right

ive got new new window ledges to fit

how do i fix them so they dont move ?

Chris you have a number of options, firstly you can drill the sill/window board with a counter sunk hole and screw them followed by filler.
Option two you could bond the board in place, this depends on what you are fixing.

Timber
MDF
Pre finished board etc etc

Maybe you could tell us what you are fixing then more answers can follow.

Hope this helps.

its mdf board

Silicone with some nails if you can get a fixing. is it a timber frame home

No brick no timber and pvc windows

i hae fixed one using 18mm wpb board as supports then gripfill on that to stick the boards down

will see how well its fixed tom

STEP 1
Use your utility knife to cut any caulking or paint between your ledge and your trim casing (if you have any) and against your window. In the example photo the window is not trimmed out and the ledge rests against plaster walls and the metal surround of the window. Cut along the bottom and sides of the apron as well. This will allow the trim wood to release more easily with less potential to damage the underlying wall.
Step 2
Using a prying bar to separate the apron.
Using a pry-type bar to gently pry the apron away from the wall. Often the apron is attached by finish nails and sometimes with a nail gun, which means the nail may have little or no head. Remove the apron and put aside. You probably will want to reuse the same trim as exists in the rest of your home. You may need to remove trim or casing at the sides of the window as well but only if it rests on top of your ledge. If so, cut and remove these pieces carefully so you can reinstall them later.
STEP 3
Use your hammer to tap upward gently on your ledge. It should be attached by three finish nails, one near each side and one in the middle. Remove your ledge and clean up the underlying area by removing any residual caulk or nails.
STEP 4
Select a piece of ledge that is longer than your existing ledge. If you need to, take your rotten ledge to the lumber store to match what you need. Use your existing ledge as a template to mark the cuts. Use your saw to cut and shape the new ledge. Use your rasp and sand paper to round the side edges to match the rounded front edge of the ledge.
STEP 5
Mount your new ledge in the same position. Use three finish nails to nail it into place. Install your apron and any trim you have removed. Fill nail holes and caulk to seal the ledge to the window framing. Sand and paint or stain to match your existing trim.

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Wicker Furniture