What is this? Salt?

[nhangler]

After removing my motor from my aluminum boat, I found some corroded aluminum near where the motor mounted. The bolts for the motor are stainless steel and seemed fine and it is possible the the corrosion is from a previous motor that was used on the boat? I did however notice this thick white powdery stuff (no oder to it) and can only imagine that it is salt? I also fear that the plywood that is in the transom is pressure treated but could it cause this?

Looking straight down, you can see that this white creamy powder is between the plywood and the transom plates. Plywood is wet near the top but seems to be in ok shape?

 

[rickryder]

Re: What is this? Salt?

Welcome to iboats

Crevice corrosion
Crevice corrosion can occur in narrow, liquid-filled crevices. The likelihood of this type of corrosion occurring in extruded profiles is small.


However, significant crevice corrosion can occur in marine atmospheres, or on the exteriors of vehicles. During transport and storage, water sometimes collects in the crevices between superjacent aluminium surfaces and leads to superfi cial corrosion (" water staining"). The source of this water is rain or condensation that, through capillary action, is sucked in between the metal surfaces. Condensation can form when cold material is taken into warm premises. The difference between night and day temperatures can also create condensation where aluminium is stored outdoors

 

[nhangler]

Re: What is this? Salt?

I'm sure the boat was used in saltwater. No zinc anode on the motor either.

The bottom of the transom plywood is dry. So it may be trapped water? Salt water?