Fire surround back panel....How!

[johnny56789]

Hi, Just wondering if anyone can help me with this problem.
Just purchased a jura-stone fireplace and everything as far as fitting looks pretty simple apart from the stone back panel which has to be fitted roughly 3" from the wall to connect with the legs and top of the fire surround?
The surround is being fitted to a bulk standard 50s chimney.
How would you fill in the 3" between the back panel and the wall? And does this need to be totally sealed.
any help very apprieciated.
Will be having a corgi fit the gas fire after.

 

[gday2uk]

Whatever happens back panel has to be air tight to the wall.
Sounds like you are missing some pieces of stone? Are there not supposed to be returns from the top and legs to the back plate?
Making up 75mm between wall and back is a large gap, if you bring it out this far will the gas fire be set back into the chimney far enough to allow it work properly? Pictures of what you've got would help.

 

[johnny56789]

Thanks 4 the reply, I have added some pictures so you may have more of an idea.
I have looked everywhere on the net for some imformation on this but very little around, although had a good idea it may need sealing dont quite know how to go about this?
think the gas fire will be fine as the hole in the hot box is directly below chimney gap.
Sorry dont know how to add the pictures to the message!

https://www.modernfireplacesdirect.co.uk/Scripts/prodView.asp?idproduct=401

//www.diynot.com/network/johnny56789/albums/

 

[gday2uk]

Presumably as long as all external joints are sealed (between mantle surround and wall) and joint between backplate and mantle is sealed you will have no problems. If the backplate needs to be secure to fix the fire to or through you could pack some timber off the wall for it to sit against.