Deal wif defects


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Deal wif defects

  1. 1. Furniture finishing Dealing with defects DEALING WITH DEFECTSIn my cabinet-making and finishing business, we always allow 20% stockoverage in our quotes for furniture. This is to accommodate various defectiveareas in the rough stock that most customers object to: knots, internal checksand splits, worm holes and sapwood. While it can be argued amongwoodworkers that these areas are what gives wood a special type of beauty, thepublic usually regards them as defects, so I err on the side of caution and try todesign around them.The last commissioned piece I built was a cherry settle and my wood suppliersaid that he had approximately 70 bd. ft. of cherry that he would give me adiscount on since it had more that the usual amount of sapwood, knots and endchecks. After extracting the clear stock for my customer,I figured there was just enough stock left to build a smaller version for myself.The only problem was how to deal with all the splits, knots, sapwood and wormholes. In this article Ill show you how I turned 30 bd. ft. of stock normallydestined for the scrap box into a cherry settle.Before starting with the various techniques I use, I would like to impress uponreaders the value of having a clear, detailed scale drawing of the piece you arebuilding as well as a detailed cutting list. This will help you to visualize how thedifferent parts of the project relate to each other and which parts show the most.A detailed drawing is also essential for the first method of dealing with defects,which is to simply design around them.Designing Defects OutProbably the easiest way of handling defects is to incorporate them into a part ofthe design so that they are hidden. This is what I did with the knots on the backof the settle. Many knots that seem large on one side disappear almost entirelyon the other side of a 3/4" board, so putting defects on a back or non-show sideworks nicely. However, be sure to take into account that furniture gets movedaround frequently, so what may be a side facing a wall one year may be a showside later on. The large knots on the oak legs in the photo of anothercommissioned piece were dealt with in a similar manner, I designed them so thatthey faced to the inside of the side table. Once the piece is completed with thedrawer, they will never be noticed. Because this weak area is near the location ofa mortise, I filled the large knot hole with a polyester filler (like Bondo) to give itstrength, then touched it up with pigments and shellac. (This will be discussedlater.) Wisdom Management Services (M) Sdn. Bhd. 1
  2. 2. Furniture finishing Dealing with defectsAnother way to handle large defective areas is to place them in the initial layoutso that they fall on an area that will be cut out. This is what I did with a largeworm-holed area on the right side of the settle. Most of the holes fell in the areathat I cut out for the arm. A few holes were left, but they were filled and touchedup later.For the back panel below the seat, I saved all the sapwood cut offs and smallwidth pieces and glued them up to make a large 8" wide piece. This panel isnever seen when the seat is down so I wasnt really worried about theappearance of this piece. However, because it is a structural part that supportsthe weight of the person sitting in the settle, I avoided wood with splits, checks,and large knots. (This is an important point to remember, any part that is a load-bearing piece should be as defect free as possible. Sapwood does not affectstructural integrity.)Dealing With SapwoodI dont always regard sapwood as objectionable, rather, I really like the sharpcontrast between light and dark, especially on dark woods like walnut androsewood. But you have to be careful that it doesnt interrupt the natural flow andform of the piece, like the sapwood on the front panel of the settle. I didnt noticethis when I was building the piece, because in freshly cut cherry, the distinctionbetween sapwood and heartwood is not that obvious. After a month however, thecontrast became very obvious when the heartwood darkened. Its wise to waitanyway before correcting this problem, so that you can match the sapwood to thecolor of the heartwood after its darkened.I handled this problem by darkening the sapwood using alcohol soluble dyes.Using a fine pointed red-sable artists brush, I mixed several dye colors togetheruntil I got the sapwood to blend in with the heartwood. I find that working withseveral layers of slightly different thinned colors gives a much better final colormatch than trying to hit the color all in one shot. Once I padded on several morecoats of shellac, the sapwood was hardly noticeable.This technique can also be used on pieces that are unfinished. Here I use water-soluble dyes, because they are easier to handle and do not dry so fast. I findspraying the dye with a small touch-up gun works best. The trick with thistechnique is to anticipate what the wood will look like when its finished, so I findwetting down the wood with water first will give a close approximation of what thewood will look like finished. This technique also works if youre planning onstaining the wood with a pigmented wiping stain like Minwax. The sapwood willliterally disappear after Wisdom Management Services (M) Sdn. Bhd. 2
  3. 3. Furniture finishing Dealing with defectsKnotsI really like knots, and particularly, the area around knots. As mentioned above,areas that will be subjected to stress should be free of knots but other areas, likethe upper right top of the settle are open ground for incorporating knots. The areaaround a knot usually has very swirly dense grain, so care should be taken whenfinishing, and the use of hand scrapers is suggested. Knots that have largecracks or are loose need to be consolidated so that they do not fall out or chiplater. I use several techniques for this depending on how bad the knot is.Where large cracks have developed, or where large pieces of the knot aremissing, small pieces of wood should be glued in with epoxy tinted withpigments. This is especially true of knots in walnut. Mix some dry pigmentpowders into five minute epoxy and glue in small pieces of wood cut into smallenough pieces to jam in the cracks. (Tip -- rather than mixing the epoxy in thesuggested 1-1 ratio, I mixed the epoxy in a 1.5 resin to 1 hardener. This results ina much harder glue that scrapes better when fully cured). When completelycured (24 hours) cut down the wood slivers with a flush cutting saw. Notice myhomemade one in the photo. Its nothing more that an old hacksaw blade with theset banged out on an anvil. I wrap tape around one end to act as a handle. ThenI finish the surface with a hand scraper.With smaller cracks, or just to consolidate a loose knot, cyanoacrylate glue canbe used. I use the water-thin viscosity because it actually wicks into the cracks bycapillary action, but I usually put tape on the other side to keep the glue fromseeping through. If you use the accelerator sold with these glues, the area canbe scraped and sanded immediately. Dont sand before the glue is completelycured, because the sawdust will mix with glue and form a light filler that doesntlook appropriate with the dark knotWith large knots that are missing or are powdery and brittle, I usually scrape outthe loose pieces and fill the area with a catalyzed polyester filler, such as thosesold in auto-body stores. If you buy these type ask for white hardener since redhardener is too strong a color when dry. These fillers also dry quickly, and I sandthe area flush after about an hour. They also have the advantage of notshrinking, which is what will happen with water-based fillers. When dry, I rubsome pigmented wax sticks over the area to fill in the small imperfection andbubbles on the surface of the filler and then blend the area into the rest of thewood area using shellac and dry dyes and pigments. As mentioned above I try tohide these large knots as much as possible in the Wisdom Management Services (M) Sdn. Bhd. 3
  4. 4. Furniture finishing Dealing with defectsCracks and SplitsDuring its life, trees may be subjected to growing stresses which cause internalcracks and splits in the structure of the wood. This is known as reaction wood.This is different from end checks and cracks at the end of the board which formas the board dries. These should always be cut out. On the other hand, cracksand splits in the center of an otherwise good board can be filled with dark tintedglue which has a nice aesthetic look. Very small cracks can be filled with water-thin super glue like "Hot Stuff" sold by Satellite City. Simply hold the tip of thedispenser against the and the glue will wick into the crack. Tape the other side ofthe board if the crack goes all the way through. When the glue dries it will lookjust like a grain line and blend in perfectly. If you dont want it to appear dark,start sanding with 100 grit sandpaper before the glues dries. Doing this kicks upsome sawdust and push it into the crack along with the glue and dry to almostthe same color as the wood.For large cracks, I use the same technique as the epoxy technique describeabove for knots. Using the dry colored pigments, you can tint the epoxy light ordark to create the effect that you want. Several applications may be in order,because the epoxy will shrink slightly as it dries. The gap-filling advantage ofepoxy is that it also strengthens the weakness in the board caused by the crack.This is what I did on the left side of the settle, where long cracks went right intothe wedged through tenons. The tenons were a tight fit and the glue-filled crackstayed put when I drove the tenon home during glue-up.Worm-HolesI cant say that I like worm holes so I usually like to place them on areas that willbe hidden or cut out entirely. The other disadvantage is that they severelyweaken the wood, so care should be used when using boards that are badlyworm-ridden. Several techniques can be used, but I like to fill them with tintedepoxy and then touch them up with shellac and dry powders to blend them intothe rest of the piece. You can also use a water-based filler and then tint themwith the dry colors. They dry lighter than the color when wet, so you may need toexperiment a bit to get the feel of this technique. The filler I made dried too dark,so I had to lighten the dried filler up with shellac mixed with dry pigments.Another quick and easy technique for worm holes are pigmented wax sticks soldby several suppliers like Behlen or Mohawk. Simply push the wax into the holeand then scrape off the excess with a wooden chisel like in the photo. Thensmooth it level with the paper back of some lightweight sandpaper. Contrary towhat you might think, most finishes can be applied over the wax, as long as thearea isnt too Wisdom Management Services (M) Sdn. Bhd. 4
  5. 5. Furniture finishing Dealing with defectsThe extra time I put into fixing up the left over stock for the settle was worth it. Ifigured that I saved over 100.00. Thats a good enough reason for me to try andsave it from the kindling bin. It may take a little extra work, but my wallet sure feltthe better for Wisdom Management Services (M) Sdn. Bhd. 5
  6. 6. Furniture finishing Dealing with defects Preventing Warping and Splitting of Hollow Wooden FurnitureAlmost everyone is familiar with a piece of wooden furniture that, in use, lastsmany many years, even centuries. As soon as that piece becomes dis-used --emptied, and put into storage -- it suddenly undergoes some dramatic changes,including warping and splitting. An understanding of why this is so can be appliedto prevent damage to pieces of wooden furniture, particularly those stored inconditions with little or no environmental controls.Splitting and warping in wooden objects is often attributed to an incorrect (toolow), or fluctuating relative humidity (relative humidity is an expression of howmuch moisture the air is holding, compared to how much it could hold at a giventemperature). This sounds reasonable, until we consider furniture -- we know,from experience, that even furniture in use may be exposed to long periods ofvery dry conditions (i.e. during a Canadian winter), followed by very moistconditions (i.e. in the summer). The shifts between these extremes can, in someclimates, occur fairly quickly -- and yet, many armoires, dressers, and otherhollow furniture exhibit no ill effects.Studies done by researchers at the Canadian Conservation Institue in Ottawaindicate that the key is not in the fluctuating relative humitidy, but rather in howquickly it affects the furniture. Wood has some "plastic" or "visco-elastic"properties, meaning that it can "give" in response to stresses, provided that thosestresses are gradual (imagine bending a stick; if done with a slow and gradualapplication of force, the stick will bend a fair bit before breaking. If bent suddenly,the stick will break sooner). In general, splitting of rigid, constrained organicmaterials (such as wood) becomes probable when the relative humidity drops25% to 50%. Note, however, that if the drop occurs over several months, a pieceof furniture may be able to survive a 40% drop without damage; if the drop inrelative humidity occurs over one week, then damage may occur after only a25% drop.The response time of the wood to changes in relative humidity can be lengthenedto help minimize damage. For a closed chest of drawers (in the test case, 5 high,40" wide, 20" deep; wood thickness 3/8" average), response time is lengthenedfrom 6 days for unfinished wood, to 8 days for wood coated with a light varnish.Most furniture, however, has already been finished; as well, a difference inresponse time of a mere 2 days is not sufficient to prevent damage.The most dramatic difference in response time occurs when the furniture is keptfull of textiles. The response time of the chest of drawers with a light coat ofvarnish is 8 days when empty, and 60 days full of textiles. Thus, the textiles Wisdom Management Services (M) Sdn. Bhd. 6
  7. 7. Furniture finishing Dealing with defectsas a "buffer" to the changes in the relative humidity, allowing the wood to reactover a longer period of time. This, as already stated, will prevent damages.It is important that the textiles used be made of natural, absorbant fibres (such ascotton), and not be coloured (there is always the danger of colour transferringfrom the coth to the wood). Old, white terry-cloth towels are excellent for this. Donot put the textiles in plastic bags before storing them inside the furniture, as theplastic will prevent the "buffering" that you are after! As well, do not store thefurniture with doors or drawers open, as this also decreases the effectiveness ofthe textile "buffering".Simply storing your furniture full of textiles will help prevent splitting and warping-- damages caused by too-rapid changes in relative Wisdom Management Services (M) Sdn. Bhd. 7