In article .com,
bp writes:

Hi,

I want some advice on blocking up the inside of a fireplace.

I live in an old terraced house which has a chimney and fireplace.

I have recently had the chimney wall and fireplace all re-plastered.
I dont have a fire and I dont want one. The fireplace is currenlty
open and it has been plastered inside. I have had it swept.

I just want to keep it like that as a decorative feature. But I need
to block off the inside to prevent soot from falling down into the
fireplace floor. I know I have to keep a ventilation hole

I've done exactly this. If it backs onto an outside wall, I would
suggest you ventilate the flue to the outside rather than the
inside. Otherwise you'll lose up to a kW of heat up the chimney
in winter.

I put an air brick from the flue to outside a few courses of bricks
above the top of the fireplace. I then blocked off the flue using
a piece of plasterboard in the top of the fireplace glued in place
with bonding coar plaster. When fitting it, I put a layer of loft
insulation on top of the plasterboard, partly to prevent it getting
cold and forming condensation, but mainly to cushion any debris
falling down the flue to reduce chance of it damaging the plaster-
board. The back wall of the fireplace was only a single skin brick
wall, and to prevent that getting cold and forming condensation and
mold, I lined it with 25mm cellotex and then plasterboard, and
plastered the whole inside.

I dug out the floor of the fireplace down to the slate damp course
in the brickwork, fitted a damp proof membrane, layed about 6" of
cement and vermaculite insulation and brought it up to floor level
with mortar. This should enable it to be used for a fire in the
future (if the flue is reestabled and the cellotex removed).
Fireplaces often relied on regular fires to keep damp out of the
base and hearth, and without fires, mine was slightly damp as the
infill wicked moisture up from the earth.

I dropped a lighting cable down the flue from the loft, to enable
a concealed light to be fitted in the fireplace.

--
Andrew Gabriel
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