I saw a cake by the amazing Liz Marek and it had a wood grain base. I wanted to try it out so I did a little search and didn't come up with anything so I thought I might give it a go.. here is what I came up with.. The middle is left as a cake wil be placed on top of it. This technique could be applied to a covered fondant cake as well.  

Because I wanted a Grey/White wash look, I covered my board in Grey fondant. There needs to be a little bit of thickness for carving the grain, but no more than 5mm.

Next I Marked my fondant with a ruler and a boning tool to make the planks of wood.

To mark the grains in the fondant, I used colour shapers but you could use anything from a toothpick to a kebab skewer or even and old pen with the ink taken out of the middle. If you do have colour shapers, these are the ones I used..

Make sure that you press hard to make a deep indent for the grain. It needs to be deep for the dark wash underneath to be effective. Also make sure that the lines on the edge are quite deep for a more realistic wood grain effect.

Next, I used a make-up sponge that I use for cakes only, to paint to whole board black. (any form of sponge will do- as long as its new and clean!, you could even use a paintbrush) You don't really have to concentrate too much on the middle as it will be covered with cake.. Unless it is cake, then don't forget the middle :D Once covered with black, I used the same sponge (that had been washed out and still wet) to wipe away the black. Keep washing off the black from your sponge and wiping away the black until the grey starts to show through.

Because I still wasn't satisfied, I then got a little bit of white paint on my sponge and went over it again to give it a more white washed look. Another tip is not to wash it all away. Wood isn't just one colour and tends to be darker in some areas than others. You could use this same technique with brown wood grain as well. Just start with a white fondant board, make grain, wash with a dark brown and wash off again.
I hope this helps someone :D

That looks amazing!

Thanks so much for sharing this technique, very cool!

AThank You Ellie, I hope you get to use it, it's simple but effective :D

No problem, it's given me some great ideas 

Holy cow, that looks amazing! thank you for sharing!

Amazing, thank you.

If all that work went into just the board, I can't wait to see the finished cake! Thanks for sharing in such detail