My first suggestion is that he cover exposed areas that come in contact with the cement.
Washing the rash thoroughly every evening with a mild soap or even using baby wipes with aloe vera and Vitamin E to cleanse, then hydrocortisone cream or Vaseline should help.
If the rash starts looking like it might be getting infected, try triple antibiotic cream.
If these things do not work, he should consult a dermatologist.
Best of luck to you two!