Sintered regolith falls into the catagory of ceramic materials. Sintering is the process most common to ceramics. When bricks are made from clay on Earth first the bricks are heated long enough and hot enough to drive out the water. Then the heating is increased to cause partial melting or vitrification. This is the sintering process. The unmelted particles provide a stable shape and size during the process which involves some shrinkage and a decrease in porosity.
On Luna water for mixing the various particles would be very expensive and recycling the water would never be 100% effective. So it is hoped that mixing of dry powders will provide satisfactory bricks. There is the example of mixing dry powders for powder metallurgy, which is a sintering process performed on Earth. More will be known about the quality of bricks possible from lunar materials when the research can be done on Luna. A possibility to consider is the sintering of bricks in an oxygen atmosphere as opposed to in a vacuum.