Hi folks,
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
appreciated.

Thanks

Frank Z

In article ,
(Frank Z) writes:

Hi folks,
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
appreciated.

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?

--
Andrew Gabriel

On 30 Jul 2003 18:52:29 GMT, (Andrew
Gabriel) wrote:

In article ,
(Frank Z) writes:

Hi folks,
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
appreciated.

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.

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.


--
John

On Wed, 30 Jul 2003 20:34:28 +0100, John Armstrong
wrote:

but presumably
if it expanded that much, it would also crack the masonry around it.


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...

Frank

Subject: Plastering onto steel
From: (Frank Z)
Date: 30/07/03 21:04 GMT Daylight Time
Message-id:

On Wed, 30 Jul 2003 20:34:28 +0100, John Armstrong
wrote:

but presumably
if it expanded that much, it would also crack the masonry around it.


Thanks to both respondees. I'm not sure how much a 31" length of steel
will expand.

0.1mm per 10 degrees C


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

The CoE of metals is many times higher than that of building materials. The
data is freely available on the web.


- 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...


Dave Baker - Puma Race Engines (www.pumaracing.co.uk)
"How's life Norm?"
"Not for the squeamish, Coach" (Cheers, 1982)

"Frank Z" wrote in message
...

Hi folks,
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
appreciated.

Thanks

Frank Z

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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On Thu, 31 Jul 2003 02:24:56 GMT, "BigWallop"
wrote:


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..

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!

Frank

(Frank Z) wrote in message ...

I need to plaster over a steel lintel over an open fore recess.

Hi

Is this a flat face, or the concave face of an I-beam?

If the latter a standardish way of fixing would be to knock slightly
tapered wooden wedges in to the concave face. You could then mount a
couple of wooden battens across this in a way that allowed them to
'float' a little. Tack plasterboard or mesh over these battens and
plaster. The metal should then be able to shift a little without
stressing the plaster face.

If you really only have a 6mm depth from surrounding plaster to this
metal then I'd think about finishing the edges nicely and using
Smoothrite in some suitable colour to finish it off.

You could also build a panel of wood, either decorated around the
edges with mouldings or rounded off and loosely mount that using
keyhole type slots/hangers. Or make a 'feature' and hang old fireware
(pokers, pans, etc.) to disguise it. Depends a bit on what your aim
is.

Final suggestion: Fire cement render?

HTH
IanC

Frank Z wrote:
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.

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.

Perhaps I'll follow Andrew's idea and stick something onto
the lintel, like brick tiles or something... not sure...

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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"Frank Z" wrote in message
...

Hi folks,
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
appreciated.

Thanks

Frank Z

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 ......