How to prepare wooden surfaces previously protected with varnish coatings, and how to prepare surfaces with enamel paint? How to efficiently remove old paint from wood? What sandpaper grit is recommended? Why should you avoid puttying exterior wooden surfaces?
Proper preparation of wood for painting is more than half the job, and the quality of these works largely determines the final results. This often involves work on old windows. The approach to preparing surfaces for painting depends primarily on the condition of the windows and the type of protection previously applied.
For new wooden surfaces:
If you are dealing with completely new wooden surfaces that have not had any prior treatment, the procedure is quite simple and involves sanding. It is advisable to use fine-grit sandpaper (P150, P180) to achieve a fine wood surface, which will later be more resistant to deterioration due to moisture exposure.
Preparing wood previously protected with varnish coatings:
If you are preparing to paint wood that has previously been protected with varnish coatings, also known as impregnation coatings, there are a few options. If the wood is in good condition, it is usually sufficient to carefully wipe the wood with a damp cloth to remove dirt and dust. Before applying a new layer of varnish coating, wait until the wood is completely dry.
Pay attention to the color. If the window color is satisfactory and only needs a minor refresh and protection, use a clear varnish coating. Keep in mind that each new layer of pigmented coating will darken the wood further.
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To remove a previous varnish coating, sanding is necessary. It is important to assess whether this work is worth it, as it often requires removing a thicker layer because the varnish can penetrate deeper into the wood. Given that window frames have a complex shape and are not flat surfaces suitable for sanding, the task can be very demanding and often not cost-effective.
One option is to prepare the wood to reach its natural color only on visible parts of the window, either outside or inside, depending on where you want the new color. Removing paint from all corners of the internal profile is a nearly impossible task.
For these extensive jobs, it is recommended to use a vibrating sander. Today, the selection of hobby sanding tools is quite large, making the purchase of such a device worthwhile. The job will be completed not only faster but also with higher quality. This is particularly important if you are sanding the inner side of windows that practically form part of the living room.
Removing old paint from windows:
This is a task for the most skilled or at least for those with the steadiest nerves. If the windows were protected with paint, or enamel, removing it is quite complex. However, there are some alleviating circumstances, and much depends on the condition of the paint to be removed.
If the paint on the wooden windows is in good condition, neither cracked nor swollen, it won’t need to be removed. Careful sanding will be sufficient to prepare the surface for the new paint. If the paint has peeled in places, it should be removed with a sharp scraper to provide a “healthy” substrate for the new layer of paint.
If the paint is in poor condition, cracked, or peeling, it needs to be completely removed, which is a more demanding task. First, remove all mechanically detachable paint with a scraper. Remaining layers that need to be removed can be tackled in several ways.
The simplest option is heating the old paint with a heat gun. This tool blows air at 900 degrees Fahrenheit, softening the paint, making it easier to remove. Be careful not to overheat the wood and also be mindful of the glass, which can crack from sudden heating.
Chemical paint removal – only if necessary
There is also the option of removing paint with chemical agents. After applying these agents, the old paint swells and softens, making it easier to scrape off with a scraper. These agents are expensive, and working with them is not the safest. The fumes are toxic, and after completing the work, the window needs to be thoroughly cleaned with nitro thinner and allowed to dry completely. Use this method as a last resort if nothing else works.
After paint removal, sanding is necessary. Then check for any irregularities, filling them with wood putty if needed. Apply the putty with a spatula in as thin a layer as possible, smoothing it out as best as you can. After drying, the putty is sanded to obtain a smooth surface. The better the putty is applied with a spatula, the less sanding will be required.
Avoid puttying exterior wood as much as possible. Due to frequent changes in temperature and humidity, putty can crack. It is much better to apply paint directly to the wood whenever possible. The interior side of the window, which is more visible and must be more meticulously treated, can be puttied without fear of cracking or detachment.
Finally, before painting, remove all dust from sanding. A vacuum cleaner with a small round dust brush can be very helpful. After vacuuming, use a damp (not wet) cloth, and ensure the surface is completely dry before painting.
Photo: Freepik, Bosch