Re post - help please on window sill cracks
 

Could anyone help with a very annoying problem.


I recently decorated my dining room which has a five sided bay. I ripped out
the very old window sill and made good
the plater underneath that broke away with plaster board sat on top of
plasterboard bonding (the whaite doughy stuff).


I made the window sill out of cill board (mdf pre coated) and stuck it down
to the plasterboard with a polyurothene adhesive that is used to fix/glue
buses together with. It's basically a very adhesive silicon sealant and
certainly better than no nails.


All went well except every couple of weeks I get the paint cracking at the
joints. I've used decorators filler. But they re-appear.


I'm thinking expansion and was going to drill through the would and screw
the sill in place.


The paint is crown solo - it's very thick like emulsion, and i've given it
about 4 sand and coats now...

On Fri, 18 Mar 2005 16:57:10 -0000, "daveasbury"
wrote:

Could anyone help with a very annoying problem.


I recently decorated my dining room which has a five sided bay. I ripped out
the very old window sill and made good
the plater underneath that broke away with plaster board sat on top of
plasterboard bonding (the whaite doughy stuff).


I made the window sill out of cill board (mdf pre coated) and stuck it down
to the plasterboard with a polyurothene adhesive that is used to fix/glue
buses together with. It's basically a very adhesive silicon sealant and
certainly better than no nails.


All went well except every couple of weeks I get the paint cracking at the
joints. I've used decorators filler. But they re-appear.


I'm thinking expansion and was going to drill through the would and screw
the sill in place.


The paint is crown solo - it's very thick like emulsion, and i've given it
about 4 sand and coats now...




I think you will find the bricks expand at a different rate to the
wood, and thats where your problem comes. To keep the wood solid in
one piece, I guess you need to make the window cill into one piece,
with biscuit joints or similar, and then stick it to the bricks with
something a bit flexable.

As to cracks between plaster and wood, the only way I have ever gotton
close to fixing this is by using silicone to fill the gap, as silicone
remains flexable.

Docorators filler goes hard, so will crack if put between surfaces
that have some movement.

Rick

Rick wrote:

On Fri, 18 Mar 2005 16:57:10 -0000, "daveasbury"
wrote:


Could anyone help with a very annoying problem.


I recently decorated my dining room which has a five sided bay. I ripped out
the very old window sill and made good
the plater underneath that broke away with plaster board sat on top of
plasterboard bonding (the whaite doughy stuff).


I made the window sill out of cill board (mdf pre coated) and stuck it down
to the plasterboard with a polyurothene adhesive that is used to fix/glue
buses together with. It's basically a very adhesive silicon sealant and
certainly better than no nails.


All went well except every couple of weeks I get the paint cracking at the
joints. I've used decorators filler. But they re-appear.


I'm thinking expansion and was going to drill through the would and screw
the sill in place.


The paint is crown solo - it's very thick like emulsion, and i've given it
about 4 sand and coats now...





I think you will find the bricks expand at a different rate to the
wood, and thats where your problem comes. To keep the wood solid in
one piece, I guess you need to make the window cill into one piece,
with biscuit joints or similar, and then stick it to the bricks with
something a bit flexable.

As to cracks between plaster and wood, the only way I have ever gotton
close to fixing this is by using silicone to fill the gap, as silicone
remains flexable.

Docorators filler goes hard, so will crack if put between surfaces
that have some movement.

Acrylic does retain some flexibility - acrylic decorators caulk is teh
bvees knees, but in very thin cracks it struggles

It is not clear between what elements the cracks are appearing- please
elucidate.
Rick

It is not clear between what elements the cracks are appearing- please
elucidate.
Rick


Sorry when i re-read my post i realised i wasn't so clear.

The cracks appear between each joint of wood. Originally I was going to
screw straps of aluminium on the underside of each piece across the joints.I
was advised it wouldn't be required. It's too late now as they are in place.

It's really depressing as the rest of the room is "perfect".

Any help appreciated.

daveasbury wrote:

It is not clear between what elements the cracks are appearing- please
elucidate.

Rick



Sorry when i re-read my post i realised i wasn't so clear.

The cracks appear between each joint of wood. Originally I was going to
screw straps of aluminium on the underside of each piece across the joints.I
was advised it wouldn't be required. It's too late now as they are in place.

So its cracks between butting pieces of MDF? Or angled corners?

The only way to clear butt cracks (ok ok ok;-)) is to either really tie
the bits togeher, or to make the crack big enough to stuff something a
bit flexible in. (ok ok ok ;-))

I would suggest if you have this type of problem that opening the crack
up with a dremel or maybe jigsaw used in a perpedndicular fashion to
normal, would allow either flexible sealer or car body filler to be
rammed in (lord: this ought to be in alt.gerbils)

Or simply scrape the wood clkear of paint, and use a bit of lightweight
glass cloth and epoxy or polyester resin to form a really solid surface.

If its a 90 degree joint, then rin a fat bead of decorators caulk down
it to make a smoothly curved fillet.



It's really depressing as the rest of the room is "perfect".


I know the feeling...Ive got some wall made of MDF and its all crcaked
between the panels.

I'll be following my advice on that some day...brobably gouge out a v
shaped crack and use caulk...



Any help appreciated.

On Sat, 19 Mar 2005 08:21:13 -0000, "daveasbury"
wrote:


It is not clear between what elements the cracks are appearing- please
elucidate.
Rick


Sorry when i re-read my post i realised i wasn't so clear.

The cracks appear between each joint of wood. Originally I was going to
screw straps of aluminium on the underside of each piece across the joints.I
was advised it wouldn't be required. It's too late now as they are in place.

It's really depressing as the rest of the room is "perfect".

Any help appreciated.


Try cutting a rebate on one side of the crack with a wood chisel, line
the bottom with thick polythene or thin foam as a 'bond breaker', then
fill with sealant, smooth it then overpaint.

Some sealants shrink a bit on curing but the stuff you used for
bonding the MDF shouldn't.

cheers,
Pete.

Thanks for the feedback - I knew I should have bloody strapped them.

Oh well - i''ve got a dremel and my dad has a rebater - so i'll create a V
and try P38.

Should have thought of that myself really as I used it for rottom window
frames in my first house....

Again thanks for the ideas.