How to Glue Foam to a Basement Ceiling

Prepare the surface by cleaning it so that it is free of dust or debris and by filling any cracks. Allow it to dry fully.

Apply a small amount of mastic to each corner and to the middle of the back of a foam sheet. The mastic should be a few inches in diameter and 1/2 inch to 1 inch in height, in the shape of a cone. If the piece of foam you are gluing is large, extra mastic can be applied to other areas of the foam sheet.

Press the foam sheet against the ceiling in the corner of the room, using a ladder if required, taking care that the edges sit perpendicularly to the walls of the room. The amount of pressure used needs to be enough for the mastic to spread and adhere to the ceiling surface without damaging the foam. While it might take several days for the mastic to fully dry, once it adheres, it will be strong enough to support the weight of the foam.

Glue the rest of the foam to the ceiling in the same manner, finishing the first row and then laying parallel rows. Lay the tiles as close to each other as possible, minimizing the gaps between them. Use the knife to trim the foam sheets, if required.

Fill the seams between the tiles with caulk; spread a thin strip of caulk along the seam and used a gloved hand to squeeze it between the tiles.

Quickly remove any extra caulk from the surface of the tiles, before it has had time to dry, using a wet sponge.