BCM Community

Hi All

I am about to cover over several window holes in my bus.  Having read the archives on this list, I intend use Sikaflex 252 to attach the aluminium to the steel supports around the window.  However, I have  a question that I hope someone can help me with.  The supports around the window opening are painted with the standard exterior paint that covers the rest of the bus (about 14 years old).  The Sikaflex rep here said to: -
  Rub the paint with scotch-brite
  clean with cleaner 205
  use primer 204
  then the 252.

My question is has anyone had success with applying the sikaflex over paint or have they ground the paint away and applied directly to the steel?

Thanks in advance for any advice!

Peter


 

I would do whatever the sikaflex rep says...

I used it with epoxy primer paint. Haven't had any problems, make sure you follow the instrutions to the "T" or it will fail. Scotch-brite the part that you are attaching too, where the Sikaflex is going.
Ron

Peter - I used 252 on my bus project and it works great.

My hobbyist thoughts on your question runs along these lines:

The Sikaflex bonds your new material to your bus.  In your case, it will be bonded to the paint which is attached to the bus.  It would seem reasonable to assume that the bond could be no stronger than the paint bond since what you are really doing is creating a sandwich with the layers being: Bus, bus paint, Sikaflex, your new sheeting.

I made sure that the areas I bonded to were paint free out of concern for the above.  I do not know if my reasoning is correct. 

Craig - MC7 Oregon

I agree with the idea that you should follow what the rep says, but the adhesion is only as good as what's under it. If the paint would come loose....... well.........
 I would ask him what to do if you take it down to bare metal. I don't think it would be that much more work as you could take it off with a very aggressive sanding disc (36 or 40 grit) rather quickly. Then you know that whats underneath is good. But I imagine you will still have to use their primer.

 FWIW,
    Chaz

HA!!!!!!!  Craig, ya beat me too it!!  LOL  :D
   Chaz

I went down to the metal and then followed instructions to the letter - great stuff!  I would do it again, no questions!!!

Danny

Thanks for all the input.  I presented your ideas to the rep this morning.  He thinks that it would be OK to glue over the paint.  However given the age of the paintwork, has agreed that we would probably be safer to strip it off along the track we are putting the glue.

Just knock it off with some aggressive sandpaper on a grinder or sander. A rough surface - altho may not be needed - sure wouldn't hurt!

  Chaz

Peter,

I have never read anything but rave reviews for Silksflex.  It must be a can't miss product.

A word of caution:  I looked at a bus that had galvanized metal fixed to the frame as you intend to do with soft aluminum.  He used rivets to really draw it together.  He ended up with waves between the rivets that I attributed to the high viscosity of the glue resisting flowing.  It was noticable as the coach was painted a glossy dark color.  Some have said that rivets or screws are not needed as the Silkaflex alone has a greater strength than a riveted joining.  Lots of questions are begged in that statement, but still.  I would have one concern no matter what you do and that is with expansion waves.  Safari coach had a nightmare time till the started heating the alu. sheets before they joined the skin to the steele frame.  Alu expands a lot more than steele and the alu tends to bunch up.  One guy rigged up heat lamps on the alu and had his coach toasty hot with heaters inside before he started riveting but he didn't use bonding cement of any kind.

I hope I haven't put you off and I know an awfull lot of folks here have skinned.  Most, I think, with galvanized and that presents problems come paint time although they are easily delt with with etchers.  For that matter, alu can be a sorry story if it isnt primed with etchers and bonders before painting.  Three step, I think.  Woe be if you think you can cut those corners.

UI think I would go with sheet steele, galvanized or not.

Best wishes fior a great outcome and let the board know.

John

I spent some time yesterday with the Sika factory tech, asking many questions, he sent me a quick reference guide on which cleaner, prep, and primer to use and on what ever your substrate may be, it was exactly what i was wanting to hear and read. Yes Sika will allow your skin to move.........is has to, there was a note that what ever your paint system was to make sure that it allowed for expansion, if you don't you might as well expect it to crack where the seams are.  There also was information on how to make the bead and how thick the bead should be. He told me that Prevost "only" uses Sika for their body panels now.  It looks like if you follow the instructions that this gives you another option for attaching body panels.  If anyone is interested I can forward this file to you its in PDF file format! 

Hi Muddog16

Can you please send me a copy of the file?  My email address is in my profile.  Although Sika here are very willing to help, the staff here (New Zealand) are generalists & don't have much experience with bus converters.  They keep having to refer back to head office for answers.

Thanks
         Peter

PS  Thanks for all the previous answers, it is a great help to have so much experience only an email away.  The professionals here are so busy building cheap motorhomes for the hire industry, that they have no interest in doing any work on bus conversions.  This means that I have to do everything myself.  This board is giving me the confidence to tackle jobs, I have no previous experience in.

Peter, It's on the way!  JohnEd, I also sent you a copy but got the dreaded demonmailer message back for some reason, lets see if Peter gets his email, if it comes back I'll look for the problem, yes it could be me!......LOL     

Muddog,
   Could you email me the PDF file?  jconradATrvbus.net  Thanks, Jack

Muddog,
Sent you an email to the address in your profile requesting a copy of the PDF file - did you get it?  Please send me a copy - use my profile email.
Thanks
Connel

Connel, its on the way!  JohnEd I tried to send you a copy, and I received the dreaded deamonmailer message, do you have another email address?

Pat

THANKS PAT! U DA MAN!!

Connel

I removed all but the front windows in my MC8 last week and used Sikaflex 252 to put up the new steel sides.  It worked great.  The stuff flows like cold molases.  I did put in a few rivets along the bottom for support.  The rivets will be covered by the trim strip I put back on.  One week later and a couple of hundred miles on the bus and it is holding great.  I still have primer on the bus to make sure it held before I had paint put on.  I wire wheeled the frame where I adhered to.  This cleaned the surface and roughed it up to hold the Sika.  No other prep was done.  One thing I noticed tht helped make it flow better was leaving the next tube in the sun while I was working with one.  This heated it up just a little and was much easier on the arms.  Hope this helps.
John