Bit slow on the uptake there as you could have offered a maintenance package that included treating surfaces with a biocide wash say every 6 months to help them keep it looking good... It self cleans don't you know

Just think how much extra revenue that could create with say 300 customers all wanting their surfaces maintained regularly instead of ad-hoc that wait untill they get really bad again.
Same can be said for the likes of render cleaning too as once clean a matainence package could be put in place that would help keep their property looking good.
Now then you could start earning some real dosh
