Sill drainage holes and underseal, a blessing or a curse

[Adrian]

Hello all

 

As I'm sure you all know you start out with one intension and it soon escalates.

 

I've been stripping the accursed underseal off the car as I didn't like the fact it could be covering up problems for the future. Glad I did as in parts where paint was still present it was working admirably but where it was absent (there was seriously no trace of paint ever having been there) the body was fairly well rusted and pitted in places, locally the underseal had actually delaminated away from the body. Fortunately it is all sound with no perforations and a good amount of strength still present so fully salvageable. The three holes at the base of the sills were however full of underseal. 

 

Can I ask - would you unseal the holes, clean out and use a grommet?

 

And also what your view is on underseal (I intend to use Por15, etch primer, Stone chip and body colour paint, possibly with clear waxoyl)

 

Thanks

 

Adrian

[Clive]

I would not block the holes at all. Clear out, and use dinitrol or similar, thje very thin runny stuff, then a squirt of the heavy duty stuff. Way way better than waxoyl.

 

Your idea of painting is a good solution. Though etch on top of POR15? or is that the POR paint system?

[Adrian]

Hi Clive

 

I've been questioning the need to etch on top of the POR15 just rough it up before it cures fully was the other option. The actual system is degreaser, etcher (metal prep), por15 and topcoat with whatever you like.

 

S you wouldn't use a grommet in the drainage holes? Is the Dinotrol the treatment of choice for the majority of the forum. 

 

I don't intend to use it in the wet so was considering just leaving the paint - a quick inspection would then show any issues that were developing.

[bluelighttaxidriver]

I've just applied dinitrol into my new sills, via the holes. Assumed I should block the holes with grommets after. Is this not the case...?

[Clive]

I like drain holes. Not sure if grommets were fitted?

[Guest]

Hello.

 

The problem with any original manufacturer drainage hole is that they get blocked and in fact their original diameter was woefully inadequate.

 

To that end a lot of owners, me included, have opened up the holes to a larger diameter. The rationale behind this is that it prevents excessive clogging, allows water to escape more freely and of course the larger the hole more air gets inside to assist drying.

 

Never bung the holes up, if that was the case why would there be holes there in the first place !!

 

Once the holes are enlarged you will also find it easier to apply anti-rusting fluids with a lance or such.

 

Regards.

 

Richard.  

[Dick Twitchen]

No grommets on the sills of a GT6 when they left the factory.

I would fully support the Dinitrol recommendations, used it when I rebuilt my car 8 years ago and a recent look inside the sills with a friend's endoscope showed all well.  Interesting point compared with Waxoyl was the Dinitrol, apart from being easier to apply from the aerosol, was it found every small gap in the plug welds on the bottom of the sill so penetration better.

Dick

[Clive]

I think it is the ML stuff ( http://www.rejel.com/dinitrol-ml-penetrator-rust-proofing-cavity-wax-500ml-aerosol/ ) I used in the sills and also into the chassis, plus in any seams/under arches etc. It is really thin, so yes, soaks into any surface rust inside a box section, and into the seams etc but not really long lasting where it may be subject to impact from stones/water splash under the car and so on. Those areas I used a much harder wax ( http://www.rejel.com/dinitrol-4941-black-underbody-wax-500ml-aerosol-can/ ) in black (my car is used a lot! it did almost 3k in a week around europe last year, plus Spa, a few trackdays and plenty of normal use on top) which is still all intact, even in the wheel arches. Happily went over the thin wax once dried. 

Amazing stuff, I am very impressed!

 

I should add that rust etc was sorted first. And I have a compressor, so used the non-aerosol version as I think you get more product. I bought a few of each, and used less than one of each. I was't skimping either.

[Adrian]

Interesting stuff - I probably know the answer but if I used the thinner stuff for the arches to penetrate seams etc - is it over paintable? - I assume probably not.

 

Having spent days removing the old black tarry stuff I am a bit reluctant to spray new stuff back on.

 

So far then it seems the consensus is unblock and leave unblocked. 

[bluelighttaxidriver]

This is exactly why clubs and forums are invaluable. Thank you...!

[Clive]

Adrian, if it is a concours car then fair enough (and do what some others do, bubble wrap the arches. I jest not)

 

But the wax is pretty easy to remove with white spirit, and it will protect the paintwork. It is not the same as underseal. Besides, there is a clear wax available, obviously it will get dirty but surely protection ranks higher than slightly grubby looking arches?

[Colin Lindsay]

The drain holes are also curved so difficult to keep grommets in; however I'd recommend as Clive and Dick have said and not block the holes at all. You can access the area behind the sills from the side carpet; remove the side strips on the inside of each sill and this gives excellent access to clean and rustproof. Pay particular attention to the areas where there are no drains i.e. extreme front and rear corners; even an aerosol can of Waxoyl (or Tetroseal which I find is thinner and covers better, but needs more frequent replacement) with a long nozzle extension will get good protection into the crevices.

[Adrian]

No it's not concours but am wanting to get it to a good standard, bubble wrap, really?

 

I wanted a sound car to learn on and boy, talk about a steep learning curve, I think I'm going to have to get a longer rope! But it is SOOO much fun! It's great that daft questions can be asked on this forum.

 

My thoughts were originally the clear waxoyl but will look into the dinitrol for the cavities. It's not a perfect job because I'm doing it with the chassis still on so there are areas I can't get too, so the spray dinitrol would be a good finisher in those areas.

 

Thanks to all

[Pete Lewis]

most drain holes are  Bi product of  the drainage of body  dip in the factory  paint shop  

 

they double up to let water out in later life  

 

Pete