Re: Altec 311-90 Restoration
If i were you I would be very careful NOT to knock off that coating on the horns.. Altec used Aquaplas back in the day to keep them diecast aluminum horns from ringing which they will do without it. I see some of it is missing by the throats. You could try an automotive undercoating to dampen them. But the coating is probably very brittle being 40-50 years old now.You could try to dust them off with a small amount of compressed air. But also do NOT get to close to them with the air as you could blow it right off. If you have a very soft sponge ? The softest you can find while damp you could try to tamp them to get clean. After you try to fix the missing dampening material I would let them dry and mask off the mounting plate and just paint them gray to try and encase the Aquaplas into the paint to prevent them from flaking off even more.. Diecast Aluminum horns ring like a bell without dampening material.. I don't think they sell dampening material like Aquaplas in 1 qt. containers. 5 gal buckets is the smallest size IIRC..And the 5 gal buckets were like $200 decades ago... So it is expensive. Your best bet would probably be the automotive undercoating or dampening material as you don't need that much from your pictures. Just take your time and be careful with the coating. I found this. It is only 4 oz. but that looks like all you will need. Apply it the same thickness of what is already there . Apply with a putty knife them tap in a bunch of times to create the same texture that is already on the horns. I would use the whole container. You can never have too much dampening on those horns.. And then just paint them after it has dried.. Best of Luck !
Aquaplas 4oz.
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However this maybe a better overall solution..
Acoust-X Sound Damping Coating 1 Gallon - Acry-Tech Coatings
And here is another one...
Antivibe™ DL - Blachford Acoustics
Re: Altec 311-90 Restoration
Thanks for the response and especially for the links. Yes there is only one small patch where the coating is missing but the rest of the coating on both horns seems very well bonded. But can't really know for sure so I will heed your warnings. Would the aquaplast normally be soft and pliable or hard?
Think I will try the Acoust X - the OEM aquaplast would normally be what I would use, but I may need more that 4 oz perhaps. I'll just need to do some tests to ensure the Acoust X is compatible. Surface prep for both the coating and paint is a bit of an unknown - guess I'll just need to experiment gently...
Re: Altec 311-90 Restoration
It is soft when fresh or wet in container.. But dry's hard to the touch when dried in about 24 hours. It is a water based like paste. But does not dry rock hard. When dry it will remain a little flexible. It is so it can handle vibrations without "breaking/flaking" off so it has to have some flexibility to it. I was trying to find something for you where you didn't have to buy too much to fix your horns. You can use a very fine Emory cloth or a wet/dry sandpaper but sand DRY ! Remember they are Aluminum so they will sand very quickly meaning don't use a lot of pressure when sanding. Lightly sand. Here is a link i posted from Google.. Google is your friend here.
Spot-treating flaking Aquaplas on diecast aluminum audio horns requires stabilizing the fragile edges of the existing coating and treating the exposed aluminum so the patch material bonds permanently. Because Aquaplas is an elastomeric, vibration-damping material (not standard paint), you must carefully build up the spot to match the thickness and texture of the surrounding horn.[1,2]
1. Remove Loose Material and Feather the Edges
- Scrape the loose flakes: Use a stiff plastic scraper or a hobby knife to gently pick away any Aquaplas that has already lifted from the aluminum. Stop when you hit sections that are still firmly bonded. [1]
- Feather the borders: Use 240-grit to 320-grit sandpaper to lightly sand the cliff-like edges where the Aquaplas met the bare metal. You want a smooth transition (taper) from the thick coating down to the bare aluminum, which prevents the old edges from continuing to lift later. [1, 2]
2. Clean and Degrease the Exposed Aluminum
- Wipe the bare aluminum spot thoroughly with isopropyl alcohol or lacquer thinner using a cotton swab or microfiber cloth.
- Ensure all metal dust from sanding, fingerprints, and environmental residue are completely gone. [1, 2]
3. Spot-Prime the Metal
- Aluminum oxidizes immediately when exposed to air, preventing new coatings from gripping. Use a small artist's brush to dab a high-quality self-etching primer only onto the bare aluminum spots.
- If using a spray-can primer, spray a small amount into the plastic cap and use your brush to transfer it to the horn to avoid overspray onto the rest of the finish. Let it dry completely.
4. Apply the Damping Touch-Up Material
Because standard paint lacks the mass and elasticity required to match Aquaplas, choose a true elastomeric or damping substitute: [1, 2]
- Option A (Authentic Restoration): Use a specialized Aquaplas Speaker Restoration Coating, applying it with a stiff hobby brush.
- Option B (The Audio Forum Alternative): Many audio restorers use automotive "chip guard" or "rock guard" spray to patch horn bodies. Spray it onto a piece of cardboard and dab it onto the primed spot with a small foam brush or cloth to recreate the original heavy, stippled texture.
- Application Technique: Apply the compound in 2 to 3 thin layers, letting it dry in between. Build up the depth until it sits flush with the original coating. If it dries with peaks that are too high, lightly knock them down with 400-grit sandpaper before a final color coat. [1, 2, 3, 4, 5]
To help refine the aesthetic match, let me know:
- What is the color of your original Aquaplas (e.g., the classic vintage JBL white, or later black/gray)?
- What is the approximate size of the flaked-off sections?
Restoring the flaking Aquaplas damping coating on iconic vintage Altec Lansing 311-90 sectoral horns requires strict attention to texture and color. Because these massive cast-aluminum horns ring like a bell without their damping layer, your touch-up needs to provide physical mass, not just a thin layer of gray paint.[1, 2, 3]
The specific protocol to spot-treat Altec battleship gray Aquaplas consists of the following steps: [1]
1. Stabilize and Etch the Exposed Spot
- Feather the Edges: Gently sand the hard edges of the flaked Aquaplas with 320-grit sandpaper. You want to create a smooth, subtle slope from the thick coating down to the bare aluminum. If you skip this, the patch will look recessed, and the old edges will eventually lift again.
- Prep the Metal: Scuff the bare diecast aluminum spot to give it some tooth, then wipe it completely clean with a cotton swab dipped in isopropyl alcohol.
- Prime: Dab a thin layer of self-etching primer directly onto the bare aluminum spot using a fine hobby brush. Do not spray it on; you want to isolate the primer strictly to the bare metal to ensure a solid chemical bond.
2. Formulate the "Aquaplas Substitute"
Original Altec Aquaplas is essentially a thick, latex-based emulsion loaded with dense sound-deadening materials. To match the thickness, density, and color on an Altec horn, vintage audio restorers on AudioHeritage forums rely on two reliable methods: [1, 2]
- The DIY Latex Slurry (Most Accurate Match): Mix a thick paste using premium flat acrylic-latex paint and a small amount of calcium carbonate (chalk powder) or talcum powder to build up heavy body. You can also mix in shredded tissue paper fiber bit-by-bit to mimic the exact pulp-like, textured structure of original Aquaplas. [1]
- The Automotive Rubberized Spray Method: Use a premium rubberized undercoating or automotive rocker-panel chip guard. Spray a pool of it onto a piece of cardboard, let it off-gas for 2 minutes to thicken, and use a small foam sponge to dab it onto the horn. This perfectly recreates the heavy, dimpled, non-resonant texture.
3. Color-Matching Altec "Battleship Gray"
Altec used a few variations of industrial gray over the decades. Once your textured patch is dry and sits completely level with the surrounding coating, you can seal the patch with a color-matched top coat: [1]
- The Industrial Standard: The closest off-the-shelf industrial color match to classic Altec pro-audio gray is RAL 7046 (Telegrey 2) or RAL 7000 (Squirrel Gray).
- The Hardware Store Match: If you want an exact match to your specific horn's aging/patina, take a small flaked-off piece of the gray Aquaplas to a local hardware store with a computerized paint scanner. Have them mix a sample-size can of exterior flat acrylic latex based on that chip.
- Application: Dab the gray paint over your dried, textured patch with a small artist's sponge or fine-bristle brush, lightly overlapping onto the old finish to blend the repair away. [1]
To help perfect the texture, let me know:
- Is the remaining Aquaplas on your horns relatively smooth and matte, or does it have a heavy, rough, stippled texture?
Please keep us posted on your progress and the steps you are taking with pictures if you have the time. All this information may be helpful to someone else in the future ! Thanks ! Good Luck with your project ! :Thumbs up:
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Re: Altec 311-90 Restoration
Great information AB thank you. It's always better to use the experience of others rather than experiment if at all possible. You didn't say this explicitly, but is it not a good idea to gently clean the aged aquaplas with a mild soap and water?
I will post pictures as I make progress, but it will take a little while due to too many projects I'm juggling (I don't know how I ever worked for a living). I am currently focusing on fabricating horn stands, just about finished then off to the powder coater. Picture attached.
I have obtained a really nice pair of 299-8a's with original diaphragms, and a set of paper diaphragms to try. I intend to pair the horns with either custom built 817a's (if I can locate four nice 515b's) or a custom designed and built horn cabinet with speakers having similar performance as the 515b's. So lots of work left.Attachment 4785
Re: Altec 311-90 Restoration
Your Welcome ! Yeah I would not use soap and water. If water gets underneath the Aquaplas it can create some serious problems with refinishing and repainting them. As long as all the loose dust and dirt is removed with compressed air don't worry about the color, you will address that when you repaint them. Use the isopropyl alcohol but sparingly. You are really only addressing the spot repair on the horns and not the entire horn.. One other thing you will run out of space quickly on this site for your pictures.. I suggest using a free picture hosting site like Flickr or something similar. Just do a little research for the right site.. One day it's free the next day you have to pay for them.. Case in point is Photobucket ! That site tried to extort me to get my pictures back.. I will never buy anything from that company...But I am sure you can find something suitable. The photo hosting at our site is very limited...
