Breathable Wood Filler?

[malcolm]

I'm Googling the wrong thing again and getting nowhere. What would you use for filling big screw holes, joints, slight rot damage etc in an exterior softwood timber frame prior to painting with linseed paint?

Would sawdust mixed with wood glue seem appropriate? I feel it would be better to avoid epoxy fillers as they would trap damp.

 

[Feltwell]

I've used ordinary linseed glazing putty to good effect.

For example, I had a wooden window window cill, sitting on a stone sub-cill, that really should have been replaced - but it would have been a big job to do so. I painted it with linseed oil, putting a lot into the rotten areas, let that dry, then filled the rather large holes with putty, shaped carefully. I let it go off for a couple of days and then whilst it was still soft I overpainted with linseed paint.

That was 8 years ago, still looks fine now. The disadvantage of course is that you can't rub it down in any way, but applied carefully with decent filling knife with a bit of linseed oil smeared on it first, you can get a very smooth finish. It's only chalk and linseed oil after all.

For minor repairs I just use 2-part modern epoxy wood filler, goes off in about 15 minutes and is easy enough to sand down. I can't see how sawdust and wood glue would be any better for breathability, would be harder to work with both to use and to sand down.

 

[malcolm]

Linseed putty is a very good idea as I will be over painting with linseed paint. There is something that looks like linseed putty in some places already and it doesn't appear to have caused any damage. I imagine the sawdust idea is for wood that will remain exposed. I still haven't decided whether to leave the inside of my new window exposed but everything else will be painted.

I'll use lime mortar for the gaps between timber and stone or render and fill the gaps in the wood where water can settle with linseed putty.

 

[wobs]

I'm currently repairing our sash windows, as all have been poorly repaired by the previous owner. Its like a lesson in how not to repair windows, looking at what they've done:

Single filler used in large holes, and painted over with undercoat and gloss. Result? More rot, resulting in an even bigger holes in the bottom rails and cills (Especially in the two side sashes in our downstairs bay window which are screwed shut).

All of the cills have been spliced in with new timbers, but all but one does not have any slope for run off, so they are also rotting, or will rot in the near future. Bascially, every repair they have done needs replacing. The only repair where they have fitted a sloping cill, is where the wood at the back is now rotten, under a fixed sash, which also needs serious repair.

Many of the outside linings are rotten at the bottom, and will need splicing.

All of this is on the south facing side, but a tree has rapidly grown in front of the house (only 15-20 years old), and blocks out a fair bit of sun.

Filler that I usually use: 2 part Epoxy resin from one of the big sheds for small repairs.

When I did a large splicing in job on a cill last year I used the Timbabuild two part filler
http://www.sealantsonline.co.uk/Products/Timbabuild_System/TIM4700
Expensive, but really good stuff. The drawback is that the linseed paint from LPC didn't really like it, so used it sparingly. I've not used it with other makes of linseed paint, but would expect similar results. I think the issue is that the paint/oil needs to soak or bond properly to the wood rather than just sit on it like modern paints do, so when it can't, such as this filler, it struggles to give a proper coat. If anyone knows of a way around this, I'd be interested.

I know some here use car body filler.

I would do all this repair myself, but time with kids is taking priority, so managing that time is tricky. Getting a joiner has proven difficult, as all seem busy. Finally got a chap, who has offered to splice in new timbers where necessary rather than replace large components.

With the two side sashes downstairs being fixed, I'm tempted to keep them that way, as he can then splice in the repairs, saving a lot of money. Also, I see no evidence that they ever worked. No neighbours have any of them working, so it suggests they never did, and I can't feel any hole where the cord would have gone into the top of the bottom sash.

 

[wobs]

As for the gap between the timber and masonry, I followed the advice of people here and used sand mastic. A tub from the builders merchent did the job.
A good explanation here:
http://www.masonsmortar.co.uk/knowledge/page/burnt-sand-mastic

 

[malcolm]

I hadn't come across sand mastic before. Linseed oil and dry sand sounds useful. I invested in a tub of linseed putty and have so far filled around 200 nail holes, many of which had started to open up and rot under the nasty old acrylic gloss paint. I guess I'm being sensible filling in the gaps between the wood joints with the stuff.

I did use car body filler on another window sill, but that one was past saving and the filler was applied over an earlier cement repair (One day I'll fix it). None of the 2 pack stuff will be breathable and I need as much breathability as I can get as the infill is currently concrete (one day very far in the future I might fix it). I've noticed the nasty acrylic gloss paint I used on that window before I knew any better is cracking badly (on sound wood) after 2 years. It will get a strip and linseed paint makeover next year.