All-risk contracts basically get the painting contractors to sign up to do as many 'redecs' as the Principal Contractor decides. This is normally determined by how 'incompetent' the site management team are (So as you can imagine, it usually involves a lot of work)!
The sole reason this type of contract exists is that Principal Contractors cannot manage site works. Consequently, they are 'hit' with 'variations' or 'dayworks' to cover re-decs due to 'damage by other trades' or 'out of sequence works'.
So in order to avoid this problem, all risk contracts were created.
The problems for painting contractors are :
1. It is near impossible to anticipate how much 're-dec' works will be required and so consequently, how much to charge.
2. Principal Contractors do not want to pay for the service that is required under an 'all risk' contract.
3. Some painting contractors have no idea what is involved in 'all-risk' contracts and so seriously 'under price', so that your prices seem 'extortionate' in comparison.
Don't say you haven't been warned!!! (Although there is always one painter who is desperate enough to sign up!!)