Sanding wood is, for most people, one of the most annoying parts when working with wood. It creates a lot of dust and dirt, it takes a lot of time, and it´s just overall an annoying thing to do. But what if I told you that sanding wood isn´t always necessary? In fact, you can avoid sanding wood in quite a lot of cases! So in this article, I will tell you exactly when sanding wood is necessary and when it’s not as well as how to prepare surfaces for painting without the need to sand them first.
As a whole, it´s not always necessary to sand wood before painting or staining it. Raw untreated wood can be painted and stained without sanding it first if the wooden surface is smooth enough. Previously painted or finished wood can be painted without sanding if a primer is applied.
As you can see you can avoid sanding wood in quite a lot of cases but you still have to prepare the surface somehow if the wooden surface has been painted or sealed previously. This is usually done by applying a primer before painting the surface. So even then, no sanding is needed!
I would generally recommend applying a primer to any surface that has been painted or sealed previously if you don´t exactly know what paint was used to paint the wood.
I wrote a very detailed guide on how to paint previously painted wood. You can read it right here: How to paint over painted wood.
If the wooden surface was sealed with a top coat, like varnish for example, then you have to either sand the surface or you can also apply a well adhering primer directly to the surface. Then you can simply paint right on the primer surface without any sanding required.
I also wrote an in-depth article about painting varnished wood. You can read it right here: Painting over varnished wood.
Generally, you only have to sand wood if the surface has a lot of uneven parts like dents or cracks in it. Then you need to use a wood filler to fix these parts and sand them smooth before applying any paint to the surface.
But even then you only need to partially sand the surface and if the surface only has a few small indents or little cracks in it then applying a primer could smooth the surface without the need to fix these parts individually but I would generally not recommend doing that.
That’s because the cracks are still there just under the primer and they could cause problems later on. So fixing them before applying any paint to the surface is almost always better.
What Happens if You Don´t Sand Wood Before Painting it
It is almost always recommended to sand wood before painting it but depending on whether the wooden surface was already painted or sealed and how smooth the surface is, sanding might not always be required. So why is almost everyone recommending to sand the surface before painting it and what happens if you don´t sand wood before painting it?
As a general rule, if you don’t sand the wood before painting then the applied paint could peel off after a while. This will only happen, however, if the new paint was applied to an already painted or sealed surface. If the paint is applied directly to raw, untreated wood then sanding is not required.
A lot of people are afraid that the paint doesn´t adhere properly when they apply it to a wooden surface without sanding it first. And while that is true in some instances it´s not always the case.
If you want to paint raw untreated wood then you can, most of the time, simply apply the paint directly on the surface of the wood and it will adhere just fine. In this case, no sanding is needed!
If you want to paint wood that was previously painted then you might need to sand over the previous paint job in order to rough up the surface. This will ensure that the new paint adheres to the surface properly.
But you don´t need to sand the surface. You could also apply a primer directly on the previously painted surface to prepare it for a new paint application.
If you want to paint over varnished or sealed wood then you need to sand over the topcoat in order to rough up the surface. This will ensure that the new paint will adhere to the topcoat.
But even in this case, you can still apply a well adhering primer directly on the coated surface without the need to sand the surface beforehand.
What Happens if You Don´t Sand Wood Before Staining it
Finally I also want to take a look at stained wood and if you have to sand wood before applying stain to the surface.
As a whole, it is not necessary to sand the wood before staining it if the wood was not stained, painted, or sealed before. If the wood was painted or sealed before then it has to be sanded down to the raw wood before staining it. Otherwise, the sain can´t be absorbed by the wood properly.
Wood stain will usually be absorbed by the wood fibers so it can only be applied to unsealed raw wood or wood that was previously stained but not sealed.
If the wood was painted or varnished and you want to stain it then you will run into a quite significant problem. Paint as well as varnish will sit on top of the wood as a coat. So if you want to apply stain directly on the painted or sealed surface then the stain has no way to get in contact with the wood fibers underneath the coat of paint.
In this case, you have to sand the paint and the topcoat completely off before you can stain the surface. This is a lot of work and most of the time it isn´t really worth it in my experience.
If the wood was stained and not sealed with a topcoat then you can, most of the time, simply apply a new stain to the surface. You should, however, apply the same or very similar color of stain because the stain will not really cover the previous stain. Instead, the new stain will “mix” with the old stain.