# Forum Home Renovation Brickwork  mortar mix for fireplace bricks?

## montiee

Can anyone tell me the mix and ratios used in mortar for bricks in a fireplace. Do you need special cement so it doesn't crack? 
TIA!

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## plum duffer

you need to use refractory mortar

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## montiee

> you need to use refractory mortar

  Thanks.  
Will it have instructions on the back wrt what I need to mix it with ratio wise and ingredients (lime, sand etc) for a fireplace application?

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## plum duffer

Sorry Mate - i only know this by learning from a mistake i recently made using std mortar in a fireplace - try these guys for more info http://www.darleyrefractories.com.au - but there is likely to be a supplier more local to you - just google refractory mortar - I believe it is the cement in the mix has a higher something or other content to stop it getting too hot and cracking.  it is just the same 3 2 1 ratio mix but the cement part is refractory cement not bog standard dust..

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## plum duffer

oh and sorry 6 1 1 mix... with refractory cement in place of regular

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## autogenous

oh and sorry 6 1 1 mix... with refractory cement in place of regular 
chuck in a small portion of Fondu or Fireclay if you want. 
Most fireplaces/barbecues are just 6:1:1. 
Pizza ovens, different story.

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## plum duffer

hey autogenous can you elaborate a little on the fondu/fireclay bit and what is different about the pizza oven mix? i thought the pizza oven mix would be the same as the fireplace?? Thanks

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## montiee

Just an additional question.  Can I mix bondcrete into the refractory mortar so it can adhere to the extisting mortar or will it cause issues?

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## Vernonv

> Just an additional question. Can I mix bondcrete into the refractory mortar so it can adhere to the extisting mortar or will it cause issues?

  I don't know for sure, but I'd say it would be a bad idea - PVA certainly isn't heat resistant and being a "plastic" it will give off some nasty fumes and may possibly weaken the adhesion of the old and new mortar.

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## autogenous

> hey autogenous can you elaborate a little on the fondu/fireclay bit and what is different about the pizza oven mix? i thought the pizza oven mix would be the same as the fireplace?? Thanks

  I typed out an answer and the site crashed, never mind. 
Fondu or Fireclay mixed with 6:1:1 prevent the cracking. 
Fondu will accelerate the setting of standard mortar. 
I have seen dozens of fireplaces built out 6:1:1 with no dramas. Mind you the mortar should be left at least a week prior to lighting a fire. Keep in mind fireplaces are open. 
What is important is the fire back be built out of "solid" clay bricks. 
Refractory mortar is near on pure clay with about 1-2mm joints between bricks. They're dipped. 
Fireplaces shouldn't get hot enough unless they are raging which shouldn't be the case. 
Pizza ovens are ovens and require a bit more care. They are more enclosed. 
I built a bit of a blog a while ago with a link on the right to Count Rumford fireplaces if people are interested in fireplaces. http://brickandstoneart.blogspot.com

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## autogenous

My old ladies fireplace is built out of creme mortar 6:1:1, 15 years old without a crack.
The reason I know there is no Fondu or Fireclay is that the mortar is creme. 
Any additive is radically going to change the colour of the "Creme" mortar. 
    Refractory cement made by LAFARGE called Fondu Cement. 
      Contact Mowatt Refactories on (08) 9419 7399 or Farinosi (Mitre 10) on (08)        9328 7311 for further information  http://www.woodworkforums.ubeaut.com...ad.php?t=31252

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