Foam sheets and screwing wood to aluminum

[infx708]

Two topics here. First off is where do I find sheet foam? I pulled out a bunch of this stuff from between the stringers under the deck:

It's about 2" thick and 12" wide. I walked around Lowes this morning with no luck.

Second, I found some screws this morning that were labeled for attaching wood to metal. They have a tip that looks like a metal boring screw - like a drill bit - and the rest is like a tight thread wood screw. I'm planning on pre-drilling the holes in the wood, filling them with silicon, and then drilling, in order to preserve the seal on the wood. Think these will do the trick? They aren't stainless, so I shouldn't have any issues with the aluminum.

 

[drewmitch44]

Re: Foam sheets and screwing wood to aluminum

The screws you saw that have the drill bit thing on the end is just that. Its a self tapping screw. Means that you dont have to drill a hole in the aluminum first before you put the screw in, it drills the hole its self. Id use the stainless, and if you are going to pre-drill the holes then you dont need those self tapping screws anyway. Also you should have been able to find the blue foam that lowes sells right in the same isle as the pink panther insulation and home wrap. I have some of that blue foam floating in a bucket of water in my shed. It has been there for almost a year and when i take it out of the bucket is still has not soaked up any of the water and its been almost a year.

 

[infx708]

Re: Foam sheets and screwing wood to aluminum

I've read that stainless steel and aluminum don't mix well. It certainly doesn't play well with the steal on my truck bumper. I'm predrilling the wood, not the aluminum - no need to preserve a seal on the aluminum.
I walked up and down the insulation aisle at Lowes with no luck. All we have here is the pink panther rolls and the blow in - I'll have to check another one. There doesn't seem to be a consistancy between the stores in this area (Fayetteville, NC)

 

[OldePharte]

Re: Foam sheets and screwing wood to aluminum

For the foam you may want to try a more contractor friendly building material dealer. According to Lowe's web page, they offer only 1/2" thick material.

I would think that either the pink (Owens Corning) or the blue (Dow) extruded foam would work. Don't use the beaded foam as it will absorb moisture more than the extruded.

People here used extruded foam for dock flotation until it was outlawed.

 

[Labman]

Re: Foam sheets and screwing wood to aluminum

Hope this helps clear the S.S. to Alum. misinfo!
Galvanic Corrosion
Because corrosion is an electrochemical process involving the flow of electric current, corrosion can be generated by a galvanic effect which arises from the contact of dissimilar metals in an electrolyte (an electrolyte is an electrically conductive liquid, I.E. Salt Water). In fact three conditions are required for galvanic corrosion to proceed; the two metals must be widely separated on the galvanic series (Most S.S. and Alum. are very close) they must be in electrical contact and their surfaces must be bridged by an electrically conducting fluid. Removal of any of these three conditions will prevent galvanic corrosion.

The obvious means of prevention is to avoid mixed metal fabrications. Frequently this is not practical, but prevention can also be by removing the electrical contact - this can be achieved by the use of plastic or rubber washers or sleeves, or by ensuring the absence of the electrolyte such as by improvement to draining or by the use of protective hoods. This effect is also dependent upon the relative areas of the dissimilar metals. If the area of the less noble material is large compared to that of the more noble (cathodic) the corrosive effect is greatly reduced, and may in fact become negligible. Conversely a large area of noble metal in contact with a small area of less noble will accelerate the galvanic corrosion rate. For example it is common practice to fasten aluminium sheets with stainless steel screws, but aluminium screws in a large area of stainless steel are likely to rapidly corrode.
See clear as mud!
Use S.S. anytime you want in Alum.!!!!

Disclaimer'
The above was copied from my College notes, when I was in Metalurgy. circa 1973

 

[BIGcarpy50]

Re: Foam sheets and screwing wood to aluminum

i have found that rivets work just as well or even better than screws. overtime the holes on the alum might get stripped....just my opinon but rivets are what i used.