Help with homebrew mortar

[GianniFocaccia]

I completed my first oven mortar job last weekend, using #120 fine silica sand, in the standard homebrew mortar recipe. The mortar was smooth and creamy and locked the front of my soldiers in beautifully. Per Tscarborough, I then back-filled the soldier gaps with a second mortar, using a 50/50 concrete sand/silica sand homebrew mix.

However, nearly half of the soldiers became loose as the mortar dried and contracted off the side of the brick. I discovered that I hadn't completely filled the soldier gap, leaving a void approximately 30% hidden inside.

So I pulled it apart, cleaned and scored each soldier side with a hand-grinder and re-mortared half the course with a 70/30% regular sand/silica sand homebrew mix. The bricks went together easily enough, but I see the same thing happening: the mortar shrinking and separating from the adjoining brick (just one side). This despite keeping the ring completely covered in a wet towel.

BTW - it's 101F in southern california today and I only got half the ring mortared before I heard a cold beer calling my name and had to call it quits.

Questions: Should I modify my homebrew ratios? Can I go with just the #120 silica sand? (It worked really nicely in the smaller joint but I'm afraid of it cracking on the back end due to the joint thickness.

Any/all masonry advice welcome.

[nissanneill]

Re: Help with homebrew mortar

One suggestion is to ensure that your bricks are thoroughly wet, submerge in water for 30 seconds or more and then batter the brick with your home brew (poor man's mortar). The wet brick will not draw out the water from your mortar causing it to separate from the brick. Some people even leave them under water until there are no rising bubbles.

Cheers.

Neill

[ThermoJax]

Re: Help with homebrew mortar

I am at the same stage of build as you, I believe, and have used a premade product (wet) and it is expensive, and I believe scchris used the same product. A contact who works on high heat professionally (goes by the name Thermo Dan, that's where I stole my name from) told me not to use homebrew, to use the premixed stuff. My soldier course and the next course took about a full bucket. I too took part of mine down, joints lining up, and am impressed with the wet. The soldiers have big gaps, but everything else is smaller gaps. I think you might want to get the wet stuff. Ensure yourself of a good bond. I need another bucket, so I have a 100 dollar bill in my pocket and will go today to buy more. I have wrung my hands over this additional spend all weekend, but I think I will spend it.

Good Luck

Tom

[fxpose]

Re: Help with homebrew mortar

A contact who works on high heat professionally.... told me not to use homebrew....

Did he give you a reason why? As you know, there have been dozens and dozens of builds here using home brew.

[GianniFocaccia]

Re: Help with homebrew mortar

Wow.....$90/bucket is really expensive, more pricey than even Heatstop 50! I have half a bag ($30/50lbs) of Sairbond left over from my firepit build, which worked out perfectly, BTW. If I can't get the homebrew ratios right I'm just gonna use that for the soldiers. Funny, I did a test with the #120 silica sand homebrew and joined two left-over firebrick wedges together with a 1/8" joint. The bond was so strong it was like the two pieces were welded together. I have no problem tapering my dome bricks to get joints like this if I get a bond that strong.

Per Tscarborough, I didn't soak my bricks, rather I just sprayed them lightly. I'm thinking I will get better results once this heat spell is over.

[ThermoJax]

Re: Help with homebrew mortar

I too am cutting my bricks on the angle and bevel (compound cut) and a slope cut, so that the brick face on the inside of the oven is smaller than the face outside the oven. I really like the way it goes together. It's like a super cool puzzle. Pretty small gaps.

[fxpose]

Re: Help with homebrew mortar

I had several areas during my build where mortar had contracted using home brew. I basically left them all alone and wasn't sure if solid bonding had even taken place between the bricks in those questionable areas. I also kept adding a layer or two of of the same homebrew mortar on the outside of the dome as I worked upward with the courses. I figured with all the weight on top of one another all those 'loose' bricks were not going anywhere.
I used a fine sand mix for joining the bricks and a plaster sand mix for filling the wide exterior voids.

[GianniFocaccia]

Re: Help with homebrew mortar

That's a good point George. An inch of refractory mortar coating the dome should effectively seal any cracks that happen. I think I'm gonna try to wet the bricks just a little more. It was 111F at home today.

[eprante]

Re: Help with homebrew mortar

Hey John,
Glad to hear you are started on the oven. I know that Tscar has repeatedly cautioned about wetting the bricks, and he is a professional mason. But with my homebrew, it worked best if I dunked the bricks for 2-3 seconds, then wiped them down with a grout sponge, layer on some mortar and place them. One thing I found as I went along was that if I put more mortar on, then tapped and jiggled the brick to force out the excess then I got total coverage and a good bond. Its messy but works well. You are a man for going out to lay bricks yesterday in SoCal, it was 109 at my house.
Eric

[Tscarborough]

Re: Help with homebrew mortar

Back up there, I am not a professional mason. The first brick I ever laid was on my oven. I sell masonry, and have for 20 years, with another 10 years working in the field as a concrete guy. I know exactly how it is supposed to be done, the standards, and the reasons why, but I am not a mason. I am the guy that assists owners, architects, and contractors perform their jobs in the best way possible.


That said, dipping is not the same as soaking. The correct term is SSD, Surface Saturated Dry. That means basically that the brick should be damp not wet. The goal is for the brick to pull moisture out of the mortar, but not suck it dry so fast that there is none left in the mortar for hydration. It is a moving target, dependent upon the environment, the particular mortar and the way it is mixed, and the masonry unit itself.

In general terms, you should NOT soak the brick, but dipping them is good.

[GianniFocaccia]

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

[fxpose]

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.

[GianniFocaccia]

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.

[eprante]

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

[thamnophis]

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.