Using Wood Plugs
On occasion you may need to relocate or remove something that has been mounted using wood screws. Doing so can leave you with some unsightly screw holes. You have several options to fix this problem and in this article we will give you some suggestions and tips on how to hide screw holes using wood plugs.
Why wood plugs?
Inserting wood plugs will yield the most pleasing results and is definitely worth the little bit of extra effort to hide the screw holes. Wood plugs allow you to match the species of wood you want to repair. The commonly used diameters for plugs are 1/4", 3/8" and ½". You can purchase plugs or make them yourself using a plug cutter. Most commercially available wood plugs have a chamfer, but if they don’t, be sure to take the time to pare a little chamfer (carefully!) around the perimeter to make insertion much easier. I use a plug cutter made by Veritas (Lee Valley Tools) that makes a tapered plug with a chamfer. The taper and chamfer makes it very easy to insert the plug in the hole. Making your own plugs allows you to achieve a better wood grain and colour match.
Cutting the new clean hole
A clean hole is essential to get the wood plugs to be nearly invisible. The common twist drill shown above right will tear the wood fibers and leave a jagged hole that is unusable. To get the best results you will need a ‘brad-point’ drill bit. An important feature of the bit is the brad point that “locks” the bit in one spot and prevents "skating" of the bit, as well as allowing accurate bit positioning. The better brad points have two lips or outlining spurs on the perimeter that score the wood fibers around the circumference of the hole before the chipping bevels begin stock removal. This results in a very clean, crisp edge around the hole with negligible fiber pull and no tearing of the wood as the bit enters.
The problem with the existing hole...
The problem is that the existing hole will not allow the brad point to do its job – that is to fix the bit on one point and give us a perfectly round hole. In other words as the bit rotates it will flop around and create a jagged, elongated hole. The solution is to make and insert a temporary wood plug. Use a hard wood, taper the temporary plug slightly oversize and gently tap it in with a hammer and make sure the plug is set good and firm. If you are repairing a screw hole in ¾” material (typically plywood) like a bulkhead, be careful when tapping in the temporary plug that you don’t force it through to the other side. In this case make a ‘fat’ tapered plug that will set without going in too deep. With the temporary plugs set good and firm, trim the excess flush using a knife, chisel or saw.
Drilling the hole
As you press the brad point bit into the centre of the temporary plug, note how the temporary plug ‘locks’ the point of the bit on its centre so it will rotate in one spot. As you start to drill do your best to keep your bit a right angle to the surface and keep your drill as stable as possible. Start at a lower rpm and starting with gentle pressure let the drill bit spurs cut the wood fibres as the bit rotates and gradually bring the drill up to speed as you remove material. The depth is determined by the length of the plugs you plan to use and the thickness of the material you are drilling into. You can make a depth gauge by wrapping some masking tape around the drill bit – the tape is set back from the point to the depth you require.
When inserting the plugs…
- Try a ‘dry fit’ to make sure the plugs will go in smoothly. Don’t force it or it will jam!
- Always have a few more plugs than the job requires.
- Have at hand your (cordless) drill with a 1/8” or 3/16” twist drill bit in the chuck.
- To avoid a big mess, don't apply glue to the plug. Simply apply a small amount of glue around the inside perimeter of the countersink hole using a small applicator such as a match stick. The idea here is to get glue spread evenly all around the inside walls of the plug hole.
- As you are inserting the plug, rotate it to spread the glue evenly around the perimeter and be sure to align the grain of the plug with the direction the grain of the surface you are repairing.
- Using a hammer, gently tap the plug in until it can go no further be careful - don’t overdo it. Use a glue that best matches the colour of wood you are using for extra invisibility.
If the plug accidentally fractures (less dense species of wood can sometimes fracture) or deforms before it is properly set do the following immediately. Trim off the errant plug to make a flat surface. Take your handy drill and drill a hole in the center of the errant plug. Go slow and careful. As the drill bit bottoms out, the drill bit should spin the plug and pull it out. Immediately insert another (dry) plug. Time is critical because the glue will cause the wood to swell making it difficult to properly seat the plug.
Trim and finish
Once the glue has set, there a several different ways to trim the plugs:
Flush Trim Saw: Typically used for the rapid trimming of plugs and dowels flush with a surface. Can be used to cut off your plug without damaging the surrounding surface. This is possible because the teeth are set on one side only. Be sure to use the ‘safe side’ when using the saw – usually clearly marked on the saw.
Razor Saw, Back Saw, Japanese Saw: When using these saws you need to protect the surrounding surface to avoid scratches or marks. Place a piece of posterboard, cardstock, plastic laminate or even two or three layers of painter’s tape around the plug to minimize unwanted marks. Cut slowly and carefully. The saw will leave the plug slightly proud of the surface and you need to finish using a chisel.
Chisels: You will need a chisel for final leveling of the plug even when using a saw.
When using a chisel for the initial trimming down, here is a safe method that will give you great results every time.
If you have say about ¼” to ⅜” of the plug protruding, hold the chisel bevel side down and put the edge about half way up the plug. Using a hammer or mallet gently tap the chisel. The resulting cut will reveal the ‘lay’ or direction of the grain. The direction of the plug’s grain will dictate direction of the next cut.
View and download a diagram detailing the trimming with a chisel technique.
An alternative...
In a pinch I have also used a twist drill with a countersink bit attached. Here are some important points to remember:
- Only use this setup if you have the wood thickness and you know what is behind the area you are drilling into.
- The diameter of the twist drill must be larger than the existing screw hole to stabilize the countersink as you drill the plug hole.
- Before you start it is important to set the depth of the twist drill bit to a short distance to minimize the penetration.
An example of three new plugs in a teak mast cover. As the fresh teak ages the colour will eventually blend with the surrounding wood. The plugs are ready for a finish.