I am by no means an expert, but I have covered 2 models with Brodak medium silkspan with butyrate dope and both have been fine. And I brushed it on. The silkspan has adhered as expected and shrinks up fine.

Being somewhat of a rookie builder, I strictly followed the Brodak document 'Finishing and Painting your Airplane'.

Those instructions say to use a mixture of 60/40 thinner/clear dope (60% thinner). And I put on 3 coats on the wing and let it fully dry before starting to apply the silkspan on the wing.

So not sure what might be going on in your situation. Maybe not enough thinner so it can easily soak thru the silkspan? And I also made sure I painted at a time of day when the ambient humidity was low, so no blushing was going on.

HAS ANYBODY HAD ANY LUCK WITH THE BRODAK MEDIUM SILKSPAN..I TRIED SOME AND IT DOESNT STICK TO THE WOOD VERY GOOD EVEN PUTTING AT LEAST 3 COATS OF BUTYRATE DOPE ON THE BARE WOOD.I PUT IT ON WET AND  THE DOPE DOESNT PENETRATE THE SILKSPAN VERY GOOD.IT SEEMS TO SWELL THE SILSPAN AND IT GETS HARD AS A ROCK WITH ONE COAT OF BUTYRATE DOPE...YOU SURE COULDNT USE IT ON OPEN BAYS

 It was probably ten-ish years ago now but I bought six packages of it once to give it a try. I had the same issues you're describing and then some. It ended up going directly into the trash can. 

The answer is simple:
https://stunthanger.com/smf/open-forum/my-source-for-tea-bag-silkspan/msg664743/#msg664743

For anyone interested in the paper piecing Dave's other post referred to, and couldn't find the currency conversion, I simply added something to the cart and the site magically converted it to U.S. currency, both in the cart and on the product page I selected from.  It was $22.68 for 10 meters.  I didn't complete the purchase, so I don't know what shipping would be.  I was just exploring for now to find out how much it cost.

How much did you reduce the dope, and what brand of thinner did you use?

I PUT 3 COATS OF 70% THINNED BUTYRATE DOPE ON THE WOOD..I THEN USED THE SAME DOPE TO ATTACH THE SILK SPAN WET...IT DIDNT WANT TO PENETRATE THE SILKSPAN VERY GOOD  AFTER IT DRIED I COATED IT WITH 60% THINNED BUTYRATE DOPE ALL BRODAK BRAND IT WAS HARD AS A ROCK AND VERY HARD TO SAND...IT SEEMED IT WAS MORE A POLYESTER COVERING THAN SILKSPAN..NOTHING LIKE THE SIG STUFF I HAD