Exterior hardener and filler for oak windows

[chromey]

Hello,

I've bought a 1930s house with painted oak window frames and steel Crittal windows. We are replacing all the casements, which have mostly corroded away, with new powder coated Crittal windows.

Some of the oak sills are rotten, some are are soft on the surface but solid a few millimetres below the surface. Whilst we inted to cut out and replace two of the sills, we are keen to retain as much of the original timber as possible, and have been told by a local joiner that the existing rot can be romoved and the wood treated with a hardener, filled with a two part filler and sanded/repainted, before the new casements are installed.

Can anyone recommend good quality hardener and wood filling system that will do the job?

Thanks.

 

[Scrit]

One company which makes the hardener is BondaVoss. Their material is on sale at many good builders' merchants (not my two local ones, but then they're a bunch of idiots ). This material is a water-reactive polyurethane so you need to wear gloves at all times (it turns the skin hard and black for a week or so) and use the cheapest brushes you can get as they will go rock hard after one session and need to be thrown away.

The two-pack filler is nothing more complex than an exterior grade 2-pack epoxy wood filler, such as Nickersons. Avoid furniture/joinery fillers as they are designed to take stains and are frequently very soft - the epoxy stuff is a lot harder and more durable.

Scrit

 

[chromey]

Thanks Scrit.
I had seen the Bonda products on that same site - though I have a similar problem with my local builders merchants too!
The Nickersons wood filler sounds ideal for this job.
Thanks for the info.

 

[oilman]

It maybe reasonable to replace the complete sill. I understand your desire to keep the original wood, as I have the same approach. There comes a point where it's not a good decision. I tried using one of these hardeners, but after a couple of years it disconnected from the wood and fell off. (Oak sills)

 

[Scrit]

There is a need to thoroughly clean out all the dead timber with a steel wire brush to get rid of all the "punky" timber before applying the hardener. If you do that, then use an epoxy filler as opposed to a softer filler (which can be slightly porous) then once sanded and sealed it should hold for many years, although as oilman says, if the rot is too extensive the only solution is to cut-out and replace. A couple of window frames I did on our last house are still holding up after 18 years, although they have been repainted every 4 to 5 years, so I know the technique works

Scrit