the better. You want that firebrick to draw water, and with the water, cement, clay, and lime from the joint into the brick. This will create a stronger bond, as well as reducing the volume of water that you are going to have to try and bake out of your bricks later which just leads to a higher chance of structural cracking.
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  #18  
Old 10-19-2010, 12:35 PM
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Default Re: Help with homebrew mortar

Thanks for the insight Nic. Yours is the first input I've seen citing reasons behind finishing a mortar joint to help reduce cracking. I believe I understand the process of mortar/brick adhesion created by the wicking of the wet mortar ingredients into the brick itself. Unfortunately, in my warm/dry location, the best results I've gotten are from pre-wetting the bricks. I am going to go get a jointing tool, however.
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Old 10-19-2010, 01:34 PM
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Thumbs up Re: Help with homebrew mortar

I tend to agree with some of what you say Nick, but when your joints inside the oven are minimalist or nil, pointing will not prevent the cracking/separation of the mortar from the bricks.
In all my experience and when working with bricklaying lecturers in an Adelaide Tafe Trade School, they maintain that the excessive pulling of water/moisture from the mortar from a dry brick will cause adhesion problems.
Therefore, thoroughly wetting the bricks will reduce this from occurring BUT a drying/curing process MUST be undertaken in order to prevent damage caused by steam generation within the wet bricks.

Neill
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  #20  
Old 10-19-2010, 02:00 PM
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Default Re: Help with homebrew mortar

It is a fine line, and it changes with the weather. So long as they are SSD, you can't go wrong. If the brick have enough water in them for it to be visible as water on the surface, they are too wet, and if a drop or 2 of water instantly disappears they are too dry.

As for tooling the joints, my assumption was that the joints were too small to bother with, but I guess in reality it would be a good idea on anything over 1/4". A spoon will work in a pinch, as will a stick.
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