myn's Tuba HT Build Thread

[bgavin]

This leads me to think a Saran wrap sheet floating on top might be a good idea...
My father in law does this with drywall mud, and it stays moist in the 5 gallon pail for years.

[myn]

This leads me to think a Saran wrap sheet floating on top might be a good idea...
My father in law does this with drywall mud, and it stays moist in the 5 gallon pail for years.

You mean on the top of the Duratex can before you put on the lid or?

[David Carter]

Put the plastic wrap directly on top of the Duratex inside the container. This keeps the moisture in and the air out. You can also use a quirt bottle to spray a light mist of water over the top the Duratex before laying down the plastic wrap. Then, when you open it up again, remove the plastic wrap and mix in the water. No need to do any of this if your just putting it away overnight, but, when you finish your THT and put the Duratex away for an extended period, the water and plastic wrap will help prevent drying/hardening. Works for drywall mud and regular paint also.

[myn]

[== 9/26/2009 ==]

I just got finished with applying the first coat of Duratex onto 5 sides of the THT. I kept swaying back and forth on how to apply it, I finally just decided to follow the directions on the Acrytech website: Heavy protective coat with textured roller followed by [light/medium/heavy] coat with a textured roller.

I applied the first coat with what I would consider to be a medium/heavy coat. It wasn't super thick, but it wasn't thin either. For reference I used a half a gallon on the first coat. Maybe I put it on too thick? The textured rollers on Acrytech's site are very impressive. I don't see any visible roller lines and the roller makes it almost screw-up proof..

Talking about screw ups. I noticed a little imperfection on the front of the horn when I was half way done. So I went back to it with a partially wet roller and I found the Duratex was actually half dried and it began sticking to the roller creating this sandpaper finish. I immediately grabbed a rag and patted it down and than reapplied with a wet roller this time which completely concealed it.

The one thing I do notice is the areas that were Bondo'd appear shiney or different from the other wood exposed areas. I am not sure if this is because the wood sucked it up where as the Bondo is non-porus and the Duratex is still perhaps a little wet in these areas? See the pics below and note the shiny area on the top, again The box is not completely dry yet so I am guessing it will look a little different in another 24 hours.

I will also note that as I was applying this in the basement and it has been raining for the past 16 hours I turned on the Dehumidifier which actually sits immediately behind where the box is.

I'll wait and see how it looks tomorrow. If I can still see the shiny spots I am guessing another coat is in order?

Oh yeah.. I've got a splitting headache.. I think the fumes from the Duratex were the cause..

[myn]

UPDATE:

I went downstairs to check on the THT. I felt the sides of the enclosure to see how the drying was going. In some areas like on the top it feels like sandpaper where as other areas it feels like a textured but smooth finish. There is one area inside of the horn mouth that still feels wet. On the front of the horn where I went back and put on another coat to fix a defect its got the nice textured but smooth finish. Perhaps the undesired sandpaper finish will go away when I apply a second coat?

Thoughts?

[maxmercy]

The sandpaper finish is usually from over-rolling, as the duratex immediately begins to harden, rolling again over it causes cusping. If you keep rolling, you'll get essentially a non-skid surface. To prevent the rough surface, modify your technique or add a little bit of H2O to the duratex so it will not harden up so quickly (what I do). You can knock down the cusps with a putty knife scraped over the surface before your next coat.

JSS

[myn]

Thanks MaxMercy

That makes perfect sense and I can confirm the areas where I went back to perfect the surface are the areas that have the sandpaper finish.

So this next coat, I shouldn't over roll it so much. Basically apply it and leave it and don't keep going back over rolling it?

How much water should I add? I am guessing you just add some to the Paint tray?

[WB]

The shiny bondo area tells me that you didn't lay down a flat black latex as primer. Chances are that that this layer will act as the primer layer and the shiny area won't show thru. Duratex doesn't seem to adhere well directly to bondo and PL.

That sandpaper affect as mentioned above is from over rolling as the Duratex is drying. Since you're doing another layer, I would lightly knock it down with an orbital sander to remove the roughness.

I've never added water, but always use a sheet of plastic touching the Duratex with the ends clampled under the lid. I still have several pails that are 3-4 years old using this technique. The Duratex plastic pails are so much nicer than regular steel paint cans for this purpose. Another reason I never mix Duratex is you'll introduce air deep inside the pail, defeating the purpose of keeping the Duratex moist.

[myn]

The shiny bondo area tells me that you didn't lay down a flat black latex as primer. Chances are that that this layer will act as the primer layer and the shiny area won't show thru. Duratex doesn't seem to adhere well directly to bondo and PL.

Whats weird about it is I did apply a nice base coat of flat black latex prior to applying the first coat of Duratex, yet the bondo'd areas still shine through:

Another reason I never mix Duratex is you'll introduce air deep inside the pail, defeating the purpose of keeping the Duratex moist.

Maybe another fault that I did . I used a squirrel cage paint mixer with a drill before applying.

[WB]

The shiny bondo area tells me that you didn't lay down a flat black latex as primer. Chances are that that this layer will act as the primer layer and the shiny area won't show thru. Duratex doesn't seem to adhere well directly to bondo and PL.

Whats weird about it is I did apply a nice base coat of flat black latex prior to applying the first coat of Duratex, yet the bondo'd areas still shine through:

That is strange. I doubt though that it will shine through the second coat.

Another reason I never mix Duratex is you'll introduce air deep inside the pail, defeating the purpose of keeping the Duratex moist.

Maybe another fault that I did . I used a squirrel cage paint mixer with a drill before applying.

I doubt you did any harm with this application, but I don't think it will help the future applications if it starts drying a little from the insides. It seems the factory mixing stays intact, unlike paint which seems to settle with time. I wouldn't worry about, I just wouldn't do it again.

[maxmercy]

Myn,

As far as how much to roll, and how much H2O to add, have you tried any test panels, or did you just get your practice right on the THT itself???

Basically, just a little H2O will do you well. Pour some Duratex into a quart or half-gallon mixing cup, and add a teaspoon or so of H2O at a time, and stir thoroughly. It does not take much water to get the duratex to run on vertical surfaces, so be careful, and play with some test panels (vertically oritented) first. You can still over-roll thinned duratex, so don't think it gives you carte blanche. What it will do is settle and flow better AFTER you are done rolling, the cusps turn into mounds.

The shiny bondo areas are visible just because you have not filled the bondo-less wood grain completely. To eliminate this problem, you will either need more coats or sanding in between coats. It may be OK after one more coat.

JSS

[myn]

[== 9/27/2009 ==]

Thanks for all the advice guys.

I used a putty knife this morning and knocked down all of the sharp sand paper points. Hundreds of thousands of little tiny bee-bee's came off. The result was a very desirable finish with no sharpness what so ever. I will say that Duratex is pretty darn durable. I was scratching the surface pretty hard with the putty knife and it didn't seem to mar at all. Very impressive.

I then applied the second coat using some pointers from this forum. I didn't over-roll to much and added a few drops of water to the mix. It looks much better with a second coat on it. The only thing I do notice is that not all 5 sides have a consistent texture. It seems as though the front and right side have a heavier texture where as the left and back have a lighter texture. Not really to noticeable to the naked eye but I noticed it as I have been staring at it all day. None the less I am now pleased with the results.

Tuesday I'm flipping it over and doing the bottom.

So its almost time to install the driver. I typically break-in the driver in the enclosure. Do horns need the driver broken in before hand?

[Bill Fitzmaurice]

I typically break-in the driver in the enclosure. Do horns need the driver broken in before hand?

If you don't the requisite voltage will likely collapse your house around you. But for that matter all drivers should be broken in out of the enclosure.

[maxmercy]

If you plan on breaking the driver silently, use subsonics; less audible noise, more excursion for smaller power. I used a 10-19Hz sweep at a low power level (enough to get the cone moving about an inch total), overnight for two nights. I just propped one side of the magnet up so that the pole-piece vent wouldn't make too much noise. You've got time before it is all cured, break that sucker in while you wait.

BTW - looking pretty good. I am always amazed at the punishment Duratex can take as well...

JSS

[Scott Brochu]

If you plan on breaking the driver silently, use subsonics; less audible noise, more excursion for smaller power. I used a 10-19Hz sweep at a low power level (enough to get the cone moving about an inch total), overnight for two nights. I just propped one side of the magnet up so that the pole-piece vent wouldn't make too much noise. You've got time before it is all cured, break that sucker in while you wait.

BTW - looking pretty good. I am always amazed at the punishment Duratex can take as well...

JSS

Talk English son........