What you need to know if you want to repaint furniture or wooden doors

Important

And the wooden doors because, in fact, that's where the idea for the article came from. Someone contacted me to tell me that he had repainted the doors with water-based varnish. Before applying the varnish he sanded the entire surface and yet, with the slightest bump, the varnish peels off and peels off the door like leather. He asked me where he had gone wrong and how he could fix it in this situation. I was sorry for all the hard work, but the answer was that nothing could be done. The layer of waterborne varnish had to be completely removed and the process restarted. Why? Because steps had been missed in the repainting process that led to the undesired result. Find out what they were below.

Degrease the furniture or objects you want to repaint

Any object that is to be repainted or varnished without removing the existing finish must be degreased. Greasy substances and dust have built up over time to form a thin film that prevents adhesion. No furniture or kitchen doors need to have greasy substances on top. The touch of your hands and the cleaning and care substances used will cover the varnish or paint and stop the next coat from adhering. The doors in question have not undergone such a degreasing process.

Another reason for degreasing is the use of maintenance products containing waxes. Pronto is just one example. Ceara gives furniture, doors and wooden objects in general a pleasant appearance and a silky sheen, while protecting them from the effects of scratches or light knocks. But wax is the final coat and can only be covered with wax. Paints and varnishes do not adhere to waxed surfaces, so this thin film must be removed if you want to repaint.

How do you remove grease, wax or a layer of dirt? Simple, by washing items with water and dishwashing detergent. Don't worry, they'll be fine. If you do it right the veneer will not come offThe chipboard or MDF will not swell and the furniture will not fall apart. Washing should be done with a cloth or sponge soaked in a solution of water and dishwashing detergent and then wrung out so that the water does not soak into the furniture or doors. Scrub the surface well, returning until the layer of dirt gives way. As the grime loosens, wipe it off with a soft cotton cloth (use old cotton T-shirts, they're the best cloths). Finally rinse with clean water, still using well wrung out cloths or sponges. After washing and rinsing, allow surfaces to soak for 24 hours before applying the new finish.

Sand to increase grip

When a new finish is applied over the old one we need to be sure it will stay put. First of all we need to make sure the compatibility of those varnishes or paints. For example, nitrocellululose paints should not be applied over polyurethane paints. You can find here explanation. If the two materials don't work together, you can end up with cracked or blooming topcoat. The compatibility check is done in a place hidden from view, where a small portion of the new finish is applied. If everything looks normal after drying, the varnishes are compatible.

Another aspect, which may not be noticed when doing the compatibility test, is the lack of adhesion between the old and the new coat. There are products that interact in the contact area and then the adhesion is very good. For example, if you apply a nitrocellulose paint over another nitro paint, the thinner in the new layer softens the old layer and the two adhere very well to each other. Oil-based paint layers also interact with each other, with the oil penetrating the old layer. Other materials can be applied on top of each other without seeing an immediate effect, but they function as separate entities. They are like layers of fabric layered on top of each other without being sewn. They stay that way, together, until an outside force intervenes. This is the case with curing varnishes, with hard, tough surfaces that cannot be attacked by thinners to bind them together. In this case, before applying another coat of paint, the old surface must be sanded. Sanding produces small ripples (scratches) which increase the adhesion of the surface.

Water-based paints and varnishes are a great option for repainting because, as well as being odorless, they are compatible with most paints and varnishes. With them, however, you need to be careful about adhesion. Water-based products are based on molecules which, after drying, bind together very well. If the conditions for good adhesion have not been created (washing and sanding), at the slightest mechanical shock (knocks, scratching) the new layer will peel off and air will get underneath. If we are talking about varnishes, it will whiten in the place of the bump or scratch. How no adhesion and the molecules of the varnish are tightly bound together, the film will not 'crack' in that spot, as with other varnishes, but peel off from the surface like a sunburned skin.

Sanding is done with fine abrasive sponge or 280 or 320 grit sandpaper. If following apply varnish or gloss paint, use 400-grit sandpaper. Sand the entire surface lightlyThe purpose is to create the rhizomes and adhesion conditions, not to remove the existing layer. After sanding, the surface must be sanded with a clean cloth (without thinners or other substances). Do not leave more than 24 hours before repainting. If more time passes you will have to sand again.

Do not apply thick layers

If you want a good and long-lasting result don't apply thick coats. Several thin ones are better than one thick one. Thick coats create drying tensions and cracks can appear. And a thick coat of varnish or water-based paint peels off much more easily than a film of 2-3 thin coats.

If possible, use a stiff sponge trowel for application. Applied in this way, the coats will be thin and even.

I hope you find the above advice helpful. If you have any questions, you can leave them below in the dedicated space. I'll be sure to reply.