Welcome to the SeeMeCNC Community

I've just got a Rostock 2 all setup, initial prints were with Taulman Bridge. Looked OK but very slow to print and require lots of string clean up.

I've switched to PLA for larger things, currently printing the Mayan skull on thing verse. Looks so much better than the nylon Bridge. At defaults it want 92hrs to complete so I set it to 10% fill and combine every 3 layers and also only fill where required. 16hr print time and looking great...

However I notice the base layer is still not solid and is a swirling mess of strings, like my other PLA prints.. Why is this?

Photograph would be useful.
There are a few prints on thingiverse that don't have flat bottoms, and don't put down very much of a first layer, the second layer is then printed in mid air. But it's hard to know if this is your issue without seeing it.

Ive tried attach photos (from android) about 4 times but this forum times out. The model looks to have a solid base is Repetier..?

Hard to say, something very wrong with the first 20 layers or so, what does it look like is happening when it's printing those?
Does it do the same thing on other models?

It's most likely either a bad slicer setting, a bad model, or a mechanical issue, what's odd is it corrects itself.
I'd try another model, I haven't printed that,particular model, I have printed the Celtic skull successfully.