Which adhesive for mass loaded vinyl

I need to add 2lb MLV to the inside cowling of my outboard. What would be a recommended glue to use? I've had mixed results with heavy duty contact cements (like 3M 90).

Even though the MLV is rated to 180 degrees, I think the consequences if it were to delaminate and fall upon the engine could be rather severe.

The glue needs to hold up to vibration, heat and acoustic shock. I'm sorta thinking about 5200 which is permanent, and might even provide a small amount of decoupling as it would absorb some vibrations.

Thoughts?

5200 would do it, could be a real sticky mess to do, and takes time to cure.

I'm thinking how you clamp and hold the MLV to the interior so as to have good consistent bonding to be the bigger challenge of your project. Maybe shape some boards or ridged foam to clamp against on the interior? Do you have to preform or slice the MLV to suit the concave surfaces?

I downloaded a decibel meter app to my phone that works pretty good, that would give you some objective before and after data too. 'Sound Meter."

Good questions. So I'll use my original crappy foam as a pattern to cut the MLV for the curved sections of the cowling (see photo).

Do you have any idea if Loctite PL Premium FAST GRAB (also a polyurethane adhesive) would work similar to the 5200 Fast Cure? It's 1/3 the price and this isn't exactly a mission critical hull-deck joint or anything.

Currently I read 95dB at my helm. BTW, 85dB is the threshold where you can suffer permanent hearing loss. Gotta fix this!

3M VHB 5952 double side tape, supports up to 90 pounds per inch.

L

I think you may be using the wrong soundproofing. I bought this for a Yamaha 50. The 10 square foot amount was more than enough for the whole cowling. Has a heat reflector layer and stays stuck. Easy peezy.

With 2 pounds per square foot I would go with a belt and suspenders approach. I would use the best glue you can find but also use some mechanical fasteners. They make little stick pin type that you use epoxt to glue to the surface and then stick the pins through the insulation and then put a cap on it to mechanically hold it in place. Amazon has them in galvanized and Soundown sells S/S ones. This is a photo of the Soundown ones.

Mako said:

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Currently I read 95dB at my helm. BTW, 85dB is the threshold where you can suffer permanent hearing loss. Gotta fix this!

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I've gotta ask: what outboard runs at 95db? Or are you running everywhere at WOT?

Will the extra cowling weight be a concern?

Good luck.

Some good ideas above that I will consider.

It’s a 2-stroke Mercury saltwater 200hp with carbs.

Yes the cowling will probably weigh in at 40lbs by the time I’m done. Won’t be easy to remove. The noise is horrible though and I’ve considered getting rid of it and buying a nice new 4-stroke.

Seems way better to use mat with peel and stick adhesive already in place. Marco lists one option above and you can find all combinations of sound and heat barriers that are made for this job and will stay in place. For sound barriers alone there are lots of choices in durable and effective peel and stick material.

Try a PM to Keysdisease for advice or call SoundDown direct. He works for SoundDown.

If you already have the product this may not matter, but I bought some "Hoodliner" (Sounddown, IIRC) and put it on the inside of the "doghouse" on a van. It came with adhesive already on it.

This sits over/beside a big, hot engine, so I would not have been pleased if it had fallen down. It did not. (I prepped well, solvent cleaned, etc.). It's been a while, but I think I used some of the thinner (also self adhesive) sound absorbent stuff first (The type that only has to cover X percentage of the surface). Then the Hoodliner.

I was mostly going for heat reduction, with a bonus side helping of sound reduction. So some other product may work better. But the adhesive that was on it sure worked well (it was a type where you peel off a paper backing to expose the adhesive).

Mako said:

Some good ideas above that I will consider.

It’s a 2-stroke Mercury saltwater 200hp with carbs.

Yes the cowling will probably weigh in at 40lbs by the time I’m done. Won’t be easy to remove. The noise is horrible though and I’ve considered getting rid of it and buying a nice new 4-stroke.

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I had a 115HP Johnson that would make ears ring when I first bought the boat.
The exhaust pipe was leaking at the joint connecting to the lower unit. The seal had been misaligned during some service the previous owner did or had done. That thing was loud. Fixing that made a HUGE difference.
just food for thought

1lb MLV would be more appropriate for a 2 stroke OB. Has to do with frequency, 1lb works great at high to mid range frequency, 2 lb adds good lower range reduction which a 2 stroke OB doesn't really create. A lot of your noise in carj noise which is definitely mid/high range.

MLV plays nice with just about any adhesive, the Loctite product looks appropriate, but I suggest you test because of this:

https://dm.henkel-dam.com/is/content/henkel/tds-us-loctite-loc-pl-premium-8x-fast-grab-2019-12-12

"Certain materials such as rubbers and plastics may have bonding difficulties. Test before use"

The product Marco used is what the automotive industry calls Dynamat. The self adhesive is very aggressive. It appears to come as 36sqft which seems way too much for 1 OB cowling. It does weigh 1 lb sqft and should perform well. Price looks high. The adhesive is not at all forgiving re repositioning, like contact cement it sticks now.

Dave's suggestion is good, but those pins in this application would call for epoxy, and as long as you're mixing some up, epoxy is the go-to adhesive for "when in doubt" when working with MLV

Great info on the 1lb. vs. 2lb. for an outboard's frequency. I have a four-stroke that's relatively quiet at low speeds but still louder than I would like in the higher rpm's. For some reason I had never thought about adding noise-reducing material.

(Would you say the same about 1lb being best for a four-stroke?)

Keysdisease said:

Dave's suggestion is good, but those pins in this application would call for epoxy, and as long as you're mixing some up, epoxy is the go-to adhesive for "when in doubt" when working with MLV

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I am not sure how hot the inside of the cowl gets, but I might be worried about high temps and epoxy. I think it starts softening at 150º F. Or are there special epoxies for heat (I'm speaking of your typical WEST System, System Three, etc. marine epoxies).

Epoxy will serve very well in adhering MLV to the inside of an O/B cowling, probably your best choice. Any 2 part epoxy will tolerate the temps of this environment.

As an example of frequency transmission, consider this:

When you pull up to a red light and some kid is cranking his stereo 2 lanes over, your rear view mirror is vibrating and you can almost feel...the bass. The band is playing organ, guitar, they are singing, but all you hear is bass.

The high and mid range frequency is being reduced by closed car windows, the low frequency bass goes right through everything.

The lower the frequency, the more mass you need in order to reduce it.

A carbureted 2 stroke has significant intake noise from the carburetors. 4 strokes are quieter, but as a general rule gasoline engines produce noise in a frequency appropriate for 1 lb mass products. For diesel engines the lower frequencies call for 2 lb + products.

Frosty said:

Great info on the 1lb. vs. 2lb. for an outboard's frequency. I have a four-stroke that's relatively quiet at low speeds but still louder than \

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Not to be too argumentative... so I've heard that before about 1lb and higher frequencies typical of a gasser. So let's say that 1lb MLV is adequate for an outboard, but that does not mean that it is better than 2lb. The 2lb should provide similar performance in the high frequencies, but in addition, will do a better job of knocking down the low frequencies. I don't think the lows are as significant as with a diesel, but they would exist in some form.

In any case, I have the 2lb so am not going to get rid of it. At this time (Thursday) I'm planning on installing this weekend and am leaning towards the Loctite Fast Cure product. I like the idea of the slight flexibility afforded by the polyurethane versus epoxy products.

I'll report back when I have performance measurements taken in about a week.

Thanks to everyone for the input.

for clamping
I'm picturing lining the cowling with a trash bag or similar, and filling with sand (or water).

skyhawk, I've been giving that same thought as well. Will have to apply in small sections (say 5) and would go with sand in order to avoid leaks. I also have some scuba weights which will give good local pressure. Will heat the vinyl with a hair dryer and hope that helps to soften it.

Mako said:

The 2lb should provide similar performance in the high frequencies, but in addition, will do a better job of knocking down the low frequencies. I don't think the lows are as significant as with a diesel, but they would exist in some form.

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This is absolutely true, but the difference for a carbed OB may only be measurable and not significant. I was making the point more to save weight on the cowling than dispute 2lb not working.

I understand, you got it, use it

Coming along real well. The front 2/3 is completed. The fast cure Loctite sets quickly. I’m stopping here and will launch it tomorrow and take sound measurements. I still have a few square feet of MLV to work with. Btw, a hairdryer on it for 5 minutes allowed it to bend very nicely.

I’m thinking that the small amount of airspace around and internal combustion engine may be needed to help the engine from overheating. I imagine that if a manufacture could make their engines that much quieter they would be doing it and advertising the lower decibel specs to promote their product.

Air works well with plastic bags and a canvas wrap

skyhawk said:

for clamping
I'm picturing lining the cowling with a trash bag or similar, and filling with sand (or water).

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In my shop, we use heavy plastic bags, filled with pressurized air and the outside wrapped with canvas to hold unusual parts in place while glueing, epoxying, etc. It mates the parts perfectly, especially in confined areas, kinda like vacuum in reverse and costs almost nothing to make the "fixture".

A bit late, but I tried thickened epoxy resin and it worked beautifully. I tested it and the material broke apart without any release of the epoxy. I can imagine it would be no fun to remove in the future, but for now it works great as an adhesive.

The 2lb MLV is thinner than the factory "insulation" it replaces. The engine is water cooled, and the combustion intake airpath unrestricted.

Noise is not a priority for engine manufacturers, unless its a byproduct of engineering improvements. 4 cycle engines are quieter than 2 cycle engines, and manufacturers call that out as a benefit and feature improvement, but the engineering was not to make the engine quieter.

The manufacturers need to ask themselves, if I make this engine 10 Db quieter, and add $20 to the cost and add 20 lbs to the weight, how many more engines will I sell?

The factory insulation is an acoustic foam noise absorber, it does little to reduce noise transmission through the cowling, weighs nothing, costs very little, and looks like insulation.

BonesD said:

I’m thinking that the small amount of airspace around and internal combustion engine may be needed to help the engine from overheating. I imagine that if a manufacture could make their engines that much quieter they would be doing it and advertising the lower decibel specs to promote their product.

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Good trick, would work well with water instead of air as well, for those without access to compressed air. Tape to hold the parts in place if necessary

CmdrDick said:

In my shop, we use heavy plastic bags, filled with pressurized air and the outside wrapped with canvas to hold unusual parts in place while glueing, epoxying, etc. It mates the parts perfectly, especially in confined areas, kinda like vacuum in reverse and costs almost nothing to make the "fixture".

Click to expand...

Keysdisease said:

The 2lb MLV is thinner than the factory "insulation" it replaces. The engine is water cooled, and the combustion intake airpath unrestricted.

Noise is not a priority for engine manufacturers, unless its a byproduct of engineering improvements. 4 cycle engines are quieter than 2 cycle engines, and manufacturers call that out as a benefit and feature improvement, but the engineering was not to make the engine quieter...

The factory insulation is an acoustic foam noise absorber, it does little to reduce noise transmission through the cowling, weighs nothing, costs very little, and looks like insulation.

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Dead-nuts-on, Mr. disease. The 1/2" foam is crap but does a wonderful job of absorbing oil which gets all over your fingers when lifting the cowling off. To address the earlier comment about epoxy - you're probably correct but I much prefer the marine adhesive (either Loctite or 3M) as it has flex and helps with the huge amount of vibration that it will experience, plus will provide some decoupling of the MLV, which is important for its effective performance.

BTW, I still have not had a chance to drop the boat in the water to take dB measurements. Combination of daily afternoon thunderstorms (with lots of pretty lightning) and I'm finishing a paint job on the engine. Looks gorgeous!

Mako said:

BTW, I still have not had a chance to drop the boat in the water to take dB measurements. Combination of daily afternoon thunderstorms ...

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I'm looking forward to hearing about your results when the storms etc. let up. Would definitely consider doing this, and knowing the benefit in the form of numbers would be really useful. Plus just your impressions.

@Frosty, I just returned from the Indian River. Took sound measurements under duplicate conditions: measurements behind windshield to avoid wind noise, 4000 rpm, 30 mph.

Prior to installing the MLV I measured 96db. Installed MLV as mentioned before with partial coverage inside 60% (see earlier photo).

Today measured 80db!

I still have about 2-3 sf of MVL to install so will do that one of these days.

Hope you find this thread helpful.

Wow, that's a huge drop! I bet you're going to enjoy that. Thanks so much for testing and reporting back

I got similar impressive results after installing Soundown Carpet Underlayment on my boat. Soundown makes impressive products for sound and vibration deadening.