I had the following problem on my own home. I’ve fixed most of it and am mainly interested in knowing what went wrong so it doesn’t happen in the future and I get a call back for life.
Cased my doors and windows with MDF, as I have many times in the past with no problems. Got a distinctive bump at some of the nail holes.
Interestingly enough only on the ones that were hand driven. No issues with the gun nails. Pre sanded the gun nail bumps before any filling. Instructed the painter to use a shellac based primer, which he did. Finished with acrylic. I am in a new part of the country with new products.
My thoughts of possible problems are:
1. The MDF is different and doesn’t seal as well. It is a light brown as opposed to a darker one that I had used before. Both face primed.
2. The spackle was inferior. It was Dap instead of Crawford’s and didn’t take the primer well.
3. The primer sucked. Can’t remember the brand. Although some areas were resanded and re primed.
Something caused the swelling. Any thoughts?
John
Replies
Were the bumps there before the finish was applied?
MDF is famous for "volcanoing" when nailed, cause the nail displaces the fiber to the path of least resistance, which is usually the surface.
"Why do you hurt me when I do bad things to you?" My youngest son to his older brother
That's why we always sand after nailing, before any paint prep work. Part of the reason I'm so baffled.John
Water-based primer?
Maybe the hand driven nails were a thicker nail than the ones in the nail gun, which resulted in them taking a little longer to finish the process of swelling the MDF that was displaced.
I did some trim work with MDF at MIL's house and I had predrilled holes that I hand nailed. Trim crew did some also which they put in with a nail gun. In both cases, nail locations were filled and sanded. In this case the nail gun holes all showed up later with swollen bumps, which leads me to the conclusion that the swelling keeps happening for a while. The predrilled ones were fine since no swelling pressures existed.
I learned that lesson to, we now predrill and use trim screws to attach MDF trim. Have not had any problems since going that way.
nailer
"we now predrill and use trim screws to attach MDF trim"Wow, there goes the percieved cost savings
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with a technique like that, shouldn't he be calling himself "screwerman"?
I had that problem years ago but you noticed the volcanoing as soon as you nailed it but since they brought out that light MDF I've never noticed the problem. Noticed might be the key word . Light MDF was supposed to stop that volcanoing.
roger
Is this volcanoing like the guys are talking about or is the filler actually protruding due to drying of the mdf?
It's the mdf by itself. When the nail goes in it(the mdf) displaces the mass of the nail and the only place it(the mdf) can go is up, therefor volcanoing.
roger
Got it. All I can rec. is skinny nails. Maybe use some glue between the jambs and casing to reduce the amount of nails too.
This is just a guess as to what might be happening. MDF is probably compressed during manufacture. If water based putty is used it may cause additional swelling of the fibers. Perhaps water based paint also swells the disturbed area more than the surrounding area, possibly because of the porosity of the spackle or the break in the factory primer coating. If true, that suggests that a non aqueous filler, such as a solvent based wood putty, might be better.
My first post refers to "light"mdf. A few years ago my supplier had a pamphlet showing the attributes over ordinary mdf. Not only did it stop volcanoing but it was lighter as well. I thought it was still heavy as hel but what do I know. To be honest I've never checked whether I get light mdf or oridinary mdf or whether there is in fact only one being sold. As to which one, I really don't know
roger
Sounds like predrilling would have been important. I've included a picture of the casing with one of the bumps I missed. I had to nail at an angle so I didn't go thru the bead, one of the reasons for hand nailing. Could have made the problem worse. Thanks for your help.John
View Image
Peace out.
I thought it was still heavy as hel but what do I know. To be honest I've never checked whether I get light mdf or oridinary mdf or whether there is in fact only one being sold. As to which one, I really don't know
Roger
There is a light weight MDF and it's still heavy!
The problem with the light weight over the regular is that the light weight will delaminate easier then the reg. also it doesn't hold a Centrex screw like the regular stuff. In some cases that might not be a problem but I know that at one time our shop had switched and we have now switched back to the regular for that very reason.
Doug