Veneering Tips by Paul Schürch

 

Veneering Tips

For many woodworkers, veneering can be a mystery that is difficult to master, prone to failure and a risky endeavor that succeeds only as long as your luck is with you. Veneer work is becoming more common in the midrange to high-end commercial and residential markets, and many shops incorporate custom veneer work in fixtures and cabinets to bring a higher level of perceived value into the products they produce.

The possibility of selecting from over 150 available veneers to achieve a unique result in veneering, with decorative borders or with marquetry is what attracts us as woodworkers, and can promises potential rewards. Veneering is a good choice for those small to medium sized woodworking shops that are attracted to the art of veneering. For those that are only into the financial gain veneering has to offer, subcontracting the veneer work to a reliable shop elsewhere may be a better choice. These custom panel manufactures have been supplying well-constructed, finely veneered MDF and plywood panels to larger commercial and custom shops for many decades and continue to produce between 1 and 3 million square feet of veneered sheet goods per day for the North American market.

In today’s modern shop environment, where exotic veneer or unusual decorative panels are desired, the flexibility to successfully press up veneer projects quickly can be a way to enhance what a shop already does.

I have learned certain tricks over the years that can help a project go more smoothly and have given me the ability to fix some mistakes before they can happen.

FLATTENING VENEER

If veneer becomes dried out, buckled, and prone to cracking, it will become necessary to flatten it before it can be worked, cut to size, or be successfully glued to the core. If it is too brittle to work, you can flatten it with the use of a veneer ‘softening’ solution available though Woodcraft, Veneer Systems, Pro-glue or other suppliers. It is a softening agent that will make the veneer more pliable.

Wet the veneer with a light spray on both sides, position the sheets so both sides can air out until solution has soaked in. After about 15 minutes the surface will feel quite pliable, and then set it between two cauls for an hour or overnight with weight on top or in a press to flatten it. I flip every other sheet to locate bumps against bumps, and valleys against valleys to assist the flattening process.

Gradually increase the pressure on the press so the veneer has time to adjust into its new shape. After a few hours, unclamp and begin the process of drying out the veneer.
Dry the veneer out to the proper moisture content by putting each sheet into the press between two layers of paper. Change the paper after a few hours and once again the next day. A great source of absorbent paper is the end rolls that you can obtain at your local newspaper plant. These end rolls are the leftovers from the 2000 lb. rolls that are used in creating the newspaper you read every morning. (Do not use regular printed newspaper since the ink may stain onto the wood.) Properly drying the veneer may take up to four or five changes of paper over the period of several days. Avoid soaking the veneer in solution or reflattening more than three times, because the glycerin in the solution may compromise the ability of the veneer to be glued down. After the veneer has been successfully flattened, store it between two platens or it will revert back to its previous buckled condition as it dries out. You now have veneer that can be worked, and this is definitely worth the extra effort when you begin cutting and assembling your creative pattern.

A CIRCULAR SAW FOR JOINING VENEER

The traditional method for joining long veneer edges to be taped into larger sheets was to ‘shoot’ the veneer edges with a jack plane on its side and holding the veneer with a pinch jig. You can cut along a straight cutting edge with a properly sharpened hand veneer saw, or by cutting the veneer on a table saw using a veneer clamping sled.
A production shop may have an 8’ to 16’ veneer guillotine or large veneer sawing machine if sheet goods or custom casework are constructed on a regular basis, and I have found that a Festool circular saw using a negative rake saw blade riding in the 9’ guided straight fence guide, is useful for cutting long sheets of veneer for straight line joining. The trick is to set the stack of veneer to be joined (one to four sheets at a time) with the depth of the saw piercing 1/8” into a sacrificial plywood or MDF underlayment, and running the saw slowly along the full length. The veneer should be flat enough that the guide can trap it securely. If not, flatten the veneer first, or if splintering occurs, gum tape the joint prior to cutting the edge. This will create long clean joints that can be drawn together first with blue tape, then gum tape the show side. I prefer to use 25 to 30 gram (thinnest available), solid (no holes) water activated hide glue gum tape, applied and brushed down with a fine bristle brass brush. Two or three layers of this tape can still be easily removed with scuff sanding and water, after glue-up. Helpful to know when multi stage assembly of decorative panels is necessary.

PATCHING BURL TOGETHER

Quilting small pieces of burl together or removing defect areas to create a larger panel can be done with a ‘squiggle’ cut done on a scroll saw.

Occasionally burl veneer sections are not quite big enough to cover the whole panel surface. Making a larger panel is done by overlapping smaller burl pieces over the main sheet edges to make the size I need. Select out the most flowing pattern from one grain into the other. The eye tends to follow straight lines, and will not see a randomly undulating line where it is least expected, hence the squiggle cut.

This technique can also be used to remove defects in the veneer, and is easily done on the scroll saw. With four-way book matches all four sheets can be done at the same time. This is accomplished by stacking the four indexed main sheets together on top of four indexed scrap pieces, securing them together with pin nails, and cutting through all eight layers at once. The scroll saw cut will undulate through the burl, loosely following the grain, and be virtually invisible when finally joined together.

A good way to replace small open knots in a sheet of burl is to clean the hole out, and cut another piece of veneer (with an intact knot) to fill the void, and will not be noticed as a patch.

STUFFING THE GAP

One of the neatest tricks I have discovered for filling small minor gaps is by ‘stuffing the gap’ with the surrounding veneer. Darker wood joints gaps up to 1/16” can be filled in this way. This process is done from the glue side, and the show face must have a piece of 3M 2090 blue masking tape on it to do this trick. I always work on the glue face of the veneer and never on the show face Stipple or kerf the veneer with your chisel along the grain, pushing veneer over to close the gap. What you are really doing is spreading the veneer adjacent to the gap to fill the void, and as long as the stippling is done with the grain, it will not be visible when the glue up is complete. After stippling, wipe a drop of white PVA into the stippled area, scuff sand the glue off the surface, and tape the show face with gum tape.

SCUFF SANDING

After the glue has fully cured, it is time to scuff sand the veneer surface. This can be accomplished by hand block sanding with 80 grit sandpaper, a 4 x 24 belt sander, or a stroke sander. This step is to surface the veneers to a common thickness, using the tape as a sanding guide. Work the entire surface evenly, taking care not to round over the edges, or sanding too much in one area. You know the veneer is quite thin, and burn throughs (sanding through the veneer into the core) can happen very quickly, are emotionally painful and very hard to conceal or correct. Baring a major glue failure, this is the only time in veneering where ‘fatal errors’ can occur. The trick is to sand the surface until the gum tape is almost gone…. If there is still a bit of tape showing, there is still some veneer underneath it…. You are finished scuff sanding when the thicker veneers have no gum tape left, and adjacent thinner veneers will still have a hint of tape on the surface.

I find using a 4 x 24 belt sander using 100 grit works best for quick removal of gum tape if some basic rules are followed:


¨ Always start and stop the belt sander while it is on the panel
¨ Only sand up to the edge furthest away from you
¨ Keep the sander moving to check the remaining gum tape under the sander
¨ Keep the belt clean with a rubber belt cleaner

One of the hardest habits for many woodworkers to break is picking up a sanding machine while it is still running. This may gouge a hole into the veneer as you lift the machine off of the panel. My favorite sander is the Makita 4 x 24 and is reasonably well balanced over the sanding platen. Keep in mind that the sanding platen is only a small 4”x 5” area. You need to apply some pressure down on the front of the sander, and using your hand on the back grip and trigger will hold the sander back from leaping forward.
When the whole panel is uniformly scuff sanded, flood the panel with water for a few minutes and scrape off the gum tape residue with a putty knife. The water will loosen the gum tape and also serve as an adhesion test, to find out if the glue-up was successful. It is a bulletproof test and a necessary one, since bad adhesion will show up at some point in the future if not dealt with now.

REPAIRING VENEER BUBBLES

It is so much better to find and repair veneer bubbles right after glue-up, rather than after the furniture has been finished and delivered.
Some of the reasons for glue failures causing veneer bubbles include using old glue, poor mixing, oil or wax on the core, too little or too much glue, not enough pressure, improper mixing, too cold during the cure cycle, a spot of glue wiped off during handling, veneer laps, foreign matter trapped in the glue line, and cauls that are not clean and flat.
Polyurethane glues seem to work well for repairing urea glue delamination problems, and can pull a project back from the scrap heap. Testing for delamination problems is done by flooding the veneer panel with water to see if a visible bubble appears. If there is a problem, the veneer expands forming a bubble. This is the best test for proper adhesion, since it is not a question of whether the veneer will delaminate in the future, just a question of when. After the panel dries out, fixing a veneer bubble is done by gently slitting the bubble along the grain with a scalpel so that moisture cure polyurethane glue can be injected or ‘stuffed’ into the crack and massaged into and over the delaminated areas. Clamping with a flat block, shielded with a piece of polyethylene plastic, will force the expanding glue down into the veneer, adhering the veneer to the core. This method will yield an invisible repair if done properly.

FILLING GAPS AFTER GLUE-UP

I tend to first use a light 2 lb. cut shellac for sealing the panel. With this slightly shiny surface, I can see all the imperfections in the veneer joints. The shellac sealer will not interfere with just about any type of top finish coat you use, and the putty will not stain or smudge the wood grain when applied into the cracks. I use creamy, acetone-based putty for the visible veneer voids or any marquetry saw kerf cuts not filled during glue-up.

I use Famowood No. 1 professional tinted filler after a panel has been finish sanded with 220 grit and a light coat of sealer has been padded or sprayed on. Press or wipe the filler into the joints using a flexible putty knife (you may need to add some acetone to get the consistency right) then sand the panel with 220 to remove any putty residue.
For a top coat, I use lacquer, French polish, conversion varnish, tung oil, wiping varnish, linseed-polyurethane mixtures, canned Deft, and water-base or clear acrylic lacquers. They all have a different feel but work quite well for veneer. It seems like the veneer soaks up more finish than solid wood, and oily veneers are harder to glue-up and finish compared to solid wood of the same species. If I have a dining table that will be subject to heavy use and possible alcohol and water spills, I will choose conversion varnish or polyurethane over a French polish top coat (which is many layers padded on shellac). That said, my favorite is French polish for giving the wood a clarity, depth, and repairability not found with other finishes.

MITERS FOR BORDERS

The scalpel is indeed the best way for creating clean miter joints on borders surrounding a background veneer skin panel, as long as you cut from the glue face of the veneer toward the show face. The border veneer is taped to the background and lapped over each other at the corner. A scalpel and short straight edge will cut the first then the second layer easily, creating a tight fit. Any open joint can be filled with a spot of white glue smeared into the gap on the ‘glue’ side of the veneer and scuff sanded with 80-grit paper. The scuffing is important so not to ‘size’ the veneer with glue, which prevents the skin from adhering to the substrate.

COLORING THE GLUE

One can assume that tinted glue will hide most open joints up to a 1/32” gap. Lighter woods such as maple will more readily show gaps, so more care needs to be taken to keep the joints clean and true. Alcohol-based aniline dyes, or titanium dioxide powder can shade or lighten the glues color to match the veneer’s color for invisible seams.


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