PLT ENCOUNTERED IMC WHILE ON VFR FLT.

Narrative

I FILED A VFR FLT PLAN FOR 3000 FT MSL; WBOUND FROM CHESTERFIELD (FCI) DIRECT TO SOUTH BOSTON (SBV) AND FROM THERE TO AIR HARBOR (W88). SEVERAL MINS BEFORE REACHING THE SBV VOR; I REQUESTED AND RECEIVED 2500 FT MSL FROM ZDC TO STAY UNDER THE APCHING CLOUDS AND WAS TOLD TO MAINTAIN VFR. AFTER HDOF TO GSO APCH AT ABOUT 45 NM FROM THE GSO VOR; I REQUESTED 2000 FT MSL AND WAS TOLD NOT TO GO BELOW 2000 FT AND MAINTAIN VFR. I DSNDED TO 2100 FT MSL AND REMAINED VFR FROM THAT POINT UNTIL I WAS WITHIN 2-4 NM OF AIR HARBOR WHEN CLOUDS BEGAN TO OBSCURE THE GND. I CONTINUED ON COURSE FOR LESS THAN 1 MIN; WHEN GSO'S APCH CTLR TOLD A DEPARTING ACFT THAT GSO AND ALL THE SURROUNDING ARPTS WERE NOW IFR; INCLUDING BURLINGTON; HIS DEST. WHEN I HEARD HIS REMARKS; I EXECUTED A 180 DEG TURN AND INFORMED GSO APCH THAT THE GND AND AIR HARBOR WERE COMPLETELY OBSCURED AND I WAS RETURNING TO RICHMOND AND REQUESTED A HIGHER CRUISE ALT (THE AREA I HAD JUST FLOWN THROUGH WAS LITTERED WITH TWRS). I WAS ASSIGNED A NEW SQUAWK CODE AND CLRED TO 3500 FT MSL AND HANDED OFF TO ZDC AT ABOUT 20 NM OUT. FROM THE TIME I ENTERED IMC UNTIL I EXITED IT 20 MINS LATER; NEITHER GSO ATC NOR ZDC MENTIONED 'VFR' TO ME AGAIN. I DID NOT EXIT IMC UNTIL I HAD PASSED SOUTH BOSTON; WHERE I CHANGED HDG AND CONTINUED ON TO CHESTERFIELD. I SHOULD HAVE DECLARED AN EMER AT W88.