Repairing Joint Delamination at MDF Trim

I don't know what a "drywall" compound is, but in Australia I often use polyester "bog", ie "Builders Bog" which is similar to car filler. Actually, body filler is better. You can also get a builders bog in tubes where you cut off what you need an catalyse it by kneeding. I think these are epoxy based. I know many builders, painters and maintence blokes who always catty these.

For what it's worth, good luck.

RRV

"Builders Bog" we suppose we call this material Bondo in the states. It is used extensively as a body filler. This is what we used as the initial repair material. Our guess is that the technicians that did the repair applied it after it had already began to set up. And because of this we believe that the adhesion to the substrate was inadequate to bond to the MDF.

Hello alex1,

I was in the building industry for some years and, though MDF is easy to use, it is not the finish material I would expect in a Library . It just gets so much use. Only a solid wood product like ply and or 'faced' block-board is really up to the task in my opinion.

There is several different grades of MDF some would be extremely dense and hard and may well be OK in your situation. And I do realise it sometimes comes down to price! They get what they pay for.

But as a 'trim' the last thing I would choose is MDF. Some of the more usual grades absorb moister from the air and swell. As well as any moister from any 'filler' which was applied.

The only way to use MDF is with a properly built system of connectors which 'hide' the edges. I am still looking on MDF but it would be more useful if you could explain exactly where the MDF is used for and whether it takes and knocks from general wear and tear? Is it on a wall, or doorway, a window sill?

Is this project finished and you are running down the 'snagging' list? Or is it still being finished, in which case you can change what you do in other 'rooms' or areas.

Take care and please keep me informed.

MDF was the trim material that was specified by the Architect. It was applied to the perimeter of aluminum storefront and around the windows in the interior of the Library. The ambient temperature and humidity is fairly well controlled. The vertical application is not where patrons are able to bump or knock the material. This is a punch list item and we need to scrape off the prior repair (Bondo) were it delaminated from the MDF and popped off the surface paint. The delamination appears to be between the Bondo and the MDF. We suspect the Bondo was applied after it's set time.

I am in the home remodeling business and although I dislike mdf for anything but counter tops , this does not solve your problem. I would suggest using a paintable acrylic caulk. This stuff sticks to about anything and is pliable enough that it will absorb some movement.

oilcan13

Do you have any product names you can suggest? We considered a caulk, but getting it smooth and flat was thought to be a problem.

You will not be able to get a caulk product to perform as you wish. It will always be a visible repair. How wide are the joints you are filling?

The caulk will always have a slight deformation, and if this is in a library, and a local, state, government job to boot, you will always be in the crosshairs of the architect if you try to use caulk as a repair material.

Dave

The joints are from 1/32" to 3/32". Some of the joint problems are that adjoining pieces are not on the same plane.

I would sand/scrape the old, failed material off and would try the bondo route again, but maybe with the glazing/spot putty as a test on one joint. It might have been a dust issue causing improper adhesion.

Are these joints laps or corners?

If you are trying to marry two pieces together to make one longer piece you may have better luck replacing the trim. Trying to get two pieces to bond at the end grain will be problematic. Since you say that the pieces are out of plane is this an issue of the MDF moving? Swelling? Absorbing moisture from the paint? From the wallboard? From the air? From the storefront?

Since we are dealing with cardboard, smashed to a solid piece, the cut ends will suck moisture like a sponge. I have shelaced the ends to seal them, used diluted glue to seal ends, sanding sealer on the ends, primed painted ends to seal, etc....

MDF is a bugger to finish due to the porosity. Keep us posted on the resolution!

Dave

The joints are butt joints. We believe the out of plane joints are due to shoddy installation.

I think you hit the nail on the head. It is far easier to butt the ends together and continue on than to cut a 45 on them and glue them/nail them together. Unless the pieces are fastened to eachother they will continue to move around just enough to cause the finish to crack and pop.

You might try an epoxy to tie them together, or something similar. I hate these kinds of surprises on a finished product. The seemingly insignificant actions of a trim carpenter makes the GC look like a boob in trying to resolve a situation where there isn't a clear cause/effect.

I would drive this down the ranks. Get the carpenter to take the piece off and replace it with one long enough to span the entire distance. MDF is a PITA to splice. Pieces aren't necessarily the same thickness either to further compound the problem. You will be messing around far more with this than you like.

5 out of 50 huh... Well at least 90% are ok! :)

Good Luck!

The store fronts are about 30' wide with with an arch on top. The total assembly is about 30' tall. The trim is both vertical and horizontal on the assembly. The MDF all from the same bundle and very same in thickness. The trim in a storefront assembly has trim shooting off horizontally as the end trim goes vertical. Scarfing joints in a linear run is possible...what besides a butt joint can you do when it shoots off horizontally from a vertical run?

I'm not following your description. A picture is worth a thousand words.... If you're able.

If you can scarf the joints on the horizontals that would fix the movement issues there. Just make sure they glue the joints as the two pieces will still move independently otherwise. I am not picturing your joint on the horizontals from a vertical run though....

Perhaps a spline cutter to spline the joint at the intersection? I'm just throwing that out since I don't have a clear picture of what your joint looks like.

Dave

Sorry it took so long to get back to You, You probably have the problem fixed by now. If not the answer to Your question < any good paintable caulk will do. it can be tooled to form the curves of the molding. Contrary to "dlingos" comment I have had good success with this method, considering the gaps are a max of only 3/32". Any larger then 1/8" would probably not work as well.

I would think this would be the least time cosuming and cheapest way to go for an acceptable repair, especially if You have to pay the costs.

Good Luck

oilcan13

I have also used MDF trim, albeit not on an aluminum storefront. I wold be hesitant due to the possibility of the extrusion sweating, low outside temps vs. inside temps, etc.. I've has storefronts literally raining with moisture when painting, finishing interior commercial spaces.

In my situation we used plain old bondo and it worked fine. I suspect that the installer/painter didn't clean the dust from the trim prior to application of the filler and this is the cause of the failure.

Is this problem systemic, as in every place the filler was used, or is it an isolated condition on one or two places?

Curious to see how this turns out....

Dave

5 joints out of 50 are failing.

Hello alex1,

You are in a pickle. And all of the architects making! I doubt whether he has ever seen any MDF let alone knows what the initials stand for!

It is singularly the worst choice of material to do this job.

I do not like to be the bug in the custard here but, MDF, no matter what filler and bodging is done will fail and you will be back there month after month!

It is not your fault. Why is this trim there, what does it do that cannot be done 1000 times better with real wood or aluminium? If it is inside, the material of choice for a Library and, a Government Library at that, would have been tile, wood, aluminium or something that did not need 'finishing' by painting. Even melamine plywood would have been a better choice. I think you should also get the architect into this discussion, rather than taking any flak yourself.

Chances are, the 'bondo' failed because it was used on paint. On a high gloss paint it is not the done thing to throw filler at it. Really unprofessional! To say the very least.

If it has to stay you want to put your foot down with a hard hand, and demand the architect and the architect's Boss looks at the problem and, that he admits he totally screwed up. You say 5 joints have failed. But, each time a 'mend' is tried the next bit gets moved or loosened. Try using some good old English words when you have your meeting with the chippy's, architects and designer. Try words like S-it, crap, load of bo-lo-ks, etc.

What you could try and you may have to show the chippy's how to use it. If it is painted we have to accept that. But bad joints are not clever. Get all the joints made tight, and, on anywhere there is a join cover that join with half round bead in solid wood. Try and make the joints simetrical around the window and the half round with its brass screws with look like they should be there instead of hiding a fault. It can be made a 'feature by using tiny brass screws. It starts at about 1/4" and goes to about 2". That is 6mm to 50mm. I would have the bead fixed on really soft putty if it it has to be anywhere near the glass. Or the wood and the MDF will rot after a couple of years from the water from condensation.

In a Library there are alway people right? Well you can bet on a visit each person will release a litre of water through breathing, and there is going to be times when that is going to find its way down behind any surface the water runs to and on.

I mentioned it once but that 10% failure will be 100% and it will continue ad infinitum.

Bad workers always get someone else to pick up the pieces. In truth they would not know how to do a good job. It is not part of any training these days it seems to me.

I would buy a house near the Library because it will be your second home!

Does this 'architect' ........bloody laugh!.........Design bridges from sawdust or talcum powder?

Hey, sorry my friend alex1, I was not getting at you so much as at the system which allows badly educated, unskilled workers to make what will be the Town eyesore very soon. Do they not have any pride? It should be a feature, not an eyesore!

Good luck and keep us posted please?

Try to have a great year OK?

My sentiments exactly!

If these so-called architects were to ever come over to the dark side and actually build these things they would understand immediately.

Why they would spec an MDF product in a public facility which I'm sure has a fairly high occupancy is beyond me. The possibility of moisture issues is far too high to negate any supposed cost savings on materials. Unfortunately, the bottom line is the driving factor and as has been stated and you all know, you get what you pay for! Besides, the architect can always attempt to point the finger at the GC, carpenter, painter, etc. to deflect the true cause of the problem which is the material itself in the completely wrong application.

I also agree on the condensation issues causing the product to eventually fail. And it will be a thorn in your backside for sure. MDF is problematic in sealing and finishing, especially in a public project as you will be in the public eye constantly. As babybear said, get a home close to this library because you will be back often.

Now with all that said, gluing, epoxying, biscuit cutting, dowling, nailing, screwing, etc. will be your only options in joining this material together to attempt to stop the movement. The sad truth of this is that had the architect not specified MDF but oak trim you would not be in this situation.

Please do keep us posted on your progress and hopefully resolution.

Dave

Definitely get the architect and carpenter in the same room, present what you know and or suspect, and ask them to develop an acceptable solution to the problem. If the MDF will continue to be used, make sure the architect and carpenter understand it must be pre-sealed and pre-painted on all sides before being installed. Make sure they understand the products must be compatible with the MDF and good quality.

The borders on "Errors and Omissions" by the architect, and shoddy workmanship by the carpenter. If either are professional and care about their reputations, they should want to work with you to get things right.

Now that I have cooled off a bit, 2 products come to mind.

First is "MH Ready Patch" by Zinsser. You clean out loose stuff in joints, you may neet to prime with Zinsser Primer-sealer.

Second is "Rock-Hard", a powder that is mixed with water and troweled in. I used this to fill holes in garage door 4 years ago, and it is still holding up. Not a pretty repair, but I am not the greatest with a trowel.

Hello Dlingo:

Appreciate the mention, thanks. It does seem most everyone on the thread is of the same mind...........MDF, good........but used in the wrong place as for sure!

If this is just a 'trim' the cost of this ongoing problem will more than out-weigh the cost of even solid oak having been used instead!

We always had the architect on site so there was no way this kind of debacle could happen. If there was something queried, the site manager, architect, and whatever Trade was concerned had a meeting then and there. No waiting days or Weeks/months/longer for decisions to finally be realised as wrong!

I would not be surprised if the 'architect' 'in charge'....sorry while I laugh!......Is about 20 and this is his first job and, he wants to 'prove' himself, so asked no one for advice?........Discusting and sad. I wonder if the same kind of ignorance to detail would have been let by in a bridge build?

I hope the OP keeps in touch. Not that it will help, unless we can somehow give him that extra little strength to get the problem sorted by using decent material for the finish of this doomed project? Can only hope it works like that. There is times when the person in charge is JUST THAT! And gets down and dirty with all and sundry to sort things out so they can all look at this Library as they drive past and think, "That looks good!, Glad I was chosen for that build"! Or similar?

Take care to you..................

I have used MDF for many cabinet projects, and especially those that took a high gloss finish. Or a finish where all defects were visible unless smoothed out well. I have used BONDO and had very little problem as long as it was applied properly. My thought is that it was improperly applied and finished. I think removal of the old bondo and a fresh, careful application will correct the work. god luck john

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