Thread: MDF Exterior Trim

A while back I posted a question about how well Exterior MDF trim held up. I had an inspection yesterday on a 10 year old house. I found that it doesn't necessarily hold up very well over time. The 1st picture shows the swollen end of a piece on the front of a dormer. The 2nd picture is the bottom of the other side of the dormer (the flashing was screwed up too). The 3rd picture is over-exposed but it is the where the second piece has expanded enough to split, crack, and bow out from the wall. These are just the best examples of failure. The second piece was probably cut too long, forced into place and nailed instead of taking the time to trim off bit for a better fit. But the first piece had at least 1/2" clearance up from the flashing.

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MDF interior trim in damp locations is prone to getting moldy. The unpainted backsides absorb moisture. Once the mold gets started, you have to tear it all out and replace it. Maybe that was the strategy here as well? A quick cosmetic facelift.

Didn't even know they sold MDF for an exterior application. How could that ever work !

Originally Posted by Stuart Brooks

A while back I posted a question about how well Exterior MDF trim held up. I had an inspection yesterday on a 10 year old house. I found that it doesn't necessarily hold up very well over time. The 1st picture shows the swollen end of a piece on the front of a dormer. The 2nd picture is the bottom of the other side of the dormer (the flashing was screwed up too). The 3rd picture is over-exposed but it is the where the second piece has expanded enough to split, crack, and bow out from the wall. These are just the best examples of failure. The second piece was probably cut too long, forced into place and nailed instead of taking the time to trim off bit for a better fit. But the first piece had at least 1/2" clearance up from the flashing.

I remember that post. Exterior envelope of a residential building and again you pointed out the trim around----window trim if I am not mistaken.
I will look at this in a new light up in Canada.
Thanks for the heads up.

Originally Posted by Phil Brody

Didn't even know they sold MDF for an exterior application. How could that ever work !

It has been used for years and it is still being used by many builders.

Originally Posted by Scott Patterson

It has been used for years and it is still being used by many builders.

It surprises me to this day of little cost it would be to upgrade the materials used when building ones home.
I live in Montreal Canada and only see this practiced by the most inexperienced builders.
They are mostly cash cows that spend every cent at times on beer and cigarettes.
We have stick regulations and guidelines and the consumer play the BIGGEST roll in letting this type of building practices happen.
Thank you Mr.Patterson. We talked before and will do so again.
I find you observations, true, concise and note worthy.
Thanks....Robert

I can't imagine using mdf outside. I don't think I've seen that in lumber yards here. Like John said, what about the unpainted back side?

Yesterday (after driving 4.5 hrs from Dallas to Tyler - normally 1.75 hrs), I was looking at my snow-covered home with brick and vinyl siding. I was thinking, "thank goodness for products that hold up reasonably well in the elements."

Most houses with exterior siding and trim built in the last 30 years or so has some kind of composite material instead of real wood. These materials hold up very well if properly installed and taken care of. As far as the backside of the boards they are primed front and back. (Actually you are able to use one side of the board for a grain look and the other side for a smooth appearance.)

Originally Posted by Jeff Langhorn

Most houses with exterior siding and trim built in the last 30 years or so has some kind of composite material instead of real wood. These materials hold up very well if properly installed and taken care of. As far as the backside of the boards they are primed front and back. (Actually you are able to use one side of the board for a grain look and the other side for a smooth appearance.)

Now you point out the obvious flaws.
Primed all side and properly painted.
The second is the use of MDF.
It is not the greatest composite for exterior use in damp and extreme weather climates. Its lack of maintenance is whats dams its longevity.
There are superior non wood composites that will out preform MDF and ( last ) weather longer even when proper maintenance schedules are extended by a year of two.

Are you sure that's MDF. It appears to have a wood grain to it. It looks more like a product called Smart Trim made by LP. It's an OSB with wood grain texture. They also make a few grades for holding up to moisture.

Originally Posted by Door Guy

Are you sure that's MDF. It appears to have a wood grain to it. It looks more like a product called Smart Trim made by LP. It's an OSB with wood grain texture. They also make a few grades for holding up to moisture.

It's MDF. It's the first I've seen with a molded wood grain surface. This particular builder (R___ Homes) now uses smooth surface face and back. Until I saw it in a pre-drywall inspection where raw edges were exposed, I "assumed" it was vinyl. When painted, the sawn edges of both materials look very similar. Now, I probe

Originally Posted by Stuart Brooks

It's MDF. It's the first I've seen with a molded wood grain surface. This particular builder (R___ Homes) now uses smooth surface face and back. Until I saw it in a pre-drywall inspection where raw edges were exposed, I "assumed" it was vinyl. When painted, the swan edges of both materials look very similar. Now, I probe

Mr.Brooks.
You point to an obvious through inspection technique.
Many are to shy to prob because of ESOP.
Others are untrained for comparison and others still walk by the issue of description of material and just point out obvious defect.
I think to be good HI you must investigate and describe.
Thank you for your obvious interest in your professional trade.
Thanks.......... Robert

Originally Posted by ROBERT YOUNG

Mr.Brooks.
You point to an obvious through inspection technique.
Many are to shy to prob because of ESOP.
Others are untrained for comparison and others still walk by the issue of description of material and just point out obvious defect.
I think to be good HI you must investigate and describe.
Thank you for your obvious interest in your professional trade.
Thanks.......... Robert

The main reason is that it is now clear to me that the MDF will require the same maintenance as wood where solid vinyl is pretty much maintenance free if installed correctly. If vinyl is painted in accordance with the manufacturer's recommendations, the paint is supposed to last much longer than on wood or other moisture absorbent materials.

The next time I inspect a new home built with MDF trim, I will ask what the sales agent has to say about the trim. Do they claim it is maintenance free?

(Brian, we need another emoticon or smile icon. A little horned devil with a grin)

I would include in my report a statement as to the particular need for routine maintenance to the MDF trim. Most homeowners would not know the difference between Azek and MDF trim but their bank account will.

Originally Posted by Stuart Brooks

The main reason is that it is now clear to me that the MDF will require the same maintenance as wood where solid vinyl is pretty much maintenance free if installed correctly. If vinyl is painted in accordance with the manufacturer's recommendations, the paint is supposed to last much longer than on wood or other moisture absorbent materials.

The next time I inspect a new home built with MDF trim, I will ask what the sales agent has to say about the trim. Do they claim it is maintenance free?

(Brian, we need another emoticon or smile icon. A little horned devil with a grin)

I might be misreading your post.
I am agreeing with you. As for your last thread I disagree.
MDF does not have the same longevity as WOOD.
There are also many species of WOOD for different applications.
As for Vinyl. It is not maintenance free and as for painting vinyl. I never and will never.
Maybe you read my post wrong but I did agree with probing materials for several reasons. All of with have to do with extracting information pertaining to that materials condition or health.
As to your comment of the devil smiling icon.
I see your true intent .There are enough icons here in my view.
Negativity and apparent alliteration has little usefulness.
So instead of going to salesmen for insight for paint ( RIGHT ) GO THE THE TRADES MAN THAT USES THAT PRODUCT OVER AND OVER AGAIN.
Medium density fiberboard. Its man made Mr.Wood.

Originally Posted by ROBERT YOUNG

I might be misreading your post.
I am agreeing with you. As for your last thread I disagree.
MDF does not have the same longevity as WOOD.
There are also many species of WOOD for different applications.
As for Vinyl. It is not maintenance free and as for painting vinyl. I never and will never.
Maybe you read my post wrong but I did agree with probing materials for several reasons. All of with have to do with extracting information pertaining to that materials condition or health.
As to your comment of the devil smiling icon.
I see your true intent .There are enough icons here in my view.
Negativity and apparent alliteration has little usefulness.
So instead of going to salesmen for insight for paint ( RIGHT ) GO THE THE TRADES MAN THAT USES THAT PRODUCT OVER AND OVER AGAIN.
Medium density fiberboard. Its man made Mr.Wood.

Things are apparently a little different here in the states Robert Few houses are built where there is a "choice" of materials. The tradesman doesn't have much choice either. The majority of houses are spec built by developers who decide what materials will be used, and how much they are willing to pay for piece work jobs. Built it as cheap as you can and try to get it to pass code inspections.

When my dad built houses he never used anything but clear fir for exterior trim, fascia, and rakes. Everything was primed before it was put up. Nail holes and joints were caulked. I see older houses today that were built with old growth Southern Yellow Pine including lap siding. Except for a few areas where the wood was subject to water exposure over a substantial period, the wood is solid and hard as a rock.

However, we can't get first class lumber anymore. Well, any that the average person could afford. The best lumber is exported. What is classified as #2 common now would have been pulp or firewood 50 years ago.

Salesman - No that was to see if they were telling the buyers that the house had a maintenance free exterior when it is now apparent that the MDF trim would have to have the same maintenance as finger jointed white pine wood trim if was used. That is where the little devil icon would go.

Originally Posted by Stuart Brooks

However, we can't get first class lumber anymore. Well, any that the average person could afford. The best lumber is exported. What is classified as #2 common now would have been pulp or firewood 50 years ago.

So true.

Looks like they do make mdf for exterior Exterior MDF Packard Forest Products Columbus Ohio
But around here they use a particular brand called Miratec House Trim by MiraTEC Exterior Trim Advantage

The problem is that installation of the material as shown in those pictures is the culprit for failure. Any end should be painted/treated and not come in contact with surfaces such as porches, driveways, roofs etc.