If I remember properly, Balsarite for fabric can be thinned with either MonoKote Trim Solvent or IronX (a cleaner for the heads of the heating irons). I am not sure which - the can should tell you which to use.

I do have a question though. Why are you using Balsarite ? The film coverings do not need it as the glue on them is normally very good. For the fabric coverings only Koverall and Coverite ( that I am aware of ) require it for adhesion. If you are using Coverite (pre painted fabric covering ) I strongly suggest switching to SolarTex.

SolarTex is lighter than Coverite and the adhesive used on SolarTex is excellent - there is no need for Balsarite.

FWIW - After applying Balsarite for fabric, you will need to let it dry for about 24 hours, then sand it with some 220. If you do not do this, you have a very high probability of having lumps/bumps under the fabric where the Balsarite was applied. I have found Sig Stix-It works quite well for both fabric and film, but does have a HEAVY, head spinning, odor.

The ONLY places I use Balsarite (or Sig Stix-It ) is where I have to cut the covering flush with an opening and can not have an overlap (I.E. around windows - see Belanca Airbus round window for an example ). I do it in these places to insure the covering will not loosen.