Problems With Wood

The main problem with wood is that it is natural. We have all become so accustomed to man made products designed to perform exactly as we wish and always in the same way, it’s easy to forget that wood is a living material.

As such therefore, the source of the difficulty lies in that fact that timber, even after it’s been cut down, will keep on moving as it adapts to the surrounding atmospheric conditions. On top of this constant movement, we have natural defects that can cause us problems when finishing and fitting. Below I will highlight some of the main problems and what can be done to prevent or prolong the life of the timber around your home.


A knot is where a branch was connected to the tree. There are two different types of knot, a live knot and a dead knot. A live knot is usually lighter in colour and will generally never fall out. A dead knot is darker and can fall out leaving a hole which can have an effect on the strength of timber. Knots are more common in softwoods like pine. These coniferous trees have many branches growing along the length of the trunk, creating knots.
Knots can enhance the appearance of a usually plain timber and when varnished or stained can look quite appealing. The main problem with knots is sap seeping out of them.
Knots can enhance the appearance of a usually plain timber and when varnished or stained can look quite appealing. The main problem with knots is sap seeping out of them. If you paint, stain or varnish over a knot without first treating it, you could end up with a stain appearing through your paint job and looking very unsightly. This is more apparent and common when painting over knots with a white paint. You often end up with a yellow stain spoiling your lovely new paint job. The remedy is to first apply a knotting solution. This is a natural resin in solution that seals knots and prevents the sap from seeping out. It is usually supplied in a small can with a brush attached to the lid and you simply paint on over the knot. It is available in most DIY stores and costs approx. €7-9. This will prevent that unsightly stain coming through.
Another way of dealing with a large knot is to remove it with a router, a drill or carefully chisel it out and set a piece in. This is normally done on high quality furniture or where the strength of the timber is jeopardised. The photo above shows an example.

Moisture Content

When a tree is cut down, it contains a lot of moisture. If you place freshly felled timber in a house, it will lose moisture as it adapts to the humidity of the room. All wood expands and contracts depending on the moisture content of the surrounding atmosphere. If the timber loses its moisture, that is dries out, at too rapid a rate, unequal shrinkage will occur, whilst wide variations in humidity leads to cracks, splits, warping, cupping, twisting and a whole host of problems. This moisture must be dried out of the timber before it is brought indoors. The amount of moisture in the timber is known as the Moisture Content (MC). There are two ways to remove this moisture after the tree is planked. This drying out process is called “seasoning”. The first method is known as natural seasoning. The advantage of natural seasoning is that it requires no specialist equipment, just the open air and a make shift roof to keep the majority of rain off it. It works on the same concept as drying clothes. The planks are stacked with each one separated by battens of timber placed between them to allow air to flow. It takes one year to dry 25mm of hardwood timber so it is a fairly slow process. This method will only get the timber to around 18% MC. To bring timber into a centrally heated room without distorting or cracking, you need to get the moisture content down to around 14%-10%. You can check the MC of timber with a device called a moisture meter. This meter passes a small current through the wood and reads how much current comes back. The more current returning through the pins, the more moisture there is in the timber. It is not necessary to record the MC of every timber in your home, but interesting none the less. Moisture meters can be bought online for €20. The other way of seasoning is to put the stack of timber into a kiln. A kiln is simply a giant oven that regulates air temperature and humidity to dry the timber faster. The obvious advantage is the speed of the process, taking only days to dry planks to useable moisture content. It requires specialist equipment and trained operators. Most timber around your home will have come from a kiln at some stage. Now that we know that timber moves, how can it affect us around the home and what can we do to prevent or limit the damage? The best example is your floorboards. Before these are fitted, they must be left to acclimatise to the humidity of the room to prevent the floor rising or shrinking. This same concept can be used for other timber entering the home such as skirting board, architrave, doors and even timber projects you buy at a craft fair. I’ve seen people cut and fix perfect mitres on skirting, only to come back later and see the joints opened up as the timber shrank. The only way to prevent this is to let the timber acclimatise to the room conditions for a couple of weeks before tackling the job. I have also bought craft pieces at a fair and brought them indoors with disastrous effects becoming apparent later on as they dried to the same humidity of my home. Everything needs moisture to live, from humans to fungi. Once our timber is below 20%MC, there isn’t enough moisture for fungi to survive. The good news is that most, if not all the timber around your home is kiln dried. This means it was brought down to at least 14%MC. This is perfect for indoors and means the chance of developing wet rot is very slim. Wet rot is a fungal disease that breaks down the timber and leaves it feeling spongy. Where this might be apparent around your home would be the fascia board, timber window frames, flooring boards in a bathroom or any exposed timber below a leaking radiator or pipe, in other words, where there is excess moisture. To prevent wet rot, the timber must be treated with a preservative. All timber exposed to the elements must be treated. Most of the water based preservatives are easy to apply. They are brushed on and are very effective against fungal attack. All leaks should be fixed as soon as possible. For timber windows, they are usually made from a hardwood like teak or iroko. These timbers have natural oils that prevent any rot occurring. Oil can be applied to prolong the colour and enhance the appearance of this timber however. Another species that rely on moisture in timber to survive are woodworm. These insects will burrow through your timber leading to degradation of the wood and loss in strength. Again, if your timber is below the 20%MC, you shouldn’t really have a problem. A clear indication that you have woodworm will be the appearance of tiny exit holes in your timber. Depending on the severity of the case, it can be usually managed with over the counter products that inject solution into the holes to prevent a return. If it seems serious, it is best to call in the experts to fumigate the home.

Sticky Doors

A lot of the finest furniture makers will wait for a humid day before sizing the drawer components on an expensive unit. This is when the timber is at its biggest dimensionally and is likely to only shrink thereafter. You might experience the same problem at home. The most common type is the sticky door or drawer. A door that swings freely in summer can become stuck in winter or vice versa. The reason it happens in winter is the heating is on inside and its cold outside. This produces water vapour as the hot air hits a cold surface such as glass or timber. The timber absorbs this moisture and the door or drawer can swell. The opposite can happen in dry humid countries when the humidity is high in summer and the doors swell. To prevent this from happening, you need to remove or plane some timber to allow it to swing freely again. You have to be careful to remove the bare minimum as remember the door will contract to its original size and you don’t want to end up with a big gap around the frame and door. Open and close the door a couple of times and examine where the door is catching. A good indication will be a shiny spot on the edge of the door where it is rubbing off the frame. A standard gap around the frame will be the thickness of a 50c/50p coin. Mark this distance on the edge of the door. Removing the door from the hinges makes this job a lot easier. When you have the door marked, proceed to plane the high points away until you reach the marked line. Rehang the door and open and close to judge results. If the door is still sticking, examine again, mark and plane until it swings freely. The same problem affects drawers. Unfortunately these can be more complex to plane as a sharp blade is essential as well as a method of holding down the work piece. An easy solution is to apply candle wax to the sides of the drawer to reduce the friction and allow the drawer to slide more freely in and out of the unit. This obviously depends on the severity of the case. The ideal product would be a material with all the versatility and beauty of timber without the shrinking, cracking and expanding. Such a product is now available in the form of acetylated wood, where the chemicals of the wood are changed so that the timber can no longer absorb any more moisture. This eliminates the movement in the timber that causes so many of the problems described above. With no more moisture absorption, decay is also decreased as the timber can no longer increase in MC to allow fungi to feast. This has been used successfully on many projects and wood treated in this way is available in Ireland. Because it grows in so many different places and there are a huge range of types, wood has many unique features, not all of which are helpful as we’ve seen. Sometimes you can have planks from the same tree, dried the exact same way and brought to the same house. One of them will twist and warp, the other will stay straight as a die. That’s the beauty of timber! Don’t be afraid to tackle those jobs yourself. Check your outdoor woodwork and apply preservative where needed, plane down those sticking doors and treat those knots before painting.

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Written by Ciaran Hegarty

Ciaran is a woodwork and construction studies teacher in Moyle Park College, Clondalkin, Dublin. He qualified from the University of Limerick in 2005 with an Honours Degree in Materials and Construction with Concurrent teacher education.

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