```ts
export function fieldMean(records: Record<string, number>[], field: string): number {
  let total = 0;
  let count = 0;

  for (const record of records) {
    if (field in record && typeof record[field] === 'number') {
      total += record[field];
      count++;
    }
  }

  if (count > 0) {
    return Math.floor(total / count);
  } else {
    return 0;
  }
}
```

Explanation:
- The function `fieldMean` takes an array of records (`records`) and a field name (`field`) as parameters.
- It initializes two variables, `total` to keep track of the sum of the numeric values in the specified field, and `count` to count how many valid records have been processed.
- It iterates through each record in the input array:
  - Checks if the field exists in the record (`field in record`) and if its value is a number (`typeof record[field] === 'number'`).
  - If both conditions are met, it adds the value of the field to `total` and increments `count`.
- After processing all records, if `count` is greater than 0, it calculates the mean by dividing `total` by `count`, rounds down to the nearest integer using `Math.floor()`, and returns the result.
- If no valid numeric values are found for any record, it returns `0`.