Underseal over seam sealer?

[AndyStobbs]

I'm in the process of doing a major overhaul on my vectra. One aspect has been to investigate some laminated metal on the main chassis rails under the floor. The car was really well sealed by ze Germans in Russelheim and I've had to scrape off no end of underseal in order to let the dog see the rabbit.
It looks to me like the underseal has been applied over a liberal layer of tiger seal type stuff, does that sound likely?

 

[the snooper]

They do spray on sealant to protect the floor

 

[AndyStobbs]

I've got an undetseal gun for use with the compressor, my original intention was to keep adding layers to build it up to the original thickness. Would it be better to apply this floor seal stuff first?
Have to say I'm well impressed with the lengths vx have gone to trying to slow corrosion down. All metal is coated to begin with. then waxoyl inside all voids, then this really thick layer of stuff to finish.

 

[the snooper]

If you have gone down to bare steel and intend to use underseal if would prime and put some top coat on first, if the stuff you are going to use is schutz it's gonna take a lot of building up first you could get some se sealer and coat it first

 

[steveo3002]

its spray on sealer from new

for home use , id go epoxy primer onto the bare metal , seal up any gaps /joins with sealer then spray on stonechip , i think repeated coats will just be more likley to peel or crack

can top that with gloss paint if you wish , washes off nice and easy and then future rust can be spotted

 

[AndyStobbs]

I'm not painting under the floor lol, I will never hear the last of it it my friends catch sight of that!
It's not exactly home use, the car is on a two poster in my garage, but I'm not a body shop. Is this spray on sealer available in small quantities? Asked the local paint shop earlier and they didn't seem to know what I was on about.

 

[Wallace]

I ordered a tube of Master Seal sprayable seam sealer from Wayside Adhesives to try in a Teroson gun I have had for years and never used, it was £12.44 delivered so quite expensive. Unfortunately it comes in a plastic tube instead of alloy and the nozzle thread is different so I have been unable to try spraying it but I ran a couple of test pieces on a sheet of steel to see what it's like and I ended up using it in a normal gun as it is so good. Once set it stays very flexible and has a nice tacky rubber feel that paint would stick to easily. The viscosity out of the nozzle is slightly runnier than Upol Grey Stripe brushable seam sealer so it brushes in really well and I would imagine that sprayed would be almost identical to some of the GM sealant I have removed over the years.

I have just done most of a floorpan with Gravitex using a cheap Shutz gun over epoyy mastic 121, first time I have used it. The Gravitex builds up very quickly if you hang about and looks awful straight off the gun wet.

 

[AndyStobbs]

Right then, so seam sealer a good way to go then for building up. Be it brushable or sprayed on. I've just bought 1l of gravitex so from what you say Wallace I could use that to build the layer up aswell. Then schutz over the top of it.

 

[Rocketman]

Well you have 2 products you need to use to seal stuff up - not to confuse the 2 products to use. The seam sealer is as it suggests = it seals seams. It's much thicker than gravitex for that reason. So you go area all the the seams edges with seam sealer first (over welds/joints/etc - nice and thick). After that you go over everything with the gravitex (stone chip). And if you want a top job you do the top coats - think you mentioned you didn't want to go that far.

 

[the snooper]

Well you have 2 products you need to use to seal stuff up - not to confuse the 2 products to use. The seam sealer is as it suggests = it seals seams. It's much thicker than gravitex for that reason. So you go area all the the seams edges with seam sealer first (over welds/joints/etc - nice and thick). After that you go over everything with the gravitex (stone chip). And if you want a top job you do the top coats - think you mentioned you didn't want to go that far.

seam sealer can be used for seams or full floor pans and and other panels that require it and is mainly applied to the floor pans for noise deadening which is what the manufacturers use hence the reason the op had to remove it

 

[Rocketman]

From what I see the manufacturers use. After the exopy primer they seam seal using a seam sealer and then use something very similar to gravetex over the entire bottom of the car - finishing off with top coats. While the stonechip/seamsealing has an effect on the noise deadening the main noise deadening is actually via the bitumen pads applied underneath the carpets on the interior of the car. Well this is how I have seen French cars done since the late 80's onwards anyway.

 

[the snooper]

the bitumen pads are to stop panels resonating, I was welding up a transit inner arch yesterday and even those are sprayed with exactly the same stuff as seam sealer its a pain to grind off and when the particles land on you hand they are hot.
One more point is that stone chip is sand able where as you will find what is on the underside of a car isn't

 

[Rocketman]

Well snoops on French cars they are using 2 very different products for sealing the seam / vs just general covering - you can pull one off from the other. The thing is the products we use are very different to what the manufacturers use anyway. You could conclude grey strip and gravetex are absolute pants compared to what the manufacturers use.

Also while some stone chips are sandable like the gravetex others are most definitely not. Some seal sealers available are sandable. It's really not that easy to pigeon hole.

 

[the snooper]

I agree there are masses of products out there and different methods from one make to another

 

[Wallace]

1 litre of Gravitex won't go far if you are spraying it with a Shutz gun.

 

[AndyStobbs]

I've only got to patch up, not looking to redo the whole floor pan. Just where I have removed the sealer to get to the rusty bits.

 

[Wallace]

First time I used the Gravitex I had a paint reaction as the new Schutz gun I bought was faulty and literally threw a thick coat on, the solvent couldn't flash off quick enough, skinned over and acted like paint stripper. I thinned some down and sprayed a couple of thin coats on with a 0.8 gravity gun, let that dry and had no problems after that.

 

[AndyStobbs]

I've bought a tin of brushable seam sealer that looks like it'll be perfect for matching the original finish with schutz on top. Thanks for the advice guys.

 

[AndyStobbs]

It's all gone wrong. I primed the pannels prior to the application of seam sealer (primed last night,seam sealer this morning) and the sem sealer is re-wetting the primer. It even appears to be softening the original underseal. Should it only be applied to bare metal?

 

[MG David]

That should not have happened. What primer have you used? How long has it been on? What seam sealer have you used?