Can I Use Joint Compound Instead Of Wood Filler?


Efficiency is a key part of getting the job done. I avail myself of handy hacks to save time and money. But too often, I end up doing the job twice – doubling the expense – when my shortcuts backfire. There’s a spare tub of drywall mud and a gape in the floorboards. What to do?

The term “joint compound” refers to two products designed to repair drywall. “Wood filler” picks out a wider range of products built to patch hardwood. While they have differing properties, joint filler can substitute wood filler but only in small indoor applications and on unpressured surfaces.

Understanding the nature and uses of the materials under discussion will enable us to evaluate, case-by-case, whether substitution is appropriate for the job at hand.

What Is Joint Compound?

Also known as “drywall mud,” joint compound is a spreadable goo used to fill holes and blemishes in drywall. It is sold premixed and in powder form, which requires mixing with water.

Joint compound is used primarily to smooth over joins between adjacent panels of drywall. It is smeared into the cracks in the seams and left to dry. Thereafter, it is sanded down to the level of the surrounding hardwood. Painting leaves a seamless finish.

The Composition Of Joint Compound

Gypsum is a soft calcium sulfate derivative that occurs naturally and abundantly. It is the basis of applications like chalk plaster and drywall. Gypsum is the main ingredient of drywall.

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Gypsum and limestone (calcium carbonate) are the main ingredients in joint compound. Attapulgite, perlite, mica, and starch are other key ingredients. In some instances, workability is improved by the addition of a vinyl polymer.

Different types of limestone contain these ingredients in different proportions. Varying the proportions influences factors like drying time, crack resistance, hardness, smoothness, and malleability. The setting compound is largely gypsum-based, while the drying compound contains more limestone.

SAFETY TIP: The materials in standard joint compound are natural and safe, but some concerns have been raised with the addition of poisonous polymers to some newer brands. It is worth doing some research to exclude the unlikely event that the brand you’re using contains harmful substances.

Types Of Joint Compound

The term “joint compound” is often used to refer to spackle, a similar but distinctly different product. Because of this usage, we will include spackle under joint compound, as some users might have that product in mind when asking the wood filler substitution question.

Prepackaged Joint Compound

Store-bought joint compound comes in the following varieties:

  • Drying Compound: These are compounds that dry through evaporation rather than a chemical reaction. They are composed mainly of limestone and chalk.
  • Setting compound: Setting compound is composed mainly of gypsum or plaster of Paris. It is known as “hot mud” and is favored amongst builders because it hardens within minutes.

Hot mud is hard to sand, and because the hardening is irreversible, mistakes cannot be corrected.

  • Topping Compound: This is drying mud used for final touching. It is limestone-based, and fine-grained talcum powder is often added to increase the smoothness of the finish. 
  • Taping Compound: Taping compound is designed for setting drywall tape. This is the final joint binding, and the taping compound is designed for heavy-duty. As a drying compound, it is limestone-based. Its heavy texture makes for tough sanding.
  • Tapeless Compound: This is a new product that targets the use cases of taping compounds without the need for subsequent taping. It is harder and less crack-resistant, melding firmly and seamlessly (after sanding) with the adjacent board.
  • All-Purpose Compound: This combines the advantages of taping and topping compounds. As a result, it is both workable and durable. It is usable in all cases of joint compound application, increasing its favor amongst home users.
  • Premixed Compound: Not a separate flavor, this refers to the method of presentation. Premixed compound is a ready-to-use material, available in all the flavors listed above.
  • Dry Powder Compound: These are sold in powder form and require mixing by hand. This creates the risk of mismanaging the proportions, but pro users prefer the control over consistency that this brings. There’s the added advantage that these compounds are easier to store and less prone to contamination.

Spackle

This paste is designed to fill small dents and holes in drywall and wood. Nail holes and chips on corners are prime examples. Spackle is premixed and sold in sealed containers. It is fast-drying, taking less than thirty minutes on average. 

Roll-Your-Own Joint Compound

Instead of buying joint compound, it is possible to create it from scratch. Here it’s key to note that despite appearances, the composition of joint compound is very different from the gypsum boards it is designed to meld with, and simply grinding gypsum won’t do the trick.

Remember also that the commercially prepared types listed above are mixed in specific proportions with selected polymers to achieve the desired finished texture.

REMINDER: While it is easy to find online recipes for making your own mud, this is a risky experiment where the cost of water damage may outweigh the intended savings.

What Is Wood Filler?

Whereas gypsum mud is designed for filling gypsum, wood filler is a mush that does the same job for wood (the name is a bit of a giveaway).

A separate product is created not only because planks have a different consistency to wallboard but also a wider set of applications. And with the latter stresses.

Wood fillers and putties will not improve the strength of wood joints as they are not true structural products. 

The Composition Of Wood Filler

As with joint compounds, the term “wood filler” is sometimes used to refer also to wood putty, which is a different substance. We’ll refer to both here, as a reader drawn to the headline question of this article might have putty in mind.

Wood fillers are made of pulverized wood derivatives lathered in a binding agent. It stiffens on drying, becoming totally unmalleable. Wood putty, though, contains a thinner to make them flexible after drying. They sometimes contain silica.

The core particles in wood filler are sawdust or wood dust. They’re suspended in either water or petroleum-based gel. Water-based fillers are not suitable for outdoor applications. While wood putty is often pigmented, wood filler is unstained and colored with the finish of the surrounding wood.

Wood putties are constituted not of raw wood dust but synthetic materials such as polyurethane and epoxy. They remain soft after setting and so are totally unsuited for joint repair. They are intended to fill small cracks, holes, and blemishes. Usually, they are tinted to fit into the surrounding wood.

7 Types Of Wood Filler

As with wallboard mud, understanding the types of wood filler gives a proper sense of when to pick one that does the job, and thereafter to understand whether substitution with joint compound is advisable at all.

1. Latex And Solvent-Based Wood Filler

These are the primary type of wood filler. The binding goo is a solvent, which gives them a distinct alcohol smell before they set. Solvent-based fillers dry slowly and never obtain a hard structure.

They are unstable when used in large cavities when they are prone to sinking or shrinking. Their intended application is in small holes and surface blemishes.

Accordingly, they are provided in a range of colors, making it easier to match the surrounding wood without the need to sand and repaint everything.

2. Water-Based Wood Filler

These might more properly have been called “organic based” fillers, as it is not only that water takes the place of latex and solvent, but the solid fillers are organic materials like cellulose and wood fiber. The use of gypsum as a core agent makes these resemble joint compounds more than the other varieties of putty.

Water-based filler dries quickly. It softens when mixed with water, allowing versatility as it can be diluted to different desired textures. Sensitive noses will enjoy the lack of solvent smell when working the fill. 

3. Epoxy Based Wood Filler

These are the hardiest of the lot. On drying, epoxy fillers are harder than the wood they repair and are suitable for large cracks and holes that endure structural stress.

Epoxy fillers come in clear and colored varieties, both in a tube and can packaging. However, it is not an easy filler to control, and skill is required to avoid a mess. Unlike the other fillers profiled here, epoxy is impossible to sand when dry. This makes smooth application critical.

Because of their drying strength, they can endure nails or screws. Their plastic finish makes them best suited to out-of-view areas in the wood.

4. Exterior Wood Filler

Exterior wood filler is highly elastic. Its rubbery design allows it to expand and contract with variations in the weather. This tracks the behavior of surrounding wood, leaving the joint between the fill and the wood intact.

This wood filler can be sanded more easily than epoxy (which is not recommended for outdoor application). It is usually applied in streaks with a putty knife and can be painted over.

5. Caulk

Caulk is a material designed to seal or fill gaps that exist between surfaces. It started as a device for maintaining pipes and boats and is now mainly used in bathrooms. In these applications, the caulk jams between damp surfaces, preventing leakage through their interfacing gaps.

Caulk is found in two main varieties: silicone and acrylic. Other flavors include vinyl latex, polysulfide, and polyurilicoethane.

Caulk is not wood filler, and as indicated, the applications were not primarily wood. It has, however, become somewhat interchangeable in some usages, which brings it into the ambit of our main question.

6. Wood Putty

Retailers don’t consistently differentiate wood filler and wood putty, creating confusion between two significantly different products.

Wood putty is pliable and is applied with a putty knife. Yet, it is denser than wood filler. It consists of a mix of oil-based solvents and plastic. It does not harden like wood filler and therefore does not crack or contract. This malleability makes it hard to sand.

Wood putty is colorized, compensating for the impossibility of painting it. It is designed for covering and repairing holes and blemishes on finished surfaces. Filler sticks package putty in easy-to-use units.

7. Roll-Your-Own Wood Filler

As with joint compounds, this is not recommended. The general availability of several types of wood filler makes it unnecessary (though it could be a fun experiment.) If you must do it, use dust from the same type of wood as the core application.

Substituting Joint Compound For Wood Filler

Armed with a picture of the nature and use cases of the materials, we can consider whether when and how to substitute joint compound for wood filler. The key idea is that substitution becomes less likely as the size, pressure, and outdoor exposure of the target application increases.

Substituting In High-Stress Applications

Wallboard is usually deployed on upright walls and ceilings. It is not used on floors and supporting surfaces. This befits the brittle nature of gypsum, which cracks under pressure. Because doors are swung shut, they endure similar stresses.

Since mud has been designed for wallboard, it is equally unfit for high-stress applications. If you’re looking to fill wood that takes stress (e.g., tables and floorboards), then the joint compound is to be avoided.

Substituting In External Applications

Wallboard is applied indoors, where the weather is relatively stable, and it doesn’t rain. This makes gypsum filler unsuitable for use outside. Remember that external wood filler is designed to flex and shrink with the weather.

Joint compound does not have this weather-tracking property. If used on outdoor wood, it will, in time, detach. Water-based mud is prone to shrinking and thinning permanently on contact with snow and rain.

Note that outside areas are less protected than the indoors. This implies that external wood is much likelier to be exposed to stresses than wallboard, which brings up the points in the section preceding. 

Substituting For Caulk

Calk is a damp sealant, and if the original application specifically calls for it, expect that these water-tolerant properties are critical. In those cases substitution with drywall mud is a bad idea, as the mud is built for a dry surface.

Water-based joint compound is particularly prone to damage under moisture. If pressed for a caulk substitute, try wood putty instead. It will not melt under moisture.

Substituting For Wood Putty

Here too, the application should be uppermost in mind. Small indoor wooden items with no stress loading and small blemishes can take joint compound as a substitute filler, and these are applications that are sometimes targeted for wood putty.

But mind windows. They look silent, but the banging on closure introduces stress that the joint compound is not fit for.

Which Joint Compound To Substitute With

If you have to substitute blindly, taping compound is your best bet. It is the toughest variety and comes closest to matching the hardness of wood filler. However, it is limestone-based and particularly prone to moisture-related caveats.

How To Substitute Joint Compound For Wood Filler

The application of joint compound and wood filler is similar, so in substituting, there is no difference in application. The compound will not be tinged to match the color of wood, and therefore will require painting (and sanding.) Unless the job is for an out-of-sight area, prepare for a total finish with sanding and painting.

Conclusion

There is no single type of joint compound. And no single wood-filling application. Whether or not you can substitute for wood filler depends on the nature of the filling job at hand and the fitness of the candidate compound.

Where possible, prefer substitution only in the use cases indicated above and only when there’s a compelling reason not to settle for wood filler. Ideally, plan your quantities upfront so that risky substitution is not required.

John

I love fixing up my own home and I set up this blog to help others do the same.

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