Filling cracks in external oak

[thepeg]

I'm making some garden lamps in oak. The oak posts are 3 year air dried and naturally enough have some cracks opened in it.
The oak is not going to have any finish applied (no stain, lacquer or paint), but will be dipped in a spirit based anti-fungal, anti-insect treatment which also has a water repentant wax included.
I have tried mixing sawdust with Cascamite, but it sands up very pale and looks "plasticy", not nice.
I don't want to attempt to hide the cracks - they're a natural fact; just to make them look more acceptable.
Something which will penetrate into the cracks is preferred, regular wood fillers are difficult to push into cracks to any depth; and it's only a matter of time before it falls out. So I suppose I'm looking for something lower in viscosity (more runny) that can be gunned into the cracks.
Any advice would be appreciated.
Thanks.

 

[jasonB]

Leave well alone, you will get more cracks and the existing are bound to move about.

Anything you put in now will stand out once the oak has weathered to its natural silver gray colour in a year or so.

Jason

 

[Harbo]

+1 with Jason's comments.
The cracks will add character.

Rod

 

[bosshogg]

On mixing sawdust with glue (in your case Cascamite) Iv'e noticed the same thing, but now mix glue, fine sawdust created from sawing the wood with a hacksaw and a small blend of random orbital wood dust of same or darker tint of the wood. Mix it all and add a bit of spit to create a good consistency, the result is a filler with a simulated grain almost, an improvement on just sanded sawdust and glue. Vary the saw teeth used until you get the right grain...bosshogg.

You can't help a man who doesn't tell you what he wants (hammer)

 

[thepeg]

Many thanks, I appreciate the comments.
I'm in total agreement about crack movement & filler falling out along with weathering in the future.
The problem is people; they don't understand the difference between the real thing and something ejected from a moulding machine in Hong Kong. So although I can explain what to expect from natural weathering in the future, when I'm trying to sell it, it's got to "look" new.

Bosshogg, thanks for your wisdom. I got somewhere near there. I've tried and settled on similar, but concerned about filler falling out I tackled it two ways. Trying to get a paste to penetrate deep enough is difficult so I used polyester resin, firstly just as a liquid so it will penetrate well inside. When it had mostly stopped being absorbed, I dusted over with finely sifted sawdust and worked that in adding resin or dust as needed to keep a workable paste consistency. I found that if it's anything less than really finely sifted, it's too gritty to work with.
I also pre-mixed in just a little pale brown colour (cellulose paint) to kill the greyness of the resin alone. The test pieces came out OK. Obviously not an attempt to hide the cracks, but cosmetically much better.

One problem I found with cascamite, being water based, the natural colour/dye in the oak was leeching out and forming a yellow halo around the repairs. And it wasn't just on the surface. I don't think it would have been easy to eradicate it.

Thanks all.

 

[jasonB]

Well lets hope you don't get a call back 18months later when the post has gone grey and the dust encapsulated in the resin is they same colour it is now.

You also run the risk of more cracks, the resin will hold the existing ones together so any shrinkage will start new ones rather than the existing opening up.

If the client wanted pristeen oak it would have been better to build the posts up from laminations or a box construction of thinner material.

Jason

 

[thepeg]

Well I know from past that the colour I added will pale in time, so I'm hoping they will weather down in tone.

I was initially going to make up the posts of 4 rebated planks. From the first one I made it was turning out a lot more expensive in both time and material. I also had doubts about long term integrity of the joints. Failure of this would definitely result in callbacks and too bigger a risk.

I shall continue testing different filling methods focussing on long-term colour as a priority.

John