Adhesive 4

[dik]

I'm looking for an adhesive that will secure stainless steel to concrete.

The concrete surface is somewhat rough (amplitude 1/8").

The installation temperature may be about 0 deg C and the general working temperature may range from +40 to -50 deg C.

The installation may be submerged for part of the year.

Looking for a Urethane, or Silicone type of material or other suggestions.

thanks, Dik

 

[unclesyd]

I would give Adhesives Technology a call with your proposed application.

http://www.atc.ws/

Here are two materials I've seen used to apply SS flashing to concrete. This was not on a large scale and mainly indoors.

http://www.quikrete.com/PDFs/SPEC_DATA-PolyurethaneSealants.pdf

http://www.stickwithpl.com/products/detail.asp?PLProductID=14

 

[dvd]

I'm not sure what your application is, but epoxy grout could be a good fit.

http://www.chockfast.com/chockfast.htm

http://www.fivestarproducts.com/epoxygrouts/index.html

 

[dik]

Thanks... will chase the info down.

Dik

 

[MintJulep]

How much strength do you need?

Is the geometry already fixed - limiting the possible adhesive selections, or can you still change the geometry to accommodate the adhesive strength to get the assembly strength that you need?

What grade of stainless? Passivated or not? Can you chemically treat it to activate the surface to improve adhesions?

What type of concrete? How long after it was poured will you be gluing to it? If it has been exposed to the environment for a long time, what is it contaminated with, and how can you clean it?

How large are the parts? The large temperature range will make relative thermal expansion an important consideration.

The low temperature of installation is challenging, and will likely rule-out epoxy.

My first thoughts would be urethane or acrylic, although I'm not sure acrylic would perform well at -50C.

 

[dik]

MintJulep...

I've inherited the condition; a large 3/8 flat plate about 2'x15' to be secured to concrete and could be partly immersed for a couple of months a year.

Fastening is minimal and I'm thinking of using belt and suspenders aka adhesive <G>.

It will be subject to Winnipeg temperatures (-40deg C) in winter and also some impact.

Dik

 

[dik]

MintJulep... forgot to add that it can be sandblasted on the back surface, too. Stainless is 304. I was a little concerned about any reaction with SS bolts and stainless and have asked that they be diaelectrically isolated.

Dik

 

[MintJulep]

You really need to give this some thought.

The coefficients of thermal expansion for concrete and 304 aren't all that different, but how massive is the concrete thing? The rates of expansion may be considerably different.

Partially immersed in what?

How porous is the concrete? How much water (or whatever) will into the concrete behind the adhesive?

If you have any voids or unbonded regions in the adhesive they WILL fill with water and they WILL grow when the water freezes and expands.

Also, an adhesive layer will make the whole thing a very nice capacitor. Eventually the galvanic isolation between the plate and any mechanical fasteners will be compromised, and interesting things will happen where the fasteners are attached to the concrete. Even more so if they happen to be near whatever rebar may be in the concrete.

From what you've stated so far, I would not recommend adhesive for this.

 

[dik]

The concrete is very massive and there likely will be a temperature differential. The fluid is river water will a fair silt/sediment load.

The concrete porosity is comparible to 4000 psi concrete of 40 years ago and is unknown at this time.

Other from surface saturation, the moisture behind the adhesive will be similar to concrete immersed in water.
Moisture can 'wick' up the concrete pier, likely the full height of the sign.

I hadn't considered the capacitance matter; I was concerned about the dielectric (spelling corrected) connection between the sign and the fastener. Do you have further information or a source on this activity and corrosion? I guess the large and relatively thin surface area would contribute greatly to this effect. Would it help to have a conductive adhesive to minimise the effect of capacitence and corrosion?

thanks, Dik

 

[PackerFan]

Epoxy anchoring material, not hybrid adhesives, like Hilti RE 500 has been used for this type of bonding before. Regardless of what is used, please read the following email from my super secret files...

"Before being in the Chemical Anchor development I was part of the HAF team. Within the HAF project we elaborated bonding behaviour of Epoxys to concrete and steel. So key finding of this project was: Bonding to concrete is not a bigger issue but bonding to steel is only possible by using a special preparation before the use (primering, laser cleaning during manufacturing process,...). Conclusion is, that we cannot recommend bonding of steel to concrete under all environmental conditions we have. If the steel plate is not prepared in the right way you'll get migration of water to the interface and failure of bonding over time. "

Basically, the steel will have to be spotless and prepared especially for this application.

 

[dvd]

I believe that a work-around to "spotless" baseplates when using epoxy is to properly prepare the steel surface and then paint with an epoxy paint. This preserves the steel surface and the epoxy-painted surface can be easily cleaned on the jobsite. As always, the epoxy grout supplier should be thoroughly involved in specification and installation procedures.

 

[dik]

One of my bigger concerns is the ingress of water behind the plate and subject to freeze-thaw eventually causing failure. The adhesive doesn't have to be particularly strong as the flat head anchors are capable of supporting the load assuming they don't corrode and disappear.

Thanks for the heads up on the preparation. I was thinking that the U/S be sandblasted and that would suffice.

I'm still trying to chase down information on capacitance related corrosion from one of the corrosion and electronics tekkies I know.

Dik

 

[MintJulep]

I don't suggest painting the bonded surface first. The overall strength is only as good as the weakest bond line. If you don't prepare the stainless surface well first, that weak line will be at the stainless-to-paint line. Epoxy paint may or may not produce an amine blush when it cures, if it does, and it is not entirely cleaned, then the weak point will be paint-to-glue. Regardless, gluing to paint is almost never a good idea.

If the concrete is 40 years old, and is subject to submersion periodically, you can be assured that the surface is throughly contaminated. Including with oil and gas that is inevitably floating on the surface of the water.

I'd be really worried about epoxy at a 0C application temperature. At best it will take a really really long time to cure. Is there any way to get some heat into the concrete and metal?

Since we're sharing secret files, to get a really good bond to stainless you need to etch the surface with a witch's brew of oxalic acid, sulphuric acid and water immediately before bonding.

 

[dik]

Thanks, MintJulep, et al...

My current solution is to break the plate into 5 pieces with an 1/8" gap between; thermal expansion for the full length is about 3/8". I'm using SS flat head bolts set into Hilti expansion anchors set in epoxy to prevent water ingress. For future installations, I'm leaning towards 3M Scotch-Weld urethane adhesive between the concrete and the stainless steel, with the stainless prepped in a fashion suggested by MJ; I'm having difficulty chasing down a suitable adhesive, capacitance corrosion and the etching process.

I'll monitor the corrosion and hope that the epoxy provides a bit of a dielectric.

Dik

 

[PackerFan]

Are you looking for the electrical resistance of the epoxy/adhesive? The adhesive I spoke of earlier has a resistance of 1.7 x 10^12 ohms/in (epoxy) and another is 5.1 x 10^11 ohms/in (hybrid adhesive). Maybe that gives you a good range to work with. I would assume that these resistances should be listed for the product you use.