The purpose of the plaster scratch coat is to provide a rough surface for the next coat of plaster to adhere to, ensuring better adhesion and a stronger bond between the plaster and the surface being covered.
Sand
The purpose of applying a scratch coat plaster in the process of plastering a wall is to create a rough surface that helps the next layer of plaster adhere better. This base coat also helps to level out any imperfections in the wall and provides a strong foundation for the final finish coat of plaster.
To plaster over foil covered board, you will first need to apply a bonding agent to the foil surface to help the plaster adhere. Then, apply a base coat of plaster over the foil, making sure to smooth it out evenly. Finally, add a finish coat of plaster once the base coat has dried to achieve the desired texture or finish.
The finish plaster is normally white all the way through. It sounds like you are dealing with a pool that has been replastered by the method of putting a "brown coat"/"scratch coat" (the gray plaster you noted) over the original finish plaster surface, and a new finish coat of white plaster on top of that. The scratch coat more like a thin concrete than plaster (doesn't have the white marble dust in it) and is used to get a better bond to the old surface.
plaster with neat coat of cement
They are the same thing. A skim means just a thin finishing coat of plaster about 3mm or so thick, just enough to cover any minor imperferctions on the wall.
I use basic drywall primer over all of those.
The purpose of applying a skim coat plaster to a wall surface is to create a smooth and even finish, covering imperfections and providing a suitable base for painting or wallpapering.
In olden days of yore plaster was applied over wooen lath which gave the plaster something to adhere to . Thus a much heavier coat of plaster could be applied because of the space between the lathes. the next day a second coat was applied called the skim coat because it's only purpose was to fill in the imperfections left from the first coat. fast forward to now the plaster comes in sheets much the same as sheetrock ex cept it is blue, and rightly called blueboard , after the hangers screw the bluboard to the wall and ceiling a team of plastererscome in and put a skim coat of plaster over the whol board, the joints require a heavier coat. After this coat dries in a couple of hoursor less the plasterers come back and apply a veneer thickness to the wall and dampen the plaster with a brush being waved in front of the board.Thus completing the plaster job. Now a oldtime plasterer like my brother-in-laws brother is a real plasterer and I was lucky enough to have him plaster my house when we built it, would walk off a job if they wanted him to use blueboard., as he is a old time plasterer who is an artist as he makes crown mouldings an other plaster designs on top of a coulple of inches thick.of base plaster. if you get a chance to see a real plaster job and a blueboard job you can tell the difference and both shine over sheetrock and compound job.
The best method for preparing a wall with plaster primer paint before applying the final coat of paint is to clean the wall thoroughly, repair any cracks or imperfections, sand the surface to create a smooth finish, apply a coat of primer specifically designed for plaster, and then proceed with the final coat of paint for a professional and long-lasting finish.
To skim coat a plaster wall effectively, follow these steps: Clean the wall surface thoroughly to remove any dirt or debris. Mix the skim coat compound according to the manufacturer's instructions. Apply a thin layer of the skim coat compound to the wall using a trowel or putty knife. Smooth out the skim coat evenly across the wall surface. Allow the skim coat to dry completely before sanding it smooth. Repeat the process if necessary to achieve a smooth and even finish. By following these steps, you can effectively skim coat a plaster wall to achieve a professional-looking result.