How to Use Expanding Foam Filler for Wood Before Painting?

Expanding foam filler is one of the essential products for those who create, fix, or restore wood items in the home.

Using expanding foam filler is pretty straightforward.

• It comes in a can that can be quickly applied to the hole, crack, or pore.
• Once applied to the wood cracks, it expands to fill the gap.
• When it dries, you can sand or trim away the excess and then paint over.

Expanding foam filler is also used to seal gaps around pipes, wires, and other openings.

For creating a more energy-efficient home, expanding foam filler is a good product to have around.

However, there are different types of expanding foam available, so you will need to consider the options.

Making the best-informed choice starts with understanding how the product is used for various projects.

And what are the things you need to look for before picking one?

So, let’s dive in straight…

How is Expanding Foam Filler Used?

The first step to using a fix and filling the expanding foam is to clean the area in which the expanding foam filler is to be used.

Use a brush to sweep away any surface dust, dirt, or debris.

Then, spray lightly with water and wipe away the area so that it is clean.

Because expanding foam filler needs a little water to properly cure, you do not have to dry the surface before applying the product.

Step 1. Put on the Protective Gear & Read the Instructions:

Be sure to wear gloves when using the product.

Now, read the instructions carefully and follow them to the letter.

In most cases, the foam will exit the can from the nozzle or gun that comes with the product. 

Step 2. Spray the Foam:

Hold the can upside down.

Place the nozzle into the area that should be filled and press the trigger.

Remember that the foam inside will expand to double the volume that is applied.

So, fill each hole or crack about halfway up and then stop.

Let the foam expand until it reaches the top.

If not, add up to half the remaining area that needs to be filled.

Step 3. Mist with Water:

Once the foam has reached the desired level, mist it with water.

You should do this for each layer of foam that you apply.

Once completed, let the foam fully cure, which under most circumstances should take about 60 minutes.

Step 4. Trim & Sand:

Once the foam fully hardens, trim away the excess.

You may need to use a hacksaw to do the job.

Once the excess has been removed, you can sand the top to get a smooth finish.

Once the sanding has been finished, you can paint, stain, or plaster over the top.

Can wood filler be used over expanding foam?

Yes, you can put wood filler over expanding foam to fill small holes.

But remember, if there is a wood rot present, it will not fix that beneath the expanding foam or polystyrene.

Using wood filler over in that case will be pointless as the rot will still be there.

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Where Should You Not Use Expanding Foam?

While expanding foam filler feels like a product you can use for most projects that require holes, cracks, or openings to be sealed, there are exceptions.

a) Heat:

Expanding foam filler is flammable.

So it should be kept away from sources of heat such as certain types of lighting, electrical boxes, and outlets near the walls.

b) Doors & Windows:

Some expanding foam sealant products may warp or distort materials like wood.

Thus they should not be used on doors or windows because they may affect how they open and close.

Instead, look for specific expanding foam products designed for such uses. 

c) Insulation:

In small quantities, expanding foam filler can seal gaps that help insulate the home.

But if you have a much larger area to cover, there are other, far better products that will provide insulation.

So, you should use standard insulation products for your home or for large areas that need to be covered.

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How to Choose the Right Expanding Foam for Wood?

Just like selecting the right type of paint, tool, or material, you should give the same consideration when choosing an expanding foam filler product.

Most expanding foam fillers are made from latex or polyurethane.

It is combined with a polyol resin and isocyanate so that it can expand on contact.

When the mixture inside the can is sprayed, its contact with the air will cause it to expand and dry.

If it has yet to dry and you need to remove it, acetone will do the job.

But if it has hardened, you will need to scrape the product away using a file, knife, or other appropriate tools.

Most importantly, the expanding foam filler you choose should match the project.

For example, areas that are outdoors (like concrete, brick, stone, and plaster) or part of a water feature should be waterproof.

There are specific expanding foam fillers designed for use on wood windows, doors, and metals.

All you need to do is choose the right one for the job at hand. 

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The Best Expanding Foam Fillers You Can Use for Your Project

There are four basic types of expanding foam filler products.

They are designed to cover specific situations, so be sure to choose the right one.

1- DAP:

This type of expanding foam is best suited for sealing up openings to your home.

It can resist entry from mice and rats and is approved by the EPA. It does take up to four hours to dry, but it is quite good at sealing up holes in the exterior.

2- Loctite:

Perfect for small cracks and holes, Loctite can be used on many types of materials.

Plus, it is resistant to ultraviolet or UV rays.

3- Red Devil:

This is to cover larger holes and cracks compared to Loctite.

This foam will expand to three times its initial size when sprayed.

It is also waterproof as well, making it perfect for sealing against the elements.

4- TotalPond:

Waterproof and designed for use with all types of water features, TotalPond will increase three times its original size and will fully harden within 24 hours.

For ponds, waterfalls, water fountains, and the like, TotalPond is the perfect expanding foam filler.

5- Gorilla:

Gorilla weatherproof expanding foam filler is a waterproof product that can quickly squeeze into gaps and fills them tight.

It’s an ideal solution for filling large cracks and holes in wood, stones, brick, and metals.

The good thing is the product can be easily cut, sewn, painted, and sanded once you have applied it tight.

6- Wickes:

Wickes is a popular brand in the UK, and the green-colored expanding foam manufactured by them is available in a 0.75 L nozzle type can for easy application.

It’s easy to use, fix and fill hard-to-reach areas. And can be applied for insulating against heat, sound, and moisture.

You can use the product for interior as well as exterior purposes, where it can expand up to 30 times its original volume.

Final Thoughts

Expanding foam fillers are great to have in your tool kit when you are repairing or renovating your home.

The foam will fill holes and gaps by expanding quickly, so the item can be repaired and painted if desired.

Of course, you can also search for many other types of expanding foam products (besides the one I have discussed above) if you have a particular project in mind.

Remember to read the label and follow all instructions before applying expanding foam sealant.

Plus, be sure to research to fully understand what the foam product does, how it works, and any quirks it might have before purchasing.