Bondo and MDF? Just mix the bondo and slap it on there fast as you can, you only get a few minutes of working time with the stuff. Don't try to flatten it too smoothly with the putty knife, leave a little extra to sand down to flat once it dries, but not too much or you'll be sanding for a long time. Once it dries you can cut, plane, sand etc just as you would to the MDF.
I never had good luck getting body putty to play with MDF without laying down a coat of epoxy first. I had better luck with the Elmers wood filler filling in low spots and router mishaps.
Good tip. I'm getting ready to apply filler to my project and I am debating whether or not to use bondo or Elmers wood filler. Right now it too cold outside or in the garage to mix up bondo. So Elmers wood filler looks like the way to go, because I can apply this indoors.
I've hated Bondo since the very first time I used it 40 years ago. My vote would be for wood filler as well, but you need to put it on pretty thin. If you have a deep and larger area to fill it will take several coats to build it up. If you try and lay it on real thick it can shink and crack. Another thought, are you going to spray or roll on Duratex? If so you can just use drywall mud. It is a lot cheaper and much easier to sand down.
John suggested some paint to try but it doesn't appear to be on shelves locally so probably lacquer paint and clear. He also suggested glazing putty but at $9 for a small tube that's going to add up quickly since the seams around the perimeter and the uhohs need fixed.
Anyhow, the bondo is on there, sanded, and a coat of bin to seal everything up. When the blocks come in I'll go at it again.
Glazing putty is good stuff and would probably do a great job filling in small joint seams. For automotive body work glazing putty is used to fill in tiny air bubble cavities that occur when the body filler cures. Hopefully Brad (HiFiSide) sees this thread and jumps in. He has 1000× more experience with automotive finishing techniques than I do.
rsta28 3" from top, offset 1/2" on 8 1/2" baffle, taken @1 meter. Everything was taken inside and no stand so the first bounce (floor) was pretty fast, gated @3ms. The big towers less than 2' away could have also affected the response.
From lightest to darkest 0 to 45 degrees w/out stuffing in the slots. Yuk ...
On my easier builds ( like square cabinets) I don’t use body filler I use the laminate method with a nice filler primer. On my OB project I’m doing now will be a lot of body filler but it will be one solid piece when I’m done so I won’t have to worry about any shrinkage. I did find some body filler that seems to work great (pictured) cost about $25 a gallon at Home Depot, our body shop stuff is around $80 a gallon. Glazing putty (spot putty) I recommend only a 2 part system only. Stay away from that red shit in the tube it’s like sanding gum.
Ill second the red spot crap. Ive used drywall putty for tearouts and such when its being coverd up. Works fine, best to use the powder you mix yourself. The pre mix stuff takes a long time to dry and usually takes more coats, seems to shrink more.
The skim coat in a tube works ok, but it is not a filler. Pin holes are about all it is useful for, and you can expect considerable waste.
It does, however, work very well as a base coat on bare MDF. The MDF absorbs the hell out of it, knock it back to flat with a block sander. You will end up with a very smooth surface on your MDF with a pink cast to it. Proceed with filler, primer, etc.
I tried various putties over the years (when I still painted cabinets), the drywall stuff and wood-based putties just seemed to be less durable than the ol' Bond-O. More prone to crumbling on high-build areas, shrinkage is a bigger concern.
No matter what I used, though, I discovered if you want sharp, painted edges on MDF you are in for a lot of work. Over time I discovered that hitting the edges at 45 degrees with the block sander to add a very light filleted edge helps. The edges of MDF will swell, and your cabinet will "mushroom" slightly as a result.
Another very useful trick is to run the edge trimmer bit around your joints after your first coat of filler primer fully cures. You might be surprised at how much seam broadcasting is actually due to slight swelling of the ends of the MDF.
Am I the only one that likes the red shit in a tube? (Bondo Autobody repair kit, about $10 for a pint). Any wood filler I've tried has been too soft, brittle, crumbly, etc. Filler is good for a split in some timber, but not for tearout on a cabinet corner. Since its softer than the wood itself its real easy to sand too much of it away, and I don't have the same problems with Bondo. I couldn't find any photos handy, but any repair I've done with Bondo sanded well, and for a corner I just gobbed on too much and went over again with the router. It smells awful, but it works.
There all about the same but I use mostly Evercoat, Upol, 3m and USC. Glazing putty’s use is minimal these days as body filler and primer filler have come along way in the last 10 years.
All open edges are cover with smooth Formica or laminate (pictured). This method bridges the mdf so the shrinking and swelling are never noticed.
what do you use for gluing hte laminate to the mdf. and do you seal the mdf before gluing on the formica? I have a MDF box which i am buidling - would like to try out laminate
All open edges are cover with smooth Formica or laminate (pictured). This method bridges the mdf so the shrinking and swelling are never noticed.
what do you use for gluing hte laminate to the mdf. and do you seal the mdf before gluing on the formica? I have a MDF box which i am buidling - would like to try out laminate
Roll on 2 coats of your favorite Titebond glue on mdf and 1 coat on laminate back. Let both surfaces completely dry and iron it on using a slow pressing motion. Of course do this all after sanding mdf FLAT with 80 grit.
No body filler. One cabinet I’m leaving square edged and other I did a 3/8 round over. I will prime the square edged cabinet this weekend as I got some roll-on 2k primer today and see how that works.
Sandpaper came in, blocks should arrive today. The cabinets are far enough along that it's probably too late to go the laminate route so I'll give the blocks a try. I'm thinking that laminate idea will make in onto the next build.
How and what kind of paint JR?
Thanks for the tips and ideas guys. Give me time, I'll put them to use.
Anyhow, got tired of playing around with xsim and pulled out a minidsp. Time for a little tinkering. These measurements are on tweeter axis @18", just over 2x the baffle width. At this distance and straight on, I did not expect that adding felt to the slots would make much of a difference. Guess I was wrong.
Messed up somewhere. Gold and purple are measured at port/woofer. Blue is unibox predicted .zma, red is measured .zma. Tuning was supposed to be 40'ish not 31hz. Also have an unwanted hump at 150hz.
And no matter how port tuning is worked in unibox, I fail to get a matching measured vs sim'd .zma leading me to believe the entered t/s parameters are a bit off. Either way, it looks like the port length will have to be altered.
Anyhow, used a swiss-cheese kind of brace, instead of a window type, to tie all sides together that rests above the port. The port opens upward after making a 90* bend, and now that everything is all stuck together the only way to the port is through the woofer hole. Guess most of the brace will have to be cut out to gain access to the port and getting a decent cut on that port is going to be challenging. Wondering if it might be better to just cut a large access hole in the side of the box then glue/bondo it back into place. I suck at bondo.
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It does, however, work very well as a base coat on bare MDF. The MDF absorbs the hell out of it, knock it back to flat with a block sander. You will end up with a very smooth surface on your MDF with a pink cast to it. Proceed with filler, primer, etc.
I tried various putties over the years (when I still painted cabinets), the drywall stuff and wood-based putties just seemed to be less durable than the ol' Bond-O. More prone to crumbling on high-build areas, shrinkage is a bigger concern.
No matter what I used, though, I discovered if you want sharp, painted edges on MDF you are in for a lot of work. Over time I discovered that hitting the edges at 45 degrees with the block sander to add a very light filleted edge helps. The edges of MDF will swell, and your cabinet will "mushroom" slightly as a result.
Another very useful trick is to run the edge trimmer bit around your joints after your first coat of filler primer fully cures. You might be surprised at how much seam broadcasting is actually due to slight swelling of the ends of the MDF.
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