Fireplace inset reduction advice needed

[SteUK]

Hi chaps,

Need some advice on fixing up my fireplace ready to accept a gas fire. The opening is currently far to large compared to the min/max dimensions the fire manufacturer dictates. The work required is closing the width by 50mm each side and fitting a lintel/bricking up to reduce the height.

I have a few questions.

What is the min length the lintel should be embedded in the chimney brickwork? It will be holding up 10 engineering bricks.

Due to the thinness of the width reduction I am using cut down paving slabs. I am concerned about whether I should tie this into the existing brickwork. If so, what is he best method? The inset is 900mm high and 360mm deep.

After reduction I will be putting a layer of bonding plaster (or would hardwall be better?) over the whole inset.

Thanks!

Ste

 

[gday2uk]

Just use an aircrete block (Celcon / Thermalite), these can be cut with a saw to any dimension and laid with sand and cement, will not need tieing in to sides and minimal linel across top; a piece of galvanised steel should be sufficient. Cutting paving slabs and using engineering bricks seems overkill.
Check with manufacturers instructions but you may even be able to use timber frame studwork and plasterboard it; loads easier.