Mortar Joints

[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

[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.

[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.

[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.

[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.

[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.

[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

[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/twist-tilt-2802.html

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

http://www.fornobravo.com/forum/f28/tapering-10-saw-19038.html#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.

[ATK406]

Re: Mortar Joints

Take a look at the thread "Tapering with a 10" saw" under Tool, Tips and Techniques. It should be pretty self explanatory.

[K79]

Re: Mortar Joints

The issue I see with a stencil is that the top of the brick is smaller than the bottom - so it is hard to get the angle right for the brick as you cut it.

That's why the jigs are so great. You set up the jig for each course, and then you can run all the bricks you need (except the last, as you will find...) for that course at once.

Can you explain the jig setup to me?

[deejayoh]

Re: Mortar Joints

The issue I see with a stencil is that the top of the brick is smaller than the bottom - so it is hard to get the angle right for the brick as you cut it.

That's why the jigs are so great. You set up the jig for each course, and then you can run all the bricks you need (except the last, as you will find...) for that course at once.

[K79]

Re: Mortar Joints

Very handy I?ll be looking this over. My method from my drawings should allow me to cut out to scale a stencil for the brick. The brick for each ring should all be the same dimensions with the exception for around the vent (same dimensions only some custom cuts into them).

[deejayoh]

Re: Mortar Joints

K79 -

Have you downloaded my dome calculator spreadsheet? It will do all the math for you on the angles for every course. Lets you adjust the mortar joints however you like. Probably helpful if you haven't. It's linked in my sig below

And for cutting bricks, I'd advise looking at Hendo's twist and tilt thread. You use a jig to cut the bricks, not a template.

I think you are maybe reinventing some stuff that folks have figured out already

[Tscarborough]

Re: Mortar Joints

Almost all firebrick are dry pressed, wire cut are easy to tell, they LOOK like they were cut, dry press are slick on all sides.

[K79]

Re: Mortar Joints

You could build the oven with no mortar, technically, but practically, the simple answer is: Keep the joints as small as possible on the face and don't worry about them on the back side.

Mortar is not used to hold brick together, it is there to hold them apart, i.e. fill in the gaps of imperfect units and allow a manufacturing tolerance to be established. This is why good firebrick are dry pressed, not wire cut; the designed tolerance for fireplaces and other refractory structures is a joint of 1/8". For normal brick the design tolerance usually requires a 3/8" joint, reflecting the manufacturing capability of fired brick.


Why not make all brick by dry press? Cost and texture considerations.

should I be looking for dry pressed and not wire cut?? What did you use?