I need to plaster over a steel lintel over an open fore recess. Its
visible surface is 6" x 31" . It is 1/4" thick steel. The steel will
get fairly hot (I guess about the pemperature of boiling water but not
much more) because it is in close proximity to a fire. That means the
steel may expand and contract somewhat. I'll be using one-coat plaster
from B&Q, and the plaster will be about 6mm thick over the steel. What
is the best way to ensure the plaster stays stuck to the steel? One
idea I had is to rivet a piece of perforated sheet-metal to the steel
before applying the plaster. Any other suggestions would be
I think the plaster will crack big time if fixed to the lintel or
fixed to anything fixed to the lintel. I would look into having a
sheet of plasterboard fixed to the wall around the lintel, and
maybe loosly fixed to the lintel so sideways movement of the lintel
can occur, but you won't get plasterboard and plaster in 6mm depth,
so it would step out in front of the wall.
Otherwise look for some other way to finish the lintel. Maybe face
it with wood so it looks like a wooden lintel from the front or
with brick fronts to look like a row of soldier bricks?
On 30 Jul 2003 18:52:29 GMT, firstname.lastname@example.org (Andrew
Maybe expanded metal lathing fixed to the wall around the lintel. Not
sure how easy it is to get some wide enough but in small quantities.
Like you say, movement of the steel could be a problem, but presumably
if it expanded that much, it would also crack the masonry around it.
On Wed, 30 Jul 2003 20:34:28 +0100, John Armstrong
Thanks to both respondees. I'm not sure how much a 31" length of steel
will expand. My guess is less than 0.5mm. To stop the masonry cracking
at each end of the lintel, I stuck some foam draught excluder onto
each end of the lintel so it will simply be compressing the foam, not
the masonry. I guess plaster will expand when hot too. With a bit of
luck, it'll expand the same amount as the steel - but that may still
not prevent cracks occurring.
Perhaps I'll follow Andrew's idea and stick something onto the lintel,
like brick tiles or something... not sure...
Perforated plywood is good for this. Make a frame around the lintel and
cover it with the plywood. The perforations lets the plaster ooze through
and when it dries it grips like mad. It's just like an old lath and plaster
wall in a way..
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Excellent tip - thanks. I came to a similar conclusion last night,
while mulling over Andrew's plasterboard coment. I was thinking to fix
a piece of 5mm cement fibreboard over the lintel - fixed to the wall
each side of the lintel - then plaster over that. Actually, I think I
may use the cement fibreboard rather than plywood, since I feel it
will be unlikely to shrink the way plywood might. Also, the bottom
edge will be close to a flame, so it needs to be something fire-proof.
Drilling holes in it is a very helpful tip. Thanks!
The coefficient of thermal expansion of mild steel is about
0.0000126/DegC. Assuming a possibility of a 100 degree
temperature change, that's 0.03906", near enough 1mm.
I don't understand your setup. Have you used a square section
tube, or what? Can you supply an ACSII cross-section?
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galvanised steel mesh using a 2 part construction adhesive (Epoxy, PU or
Acrylic) to adhere it to the lintel....... and for extra heat security ...
use a fibre reinforced heatproof screed (available online from BES) with a
plasticiser, and Don't use plaster ......
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