Thursday, May 24, 2018

Spalted Sweet Gum by Fred Messer - April 2009

Spalted Sweet Gum

I turn a lot of spalted wood.  Magnolia, Pecan, Maple, Sycamore, River Birch, Popcorn Tree, Water Oak, Black Gum, and last but not least Sweet Gum.  I think the main reason is that you never know what will show up in the spalting patterns of various types of wood.  This process can turn a bland type of wood into something else entirely.

Sweet Gum - (Liquidambar Styraciflua) grows from Connecticut southward throughout the east into central Florida and as far west as eastern Texas.  It is a hardwood and old trees will have dark brown heartwood which looks so much like walnut that during the wars a lot of it was used for furniture while walnut was consumed in gunstock production.  If you are going to allow the wood to spault, choose clear all sap white wood.  If you are going to turn it natural pick trees old trees which have broken tops or large knot holes because this allows water to seep down through the wood giving dark brown heart wood.

The two main fungi involved in the spalting process for sweet gum in South Mississippi seem to be Ganoderma Licidum which is called Lingzhi in China and has been used as medicine for over 4000 years and Pleurotus or Oyster Mushroom which is one of the favorite edible Mushrooms in the south.  The various colored lines in sweet gum are formed by various types of fungi most of which I have not identified.  After Katrina a pink spalting has that looks like that in Box Elder has appeared along the coast.  I have seen it in sweet gum and sap cypress.

There are various methods of inducing spalting in wood but the Pascagoula River basin in south Mississippi seems to have an over abundance of Fungi.  All I have ever done is just leave the wood on the ground or in a pile and it and it happens.  The primary spalting which occurs while the wood is in large pieces seems to be black and formed in lines where the spreading fungus from individual spores will not cross into areas where other fungi have already broken down the cellulose.  The various colored secondary spalting occurs during the drying process using plastic bags.  If you wax the roughs less will occur.

Wood Preparation - I like to cut the wood into lengths of about 4 diameters + 16 inches.  The extra 16" is for saw kerf loss and end loss (the end 6" or so will not spalt well and also will check.  Most woods will have better patterns if cut while the leaves are on.  I lay the wood down in the shade and turn it monthly.  The time needed to spalt will vary depending on diameter, wood type and humidity and temperature but is at least 3 months for the smaller logs and a year max for the big stuff.  There should be very little heartwood  in your blanks, the heartwood will not spalt so any blanks with a lot of heartwood should be turned green.  You just have to let it go for a month or two and slice off 6" on one end and check.  When the wood is ready, cut it into diameter length pieces and slice it down the center or cut it cross grain if you wish to turn it end grain. At this point the wood should be rough turned and bagged or waxed if possible. A wall thickness of about ¾ - 1" seems to work well for sweet gum, pecan and magnolia.  Other woods do not warp as much and may be cut thinner. The wax will stop or slow down the spalting process.  If you want the process to continue do not wax but put the rough turned pieces in to a plastic bag remove the pieces every few days and turn the bag inside-out to get rid of the water which will collect inside. When there is very little water in the bottom of the bag take the roughs out and let them dry. I dry them inside in my basement part of my shop where they stay cool.  For the wood to go translucent it has to be very well spalted, soft and very, very dry. 


Chain Saws: I like Huskey's because they seem to start better.  My smallest is a 136 with 16" bar and the largest are 395's with 36" and 40" bars.  Chainsaws are a requirement in hurricane country and I live on the Gulf Coast on the water.  You never evacuate without at least two saws (one for cutting trees and one for cutting the first saw out when it gets pinched) in the truck tool box to cut your way back home.  Ripping chain is nice for cutting down the end grain.  A good chainsaw grinder is necessary if you do much cutting as files are ok for touching up a chain but you can not keep the proper angles long.  Remember a chainsaw is like a snake, mess with them much and you will get bit and one which is dull is very dangerous. Most of the bigger blanks (up to several hundred pounds) are split and the corners cut off with the saw instead of trying to round them up on the band saw. 

Band Saw:  I have an 18" Jet with a 1" blade for straight cuts and a 14" Delta with riser and a ¼" "Woodturners" blade for circular cutting

Work Holding:  I use faceplates on all blanks for roughing the bottom of the bowl and cutting the expansion dovetail.  Very large pieces I will use a faceplate around a dovetail for hollowing out the center and then use the dovetail for returning.  I have found that expanding smooth dovetail jaws and very slow speeds (most of my roughing of spalted wood is at speeds from 30 - 200 RPM) will safely turn very large blanks.
Compression works well on end grain work but for side grain expansion plus super glue works far better for spalted wood.  Smooth jaws work far better for expansion.  My best chuck is the Axmister with 4" smooth jaws, the second best is the 5 ½" Vicmark with smooth jaws.  I use the Oneway Stronghold more since they now offer smooth jaws.  Vicmark offers the largest pie jaws (19") another plus for Vicmark chucks.

Turning Tools:  By the time the wood is ready to rough into bowls it is still damp and very soft. If the wood is dry it is hard to turn.  At low speed, rough the bowls into shape using a ½ inch bowl gouge as a large ¾ or 1 inch gouge may cause breakout of the expansion dovetail.  You can use a large gouge while the blank is on a faceplate but even a ½ inch may be too large while on the chuck.  I use a 45 degree angle for both roughing and finish. Do not worry about a smooth finish at this point.

Pre-finishing:  When the roughed out blank (3/4 to 1 inch has gone through the sacking and drying process it may need to be trued up slightly by holding the out of round blank with pie jaws or a vacuum chuck and held by the top edge while the dovetail is trued first.  After the dovetail is trued up it is placed in the chuck and the rest of the bowl trued up.  This truing need not be exact because after drying the blank is now ready to start the soaking process in 1 part boiled Linseed oil and 2 parts Mineral Spirits.  After the first overnight soak in the oil it is removed and put outside in the shade and dry for a day.  You can now true up the bowl to close to the final thickness.  You will find that the almost impossible to turn wood will now turn easily.  After turning, sand the wood for the first time with 100 grit paper. There will be no dust as the oil/dust mixture is a slurry.  The blank can be resoaked several times with drying for a day followed by resanding and resoaking.  When you have the piece like you want, put it up inside in a cool place and let it dry as long as it takes for the finish to get dry.  At this point you should have no finish on the wood only in the wood.  The blanks may now be left in this stage as long as needed prior to final finishing.

Finishing:  After the blank has dried, sand down to 400 grit and finish with steel wool.  The final finish I generally use is Tung Oil.  It should be applied in very thin coats with a small pad of nylon.  The more and thinner the layers you apply the better and harder the finish will be.  I have used just about any kind of both oil and water based finishes made and they all seem to work.  Just go for the look that you like. You can leave only the Linseed Oil sanded down to 400 grit and steel wooled till smooth.  This is a very soft finish but allows for easy refinishing as you only have to sand scratches smooth after applying a light coat of linseed oil.


1.    Rough Log:

2.    Half Log:

3.    Chain Sawed Hex Half Log:

4.    Initial roughed:

5.    Drying in bags:

6.    Returned:

7.    Final Drying:

8.    Soaked in Linseed oil:

9.    Returned:

10.    Final finishing With Tung Oil:

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