Brett said:
After reading John's thread (post #20) I'm not so sure I'll continue doing this without prepping the MDF first. And as this stuff works better with a small amount of moisture (I generally wipe one surface with a dmap cloth before applying it) I'm not sure that I'll continue using it with speaker joints.
That said, all I can remember at the moment is that it's got a 'mostly' green label, and that iut's been sitting in the dark cupboard for about 4 months, unused and unloved. I'll see if I remember to look at it and post when I get home...
Hi Jon,
A small amount of moisture applied to the surface prior to the urethane glue shouldn't be too much of a problem. My reference in that thread is for the kind of finish that Ant (Shinobiwan) does and Gordan (Sploo) is doing - the high gloss piano black.
Given an adequate time to dry out, it should be fine.
A small amount of moisture applied to the surface prior to the urethane glue shouldn't be too much of a problem. My reference in that thread is for the kind of finish that Ant (Shinobiwan) does and Gordan (Sploo) is doing - the high gloss piano black.
Given an adequate time to dry out, it should be fine.
Agreed. My prep has previously not involved sealing the inside of the cabinets before construction. As they're invariably sealed boxes I haven't worried too much - but as the bones get older (I think I've got 3 years on you) the number of boxes I intend to build gets smaller. So I want to do them right.
Is that the Gorilla WOOD glue or the 'standard' glue that is PU and expands?
Which one is recommended for the MDF of the enclosure?
I used a polyurethane glue for all the joints. No point in quoting a brand name because it came from a general builder's supplier in UK. The boxes were made from 30mm thick MDF with simple overlapped joins using bisquits. Then the exterior edges were rounded off with a router. With no special coatings on the cut/routed areas I gave them several coats of nitrocellulose car primer. Then stopper on any defects. Another coat of primer then flatted off with 400 wet or dry. Then 5 coats of nitrocellulose colour coat. Let cure for about a week and then wet sanded with various grits up to 1200. Then compound polished with a buffer. They have been in use for about two years now and are still in perfect order. Nothing has moved or cracks appeared. I am much happier applying a paint finish than trying to veneer around corners.
I like Poly glue for MDF joints as well, but for sealing the edges of late, I've been using West Systems clear epoxy. This has worked BETTER than EVERYTHING I've done prior. I just coat the entire cabs in prep for paint or whatever. It takes 2 coats; 1 soaks in and seals, 2 adds thickness and gloss.
I used to use straight Elmer's white/school glue rubbed in with my fingers, and it does the job. It just does not do it as well as the epoxy.
Wolf
I used to use straight Elmer's white/school glue rubbed in with my fingers, and it does the job. It just does not do it as well as the epoxy.
Wolf
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I was pleased to see someone using West Systems for speaker building. It would be my first choice for anything structural and it excels in any sealing role. I used it for many years for boat building. It is designed to penetrate rather than just stick to a surface like most adhesives. Great stuff if you can find it, and afford it.
edit: It is essential that anyone using it read the full instructions and guidance from the manufacturer. Before any sort of finish the epoxy surface needs to be cleaned of any "waxy" residue and abraded to form a key for later coatings.
edit: It is essential that anyone using it read the full instructions and guidance from the manufacturer. Before any sort of finish the epoxy surface needs to be cleaned of any "waxy" residue and abraded to form a key for later coatings.
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Premium lightweight body filler works well. Not Bondo unless you like sanding stuff that doesn't like to be sanded. Of course, paintable laminate sheet would work perfectly too, except if you've got curves.
I think Dave Pellegrene (apologies I am misattributing) had a really good method which involved use a crown router bit to create a wide, shallow groove running along the length of the butt joint, which, after filling with body filler, effectively mitigated the tendency of MDF to "telegraph" the presence of the joint. No clue how I will be able to find that thread again... was it diyAudio? Or PE's Tech Talk?
EDIT: Here we are! https://techtalk.parts-express.com/...kers-Using-my-Trench-Method-on-the-MDF-Seams=
I think Dave Pellegrene (apologies I am misattributing) had a really good method which involved use a crown router bit to create a wide, shallow groove running along the length of the butt joint, which, after filling with body filler, effectively mitigated the tendency of MDF to "telegraph" the presence of the joint. No clue how I will be able to find that thread again... was it diyAudio? Or PE's Tech Talk?
EDIT: Here we are! https://techtalk.parts-express.com/...kers-Using-my-Trench-Method-on-the-MDF-Seams=
I have tried pretty much everything and found drywall putty to be the best and most cost efficient treatment. I first read about it in several wood working forums and I was a bit skeptical until I tried it out myself.
Cut the MDF and fill the “end grain” with the drywall putty. Not a thick layer, just fill the pores and it will get a slick feel when it’s enough. Lightly sand any excess off and apply your primer (if painting).
Cut the MDF and fill the “end grain” with the drywall putty. Not a thick layer, just fill the pores and it will get a slick feel when it’s enough. Lightly sand any excess off and apply your primer (if painting).