I presume he is looking for the fungicidal wash to be applied after cleaning
I would use a sprayer to apply the wash prior to sanding
Will kill off any spores still lurking
I would charge
2-50 cleaning
0-50 f wash
0-50 re sand
total £3-50m2 on that area
sealing additional 0-75m2
look at the weather conditions it may be a long drawn out process to complete
It's pointless attempting sealing this time of year unless you're prepared for the customer to call you in the future to fix the problems.
An extra 75p for the seal would be too low anyway. 4.25 for the full process is not enough unless you're using crap sealant that is costing you 30 quid a drum.
Good sealant averages 80/90 quid a drum. I've used cheaper stuff round the 50/60 quid mark and you can see the difference.
5.50/6 quid for a good profit.
In terms of applying chem, we use a black dustbin and suck from it with a pressure washer turned down a bit on the unloader with a wide fan nozzle then giving the pump a good flush through with fresh water to clean the seals.
Low pressure sprayers will take too long for a large area of this size.