Pressure washing large gravel tarmaced drive

Job is part of a large exterior clean - the driveway is tarmac but its not a clean finsh - looks like it wasn't properly compressed when it was laid and there is green algae growing amoungst the small gaps in the tarmac - i pressure washed a test area and it was difficult to get the green stuff up and left a decent sized holes in the tarmac, also there was a lot of debri blasted off onto the wall. I have some pics which i will post later but wasn't sure if this kind of job is worth just saying no to ?

You do need to be careful pressure washing tarmac , lower the pressure , I generaly pre treat with weed killer if bad if it’s just green algi softwash it first then pow at low pressure. 

Pjj said:

You do need to be careful pressure washing tarmac , lower the pressure , I generaly pre treat with weed killer if bad if it’s just green algi softwash it first then pow at low pressure. 

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Thanks man - any tips on weed killer to use 

Depends what the green is is it algi or moss or what ???? 

Ah just seen the picture that’s moss get some moss killer spray it with that leave it a week or so then pressure wash on a low pressure using a flat surface cleaner if you have one, i have used hypo on mine in the past with good results ,I need it do mine  again in the next few weeks .