One of the first problems associated with any discussion on the subject of blowholes is to find a suitable standard of reference against which different types and degrees of formation of blowholes may be compared and which may form a basis for specification. The failure to establish such a standard can lead to much misunderstanding between architect and contractor. Ideally, the standard should take the form of series of large panels, preferably full-sized section of the structure under discussion. When this is impracticable, smaller panels may be adequate, and failing this, one foot square, full sized photographs may be used. When describing the quality of finish, the percentage area of the covered by any one or more "degrees of blowing" is stated. Several factors influence the formation of blowholes, but the most critical consideration appears to be the way in which the concrete is placed and compacted. By carefully observing the details of these operations, it is possible to forecast the locations at which the incidence of blowholes will be greatest. The generally accepted correct method of compaction, whereby the immersion vibrators are kept a little distance below the surface of the concrete and both vibrators and concrete are raised at the same time, is soundly based. Unfortunately, except when concreting columns or short walls, a sufficient number of vibrators is rarely available to follow this practice. Inserting a vibrator into concrete that is only partially compacted tends to compact the upper layers first, making the escape of trapped air from below the surface more difficult. This operation, where necessary, should be done rapidly. The vibrator should be inserted into concrete which has been previously compacted before fresh concrete is placed above it. To summarize, no magical solution to the problem of blowholes has yet been discovered. Both architect and contractor would be unwise to expect to produce concrete surfaces that are completely free from blowholes, but well trained and experienced concrete placers can usually achieve acceptable finishes which may sometimes even approach perfection.