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...

Reply to
daveasbury
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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

Reply to
Rick

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.

Reply to
The Natural Philosopher

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.

Reply to
daveasbury

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.

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...

Reply to
The Natural Philosopher

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.

Reply to
Pete C

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.

Reply to
daveasbury

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