Filler is generally seen as a weak link in the construction of a paint system. Nevertheless, within good and durable maintenance, it may be necessary to use filler when painting. Broadly speaking, you use a lacquer putty to level or repair small irregularities in the substrate of existing or pre-treated paintwork. A two-component filler or wood rot filler is more suitable for larger damage or open joints on new untreated wood or older damaged paintwork.
The how and why of filling wood
- Fill when painting
- Use of the different filling knives
- Filling two-component filler or wood rot filler
- Fill with paint filler or a water-based filler
- Trim off and remove excess paint filler
Fill when painting
Filling the wood in and around the house can have both a functional and aesthetic function. If filler is mainly used outdoors to protect the wood against weather influences and moisture penetration, it will mainly be used within the home to obtain a smooth-looking result of the paintwork.
Use of filler and moisture
Especially outdoors it is recommended to only work with filler where necessary. In practice, this means that especially the mitred / open joints and the horizontal parts will be filled. Filler seals the wood so that no moisture regulation takes place in the filled areas. Partly for this reason, it is advisable to filler outdoors after a longer period of dry weather. At a wood moisture content of more than 18%, it is generally not recommended to filler, because the (core) wood is then too moist, which can lead to detachment of the final paint layer. If you paint the house yourself – and it appears that there is a lot of filling to be done – the exact moisture content will be difficult to determine and waiting for a period of good and dry weather is extra important.
Checking the paintwork
If the condition of the paintwork is regularly checked and any problems in the substrate or paint layer are resolved in good time, it is possible to work with filler on a larger scale, if desired. Keep in mind that the first problems will manifest themselves where the wood has been too moist during the build-up of the paint system.
Apply a base coat and “let it stand”
If you have doubts about the moisture content of the wood and the paintwork does not need to be completed immediately, you can choose to thoroughly clean and sand the wood to be painted and then paint it well in the primer. If the flaws are not too severe, this may be enough to wait a year for the rest of the painting. In the intervening year, the wood then has the opportunity to ventilate / dry more.
Use of the different filling knives
General
Working on a clean and dust-free surface and the use of clean, burr-free filling knives is a prerequisite for tight filling, without furrows or scratches. Adjust the width of the putty knife as much as possible to the surface to be filled. It is preferable to use a putty knife that is too wide, rather than one that is too narrow (provided there is enough space to work with the putty knife).
Correct way of filling
You handle the putty knife as shown in the picture. By placing the middle and index finger on the blade, you are able to exert a proportional pressure on the putty knife, and thus “steer” the putty in the desired layer thickness and the right direction. In principle, you apply the putty by roof tiles, working from bottom to top. You should always have some overlapping layers applied next to each other.
Duo-flex – Putty knife for larger surfacesPreferably use at least two filling knives. You use one wide putty knife as a hold-up knife for the (prepared) putty and / or to level off the excess putty, the other putty knife is used to pick up the putty from the wide putty knife and apply it to the surface to be putty .
Duo-flex putty knife
If you have sufficient skill in filling – especially paint filler – it may be advisable to use a Duo-flex putty knife for filling large surfaces. Due to the large width of the duo-flex putty knife, fewer scissors are created when applying the putty, which means less sanding at a later stage.
Filling two-component filler or wood rot filler
| Small repairs | Problem and solution | Rip |
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Fill with paint filler or a water-based filler
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Trim off and remove excess paint filler
By cutting off the dried paint filler, shears are flattened to a large extent, so that less sanding is required. The drying of the filler depends on the applied layer thickness of the filler in combination with the substrate and the environmental conditions.
Once the filler has dried sufficiently, run a clean filler knife as flat as possible over the filler surface, without exerting too much pressure on the filler knife. If the filler curls up, it has not yet dried sufficiently. The correct cutting of the filler is visible by the flattening of any scissors in the filler, a slight shine of the surface of the filler and the remaining slightly gray streaks of the steel of the filler knives on the surface.
Remove the excess filler that protrudes over edges and short sides by gently pulling a filler knife along these edges after it has dried sufficiently.
