Over the course of my 25-year career as a cabinetmaker, I encountered MDF on a daily basis. The amount of times I’ve been advised to “use MDF instead” in outside projects is more than I care to count. They had no idea that I have been working with MDF for over twenty years and have even used it outside.
Waterproofing MDF and providing some degree of indirect protection from the elements are prerequisites for its use in outdoor settings. Regular MDF can quickly decay when exposed to the weather. Standard MDF is not the same thing as the type of MDF designed for outdoor use.
However, MDF occupies a special position in that it is suitable for occasional outdoor use but is susceptible to damage over time. Learn how well MDF stands up to rain and whether or not it warps in this in-depth guide to using the material outdoors.
MDF and Exterior Use: A Brief Overview
Most woodworkers agree that MDF should not be used in outdoor applications. This viewpoint is supported, to some extent, by my personal experiences. Depending on the severity of the weather, MDF can withstand it, but it still needs heavy covering.
Let’s take a closer look at what can cause MDF to deteriorate in the outdoors, starting with water.
Check out my piece for more info on the durability of MDF. You might be surprised at how far it can go.
Can MDF Get Wet?
Simply said, unfinished MDF cannot tolerate contact with water. Because MDF seems so smooth and without any visible grain, it is easy for inexperienced woodworkers or homeowners to assume that it is impervious to water.
Moisture doesn’t have as big of an effect on MDF because of its resistance to airborne water. However, it is irresponsible to use ordinary MDF in constructions that will be subjected to prolonged contact with water.
This video demonstrates how even minimal exposure to water can negatively impact MDF:
Cabinets in the kitchen ruined by water? Composite Lumber (Plywood/MDF Ultra/MDF/Particleboard)
View a video of MDF being submerged in water.
Finally, MDF is not completely water-proof, so don’t count on it. However, because it contains materials other than wood, the board is more water-resistant than untreated wood.
In my opinion, MDF is not a good choice for usage in the outdoors. Much effort is needed for setup and upkeep.
Does MDF Swell When Wet?
Long-term water exposure causes MDF to swell, especially at the end grain, however the entire material is porous and will take up water. The areas that have been exposed to water will become thicker and the face will begin to sag.
Water is still not a safe environment for MDF. Although I frequently encounter water stains and mushiness in MDF, I have never witnessed the material expand immediately after being exposed to moisture. See a man making an analogous case in the video below:
I was wondering if MDF will expand just from contact with water.
See a video of what happens when MDF gets wet
In spite of the fact that the MDF shows essentially no outward signs of growth, it degrades rather rapidly. This occurs when regular MDF is placed outside and subjected to frequent, heavy rain.
Please weigh the benefits and drawbacks of working with MDF that I’ve discovered over the course of my 25 years of experience in the industry before reading on.
Uses and Abuses of Medium-Density Fiberboard
less complicated to paint on
needs to be painted before being used outside
Insects won’t be able to eat it!
Sunlight might cause it to fade.
In other words, mould cannot develop on it.
Exposure to water causes it to swell.
It’s not as sturdy as wood, but it’s far cheaper than the real thing.
The MDF panels are available in a variety of conventional sizes, making them ideal for use in custom cabinetry.
It’s nearly impossible to hammer nails or screw into it.
In most cases, it has a smooth surface and simply sawing it can release harmful particles.
Advantages and Disadvantages of Using MDF
Did you know that standard wood screws can be used to fasten MDF without fear of splitting? In this tutorial, I explain how to screw MDF without cracking it.
Is MDF Ruined If It Gets Wet?
The structural integrity of MDF is compromised by even a little amount of water. Due to fibre expansion, mending is a tedious task. MDF’s once smooth surface will eventually become bumpy and unrecoverable.
Therefore, before putting something outside, it should be treated to make it waterproof. The way that water deteriorates wood and the way that it deteriorates MDF are distinct. When unfinished wood absorbs water, it provides an ideal organic medium for the growth of mould and fungi.
Whenever MDF is exposed to water, it expands somewhat and develops water stains. Wet MDF need not be a problem if you dry it quickly enough.
Woodworking
@woodworking
I managed to get them all cut out…the MDF I used was fantastic for painting and was incredibly straight. Don’t get it wet, and it can be quite hefty.
Steps to Take When MDF Gets Wet
You can either take the MDF out of its watery surroundings or drain the area around it.
Dry the board with heat (a hair dryer works well) or other means (a heat gun or indirect sunlight are also options).
If you want to prevent this from happening again, you should waterproof the MDF by coating the board with a waterproof sealer.
To be clear, the foregoing is only feasible in extremely rare instances of MDF being exposed to water.
How Do You Dry Wet MDF?
You dry wet MDF with a heat gun or a hair dryer. This speeds up the natural evaporation of the water, soaking up the board. The adhesive holding the board together can be damaged if the heat gun is brought too close to the board.
The adhesive failing to hold is theoretically possible, but in over 25 years of on-and-off work with MDF, it has never happened to me. Naturally, I didn’t leave any boards out in the open for twenty years. On the other hand, I used to leave boards outside overnight, especially in my early experiences with the material.
Wherever the sunshine was strongest, I found that MDF would fade and warp. So my advise would be to utilise a short-exposure heat source to dry the MDF instead of putting the material in the sun.
Hosegood Heating.
@HosegoodHeating
Wet MDF! The ideal holder for a cylinder. I doubt they gave it much thought.
Why Is MDF Not Suitable for Outdoor Products?
Because of its susceptibility to weathering, MDF is not ideal for outdoor applications. MDF is susceptible to deterioration from the elements, especially rain and sunlight. Material that is both watertight and fade-resistant is ideal for outdoor use.
MDF is resistant to termites, but it’s not waterproof enough to be used outside. In addition, prolonged exposure to sunlight causes the colour to fade. Only regular MDF will work for this.
There is exterior grade MDF, which is resistant to water and heat and hence suitable for use outdoors. This type of MDF retains its colour well and doesn’t fade when exposed to sunlight.
Where does leftover MDF go? Will you be burning it? BEWARE! You might want to check out my blog post on whether or not MDF is flammable first.
Is MDF Exterior Grade?
Unfortunately, not all medium-density fibreboards (MDF) are designed for outdoor use, and the majority are not watertight. There is such a thing as exterior MDF, which is made from denser and sturdier components. Most significantly, it does not let water in.
The most crucial quality of external MDF is its ability to repel water. If it weren’t there, not even the most well fortified MDF block would be completely safe. The “MD” in MDF stands for “medium density,” and MDF can only be manufactured so dense before it ceases to be MDF. To use proper terminology, it is now a wooden board.
Trey Lipscomb
@TrentonL
Thus, this is what occurs if you put MDF in a location where it might get wet periodically. What can I use instead of it?
Is MDF Waterproof?
In spite of the fact that waterproof MDF does exist, the vast majority of MDF is just moisture-resistant. In this way, the typical fibreboard is adequate for use in dry, indoor environments. A lot of people who work with wood consider this to be severely restrictive.
In such case, it is preferable to look for an alternate outside application.
Can You Make MDF Waterproof?
Using a waterproof coating, MDF may be made watertight in the comfort of your own home. Medium Density Fibreboard can be made waterproof with any sealant that can withstand water. As long as the seal is intact, the MDF it protects will be impervious to moisture.
Eco Advance Wood Siloxane Waterproofer, which is designed specifically to protect wood in the great outdoors, is the product of choice for waterproofing MDF. Even while MDF is somewhat impervious to water, a siloxane coating can make it practically indestructible.
It’s a touch more expensive because it’s made with an eco-friendly formula. Gorilla Waterproof Patch & Seal Liquid is a superior choice for individuals seeking a low-cost sealer for waterproofing MDF.
Plognark
@Plognark
For example, the medicine cabinet in my bathroom is made of prefabricated MDF, as mentioned by @Evelyn Hewett and @Hannah illo. It has never actually gotten wet, but just being in a humid area is enough to start destroying it everywhere there is a crack or gap.
Can You Leave MDF Outside?
Unless coated with a watertight varnish, sealer, or paint, MDF should only be left outside for brief periods of time. Heat has a deteriorating effect on MDF since it dulls the board’s colour over time.
This raises the issue of whether or not MDF should be placed in direct sunlight. As far as I can see, leaving MDF outside in the shade has no ill effects. Everyone can do fine if they only pay attention to their surroundings.
Leaving plain MDF outside in a very humid area can impair its integrity. The MDF boards can be left outside once they have been properly sealed against water.
Can Moisture-Resistant MDF Be Used Outside?
Outside use of moisture-resistant MDF is done so at the user’s own risk. Resistance to moisture is not the same as resistance to water. Because it is just moisture resistant, MDF can be damaged by rain. However, if a waterproof coating is applied to the boards, they will be protected.
If you won’t be using the MDF outside, there’s no need to go to the trouble of waterproofing it. When compared to treating or finishing wood, the importance of treating MDF for durability is lower.
If you’re wondering if you can plane MDF, check out my advice.
With the exception of kitchen cabinets, I wouldn’t recommend spending the time or money to seal MDF for usage inside. Furthermore, MDF is not something I would suggest installing in a restroom. There is a risk of water damage in each of these indoor settings.
Irishlck58
@irishlck58
Frustrated by @HomeDepot’s poor service as I try to finish a work in #waxahachietx. Despite the website’s assurance that there are more than 50 pieces available, every single one of them has been damaged by water. Wet MDF boards are still on the shelves. Transported a pallet containing additional water-damaged planks.
Can I Paint MDF Outside?
If the MDF board is of average quality, you can paint it outdoors without a priming if it is an exterior grade or weatherproof. Once MDF board has been treated with a sufficient number of waterproofing coatings, it can be used in outdoor settings.
When utilising MDF, you can rest easy knowing it will last a lifetime as long as it is painted with a coating that is both watertight and resistant to ultraviolet light. After then, it’s as sturdy as the design of the board will allow it to be. When MDF isn’t watertight, you have to prime it. Moreover, that’s the case in the vast majority of situations.
Waterproof MDF is not something I’ve ever bought by accident. So, you should probably presume it is not waterproof if you didn’t go out of your way to find exterior-grade or waterproof MDF.
Outside use is not recommended for pocket holes made in MDF. The reveals MDF’s exposed interior.
Will MDF Dry Out?
If you store MDF in direct sunlight or use a heat gun or hair dryer to dry off small areas, the wood will dry out and crack. The MDF building material is not meant to soak up water for extended periods of time. However, if water is allowed to pool within the board for an extended period of time, it might cause warping.
So, it’s in your best interest to hasten your recovery. However, MDF cannot be scalded in an effort to speed up the drying process.
The following are the ways for drying MDF, from safest to riskiest:
We recommend placing the MDF outside, but in a shady area, to allow the water to evaporate.
Hover a blow dryer over the damp area very gently. Keep a distance of at least six inches for this.
You can heat the water with a heat gun, but you’ll need to adjust your distance from it.
Position it in direct sunshine; this may speed up the drying process but may also dull the colour of newly manufactured MDF. In most cases, you shouldn’t use that approach.
Outside storage of MDF is fine, and the material is not as delicate as some woodworkers claim. Its colour will fade in bright sunshine, and if you live in an area where it rains frequently, you should generally avoid using MDF altogether. If you insist on utilising MDF, though, you’ll have to either upgrade to exterior-grade MDF or treat it with a waterproof sealant.
