Do you get a significant traffic spike on the weekends? particularly Sunday? Or is the flow pretty steady? How long has this been occuring?

If you get a spike in traffic on the weekends, my guess is the extra traffic is mostly "window shoppers"...people who type the wrong thing in a search engine, who don't really know what they are looking for, etc. Do you get most of your b2c sales on the weekend? I could see a lot of garbage traffic just jumping around, checking prices, viewing sites, surfing the internet, playing with stumble upon; they just drop by and move on giving you a bump in traffic and a corresponding bump in bounces. Especially if you are mostly e-commerce with relatively little content -- they might be looking for information on products before they buy, which brings them to your targeted site but isn't quite what they had in mind.

Also, is your traffic mostly CPC or from natural listings? If it's CPC, you might want to mess with your negative keywords to ensure you aren't showing up for near matches/related terms which really don't apply to you at all. I noticed a similar spike when Google introduced some of their new automatic term matching. I had to add quite a few negative key words to keep from appearing for "random" terms. I.e. you might sell electrical equipment, so Google might match you with "electrician," for which you see bounced traffic.

Do you know which pages are seeing all the bounces? It's always possible a single page is responsible for the additional bounces. Find out which page(s) and which keyword(s) are involved in the increased bounces. Maybe you've managed to rank well for some inadvertent terms or non-competitive terms which draw unintended traffic.

If B2B account for 2/3 of your orders, is it possible that your bounce rate for your B2C is always higher, but because you are more likely to get B2C customers on the site at the weekend, and no B2B it will appear higher.

So if your B2B bounce rate is 10% and your b2c bounce rate is 25%, during the week when you have 2/3 b2b searches and 1/3 b2c searches your bounce rate will average out at 15% but at the weekend when you have 90% b2c searches your bounce rate will reflect that and will show at 20-25%

Thanks for the responses.

Our highest traffic days are Monday and Tuesday. The weekends are the lowest traffic days of the week with Friday a lower traffic day as well. 95% of our traffic is organic, happily ;-) .

I have never really broken it down to see if our b2c has a higher bounce rate than the b2b and now I am intrigued to see if that is the case. Not even sure how I could accomplish that but I will dig into the stats programs to see if I can harvest that data somehow.

We still get b2b sales on the weekends because a sizable segment of our b2b sales are small businesses and those folks also seem to work from home on the weekends.

You have given me some food for thought.

Not even sure how I could accomplish that but I will dig into the stats programs to see if I can harvest that data somehow.

If b2b customers buy different items than b2c, you might be able to get a better idea of their different bounce rates by looking at the specific product pages and their bounce rates. It'd be a rather rough figure, but at least you would get some idea of their habits and bounce rates.

95% of our traffic is organic

First off, congratulations. Second, that could very well be why you see the spike, if you are high in the SERPs, now that I think about it. Of course, not having any real knowledge of your industry, customers, products etc. I can only conjecture...but...
If your products require any kind of technical knowledge to install or use, your weekend b2c shoppers are going to be looking for information and then eventually the actual products. I have some products which many homeowners own/use, but never really see, touch and certainly don't install. My bounce rate for these products is through the roof as I rank quite well but don't offer an encyclopedia page on them or detailed installation instructions -- they're meant for the tradesmen who know what they want. Still, since I rank well, I see a lot of "foot traffic" through the pages; they see the product and a price, then leave. Voila, high bounce rate...which I have no interest in correcting as selling to a more retail audience would simply mean huge hassles with returns and warranties due to improper use. It's the one downfall of e-commerce; anyone can show up at my site since I rank well, even if they're not my true target demographic, and skew my stats!

We have a few thousand product pages and about 13 000 products and parts in total. There are definately some products that require expertise.

I am going to take your suggestion and dig down into the stats and figure out if the b2c pages get a higher percentage of traffic on the weekends. Then its likely the consumers who are coming directly to the product page from Google, seeing the price and then leaving.