Can You Paint Over Non-Hardening Wood Putty?

It’s inevitable that we will make holes in or dent wood as we work with it on a project.  We have sharp tools in our hands and in our shop, and sometimes our hands are clumsy.  We have hammers and other instruments that can mar wood as we work on our project.  Beyond that, though, we will use nails and a nail punch,  or recessed screws, or brads, during assembly, and they will leave holes in the wood.

To give our projects a professional appearance, we will want to fill those holes, dents, dings, and such before we finish the wood.  Even finished projects might need some attention if damaged or dinged.  This is where fillers come into play, and we have some choices to make about their use.

Wood Fillers

We recently wrote a piece on wood fillers where we discussed whether they needed to be primed before painting.  We know that wood fillers contain real wood in the form of wood fibers and sawdust, along with a medium to bind it all together, water-based and petroleum-based fillers. 

They should be used on raw wood – unfinished furniture, for instance.  Raw wood is porous, and the filler will adhere well to it – the moisture of the filler binding to the wood.

These wood fillers dry hard, and water-based fillers dry very quickly.  Once dry, they can be sanded smooth and then finished, whether with paint, stain, or a clear coat.  After all, they contain real wood, and real wood is a sandable material.  

If paint is the chosen finish, you should apply a primer before the finish coats.  We do that for wood generally, so why wouldn’t we do it with wood fillers, too?

You can even make your own wood filler.  A little bit of sawdust and fibers from the wood you are working with, a little Elmer’s Glue, mixed well to a smooth consistency, and pushed into the hole until full and then a little extra.  Give it 15 – 20 minutes to dry well, and use a fine grit sandpaper to bring it flush with the surrounding wood surface, and it’s ready for the finish of your choice.

That finish, as we said, could be paint.  But, it could also be stain.  Again, wood filler contains real wood, and if you have made your own filler with sawdust from the wood of your project, even, it will take stain just as the wood you just filled.  

Wood filler is durable and will last well for interior use.  It dries very hard, and something like Minwax High-Performance Wood Filler will be dry in 10-15 minutes and ready to sand in 30 minutes.  That won’t slow down your project long – make yourself a cup of tea to enjoy, and by the time you’ve finished, the filler is good to go. 

Wood Putty

Wood Putty Being Applied

Another material used to fill holes in wood is wood putty, but it is a different animal from wood filler.  It’s manufactured with plastic-based and petroleum-based compounds and should be used on finished wood rather than real wood.  Those compounds can cause damage to raw wood, while wood that is already finished can withstand the chemicals.

Unlike wood putty, which usually comes in a white or off-white color, wood putty will come with tint and color.  This gives you the ability to match the color of wood putty with the finish on the wood, so it blends in without notice.

Does Wood Putty Harden?

Also, unlike wood filler, wood putty will dry but will not harden.  When applying wood putty, you will want to wipe away any excess putty around the hole you’re filling, either with your finger or a damp cloth.  The top coat of your choice, whether a varnish, shellac, or polyurethane, can then be applied, and the color-matched putty will blend in with the wood surrounding the hole.

Since wood putty does not harden and remains flexible after drying, it can withstand the expansion and contraction of the wood around it due to environmental changes (temperature and moisture).  This makes it a better choice for outside use than a wood filler that cannot withstand environmental changes.  Wood putty can also be used for indoor applications too, though, on finished woods.

Drying Time for Wood Putty

It’s nowhere as fast at drying as wood filler.  You are looking at 2 – 8 hours of drying time for wood putty.  Again, though, it does not harden, so it can’t be sanded as wood filler can.  

We know from our work with finishes that temperature and humidity can affect drying time.  Also, the amount of wood putty used will have an impact on drying time.  If the hole was small and only a little putty was used, it will be closer to the 2-hour drying time; if the hole was larger and a lot of putty was needed to fill it, you’ll be closer to the 8-hour drying time.

Types of Wood Putty

Minwax 13612000 Wood Putty, 3.75 oz, Colonial Maple

Wood putties come in two types generally:  water-based and oil-based.  The surface coating of the wood being filled with wood putty will determine which of the two you will use.

  • Water-based wood putty will dry in about 24 hours and be ready for a topcoat to match the wood it is repairing.  Temperature and humidity will affect that time a bit, as will the amount of putty used to fill the hole or crack.  Water matches well with water – if the topcoat on the finished wood being repaired is a water-based one (polyurethane, for instance), then a water-based putty should be used.
  • Oil-based wood putty will take twice as long to dry, and 48 hours is a good average.  The same variations in environment and amount used will affect the actual drying time.  Oil and water don’t mix well, so if the topcoat on the finished wood being repaired is an oil-based finish, an oil-based wood putty is the right choice.

Drying times can be sped along by making sure the environment is warm and dry, of course.  There are hardeners you can use in addition to speed up the drying time, also. 

Which to Use If Paint Is the Topcoat?

We’ve already noted that wood filler, used on raw (unfinished) wood, can be painted or stained, and we know that wood putty comes in a variety of colors that can be chosen to match the finished wood being repaired. 

If the job is on wood that has been painted, though, you would not want to use wood putty as your solution.  It dries but does not harden.  Its surface will not take paint; the paint would eventually just peel and fall off the wood putty, no matter which type of wood putty it is.  It doesn’t harden and remains flexible, and that flexibility will stand in the way of paint adhering with some permanency.  

The better choice by far is to sand the area around the hole being filled right down to the raw wood.  Then, apply a wood filler, allow it to dry and harden, sand it smooth, and apply new coats of primer and finish coats.  

Add to that the fact that wood filler is the better choice for unfinished wood, and thus we would not be using a wood putty anyway since it is for use on finished wood only.  

For more information on wood fillers generally, and specifically which type of filler to use on large holes or cracks, take a look at another earlier piece we wrote on the subject.  

General Rules Regarding Fillers and Putties

Unfinished wood will require we use wood filler; finished wood calls for us to use wood putty. This is the general rule to follow.

Additionally, wood putty and paint do not work well together.  Limit putties to woods that have been stained.  Wood fillers, though, can take either paints or stains.

Keep to these simple guidelines, and your project will go well.

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