Best methods for finishing MDF

[davepellegrene]

Re: Best methods for finishing MDF

This thread was mainly about finding a way to stop the seams from telegraphing on a b u t t joint MDF box using a method that inexperienced builders could do inexpensively. It was discussed that the ultimate way would be West System Marine epoxy. The down side is the price. I think when I looked into it it would be over $100 in materials which is high for a budget build. Also takes experience to use properly. I should also add I have become sensitized to epoxy from using it without proper protection. After all my testing the only method I found that worked well was the trench method filled with finishing putty or just plain body putty. Putting a thin layer over the entire box also helped on the transition from the putty to the MDF. I had also came to the conclusion the less moisture you add to the MDF the better. Thinning products down to soak in only seemed to break down the binding material in the MDF and allows it to expand. It also seems the more it expands the more unstable it becomes. Probably why the epoxy works so well. It sets up on the surface, seals out moisture and will bridge any movement in the seam. Here is a link to the boxes I built to test the trenched seams. I really abused these boxes by heating them up with a heat lamp and catching one on fire,painting, clear coating then putting self leveling resin on them. Then stripping them and repainting and clear coating. As of today still no seams. Interestingly the box I caught on fire does seem to be showing signs of movement in the box . Not sure why other then too much heat destabilized the MDF. I'll have to update how each sample I made is doing when I get some time. Post #36 and #115 show some of the samples I did and post #172 shows my test box updates from almost a year ago.

Dave

[bmaupin]

Re: Best methods for finishing MDF

Dave,

This past summer I found that a pair of cabinets that I had just built would show the seams after a hot day - unfortunately after the paint had been started. The other pair of cabinets I had on hand I ended up letting sit in the sun for 3 days, turning each day. I have not painted those cabinets yet, but the "end-grain" is yet to raise. I think this is the solution because I always wondered why Aaron Hero would always heat/bake his cabinets for a few days before applying paint - his results were awesome:

[jone.g151214]

Re: Best methods for finishing MDF

I started taking 500mg Cipro 2x daily yesterday, so it has not been 48 hours yet.
Fever gone, but the throbbing ear pain has turned into a sometimes sudden stabbing pain, & more popping.
I take that as the fluid moving, but when will it clear up so I can hear clearly again?
Should I take a decongestant in addition to absorb it more.

[jcandy]

Re: Best methods for finishing MDF

I absolutely don't want to derail this thread, and I understand that its about finishing MDF not about MDF alternatives. However, I want to point out, to those who are building projects in MDF for no reason other than tradition, that I don't use MDF in any projects (speaker building or otherwise) unless I simply can't avoid it. MDF dulls tools, the dust is finer than that coming from plywood or hardwood and contains formaldehyde resin. I think the consensus is that MHD dust is significantly worse for your lungs than plywood/hardwood sawdust. In addition to the often serious negative health implications, finishing it is also problematic (as this thread illustrates).

My workshop is also my garage, so often I have kids running in and out of it, things are stored there, its used for workouts, etc. So any dust is an annoyance.

Consider building with BB plywood and hardwood, with which is is possible to produce a very attractive enclosure without veneering, and with only minimal sanding. One can use only traditional wood glue (with absolutely no fumes or skin irritation). I also think that plywood furniture and enclosures look less "artificial" than MDF equivalents, but perhaps that's just personal bias.

I short, unless you have a really good reason for using MDF, try a project with plywood/hardwood as an alternative.

[dsrtdude]

Re: Best methods for finishing MDF

I just got through with my Tritrix kit the other day and used a product called Glaze-it made by Evercoat I used to use it for bodywork and it is thin fills scratched pits nicks and the edge of the MDF very well , its a 2 part deal and you have to work fair quickly but I applied it sanded it in 30 minutes and primered my boxes about an hour later. The stuff sticks to just about anything , wood , fiberglass , metal , paint , primer etc. it runs like $25 but it goes a long long way .

[davepellegrene]

Re: Best methods for finishing MDF

I absolutely don't want to derail this thread, and I understand that its about finishing MDF not about MDF alternatives. However, I want to point out, to those who are building projects in MDF for no reason other than tradition, that I don't use MDF in any projects (speaker building or otherwise) unless I simply can't avoid it. MDF dulls tools, the dust is finer than that coming from plywood or hardwood and contains formaldehyde resin. I think the consensus is that MHD dust is significantly worse for your lungs than plywood/hardwood sawdust. In addition to the often serious negative health implications, finishing it is also problematic (as this thread illustrates).

My workshop is also my garage, so often I have kids running in and out of it, things are stored there, its used for workouts, etc. So any dust is an annoyance.

Consider building with BB plywood and hardwood, with which is is possible to produce a very attractive enclosure without veneering, and with only minimal sanding. One can use only traditional wood glue (with absolutely no fumes or skin irritation). I also think that plywood furniture and enclosures look less "artificial" than MDF equivalents, but perhaps that's just personal bias.

I short, unless you have a really good reason for using MDF, try a project with plywood/hardwood as an alternative.

I also did test boxes with birch plywood. For painting it was more work to finish smooth and the grain eventually telegraphed through the body putty. In my opinion plywood dulls a blade much quicker then MDF. As far as the dust goes I use a dust collection system and my shop is only used for woodworking so it's really not an issue. MDF is much more consistant then plywood and will not splinter. It is almost impossible to round over a b u t t joint on a plywood edge and get a nice finish. Not trying to knock you just stating my experiences. I also used 45 degree angles rounded over on plywood and MDF. It will still show slightly but you really have to look for it. On the plywood the end grain was almost impossible to hide. If I were wanting a wood finish I wouldn't waist my time with plywood to me it really doesn't look nearly as nice as real wood or work as nice.
Just my opinion
Dave

[davepellegrene]

Re: Best methods for finishing MDF

I just got through with my Tritrix kit the other day and used a product called Glaze-it made by Evercoat I used to use it for bodywork and it is thin fills scratched pits nicks and the edge of the MDF very well , its a 2 part deal and you have to work fair quickly but I applied it sanded it in 30 minutes and primered my boxes about an hour later. The stuff sticks to just about anything , wood , fiberglass , metal , paint , primer etc. it runs like $25 but it goes a long long way .

Glaze it is a polyester finishing putty. It's the same product that I used on my test boxes. I used a product called Icing. I got it at my local auto paint store.
Dave

[davepellegrene]

Re: Best methods for finishing MDF

Dave,

This past summer I found that a pair of cabinets that I had just built would show the seams after a hot day - unfortunately after the paint had been started. The other pair of cabinets I had on hand I ended up letting sit in the sun for 3 days, turning each day. I have not painted those cabinets yet, but the "end-grain" is yet to raise. I think this is the solution because I always wondered why Aaron Hero would always heat/bake his cabinets for a few days before applying paint - his results were awesome:

When I did my testing I went back and read all of his threads to get as much info as I could. Unfortunately most of his pics were no longer there. He is were the idea for heating the MDF came from. In my conclusions I real don't think heating the MDF, to get the moisture out, is that necessary and over heating is not good for the MDF. I think having the MDF moisture content close to the environment, it will be in, is a better idea. Heating as you apply the body putty helps speed up the shrinking process of the body putty, which will help keep waves out of the finish down the road, as it dries out. Again to much heat seem to effect the body putty as well. I had my boxes ready for paint quite a few times and put them under heat and ended up resanding the body putty because it seemed to have expanded in spots even after applying primer. It also could have been over heating of the MDF causing it to expand.
Another thing I found out is the primer in spray cans is almost worthless to build up primer. If at all possible using auto primer through a paint gun is much better.

In conclusion to much thinned down product or over heating seemed to cause the MDF to expand. The more the MDF expanded the more unstable it would become. Once you loosen the binding material that keeps it compressed the more it will expand and contract causing problems in the seams.

Just more of my experiences and opinions
Dave

[jcandy]

Re: Best methods for finishing MDF

Again, this is not an MDF-versus plywood thread, so I'll keep it short. It is generally accepted that MDF is harder on blades than plywood, although the difference may not be so great. Many people do not have a dust collection system, so for them MDF dust is a real health issue. Finally, I am not sure what the body putty was for in your application. If you use hardwood and plywood, the end-grain can be hidden as desired. The unfinished enclosure below used absolutely no wood filler, veneer, putty, etc. Frame is BB ply and baffle is walnut+ply laminate. Very simple. The finished product (not shown) required minimal sanding and a few coats of lacquer (although poly works just as well). It just seems far less labour intensive than what people here are proposing.

I also did test boxes with birch plywood. For painting it was more work to finish smooth and the grain eventually telegraphed through the body putty. In my opinion plywood dulls a blade much quicker then MDF. As far as the dust goes I use a dust collection system and my shop is only used for woodworking so it's really not an issue. MDF is much more consistant then plywood and will not splinter. It is almost impossible to round over a b u t t joint on a plywood edge and get a nice finish. Not trying to knock you just stating my experiences. I also used 45 degree angles rounded over on plywood and MDF. It will still show slightly but you really have to look for it. On the plywood the end grain was almost impossible to hide. If I were wanting a wood finish I wouldn't waist my time with plywood to me it really doesn't look nearly as nice as real wood or work as nice.
Just my opinion
Dave

[fbov]

Re: Best methods for finishing MDF

This thread was mainly about finding a way to stop the seams from telegraphing on a b u t t joint MDF box using a method that inexperienced builders could do inexpensively. It was discussed that the ultimate way would be West System Marine epoxy....

I suggested this as it's what I've used extensively on Baltic Birch used to make Dobsonian telescopes. You may recall the little Triska-like sub I had at InDIYana last year. It's now painted, and you can clearly see the seams through the truck bed liner paint. Ironically, you can also see where the seam is on the speakers I veneered to go with the sub. Through several cycles of shellac application and sanding, the top/bottom are now lighter above the side panels, where I've sanded more of the color off.

So, from what I've seen, trench is best for joints that are not subject to jokes (just another way around saying "****").

HAve fun,
Frank

PS Colin's speakers were great learning; I think I saw the promised land last night - shiny speakers.

[davepellegrene]

Re: Best methods for finishing MDF

Again, this is not an MDF-versus plywood thread, so I'll keep it short. It is generally accepted that MDF is harder on blades than plywood, although the difference may not be so great. Many people do not have a dust collection system, so for them MDF dust is a real health issue. Finally, I am not sure what the body putty was for in your application. If you use hardwood and plywood, the end-grain can be hidden as desired. The unfinished enclosure below used absolutely no wood filler, veneer, putty, etc. Frame is BB ply and baffle is walnut+ply laminate. Very simple. The finished product (not shown) required minimal sanding and a few coats of lacquer (although poly works just as well). It just seems far less labour intensive than what people here are proposing.

I think you are misunderstanding what this thread is about. It's about painting a cabinet not varnishing. The seams telegraph though after they have been painted. Stain and varnish is not a problem at all. You won't notice the seams because of the wood grain.

Nice looking cabinet by the way.

Dave

[lunchmoney]

Re: Best methods for finishing MDF

Again, this is not an MDF-versus plywood thread, so I'll keep it short. It is generally accepted that MDF is harder on blades than plywood, although the difference may not be so great. Many people do not have a dust collection system, so for them MDF dust is a real health issue. Finally, I am not sure what the body putty was for in your application. If you use hardwood and plywood, the end-grain can be hidden as desired. The unfinished enclosure below used absolutely no wood filler, veneer, putty, etc. Frame is BB ply and baffle is walnut+ply laminate. Very simple. The finished product (not shown) required minimal sanding and a few coats of lacquer (although poly works just as well). It just seems far less labour intensive than what people here are proposing.

That is simply gorgeous.

The main advantage of mdf is cost. If that weren't an issue, I'd use nice birch plywood in a heartbeat.

[mortron]

Raaawr!!! Zombie Thread!

Sorry!! But I am curious davepellegrene, how did those speakers in the demonstration on page 12 hold up long term? It's been about 5 years, no? Did the seams ever show? I am considering a painted MDF build and wonder if your trench technique is the way to go or not. Thanks in advance.

[Æ]

Re: Best methods for finishing MDF

Thats the way I was taught to put on tongue oil.

You're not supposed to lick it!

I purchase my two part liquid epoxy from Tap Plastics which is still rather expensive but not as bad as Marine Epoxy. For many years now I've used liquid epoxy for all my MDF glue ups, since then I've never had a seam telegraph or show through. During assembly I apply it liberally and let it ooze out of the joint. After the initial assembly I go back and refill any open joints and uneven areas as necessary. Only drawback is that it's rather messy and it requires a heck of a lot more sanding.