Sikaflex 252 Question...

Highway Yacht · January 05, 2009, 11:25:59 AM

Anyone ever use Sikiflex 252 to hang plywood? I made my sides (skins) to cover my windows in a 15ft long fiberglass covered plywood panel. The inner side of the panel that will adhere to the bus is raw plywood covered in resin only but the outer side of the plywood is covered in a fiberglass woven material and then covered with resin. They are sanded down to a smooth seamless panel. I now want to attach them to the window frame post but not sure if the Sikaflex 252 will hold to the resin covered plywood. I've read many great things about people using it to hang metal and aluminum but not much on fiberglassed plywood. Any help or input would be appreciated.

Jeremy · January 05, 2009, 11:54:34 AM

I was interested in the answer to this myself as I have noticed that one of the only places on my bus where rivets are used is where the GRP caps are joined to the aluminim roof and sides. The aluminium itself is only held with Sikaflex-type adhesive (obviously I don't know the actually brand Plaxton used), but for the GRP they chose to use rivets as well.

I have in fact already used just polyurethane adhesive (not Sika specifically) without problems to attach some new GRP panels as part of the conversion, but your post has prompted me to see if it is 'officially ok' to do this.

Below is a brief description of Sikaflex 252:

Sikaflex 252 adhesive may be used in place of screws, rivets, welds, and other fasteners. This is a polyurethane adhesive that seals and bonds in one to step to provide high strength elastic bonding. Suitable for a wide range of substrates.
Sikaflex 252 bonds and seals at the same time, offers excellent gap filling capabilities and compensates for loose tolerances in the building process. Sikaflex 252 exhibits excellent Green Strength and that means reduced clamping time. Some surface preparation is generally recommended for Sikaflex 252. Sikaflex 252 is sandable, paintable and NSF approved for incidental food contact.

Applications:

Particularly suited for bonding of metal of wood, trim, molding, styling elements, structural bonding of large parts including sheet metal and composites including large panels. Bonding of FRP roofs, sandwich panels and walls. Sealing applications especially for large joints. Replaces rivets and mechanical fasteners.

Substrates:

Wood, primed metal, and composites.

The full tech sheet is here: http://www.sikaindustry.com/tds-ipd-sf252-ind-us.pdf

There is no suggestion anywhere that I can see that special measures are required when gluing GRP, except one proviso that says "Seek manufacturer's advice before using on plastics that are prone to stress cracking."

Other than that I don't think you have anything to worry about.

Jeremy

hargreaves · January 05, 2009, 12:02:44 PM

I Sikaflexed some 1/2" plywood to the structure on the inside of my unit. Made a mistake and hade to take it off. The plywood separated and I had a bunch of scraping to do. It stuck real good. The plywood was bare. The resin you used probably was waxed and the wax would have to be removed before gluing, otherwise I think it will work fine if you follow the recommended application thickneses.

How do you propose to clamp it? Gerry

Highway Yacht · January 05, 2009, 12:38:45 PM

Quote from: Jeremy on January 05, 2009, 11:54:34 AM
I was interested in the answer to this myself as I have noticed that one of the only places on my bus where rivets are used is where the GRP caps are joined to the aluminim roof and sides. The aluminium itself is only held with Sikaflex-type adhesive (obviously I don't know the actually brand Plaxton used), but for the GRP they chose to use rivets as well.

Jeremy

Thanks for all the links. Looks like I should be fine with it. It almost sounds like I would be better off to grind the resin off the inner side down to bare plywood before attaching it with Sikaflex.

Highway Yacht · January 05, 2009, 12:50:16 PM

Quote from: hargreaves on January 05, 2009, 12:02:44 PM
I Sikaflexed some 1/2" plywood to the structure on the inside of my unit. Made a mistake and hade to take it off. The plywood separated and I had a bunch of scraping to do. It stuck real good. The plywood was bare. The resin you used probably was waxed and the wax would have to be removed before gluing, otherwise I think it will work fine if you follow the recommended application thickneses.

How do you propose to clamp it? Gerry

Good Question but not sure I have a good answer.... I had thought about using 3 C-Clamps on each end of the panel since I have room and brace the middle span in place with a few Load Locks like they use in the back of semi trailers to hold the loads from shifting. I would sandwich the Load Locks between the side of the building and the Fiberglass panel on the bus. I estimate the 15 ft panels weigh abround 60 to 70 pounds. My only other option is to screw them in place and then remove the screws and bondo the screw holes shut after the Sikaflex cures.

coachconverter · January 05, 2009, 01:19:56 PM

Do you have access from inside the bus? Could you attach some angle to the posts, thus giving a surface that you could run some extremely short screws through the angle and into the plywood backer? That, plus the Sika would certainly be more secure than just Sika.

I'm going to Sika 252 a sheet of steel on a bus tomorrow, if I have leftovers I'll experiment with some plywood and scrap box steel for you.

Todd

TomC · January 05, 2009, 10:47:28 PM

I used 3M 90 spray contact adhesive on both my window cover up and in my shower for the fiberglass overlay. It works well and hasn't come down-only disadvantage-since it is a contact adhesive, you have to position it correctly the first time. Couple of trial runs without adhesive is always good. Advantage is no clamps are needed.
Sikaflex has the advantage of being able to position it correctly first, but have to use clamps or a means to put compression on it while it cures. Good Luck, TomC

CraigC · January 05, 2009, 10:59:34 PM

I would not use bondo as a plug. In my experience it will show the complete small circle and may even pop out a few thousands of an inch over time. You will be very unhappy.

Craig

Highway Yacht · January 06, 2009, 11:51:31 AM

Quote from: coachconverter on January 05, 2009, 01:19:56 PM
Do you have access from inside the bus? Could you attach some angle to the posts, thus giving a surface that you could run some extremely short screws through the angle and into the plywood backer? That, plus the Sika would certainly be more secure than just Sika.

I'm going to Sika 252 a sheet of steel on a bus tomorrow, if I have leftovers I'll experiment with some plywood and scrap box steel for you.

Todd

Yes.. I do have access to the inside of the bus and I never thought of that idea. I think this by far is the best solution to get me what I am trying to achieve. Keep me informed on your Plywood to Metal Experiment. Thanks.

coachconverter · January 06, 2009, 09:31:03 PM

Yes, get a couple of sticks of 1.5-2 inch angle, chop them to the size you want (the precut angle pieces are extremely pricey), and build you a vertical platform.

Had a couple of set backs this week, but will try that experiment tomorrow.

Thanks
Todd