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Old 17th November 2012, 11:23 PM   #1
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Default MDF Telegraphing lines under paint.

Have done a bit of searching on this subject, i know a lot has already been said, but i do not see a lot of info on a possible solution i am considerind to eliminate the problem.

I have just completed my cabinet construction and next stage is filling screw holes and painting. cabinets are glued pva and screwed.

I'm wondering how successfull a trench or a "V" machined over the mdf overlaps would be, and then filled with automotive bondo.

Would this eliminate the usual lines that appear on the painted joins?

or am i creating a bigger problem?
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Old 17th November 2012, 11:42 PM   #2
Einric is offline Einric  United States
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Generally I try to have the front baffle be the full dimension piece to avoid this problem.

Lay the speaker down on it's back and "fill" the cracks with glue.
Do this multiple times if need be.
Then sand smooth.
After that, use drywall spackle to seal the end gran and compensate for the transition.
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Old 18th November 2012, 12:13 AM   #3
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I have previously on a smaller job used 2 part epoxy resin on the "end grain" that i have a supply of.
It worked ok. It did fill the "end grain" well. What do you think of using epoxy to fill the cracks, laying face up as you describe. Then skim off with bondo.
Im aiming for a dead flat paint surface.

Alternatively, what do you think of the trench idea? I have seen a postind somewhere where they used what looked like a 20 - 25 mm wide trench.
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Old 18th November 2012, 12:13 AM   #4
dewardh is offline dewardh  United States
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Quote:
Originally Posted by ermat1234 View Post
I'm wondering how successfull a trench or a "V" machined over the mdf overlaps would be,
It might be quite successful if you left it that way, and treated the relief as a deliberate "detail". Otherwise, veneer . . .
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Old 18th November 2012, 12:21 AM   #5
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Quote:
Originally Posted by dewardh View Post
It might be quite successful if you left it that way, and treated the relief as a deliberate "detail". Otherwise, veneer . . .
Veneering is not an option. Definitely going to paint.

Can you elaborate on the "deliberate detail" option, like a particular router bit?
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Old 18th November 2012, 12:21 AM   #6
Einric is offline Einric  United States
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Epoxy could get messy and hard to remove.
Just be sure to prime before painting.

Bondo works well, if you are good with it then use it.

I would maybe just get a V groove bit for your router and use an edge guide.
It should make a nice 6mm groove that shouldn't be hard to fill.
I have never heard of doing this so I would be reluctant to try it myself.
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Old 18th November 2012, 12:23 AM   #7
Einric is offline Einric  United States
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Use a bit similar to this.
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Old 18th November 2012, 12:57 AM   #8
kevinkr is offline kevinkr  United States
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I'm wondering whether routing along the joints would seriously compromise their strength, probably not something I would consider doing on a pair of cabinets I'd just constructed..

Perhaps a textured or faux finish would hide/disguise the joints?
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Old 18th November 2012, 01:12 AM   #9
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The MDF is 25mm with plenty of screws so my feeling is routing the joint lines would not compromise cabinet strenght.
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Old 18th November 2012, 06:48 PM   #10
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You could use a sandable primer to build up layers which will help cover joints and imperfections. It comes in gray spray can or regular paint can for rolling on. I like the color and the smooth satin finish enough to leave as-is without a topcoat...
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