A robust, chemically, structurally, and thermodynamically compatible ablative gap filler that can be processed with ease is provided. The gap filler uses a carbon phenolic mixture that has nearly the same material property characteristics as the adjacent PICA or carbon phenolic tiles. The gap filler is applied into the gaps using an innovative processing approach that involves preparation of a ‘dry mixture’ of the ingredients, which is then packed manually or robotically (if needed) into the gaps. During the packing process, the dry mixture may be vented, and pressed periodically to ensure that there are no trapped voids. After each gap is adequately filled with the mixture, the assembly is bagged and cured in the oven at about 250 or 300° F. for about 1.5 to 2 hours. The gap filler thereby forms a bond with the adjacent PICA or carbon phenolic tiles, without degrading or modifying the properties at any of the interfaces (e.g., with the tiles, adhesives, substrate, etc.).