My gas boiler has a horizontal exhaust about 15cm below the underside of a
car port roof. Under certain cold atmospheric conditions the plume
condenses into droplets on the roof underside surface. The surface appears
to be made of MDF or similar and I would like to protect it from
deterioration which may be caused by the warm, wet plume of exhaust gas.

Please can anyone recommend a suitable protective paint for this
application.

TIA

Malcolm H