I would have to disagree with your decorator and say it is much more likely the white emulsion paint is to blame for the bad gas-like smell experienced in your daughter’s room.
What’s more it’s not a smell that will simply go away in time or be relieved by any of the familiar remedies, such as using vinegar or onions. I’m afraid that for the room to be made habitable again, the walls will need to be completely redecorated.
The problem could be either due to poor quality out-of-date paint – buying new doesn’t guarantee new paint – or, more likely, a bad batch of paint that reacts with underlying coat.
Re-Coat with Alkali Resisting Primer
To solve the problem effectively the walls will need to be coated with an international alkali-resisting primer before a completely new coat is then applied.
One of the well known paint manufacturer has recently been bombarded with a number of consumer complaints that recount dilemmas very similar to yours. Common symptoms include the smell becoming worse when doors and windows are left open or when the room warms up in warmer weather. The smell has variously been described as sulphur and ammonia-like. If this matches your own experiences then you likely share the same trouble.
Ask Decorator to Rectify the Problem
As is it clearly nothing you have done wrong, you shouldn’t be expected to shell out for any more paint and for any more of your decorator’s time. By rights the decorator should rectify the problem free of charge, as they are responsible for choosing the paint and performing an unsatisfactory job. However, this is a complex problem and it will be difficult to prove that the fault lies with them.
If they are unwilling to concede the responsibility then you could try contacting the trade organisation Painters and Decorator Association to ask them for advice on how to proceed.
Complain to Paint Manufacturer
Alternatively you could complain to the brand responsible for the paint – or advise your decorator to do likewise – and explain that their paint is responsible for the release of gas-like fumes and will require a costly redecoration. If the paint manufacturer wishes to investigate then you will need the tin to hand so that the batch number can be quoted.
The company has reportedly not officially acknowledged the problem as being due to their paint, but have nevertheless offered unhappy customers vouchers for alkali-resisting primer and more emulsion paint. If the paint manufacturer is at least willing to offer this kind of compensation then you may be able to come to an arrangement with your decorator that won’t leave you out of pocket.