It is practically difficult to monitor each and every painter in rooms or elevation faces of buildings.
When paint is diluted by more than a dilution ratio, there will be change in the shade and thickness of paint may or may not be visible or proved as diluted at higher rates.
No doubt painting contractor will always try to make more money by diluting more.
To overcome the problem we can implement one of the following solution for it.
1. We should buy the paint and supply it to contractor - there is no benefit to contractor by saving my paint.
2. We should keep complete control on the drums of paint received used and balance on daily basis for contractors material.
It is not only the painting contractor but a paint company can also cheat you.
It may be the possibility that, paint is not giving coverage so contractor is trying to get coverage by diluting it more.
To overcome this issue you can do following;
At the time of finalization of paint manufacturer (in both case of paint is purchased by you or contractor) get the samples of paint done in front of paint manufacturer contractor at place which can be remain their till completion of Project.
When it comes to sample work, some smart companies do come with a samples whose figures and appearance can make you get trapped into that.
We should let them allow to do whatever they want to show and in a way they prefer to do it.
We should record all the data like coverage of paint, dilution ratio (this is mostly looked by all during finalization and here a paint manufacturer can fool you for sure) appearance etc.
Once we finalize, when we give purchase order / work order, we should mention in clause following.
After receiving every new lot of paint, a sample on wall will be done for 1 liter diluted paint as per proportion and it should give coverage of minimum 95% of what we achieved with same tone of paint.
If it fails to give coverage, quantity of paint will be payable as per calculation of sample done.
For an example you got 100 drums of 20 liter paints.
your standard coverage was 100 sft per liter after dilution.
now you did sample and got only coverage of 80 sft.
So the manufacturer or contractor will get the bill on only 80 drums even though we got 100 drums (because paint is not performing to what it was shown during initial sample).
This way a smart sampler who fooled us get tricked and as soon as you specify above thing, they will only make true samples and you will able to better judge which paint to buy during sampling stage only.
If paint performance to its 95% + efficiency and if the painting contractor is good and not corrupt, there will not be any problem.
When you get a doubt of contractor is diluting more, you can always compare it with standard sample or you can get one patch done near executed work by ensuring correct dilution and comparing both shades.
when there is more dilution, the shade of the paint will go dull.