Sanding "spalted" beech/birch.

[Munty Scruntfundle]

Hi there. See, using my new vocabulary already!

I'm finding heavily spalted wood a bit of a challenge to sand and finish. I can turn it ok, an unexpected hard spot can be interesting, but the finishing is an issue.

It's the softer spots, the bits that look perfect until you put a coat of finish on, then all the tiny imperfections start to show. I'm talking about very well sanded pieces, in this last case well over an hour decreasing grits slowly, this is because I couldn't get a clean scraped finish, the surface is just too unreliable.

With something like this do you just have to accept the imperfections as part of the aesthetic?

I've thought about mixing sealers with dust and/or glue washes, but I don't have enough of this stuff to ruin at the moment.

Any advice for this unpredictable stuff?
Many thanks.

 

[TopCat 32]

have you tried finishing sanding to about 320 grit then do 2 or 3 coats of thinned sanding sealer (i thin cellulose sanding sealer with thinners about 2 parts SS to 1 part thinners) to " glue "the fibres together in the softer areas then take a very light finishing cut sand again to whatever grit you want, i go to 600 then a coat of undiluted sanding sealer, then de -nib i use 0000 wire wool or 600 grit paper, then wax of your choice

 

[CHJ]

The 'Hardening' routine as per TopCat or a version to achieve similar results is the way to go if the wood is worth the time and effort *.

Sanding in itself is an art, one facet of which is to learn how to do it whilst minimising the uneven removal of softer areas, and it does not need to be spalted wood to need this caution.


* An important factor in selecting wood for turning is developing the art of knowing when it is more sensible to confine a bad piece of wood to the firewood pile, saves a awful lot of frustration and better quality output with enhanced satisfaction.

 

[Richard_C]

I'm pretty new to this and it seems self-evident that the less experience and skill you have with the tools and tool sharpening the more sanding you will be doing. I do lots of sanding.

Is it getting hot while you sand? With some timbers that opens up the grain in soft bits and you end up making things worse. Slow and lots of pauses.

I've just finished a small bowl using some really rough looking brown oak I've had for years. Dusty to turn let alone sand. I used MDF sealer - sort of thin acrylic that's milky but dries clear - before final cut and sand. Takes longer to dry than proper sanding sealer - 30 minutes perhaps (brush it on, have lunch) - but maybe that lets it soak in a bit more and bind things together. My plan was to practice skills and add result to the fire but ended up with a really nice burnished finish with just one application of wax after sealing and sanding so worth keeping.

 

[KimG]

You're always going to struggle if you take a scraper to spalted timber, even a negative rake scraper is going to cause tear outs of the softer wood. Working delicately with a good sharp gouge can minimize this, but rarely will you have no blemishes. My own approach is to get as good a finish off the tool as I can, then I static sand the softer parts (I lock the lathe so the item cannot turn) until the marks are removed, I may do a few passes with the lathe turning at first just to even things down a little and highlight the problem patches (usually end grain), but doing the stationary work until either the blemishes are removed, or are acceptable, depending on the nature of the piece. After that it is a case of working down through the grits using the normal sand while spinning method being careful not to apply too much pressure and cause noticeable unevenness. A lot of what to do comes less from advice and more from experience though, you have to keep trying till you get a feel for for it.