Many of us refinish audio gear with whatever is handy and don't really give it a second thought. I offer these learnings in the hope to save some grief in our community.
16 years ago I was blessed beyond measure by the wood gods and obtained 3 large planks of Koa from a retiring cabinet maker. By large I mean immense 9 ft long x 2 ft wide x 2 in thick. He got them from a guy that brought them over from Hawaii in the 60s when you could still get it. He only wanted $300 making this the score of a lifetime. I used 2 of them to make my wife an 8 ft dining room table. These 2 boards had a retail value of at least $6,000 at the time. I don't say this to boast, only to point out that this is serious wood, it deserved my best and I came up way short.
I put my heart and soul into this table, it's mahogany base and a set of 8 mahogany chairs to go with it. The finish took weeks. Hand-rubbed BLO (Boiled Linseed Oil), a barrier coat of de-waxed shellac and several sprayed top coats of Enduro water-borne poly. It was absolutely stunning. The suite 'debuted' with the whole extended family over for our traditional spaghetti dinner before the candle light service at church. Much to the horror of all the warm moist paper plates stuck to the table and the finish was ruined.
Lesson 1 - Read The Label And Test In An Inconspicuous Place. I waxed the table with dark Briwax which I later learned uses toluene as its solvent. Toluene softens water-borne finishes. Had I tested the wax on the bottom and taken my time things would have been very different. The sticky mess required bagging the room in plastic and wet sanding with a pneumatic RO sander. I was so disgusted with myself I only stripped the top which brings me to ...
Lesson 2 - Always, Always Finish Both Sides Of Solid Wood Exactly The Same Way. Wood is dead as dead can be, it doesn't breath, but it does react with it's environment and takes on and releases moisture with changes in humidity. Unequal finishes affect the rate at which this occurs. More moisture content swells the fibers and less moisture constricts them. So I took a short cut and I refinished the top with a wiped oil/varnish blend. I though "close enough", but time wood tell (sorry). The top didn't have nearly the same atmospheric moisture resistance as the bottom so over the years the table top cupped - a whopping average of 7/32". That table was dead flat when I made it. After glue-up I took it to a shop and they ran it through a 48" wide belt sander. Nobody else noticed the cupping, but it's been chapping my hind-end at every meal for countless meals over the years.
The straight edge is 2" wide.
Today was the day to right this old wrong and take care of unfinished business. Armed with a couple of RO sanders, a Fein Dust Extractor and a bunch of sanding disks it got sanded down to bare wood. To further demonstrate the differences in the finishes the gentle Makita palm sander took the top down with (5) 320 disks.
The poly finish on the bottom took the beast mode Bosch and the rest of these spent disks starting with 180 grit and followed with 220 before going back to the Makita with 320. Which is brings us to ...
Lesson 3A - Don't Skip Grits and 3B - Use Dust Extraction. More consistent scratch refinement, longer disk life and way less mess. I would not dream of sanding like this in the house.
Lesson 4 - De-Waxed Shellac Is The Be All, End All When It Comes To Barrier Coats. BLO and water-borne top coats mix just like, err, well, oil and water. W/B top coats are far healthier to spray, but they leave the wood looking dull. BLO brings out the beauty of the wood, but W/B top coats won't stick to it. Bullseye Superblond Shellac is key to having your cake and eating it too. How good does it seal? This next picture blew my mind.
I thought the dark spots in the middle were missed finish until I smeared them with my hand. WTF? That is 16 year old BLO weeping out of the end grain of the under bevel surface. Evidently BLO is classified as a non-drying oil for a very good reason. Even when cut 1:1 with mineral spirits and dosed with a couple shots of Japan Drier.
Lesson 5 - Working Wood Takes Great Patience - As Tom Petty said, the waiting is the hardest part. All I can (should) do now is give nature time to do it's thing and let the open wood acclimate and reach equilibrium. If it was thinner I could use a steam iron on the dry side to speed things up, but this is 1 5/8" of very dense wood and I have to follow Lesson 5 to the fullest. I'll know it's done when the table is flat again. Then I can open the can of Sam's oil/varnish blend and let the magic out.
16 years ago I was blessed beyond measure by the wood gods and obtained 3 large planks of Koa from a retiring cabinet maker. By large I mean immense 9 ft long x 2 ft wide x 2 in thick. He got them from a guy that brought them over from Hawaii in the 60s when you could still get it. He only wanted $300 making this the score of a lifetime. I used 2 of them to make my wife an 8 ft dining room table. These 2 boards had a retail value of at least $6,000 at the time. I don't say this to boast, only to point out that this is serious wood, it deserved my best and I came up way short.
I put my heart and soul into this table, it's mahogany base and a set of 8 mahogany chairs to go with it. The finish took weeks. Hand-rubbed BLO (Boiled Linseed Oil), a barrier coat of de-waxed shellac and several sprayed top coats of Enduro water-borne poly. It was absolutely stunning. The suite 'debuted' with the whole extended family over for our traditional spaghetti dinner before the candle light service at church. Much to the horror of all the warm moist paper plates stuck to the table and the finish was ruined.
Lesson 1 - Read The Label And Test In An Inconspicuous Place. I waxed the table with dark Briwax which I later learned uses toluene as its solvent. Toluene softens water-borne finishes. Had I tested the wax on the bottom and taken my time things would have been very different. The sticky mess required bagging the room in plastic and wet sanding with a pneumatic RO sander. I was so disgusted with myself I only stripped the top which brings me to ...
Lesson 2 - Always, Always Finish Both Sides Of Solid Wood Exactly The Same Way. Wood is dead as dead can be, it doesn't breath, but it does react with it's environment and takes on and releases moisture with changes in humidity. Unequal finishes affect the rate at which this occurs. More moisture content swells the fibers and less moisture constricts them. So I took a short cut and I refinished the top with a wiped oil/varnish blend. I though "close enough", but time wood tell (sorry). The top didn't have nearly the same atmospheric moisture resistance as the bottom so over the years the table top cupped - a whopping average of 7/32". That table was dead flat when I made it. After glue-up I took it to a shop and they ran it through a 48" wide belt sander. Nobody else noticed the cupping, but it's been chapping my hind-end at every meal for countless meals over the years.
The straight edge is 2" wide.
Today was the day to right this old wrong and take care of unfinished business. Armed with a couple of RO sanders, a Fein Dust Extractor and a bunch of sanding disks it got sanded down to bare wood. To further demonstrate the differences in the finishes the gentle Makita palm sander took the top down with (5) 320 disks.
The poly finish on the bottom took the beast mode Bosch and the rest of these spent disks starting with 180 grit and followed with 220 before going back to the Makita with 320. Which is brings us to ...
Lesson 3A - Don't Skip Grits and 3B - Use Dust Extraction. More consistent scratch refinement, longer disk life and way less mess. I would not dream of sanding like this in the house.
Lesson 4 - De-Waxed Shellac Is The Be All, End All When It Comes To Barrier Coats. BLO and water-borne top coats mix just like, err, well, oil and water. W/B top coats are far healthier to spray, but they leave the wood looking dull. BLO brings out the beauty of the wood, but W/B top coats won't stick to it. Bullseye Superblond Shellac is key to having your cake and eating it too. How good does it seal? This next picture blew my mind.
I thought the dark spots in the middle were missed finish until I smeared them with my hand. WTF? That is 16 year old BLO weeping out of the end grain of the under bevel surface. Evidently BLO is classified as a non-drying oil for a very good reason. Even when cut 1:1 with mineral spirits and dosed with a couple shots of Japan Drier.
Lesson 5 - Working Wood Takes Great Patience - As Tom Petty said, the waiting is the hardest part. All I can (should) do now is give nature time to do it's thing and let the open wood acclimate and reach equilibrium. If it was thinner I could use a steam iron on the dry side to speed things up, but this is 1 5/8" of very dense wood and I have to follow Lesson 5 to the fullest. I'll know it's done when the table is flat again. Then I can open the can of Sam's oil/varnish blend and let the magic out.