fireplace and plasterboard?

[diyfromusa]

Is foil backed plasterboard suitable to screw directly into a brick fireplace wall and if so, does the plasterboard go behind the fireplace or up to the surround?

My fireplace is a 1 piece cast iron combination wood burning fireplace.

I worry that the cast iron will get hot and either burn the plasterboard or destroy the foil.

Any links to installing a 1 piece cast iron fireplace with pitfalls and how to deal with issues would be helpful as well. My fireplace doesn't seem to sit very far back into the builders opening and I can see where smouldering embers can backflow up the sides and to the top of the surround- unless, that is expected?

thanks.

 

[gday2uk]

Good link - http://www.antiquefireplacecompany.co.uk/fitting.php
Best to use 'pink' firecheck plasterboard.
Make sure insert is sealed around sides touching wall.
Fill void behind insert with bricks leaving a 2" gap between bricks and insert then backfill with vermiculite capping off with a vermiculite/cement top sloping down toward the throat of the insert so any soot etc. rolls back into the fireplace.

 

[diyfromusa]

Thanks for your very helpful response

 

[Richard C]

Be aware when renovating around fire places taht conventional Gypsum plaster products (including Fire board) are only suitable for applications up to 49 degrees C; no idea why it’s 49 degrees & not 50!

If the temperature surrounding the fire regularly exceeds this, the plasterboard & ceratinly any plaster on it will, in all probability, blow & crack.

 

[gday2uk]

conventional Gypsum plaster products (including Fire board) are only suitable for applications up to 49 degrees C

I never knew that.
Thought it would be more as it's meant for fire walls etc. I suppose it has a long burn through time.
TBH though I used it to pack out my cast iron insert (with plumbaflue) with no issues so far and just plastered around with browning and multifinish before putting my mantle on and again have had no issues whatsoever.

 

[diyfromusa]

conventional Gypsum plaster products (including Fire board) are only suitable for applications up to 49 degrees C

Thanks for that info! Definitely special considerations need to be made when using plasterboard on walls vs standard plaster.

Actually just chatting here gave me an idea. I have previously purchased some refractory plaster and will use that right around the edges of the fireplace up to where it meets my plasterboard. I'll also put a bit on the inside of the surround since there is a bit of a gap. The special plaster is rated to handle up to 1700 degrees.

 

[Richard C]

I never knew that.
Thought it would be more as it's meant for fire walls etc. I suppose it has a long burn through time.
TBH though I used it to pack out my cast iron insert (with plumbaflue) with no issues so far and just plastered around with browning and multifinish before putting my mantle on and again have had no issues whatsoever.

Well I suppose it’s natural to assume that something called “FireLine” or “Fire Board” would be OK but the difference, as you’ve realised, is that it’s designed to provide protection during a specific one off fire situation after which it’s done it’s job & spent!

I will confess that I was a little surprised to learn that none of the conventional Gypsum plaster or plasterboard products are designed for continuous use above 49 degrees & it’s plastered all over the manufacturer's design fact sheets.

 

[noseall]

The reasoning behind fire resistant boards is they resist direct contact with fire for 1/2 an hour or so before degrading or decomposing, this does not automatically qualify them for dramatic changes in temperature.

Dealing with large differences in temperature is a different ball game. Few building products will actually be able to deal with large temperature changes without some visual anomalies.