Flexible filler for wood window frames

[RichD1]

I've been restoring the bay windows on my 1940's. I've stripped the main frames back to remove the layers of paint which has built up over the years. I've primed and undercoated the frames and any gaps in between the five casements and the casements and the cill, I filled with Brewers external filler. That was about a month ago. I've just gone out to lightly rub down for a second undercoat and where I used filler has cracked open. See attached photos.

Is there a better flexible filler or do I have to use Decorators caulk?

 

[Justin Passing]

Not "Decorators", it's no good outdoors.

Low modulus means it more likely takes expansion/contraction without coming unstuck.

Dow 791 Weatherproofing Silicone Sealant White 310ml - Screwfix

Order online at Screwfix.com. Low modulus silicone provides excellent, unprimed adhesion to both porous and non-porous substrates. Suitable for weather sealing and expansion joints. FREE next day delivery available, free collection in 1 minute.

www.screwfix.com

 

[RichD1]

But silicone won’t take paint will it?

 

[opps]

But silicone won’t take paint will it?

The silicone will repel the paint. Modified Silane Polymers (MS Polymers) will accept paint but generally need to be primed with waterbased paints first otherwise the oil based finish will stay sticky for months.

They are however more difficult to "taper" off at the edges. Dipping your finger in white spirits will help though.

 

[RichD1]

As there appears to be nothing exactly what I’m after, I’ve opened up the gaps in the frame and have used Ronseal 2 pack.

 

[opps]

As there appears to be nothing exactly what I’m after, I’ve opened up the gaps in the frame and have used Ronseal 2 pack.

If you leave itwith undercoat only, the two pack will probably split as well. At a minimum, undercoat and gloss that section. Then paint the rest at your leisure.

 

[RichD1]

OK, thanks. With the current good weather I'm hoping to get the whole window done.