We all know that with painting preparation is key and filling holes and cracks is a big part of that.
One of the crucial factors in achieving a beautiful finish to your painted surface (whether it be walls, woodwork, ceilings or furniture) is to ensure that surface is uniform underneath. Any holes, gaps or cracks will show up even more with paint applied and although paint is great stuff, don’t expect it to fill holes or gaps.
Apart from being aesthetically pleasing, filling gaps and holes also helps protect the building material itself, particularly exteriors as water and weather getting into these areas will eventually undermine the whole paint system, causing delamination, blistering and possible rot forming.
A couple of important notes to start with here on filling:
- Read the instructions on the packaging for any fillers you are about to use.
- Keep the filler blade or putty knife clean and smooth. Use a window paint removing blade and sandpaper (fine grit) to achieve this, see earlier blog.
- Whatever the surface is to be filled or gapped make sure it is dry and free of dust.
- Apply the appropriate primer coat to the surface to seal it whether it’s wood, metal, gib, concrete or plaster. Sand and dust down before you apply filler.
Putty and Glazing Compound
Putty is made up of whitening and linseed oil and is one of the oldest and most common putty and filler. It was used to glaze glass into window frames, fill nail holes and cracks.
It is easy to use and once dry (although glazing will take three to six weeks to dry enough to be painted) can be painted with an oil based primer first.
Linseed based putties can be tinted to different colours to match varnish or stain wood when nail holes need to disappear.
Glazing Compound is now the super putty because it can do the same as putty however it can be painted with water based paint systems. It also has the advantage that it generally won’t require much, if any sanding. Very clean and easy to use for a wide range of jobs.
Here are the two main ways of using the glazing compound”
- Holes – Holding in your hand a tablespoon amount of compound, use your thumb to push compound into the hole, hold it there, while with your clean putty knife gently slide in between the surface and the compound which should leave a neat plug of compound in the hole level with the surrounding surface. This may need to be repeated if the hole is not quite fully filled, sometimes referred to as a half moon so just repeat the first step.
Final step is to gently rub compound across plug to remove any crumbs and smooth down, this is why not much sanding is required when using putties.
- Cracks – Holding in your hand again about a tablespoon amount of putty or glazing compound, rub the putty back and forth across the cracked surface till it fills up then gently rub across to pick up crumbs and smooth down.
When selecting premixed filler check the instructions to make sure it is the correct one for the project, some are formulated specifically for interior only and some for exterior only and within this range will be fillers for wood, masonry, plaster, gib, concrete and even metal. Again any surfaces that are to have areas filled need to be clean and dry and primed or sealed.
It’s good to have a couple of filler blades of different sizes and flexibility and keep them clean and polished. This is important to help achieve a smooth fill. These premixed fillers can be used quite thinly or built up to fill a sizeable hole. Yes, it will need to be sanded however try not to over fill as this creates more sanding and can leave a slightly raised area over the hole rather than being flush with the surrounding surface.
- Use a large knife to hold a tablespoon of filler to take filler from rather than straight out of the tub. It’s not a good idea to work straight out of the tub as the product will start to set/dry out and get crusty bits which is not what you want in smooth fillers. If you do end up with debris in the tub try with a spoon to scoop the top layer away to get back to the good stuff.
- The knife you choose to fill with requires a certain amount of flex rather than being a stiff or firm blade. Take slightly more filler than needed and apply the filler with firm pressure on the blade using a vertical motion, then horizontal so the filler is being worked into the crack, hole or indentations. The idea then is to give a couple of light wipes or skim coats across the filler to give a slightly raised surface to the fill. As these premixed fillers tend to dry rather quickly when applied thinly you are able to apply a second coat or build up filler in large holes and cracks which is better than trying to fill it in one hit.
- Once the fill has dried then sand with 120 – 180 grit sandpaper, dust and under coat.
If there are any missed holes or cracks apply more fill, sand, dust and spot undercoat.
- Apply finishing coats of paint.
As you will probably have gathered there is a lot of sanding and dusting involved in this preparation business.
Caulking (Gapping) products
Fantastic filler for lots of areas however these can not be sanded so remove any excess prior to curing time. Generally used where two surfaces meet at an angle.
These products come in a tube designed to fit in a caulking gun for application. There are a few that come in a smaller toothpaste type tubes for the smaller jobs.
It pays to check the end of the nozzle for a clean 90 degree cut, this helps to give a clean line of filler, some people cut the nozzle on an angle which means the gun has to stay on that angle which limits your range of movement. For larger gaps the nozzle can be trimmed down giving a larger bead and even larger caps can be filled in two or three applications letting each one curler before applying the next.
To start gapping you will need a caulking gun loaded with a tube of filler, a wet rag and a tissue. Again make sure the surfaces have been primed/sealed and sanded prior to applying the filler.
- Place the nozzle end into the gap holding the gun at around 45 degrees to it and gently squeeze the trigger while moving along the gap. Now there are two ways to do this; either you push or you pull the gun, both ways work depending on what you are gapping. Have a go at both ways and if you find the filler is just falling out change the angle of the nozzle.
- Wet a finger and run along the gap, this helps to bed the filler in.
- Using a wet rag gently wipe along fill. This will remove any excess fill. Wash this rag out frequently and don’t use a bucket of water to do this as you will end up with gap soup that will cover your hands and is really time consuming to remove. The tissue is to wipe the nozzle and keep it clear and clean after each use.
- One more time with your finger to smooth down.
- Let dry and paint.
Handy caulking gun tips
There is a small release tab on the caulking gun that stems the flow of product to the nozzle and needs to be depressed after each time filler is applied.
Once you have finished with the caulking place a small nail in the nozzle to prevent dry caulking from blocking nozzle.
Ideal for larger holes, dents and gib stopping on walls and ceilings.
Depending on how much is required, plaster can be mixed up on a clean 10 litre lid. There are different times that the plaster comes in, meaning how long once mixed before it starts to dry and cure. ie 90 minutes, 45 minutes.
We won’t cover gib stopping on this blog however we will show two ways to patch a hole in the wall or ceiling:
- Trim a piece of cardboard 30% bigger than the hole and make a small hole in the centre of the cardboard.
- Thread 200mm of string through this hole with a knot at one then gently bend card and push into hole to be patched while holding on to the string.
- Still holding on to string start working plaster into hole, the card stops the plaster from falling away, don’t try to fill in one go rather when you feel the plaster drying off you can let go and when completely dry trim the string up against the plaster patch.
- Work the second coat of plaster into the cavity left.
- How big the hole is will determine how many coats you will require.
- When the last coat is fully dry the area will need to be sanded, dusted then primed.
This technique can work very well for quite large holes in plasterboard.
- Cut a piece of plasterboard 40% bigger than the hole and mark it with a pencil as close as you can to the size and shape of the hole on to the middle of one side of the piece of gib.
- Using a knife cut through just the layer of paper around the marked hole.
- Carefully snap then peel each piece of gib away from the main patch.
- You should end up with a piece of gib the same size as the hole with a flange of paper on the front side. Check that it fits in the hole and trim if needed.
- Apply a generous amount of plaster around the inside of the flange and position in the hole.
- Starting along one edge with a broad knife smooth out the plaster to the edges all the way around the patch.
- Once this first coat of plaster has dried apply a second coat around the edge and then a skim coat over the face of the patch. Remember to cover a little bit more of the patch with each coat of plaster.
- When completely dry sand, dust and prime.
Old school tricks
Another plaster mix used well before the new premixed products was just plaster mixed with oil based under coat paint to a paste then applied with filler knives. Once dry sanding gives a super smooth surface.
Saving saw dust from the timber as it is cut to use as a filler on the same wooden surface or structure is done by mixing it with a flat drying white glue to a paste and worked into any holes. This can be sanded and varnished.
This one may seem pretty rough however it works well for a quick and easy patch on a roof. Take an old rag and soak in oil based paint till completely covered then drape across where the patch is needed. Work it around and smooth down with a brush then leave to dry. As I said primitive but effective.