I'm debating if I should add an extra layer of protection under the Dynamat. My concern is that it won't stick well to the undercoating...anybody experience this? If not recommended, do I need to rough up the floor (mine has a coat of flat black paint)?

So long as the coating is tightly adherent to the body I think you'll be fine laying soundproofing over it. I'd opt for a hard drying undercoating versus the softer type.

That's what I had planned, just wasn't sure how well it would adhere. Thanks...

I don't think that would be wise, lay down the dynomat, then you could spray rubberized undercoating over that if you want but there is no need trust me... I've dynomatted 4 cars, including my 69 camaro.
The deadening works best when it adhears perfectly to the metal surface, if you have a material between the dynomat deadener and the metal, its not going to deaden the metal as much!

[ 02-10-2004, 03:36 PM: Message edited by: Brian Lewis ]

DO NOT lay Dynamat over anything other than bare metal as it will not adhere. If anything prep all trunk surfaces, install Dynamat then undercoat over(depending on the type of Dynamat may not be required) ?'s let me know.

Originally posted by toolfan:
DO NOT lay Dynamat over anything other than bare metal as it will not adhere.Gee that's strange, how many modern cars (and hot rods) have bare metal floorpans? How many people take the time and trouble to remove every bit of paint from their floorpans before installing Dynamat? Not many I'm sure.

Dynamat (and its variants) will stick to any clean surface. That means free of grease, dirt, wax etc. You could lightly sand the paint film to knock off any gloss and allow more surface area for the Dynamat to stick to, but it is not 100% necessary. If you have a sound paint film or undercoating installed it should stick over them both just fine. To be safe you could choose to apply the undercoating over the Dynamat.

The undercoating surface will be rough enough that even if the Dynamat sticks well, it will leave tons of small air pockets etc.... that will affect the ability of the Dynamat to work the way its designed to work...

You want the surface very clean, but it doesnt have to be bare metal. Most undercoating is a rubber compound..... that won't allow the Dynamat to stick very well....

I wouldnt use the undecoating before the Dynamat........

I used POR15 for my floorpans and then did sound material over that...... if you really want, spray an undercoating over the Dynamat, not under it....

I apologize, on my last post what I meant to get across is that Dynamat will not adhere as well and not be as affective when applied to a rough surface(as undercoating would leave) as it will to a smooth surface (not bare metal but to a clean dry surface).

I'm just concerned about the floors getting rusted again. I don't know if I'll be able to truly make all of the dynamat seams water tight with aluminum tape. So if I'm reading correctly, as long as the primer/paint is scuffed and clean, the dynamat will adhere and the primer should protect against rust?

BTW, I had to choose between dynamat and POR15 for the floor pans for budget reasons, I hope I made the right choice. Also, there is a car stereo dealer in Yukon, OK selling the Dynamat Extreme Bulk Pack (36 sq ft.) for $150. Email me for the info if you are interested...

I just put some por 15 and it can out great...

POR 15 Gray and 'death metal' sound and heat reflector, works great graemlins/thumbsup.gif
http://www.brainerd.net/~knudsen/69RS/Interior/DCP02577.JPG http://www.brainerd.net/~knudsen/69RS/Interior/DCP02623.JPG

If $$ is a major factor... dont buy Dynamat !!!! Its way over priced. There are quite a few good products out there that you can get alot cheaper than Dynamat, that will still do a really good job.

Do a search for sound deadeners etc......

I dont think the sound material will offer any rust protection at all.... it may seal well, but not totally water tight....

I think undercoating should be illegal, I've always had a bad experience with that s--t :D

do what click said, por15, then soundproof it