Linseed oil putty: limestone versus chalk

[Mingwa]

Hi, I have been hunting around on this forum and through various other places for an answer to this.

There are various kinds of linseed oil putty out there. I recently bought some chalk-based linseed oil putty for about 15 quid for 750g. That's quite a lot of money. I also recently found some linseed oil putty from a large DIY chain for just over 6 quid for 1kg. The cheaper one is limestone based.

My understanding, broadly, is that the chalk-based stuff might be a little bit more breathable but that there isn't too much in it.

I am using it for sealing gaps in a timber frame, mostly over the top of oakum. Gaps sometimes between timber and brick infill.

What's better? I don't really see the workability of each as a substantive consideration.

Cheers

 

[Cubist]

Hi there and welcome.

In my opinion neither is appropriate for the job. Ultimately they will dry out as either the timber leeches the oil from chalk/limestone or as the oil evaporates into the atmosphere. The continuing movement of the frame will then break up the hard material will and it will fall away. Personally I prefer a fillet of lime mortar or a lime/chalk filler for the final closure of any gaps - and to prevent birds stealing the oakum or caulking cotton - or alternatively in some instances a burnt sand mastic. On occasion though I have also used a product called PlumbersMait which is a none-setting putty used by plumbers to seal sanitary ware. Whilst this never sets it does develop a surface skin that can be painted but remains malleable for donkeys years and will cope with even daily significant movement of the frame, Its also worth noting that any such closing fillets, no matter their nature, are ultimately sacrificial and will need a little TLC in the future.

 

[Cubist]

Oops, forgot to mention - PlumbersMait is not a breathable product.

 

[Mingwa]

Thanks a lot--appreciate your answer.

 

[TudorCottage]

When we first moved in here, sealing the gaps between the timber frame and window frame was some good old modern mastic. I ripped all that out and replaced it with oakum and finished it off with some burnt sand mastic. A few years later and all is good and no sign of seapage from the oakum. You can get burnt sand mastic in different shades so you can try and match it to the existing wood colour.

For gaps between the timber frame and render I used a lime putty/filler. As Cubist said left to the elements it can be prone to cracking but is still in relatively good condition and helping to keep the elements out. In some areas I over painted with Barn paint. As all products used are allegedly breathable, any rain getting through should dry quickly once the sun comes out.