Working with Cracked Timber

Alan Wasserman looks at using timber with small cracks and similar imperfections.

I am constantly searching for the solution to using and resolving the issues connected with cracked and otherwise imperfect wood. This search has taken me from viewing almost every DVD on the market, researching and reading every article written (of modern day) to questioning constantly (to the point of annoyance, I admit) the Masters and others on their solutions. There are legitimate reasons (or excuses) for this endeavour.

When it comes to turning and working with some timber, it is not always obvious the timber is cracked or flawed to start with. Also, you may see a crack or imperfection at the start and not be wholly sure if it can be removed or if it is bigger than you think it is. The full extent of such things are often only revealed when turning the timber. Then you are faced with having spent time truing up and shaping and either finding a split of blemish, or creating a crack or blemish by aggressive sanding, which causes too much heat, in turn causing the crack(s). Blemishes and flaws can create great design opportunities, but you may have to look at other ways of working with the flaws to fully explore them. 

I am always asking myself why am I working with imperfect wood? The answer for me is because it is fun, challenging and creative. Also, I have discovered over the years that my charm has not been effective on humans, so I now apply it to imperfect wood. 

Safety

I cannot stress enough that the primary consideration in working with, what can only be described as, less-than-perfect timber is that of safety. If you have any doubt about the integrity or cannot effectively mitigate the risks of working with a piece of wood, please do not turn it.

• A piece of work, approximately 330 x 150mm once flew off my lathe, hit my mask and shattered the mask into pieces (not even a scratch on my face!). It then proceeded to hit me in the upper chest (the force throwing me to the ground) and then the errant piece ended up stuck in the ceiling, five metres in the air. Clearly, had I not had my face mask on I would not be writing this article; so please heed and always wear properly certified full face and head protection.
• Wear some form of properly certified dust mask to deal with wood dust and similarly rated particulates, but also consider a suitably rated mask for use when dealing with potential chemical fumes when using fillers and finishes. You may need to use different cartridges for turning and using finishes.
• Nitrile/chemical resistant gloves are also a must when mixing epoxy and using some types of finishes.
• Suitably rated eye protection is also needed.
• The use of an appropriate filter and correctly rated extractor is a helpful tool during the application of various noxious substances.
• Cutting wood to size often requires the use of a bandsaw. Make sure your hands and fingers are out of the way of the line of cut and ensure the piece you are cutting has a relatively flat surface that will be resting stably on the bandsaw table during the cut.
• Since dealing with small cracks and fissures might involve the use of rotary carving tools and such-like, make sure you have read the instructions before working with them, wear protective gloves when using them and keep hands, fingers and body parts out of the way of the direction of cut.

Tools

I use a variety of tools. Of course the standard turning tools, of which gouges are the primary tools for shaping the wood and scrapers for refining, but for dealing with the cracks and so on I use a combination of dental picks, power carving tools (typically rotary ones with burrs and cutters) to suit the job and can be used to deepen, widen and cut across so you can stitch and fill, etc. 

In addition to these tools I use epoxy, two part fillers, PVA, cyanoacrylate (CA) adhesives and other resins in conjunction with timber, shavings, dusts and powders of various sort – including wood, metals and foodstuffs, e.g. rice, pasta, eggshell, coffee – to fill and stitch with. Note the welcome card in the photograph; it is a piece of plastic and is a good spreading device. Any thin flexible plastic will do, so old hotel key cards, credit cards and such-like will be useful to spread the filling mixes in the voids and cracks.

What we can do with cracks and similar blemishes

Cracks, splits and similar faults and other blemishes can be treated in various ways. Of course, one has to decide what is right for the given piece one is working on, and it should come as no surprise that not everyone thinks the same as how best to proceed. The most commonly routes for dealing with them are as follows:

• Leave the imperfection as is or use just a slight dress up. Many people like the natural look and this is an option well worth exploring. But remember the bigger the void, the bigger the problem with turning it due to loss of integral strength within the wood, so be careful.
• Highlight or accentuate the feature. Highlighting an area or ‘distractions’ such as beads and colouring can add another element that is well worth exploring.
• Another option for larger voids is to insert a very thin flexible mirror on the inside – some people place photos. I am sure you can think of other options to highlight or work with larger voids. Here (see overleaf) you can see my grandson in a mirror placed on the inside of this piece.
• Some people have drilled holes along each side of a large crack and then used leather to stitch the piece together. Other people stick to using metal clips running across the gap and some people cut slots across the gap and fit in contrasting wood stitches. Some people even use biscuit jointers and use wooden biscuits to do the same. Wooden stitches can prove to be very visual and highly effective.
• The size and location of your crack or hole may force you to either throw the lump of wood into the fire pile, or attempt other salvaging/design techniques. In reading Decorating Turned Wood by Liz and Michael O’Donnell, I began cutting and then colouring some of my turned projects to correct imperfections in my projects. Imperfections can be removed by power carving, or hand cut using a coping saw to create your preferred form.
• Pyrography is a great tool to mask or redesign imperfections. If you are not artistically inclined, source legally free-to-use designs and use those as a starting point for exploring pyrography.
• Another option for larger voids is to use some sort of filler to bridge the void – this can be tricky if large areas are involved, but is a very common one for dealing with small cracks and voids. In truth, due to movement of the wood and differential expansion and contraction rates, cracking is not common when using fillers to fill very large voids. Experimentation is well worthwhile. 

Typical adhesives and fillers

There are numerous option adhesive and filler-wise and you can experiment to your heart’s content. Here is a few commonly used options that will get you going:

Two part – liquid-epoxy resins can be used to bond and fill gap and cracks. The beauty is that these can be mixed with crushed stone, shell, colours beads, solid coloured resin beads and chips, wood dust, metal powders and filings – depending whether you want a uniform metal look or a grainy look – and much more to create different visual appearance. If you want to explore using metal powders for colour and fill, I recommend you look at: Ted Sokolowski’s DVD, Metal Inlay Techniques.

It is worth noting that two-part liquid epoxies come in various viscosities and colours. It is worth bearing in mind that clear ones can often be coloured with powder pigments and dyes too. I found out when using artist oil paints to colour epoxy resin that if you mix the colour first into the resin until you reach your desired colour and then mix it together with the hardener, this process will create a true colour. 

Ground coffee grinds – which will match most barks and knots, perfectly – can be mixed with epoxy resin to create this decorative filler. Some people use fresh coffee and others make use of used coffee grinds that are then baked in the oven and used in conjunction with with either epoxy or CA adhesive.

Two part epoxy putties can be used as stand alone bonding agents and also fillers, or used as a gap filling adhesive and holding agent into which items can be held too. They come in various colours, but can also be coloured by variants stains and dyes.

Stones and rocks can be crushed and broken and ground down to create fillers of varying colours and sizes.

Cyanoacrylate (CA) adhesive is often use as an adhesive to bond, repair and also fill small areas. It can also be used as an agent to hold beads, shells, stones, wood dust and other metal filings and man-made and natural powders and materials in place too. I caution you that CA typically has a darkening effect on most pigments and wood.

Natural timber filler – I had trouble finding extra fine wood filler from either the wood I am working on, or obtaining contrasting shades of wood to highlight a particular imperfection. I tried putting shavings in a coffee grinder and the result was not fine enough for most of my usages, but is worth a tryout. Sanding dust works, but that is very hard to accumulate without mixing in other contaminants. 

What I discovered is that by using a bandsaw to scrape – not cut – across the end grain of a piece of the wood you will end up with fine dust that is useful. While you are at it, make enough passes to fill a small plastic bag, label it and you have started your collection of wood dust. Note that this can be used as it is, but can also be dyed and stained a different shade too. 

Top tip

Go to your upper shelves in your ’shop and scape off the dust into a bag – thank you to Glenn Lucas for the idea. Be aware that irrespective of the colour and shade of your dust, when using CA as your adhesive, the shade will turn darker. 

Acrylic-based moulding paste – another choice of an adhesive/colour mix is the use of an acrylic-based wood moulding paste. The product is Golden Gel Mediums Hard Molding Paste. What makes this product special for us as turners is that it affords the turner an unlimited colour array of acrylic paints to mix with. Being completely water-based, it is also easy to sand. Take enough paste that you determine will fill the crack in question and pick any (unlimited) colour of your choice.  Once mixed, press in the crack and level off with a plastic hotel key. You may have to apply a second coat, but this is not so prevalent as with epoxy based fillers.

Note: Each of these adhesives and fillers mentioned have a different sanding characteristic when in situ and cured. You may have ultra hard filled areas or very soft filled areas so please do experiment in using them on waste wood before using on projects you are currently trying to finish. 

Without doubt the most commonly used method of dealing with small cracks and blemishes are the use of fillers and adhesives whether to highlight, contrast or blend in with the surrounding area. So whether you intend to contrast, accentuate or blend in areas to make them almost invisible, there are the options listed and numerous other bonding agents and adhesives, decorative items and methods to explore which of course give you, the user, far more options than I can explore in this article. 

Prepare the cracks for filling

On most occasions a crack is irregular and typically has wispy wood fibres flowing back and forth in the crack. To ensure that we get a good bond and fill, it is the turner’s job to clean and clear out the torn grain and wispy bits within the crack so that there is a clean seat for the intended filler. While doing this, you need to decide if you need to alter the shape of the natural crack or fissure. You might want to make it bigger, or you might want to add a man-made extra crack of fissure to balance the look of an item.

A rotary carving tool to which burrs and brushes can be fitted help shape and clean up the area to be filled. But likewise, a suitably-shaped carving tool, scalpel, dental picks and such like could also be used. Whatever method you use, make sure you clean up deep enough to get a good amount of space for any filler and adhesive before moving on to the next stage.

Avoiding staining

The next stage of preparation is to avoid staining. OK, you normally fill cracks and blemishes while the work is oversized, but some resins, colours and adhesives can penetrate the grain and pores quite a long way. Most people are using CA, epoxy or PVA-type adhesives in conjunction with some other metal or powdered agents to bond and fill cracks together and these vary as to how far they penetrate and stain. Most of us have learned the staining lesson very quickly when we attempt to save our piece by applying adhesive – usually CA glue – to stop a crack, prior to any protection. Invariably, without the proper preparation, your piece will be stained and sanding may or may not remove it.

A common method used to minimise staining is to cover the crack and the area around it (where unintentional spill of the adhesive/bonding and filling agent will occur) with either full strength or thinned down sanding sealer. That said, sanding sealer can at times darken the wood, so it might be prudent to give it all a coat before filling.

Useful tips and tricks to know

• Experiment with using a contrasting or highlighting filler. If your choice requires CA, after employing the crack and surface preparations mentioned above, stuff the filler in the crack and rub it in with a pointed object. Cover the crack with a slight mound of the filler and then apply thin CA. Let it cure without accelerator (1 minute or less). Some shapes might mean you have no option in order to fill a given surface, but using an accelerator can prevent the CA from penetrating to the right depth and – depending on the type of CA and accelerator used – foam up the CA and also cause it to go white. Note: It is advisable to always overfill the voids and cracks to ensure you can cut to the right bodyline shape.
• If using wood dust/ground wood of the timber being used, after tamping down the filler – to ensure that it is packed well with no voids – and applying the CA glue, before the glue dries, start a light sand with, say, 220 grit abrasive. This blends in some of the natural dust from the surrounding timber to fill micro imperfections. Two applications of this latter process will yield results.
• If you have micro cracks, you could try using PVA or CA and fill the crack with adhesive and sand while the adhesive is wet. This can blend in the filled sections to the main body of the work well with no need for extra filler.
• If you are using two part epoxy resins, only use the quick set versions if you have small areas to fill and you are not using home-made coloured ones. I metioned that if you have to make extra home-coloured epoxy you will be unlikely to get the same colour tone. But critically, If you have a larger void, use slightly longer set versions where possible in order to get the adhesive and fill mix right and properly pressed into the cracks and voids without building up lots of layers.
• If the crack goes right through the wood use painter’s tape on one side as you fill the other. Then reverse the same process to fill everything evenly. If the crack goes through a hollow form, inflate a balloon in the hollow form to create a barrier so the glue/fill will not leak to the other side.
• After using fine metal powders, colours fillers and adhesives of any sort for filling cracks and voids, seal the work with a sealer after turning and prior to sanding to minimise the risk of the fine sanded adhesive/filler dust colour contaminating the surrounding timber.

Conclusion

Use your imagination to test your artistic wonderings and whether you use a biscuit jointer, slice a peach pit, grind up fabric or other materials, use metal, dry rice other fillers to contrast, disguise or highlight and fault or area, or otherwise work with faults it is an interesting avenue to explore. I would be honoured if this article has inspired you.

Further reading