Paint Cracks in MDF Painted Boxes - diyAudio
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Old 9th October 2006, 02:44 AM   #1
slhijb is offline slhijb  United States
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Default Paint Cracks in MDF Painted Boxes

PAINTING MDF SPEAKER CABINETS. With MDF painted cabinets, several posts over the years have mentioned that the paint eventually cracks at the joints due to expansion and contraction of MDF. Most of these diy builders have apparently used recommended procedures using Bondo, glue compounds or some sort of filler material to seal the cut or routed joints prior to prime and paint.

Some have suggested that there is no good solution for this problem if MDF is used and to use plywood as the exterior cover material instead of MDF. None of the posts I read gave a final solution to this problem.

QUESTIONS. Is this true the painted MDF cabinets will eventually develope paint cracks at seams and joints?

Does anyone know how to prevent eventual cracking in painted MDF enclosures?
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Old 9th October 2006, 03:29 AM   #2
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Only issue i have ever had with mdf was the edges soaking up more paint than the faces, that came from using cheap paint, never had an issue with high quality primer+paint.
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Old 9th October 2006, 05:22 AM   #3
soongsc is offline soongsc  Taiwan
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I believe the process is using Bonda or some other sort of wood hardener after you have finished with all the wood work. It needs to be done on the inside and out to prevent mosture from getting into the MDF. Bonda actually soaks in taking place of musture and using mosture to harden. There are also other compounds that furniture painters know about but I just don't know the name of the stuff.
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Old 9th October 2006, 09:34 AM   #4
Vikash is offline Vikash  United Kingdom
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I thought Bonda was filler? In any case, you could try some wood hardener as suggested and check out this thread: A solution to MDF expansion on joints, translams etc.
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Old 9th October 2006, 09:41 AM   #5
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I've been painting MDF for years, (not just for speakers), and have never had any cracking issues. However, that might be due to the relatively benign climate in the UK, so I wouldn't worry about it unless you suffer from excessive temperature or humidity.
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Old 9th October 2006, 11:29 AM   #6
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Living on the wet coast of Canada, MDF is exposed to nasty extremes in humidity and temprature and I have yet to experience any problems with paint. Though I choose to use fairly flexible stuff, definately no automotive emamels.

I have found the reaction to the binder in MDF to be more problematic. With strict environmental laws making most decent sealers unobtanium here, I seal off the boxes with a mixture of wood glue/water. Let it dry for several days, then paint.
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Old 9th October 2006, 12:18 PM   #7
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I use automotive primers and automotive paints and stay with a system, ie DuPont paints. Automotive paints are made to with stand extreme temperature changes (like the hood) and flex (like the bumpers).

I would suspect that cracks at the seams are due to the two pieces being allowed to separate. Standard old wood glue will shift with temperatures, so I always use screws (screwed and glued as I say) to hold joints together and bracing to keep the walls good and tight.
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Old 9th October 2006, 04:24 PM   #8
poobah is offline poobah  United States
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Use epoxy for your gluing and priming... problem solved... forever.

There is a place in Florida where I buy mine... $80 for a gallon... "U.S. Composites".

I use the stuff to make wooden boats... no cracks.. no swelling... no telegraphing... no nothing.

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