Techniques for infiltrating a CMC substrate may include infiltrating the CMC substrate with a first slurry to at least partially fill at least some inner spaces of the CMC substrate, where the first slurry includes first solid particles, drying the first slurry to form an infiltrated CMC including the first solid particles, depositing a second slurry including a carrier material and second solid particles on a surface of the infiltrated CMC, where the second solid particles include a plurality of fine ceramic particles, a plurality of coarse ceramic particles, and a plurality of diamond particles, drying the second slurry to form an article having an outer surface layer including the second solid particles on the infiltrated CMC, and infiltrating the article with a molten infiltrant to form a composite article.