Second fix technically starts with the job of applying an internal wall finish/covering, and it is usually plaster.
At this stage the fitting out of all the bathrooms as well as kitchen and other rooms can take place. From a plumbing point of view, the heating system will be commissioned, the fixtures and fittings (sanitaryware, taps etc.) and appliances connected. As the walls have now been plastered, there is no means to correct any errors.
The exact definition of second fix needs to be agreed to with your builder in particular, especially if he expects to be paid at the end of it being completed.
There are two common options for plastering. One is to fix plasterboard then taping the joints where the boards meet ready for painting (dryline). The second is to plasterboard then apply a skim coat on the boards.
At this stage there will be drying out to take into account – as with poured concrete the plaster will need time to cure. You can plaster directly on concrete blocks, leave them exposed and painted, or clad them but this requires battening. Other building methods will have similar options.
This means the building will have a high level of moisture which makes it unsuitable to paint the walls (the paint won’t stick) or to install flooring, e.g. wood will absorb the moisture and once the house has dried out the floors will shrink leaving unsightly gaps.
Some people get dehumidifiers to speed up the process, others will allow cross ventilation (windows and doors open to create draughts) to do the work. How long it takes to dry will mostly depend on the buildup; plastering directly onto blockwork for example can take eight weeks. The best way to check is with a humidity reader and ask for advice as to what level the wall, floor or ceiling needs to be from the manufacturer of the covering you intend to use.
As a general guide, timber flooring will require concrete floors or screeds to have a stable and uniform moisture content of no more than 3 per cent and wooden sub-floors no more than 10 per cent; with a relative humidity (air) of 35 to 40 per cent.
Once the house is fully dry, if you plan to paint your walls consider the option of spray painting the undercoat. Specialist companies will do this for you; it will save time and isn’t as costly as you might imagine. Agree on paint quality and number of coats beforehand.