How to fill large gap in window sill?

tod

Hi,

Any suggestions as to the best product to use to fill this trench-like gap in a window sill? I won't bore you with the details of how it came to be, but it was routed out (badly). As far as I can tell the material is mdf. I'm going to first place a gap filler rod into it and then i need a filler that will harden, can be sanded and painted and that won't shrink. The trench is around 1.6m long, 20mm wide & 10mm deep (before putting in the filler rod). Would greatly appreciate advice on the best product to use. Thanks in advance.

EricL

Hello @tod

Thank you for sharing your question about filling a gap in your window. As a possible alternative, I suggest filling the gap with a cut strip of MDF. This will negate the possibility of the surface collapsing should anyone happen to lean or push into the gap. As I'm sure you are aware gap filler rod is compressible and will shrink if enough pressure is applied to its surface whereas MDF will not.

Your goal is to get a cut MDF strip close enough to the size that the gap needs, it does not need to be perfect just close enough that it will require a minimum of filling. I suggest using https://www.bunnings.com.au/selleys-320g-liquid-nails-construction-adhesive_p1233751 to anchor the MDF into the gap. I then recommend using https://www.bunnings.com.au/turbo-500ml-builder-s-bog_p1212026 to fill and flatten the rest of the gap. My best advice is to get it as flat as possible so that you won't have to sand down a great deal of the bog. Once the bog cures you can then sand the surface down until it is flat or at the same level as the window frame. The rest of the steps will be to clean the surface then prime and paint to finish it off.

Please remember to wear personal protection such as gloves, goggles and a mask.

Let me call on our experienced members @Dave-1, @Nailbag and @DIY4Knuckleheds for their recommendations.

If you need further assistance, please let us know.

Eric