I'm assuming that this is a 'water-borne' satin varnish for floors, in
which case as mentioned by an earlier poster, the temperatures we are
experiencing at the moment will probably contribute to the patchy finish
you are seeing.

I'd also guess that the bamboo flooring which you are coating is quite
varied in it's porosity, and thus some areas will suck the moisture
straight out the coating quicker than other areas leading to different
finishes and contributing to your problems.

As this is a water-borne coating, you are best not to use a pure bristle
brush. A Synthetic SRT filament brush will give better results as the
filament won't absorb any water, unlike pure bristle which is hollow and
absorbs water... swelling up to give a more scratchy finish. We're about
to launch some excellent Synthetic SRT brushes this week which we've had
on test for 4 months... and the feedback has been excellent.

You could also try a foam brush, these are good with both solvent-borne
and water-borne products and are a popular tried and tested applicator
for varnishing projects where the surfaces you intend to coat are flat,
and they certainly avoid brush marks.

http://www.decoratingdirect.co.uk/viewprod/r/RODFBS3P/

Between coats do denib the surfaces gently using a very fine grade wet
and dry paper (used dry), and then tack rag gently to remove any dust,
before applying the next coat. You should get a more acceptable finish
on the application of further thin coats. Work quickly and try to keep
your wet edges going, don't be tempted to brush over areas which have
just been applied, get the material on and leave it alone... water-
bornes don't like being played around with.

Regards
--
Max Bone Decorating Direct Ltd
http://www.decoratingdirect.co.uk/
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