Mortar Joints

[deejayoh]

Re: Mortar Joints

Can you explain the jig setup to me?

I could try, but others have done it so much better

The original guide by hendo
http://www.fornobravo.com/forum/f28/...tilt-2802.html

and I always give mad props to Russell for his jig design, shown here

http://www.fornobravo.com/forum/f28/...tml#post147037

I used a series of two wedges made of wood (not brick as Hendo shows) because I could cut with my miter saw. But a hinged design like Russell's would be the way I would go if I had to do it over again.

[yorkshireknight]

Re: Mortar Joints

Hi Guys regarding mortar joints:

On the bag of fire cement I have, it states that it is NOT to be used with any other building material.
It has a resistance up to 1000 deg C
It also states that the maximum joint size is 8mm.

I have tried the home brew mix with my mortar to no effect although I shall endeavour to keep experimenting, but until I sort this out I cant progress.

I did have success with the mortar on its own.

So here is my dilema

1) I know its important to keep the inside close but its the back which maybe as wide as 15-20mm. I know you guys have said 'just stuff the back with mortar' but are you referring to the home brew or refractory on its own? (as this would be over the recommended fill)

2) If I placed a very thin shin between the large gaps and then had 8mm either side of the shim would this get me out of the problem.?

3) Must the inside bricks touch OR should there be just a slight gap for mortar?

Sorry but my lack of building knowledge adds to my confusion and wish for clarification from you experts out there.

Paul

[david s]

Re: Mortar Joints

Hi Guys regarding mortar joints:

On the bag of fire cement I have, it states that it is NOT to be used with any other building material.
It has a resistance up to 1000 deg C
It also states that the maximum joint size is 8mm.

I have tried the home brew mix with my mortar to no effect although I shall endeavour to keep experimenting, but until I sort this out I cant progress.

I did have success with the mortar on its own.

So here is my dilema

1) I know its important to keep the inside close but its the back which maybe as wide as 15-20mm. I know you guys have said 'just stuff the back with mortar' but are you referring to the home brew or refractory on its own? (as this would be over the recommended fill)

2) If I placed a very thin shin between the large gaps and then had 8mm either side of the shim would this get me out of the problem.?

3) Must the inside bricks touch OR should there be just a slight gap for mortar?

Sorry but my lack of building knowledge adds to my confusion and wish for clarification from you experts out there.

Paul

The refractory cement probably contained calcium aluminate if it can withstand 1000 C. If you are using this mixed with homebrew ( "I have tried the homebrew mix with my mortar...") it will react badly with the lime and accelerate the brew to go off way too fast. This is probably why they state not to be used with any other materials. 1000C is way over what you need, the homebrew on its own is quite sufficient. Perhaps you could save your refractory mortar for the top third of the dome which will get the hottest.
Yes, use offcut wedges to fill the larger gaps in the back. You will have plenty of offcuts from your saw.
A slight mortar gap or none on the inside, it makes little difference.

[K79]

Re: Mortar Joints

Aim for the smallest joints possible on the inside. Use wedges when possible and stuff the rest with mortar. That's what I did and no issues with mine to date.

[yorkshireknight]

Re: Mortar Joints

Thanks Dave & K79,

You say the homebrew is quite sufficient on its own, but there lieth my problem at the moment, I cant find any other type of refractory cement although I do have a young lady at the building suppliers who speaks good enough English to understand what I need.
If I can not source another type should I go with this and use the wedges, which as you rightly point out I have plenty of.

[david s]

Re: Mortar Joints

Surely you must be able to get Portland cement and hydrated lime. The recipe is 4:1:1:1 sand, lime, clay,Portland cement.

[oasiscdm]

Re: Mortar Joints

I used refractory cement similar to what you refer. With a 3 sand 1 cement .5 fire clay. However I used arch bricks which left my joins around that 3 - 8 mm mark you refer.

I also copied Russell's jig a little more elaborate and infinitely adjustable, but still Russell's idea, works a treat. I went with a brick to brick fit inside the dome. Maximum rear joint on mine would be 6mm.

[yorkshireknight]

Re: Mortar Joints

Yes I can get Portland cement David and I've sourced lime as of today.

So are you saying I can use the home brew with this 1000 deg C fire cement I have?
I will purchase some Lime and fine sand and give the home brew another go.
I did attempt the home brew but it was with a sand/lime premixed, but it failed to work.
Thanks for the that anyway David

Colin, thanks too for your input I shall shim or endeavour to get joints closer, but first I will purchase a bag of lime to experiment with.

Paul

[yorkshireknight]

Re: Mortar Joints

Today I made my IT from a castor wheel and a piece of wood.
I think I may have to exchange the big lump underneath for a slimmer one, it is at a 90 deg angle to the top part should this be so?

I also made the template for the arch many thanks to those who gave me some idea how to do it, geometry is all Greek to me.

I am nearly ready for sticking bricks together (when I learn how)
as always if you see anything out of order please feel fee to criticise.
Paul
PS a picture of the fire cement I bought.

[deejayoh]

Re: Mortar Joints

That IT design won't work. The arm of your IT needs to hit the center of the brick on each course.

See this post for explanation: http://www.fornobravo.com/forum/8/tr...tml#post132328

[texman]

Re: Mortar Joints

Paul

Ditto DJ on the IT. It wont work. The shaft of the IT should contact the center of the brick vertically and horizontally. The 2x4 is too wide and not offset enough for the brick to be centered vertically. Also, a cheap clamp will help hold the brick in the proper alignment as you set it and squish into place. That caster is fine; looks like what i used. i would cover the bearings of the caster with tape or something to keep mortar out. Mortar will lock it up and it wont move. The caster changes the dome curve slightly, but not enough to worry about unless you want to recess it in your floor by removing a floor brick and replace it later. I dont think that is necessary, but that is how you would do it.

I think what Dave is saying is if you can make homebrew you do not need the fire cement. Homebrew is proven is cheap to make.

Tex

[david s]

Re: Mortar Joints

Yes I can get Portland cement David and I've sourced lime as of today.

So are you saying I can use the home brew with this 1000 deg C fire cement I have?
I will purchase some Lime and fine sand and give the home brew another go.
I did attempt the home brew but it was with a sand/lime premixed, but it failed to work.
Thanks for the that anyway David


Paul

No, reread my post. I'm saying you should not use the fire cement with the lime. I think the plans show an alternative recipe that includes calcium aluminate cement, sand, fireclay and lime. I have warned about this error many times, but maybe the changes still have not been made. Stick to the Portland cement recipe, or if you want to use the fire cement the recipe should omit the lime component.

[oasiscdm]

Re: Mortar Joints

David is right. You have fire cement use it without lime as this is what I used. You need only get sand and fire clay. If you cannot get fire clay you will get enough from cutting your floor just sift it to get a fine powder once the clay is dry.

[david s]

Re: Mortar Joints

Also, the calcium aluminate cement is quite temperature dependent, more so than Portland. In the summer I have to add chilled water to give me enough working time.

[oasiscdm]

Re: Mortar Joints

David is right about refractory cement as this is what I used. You need only get sand and fire clay. If you cannot get fire clay you will get enough from cutting your floor just sift it to get a fine powder once the clay is dry. You have cement you do not now need to go and buy Portland cement and lime it is not necessary.