Can/Should I Grain Fill A Soundboard?

As per the title, I have a piece of Cedar that I have thicknessed to arouind 1.6mm (1/16?) to use as a soundboard. The grain is very rough and no amount of sanding is improving it. Should I grain fill it for aesthetics or will this be detrimental to the sound quality? Should I just go with the "rustic" look and leave it alone?
Cheers!
Pete.

That's pretty thin for cedar; I wouldn't use it. And why so rough? This is not adding up for me...

No idea why it is so rough. Maybe I just got some poor quality timber? What sort of thickness should I be aiming for?

Depending on stiffness, I'd go somewhere between 2 mm and 2.25 mm. And it should be smooth. Did you buy this as top material from a lutherie supplier?

Thanks for that Rick. It was just "random" timber hanging around for one of my "Budget" builds. I like to try to build things with stuff I have hanging around. I know it won't be good quality, but then neither are my woodworking skills!

What sort of cedar? does it have open pores?

Good question, Liam! There's cedar and there's cedar, and there's cedar and they're all quite different from one another.

Western red cedar isn't even really cedar http://en.wikipedia.org/wiki/Thuja_plicata

And neither is Port Orford cedar http://en.wikipedia.org/wiki/Chamaecyparis_lawsoniana

And Aussies call timbers by all sorts of strange names. Tassie oak, for instance, which is also called mountain ash, which is also called swamp gum. And it describes at least three species of eucalypt!

Spanish cedar, http://en.wikipedia.org/wiki/Cedrela is yet another cedar that isn't a cedar...it's a mahogany relative. It does have large open pores...

Fair comment guys. It is just a piece of Cedar of "indeterminate" origins. I realise it isn't going to be great, but the idea was to have a bash at building something with cheap (or free!) materials so it doesn't matter so much when I mess up. And I will mess up. Repeatedly! Hopefully I can hone my skills a bit and then get some decent timber to build something nice.
For now I have glued up another couple of bits so I can start again and leave them a bit thicker.
Back to the original question, is it worth grain filling, or should I leave it?

Back to the original question, is it worth grain filling, or should I leave it?

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To be clear, the process you are referring to is not grain filling, it is pore filling. All wood has grain, but only open-grain woods have pores that need to be filled. In addition, it is not a requirement to fill pores even in woods like Spanish Cedar, which has particularly large and deep pores. It depends on the look you are after. If you want a mirror-like finish, fill them. If you want a more "natural" look, leave them unfilled.

I think shiftysquirrel might have meant something else, having re-readhis original post. He says the grain is very rough, and no amount of sanding will smooth it.

This sounds to me as if his "cedar" has particularly soft wood between the grain lines. The sanding takes more of this away than the hard lines, leaving a ridged surface. If I have this right, the sanded surface should feel fuzzy or fluffy when stroked gently.

My solution would be to apply a coat or two of the intended finish, let it cure, and then sand. Maybe repeat once or twice. This should stabilise the softer material and allow you to get a reasonably flat surface.

It would be worth trying this out on the discarded soundboard.

And is 1.5mm really too thin for eg a soprano top? I can see that it would be for a tenor, but even here slightly taller bracing might make it usable. But I've never built with any kind of cedar - I've taken a spruce top to around 1.5mm and it worked fine, but I gather cedar is floppier.

With guitars, Western red cedar is typically thicknessed about 15% thicker than spruce. Your mileage may vary, cross grain stiffness varies a lot.

ProfChris said:

I think shiftysquirrel might have meant something else, having re-readhis original post. He says the grain is very rough, and no amount of sanding will smooth it.

This sounds to me as if his "cedar" has particularly soft wood between the grain lines. The sanding takes more of this away than the hard lines, leaving a ridged surface. If I have this right, the sanded surface should feel fuzzy or fluffy when stroked gently.

My solution would be to apply a coat or two of the intended finish, let it cure, and then sand. Maybe repeat once or twice. This should stabilise the softer material and allow you to get a reasonably flat surface.

It would be worth trying this out on the discarded soundboard.

And is 1.5mm really too thin for eg a soprano top? I can see that it would be for a tenor, but even here slightly taller bracing might make it usable. But I've never built with any kind of cedar - I've taken a spruce top to around 1.5mm and it worked fine, but I gather cedar is floppier.

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I was going to post about this earlier but Prof. Chris beat me to it and I think he hit the nailio on the headio. I learned from this build that "cedar" likes scrapers over sandpaper... definitely. Of course it's best to use scrapers anyway but on this one I was feathering the outside of the lower bout with sandpaper and the cross grain action got absurdly wavy.



The back wood on this uke is aromatic eastern red cedar, which oddly enough is evidently not cedar either. This is my personal uke about to be completed. It's made from pieces that didn't make the grade due to being too thin or knots, pitch pockets etc. I made this sucker real thin, probably as thin as 1.5mm along the feathered edges graduated to about .06" in the center, and don't have enough thickness to fix the wavy situation in the cedar but oh well... good enough for me. I bet it'll sound righteous. Like Prof. Chris suggested, I aim to level it a bit with the finishing process.

And that soprano behind it with the old growth redwood top that was air dried for 50 years is getting black back, sides and neck... black and red.

That is just about spot on Prof Chris and Vic D. I will experiment some with both the scraper and applying some finish and then try smoothing again. It will probably be shellac on this one.
Cheers everyone.