Coating the insides of small ID pipes, headers, exhaust manifolds and all sorts of circus act advise.

Many coating applicators and individuals claim to be able to efficiently coat the interiors of small diameter pipes and parts.

With many years experience in the Ceramic Coatings applications business I fail to grasp the technique, if there is any, to prepare the interior of the headers to receive and maintain the ceramic material for any worthwhile period of time.

Even with proper preparation using a professional Sand Blast Cabinet, using clean Aluminum Oxide blast media and adequate consistent air pressure the preparation of the surface to be coated will simply be that line of sight that the Blast Media can reach and the line of sight that the ceramic spray application can reach. This certainly doesn't qualify to say the part is coated on the inside.

Using a very high volume blast at very high pressure (180 PSI) with 80 grit Aluminum Oxide media will not reach all surfaces even on a mandrel bent header pipe. Pipes with splice welds are even less prepared because of the interior bubbles caused by the welding process.

Even running the parts through my Vibratory Polisher with abrasive chips that thoroughly clean and roughly burnish the interiors of the parts / pipes still doesn't provide the quality of surface profile required for guaranteed bonding results.

Often I can reach every tiny crevice, around every bend on small turbocharger housings, cast or tube turbo exhaust manifolds. In these exceptional cases I can coat the interior of parts with a Ceramic Coating that will remain bonded for the life of the part.

It has been suggested that using a flapper sander on a flexible shaft driven by an electric drill motor can sand out any residue, sealer etc inside the pipe and allow the ceramic material to bond properly. All in All this sounds reasonable until you envision getting a spray mist to coat every inch of the interior with a thin coat of ceramic.

Some could argue that you could prep the interior the tubing then pour ceramic material through and get a consistent coating thickness. In theory this sounds good however the ceramic needs to be a very thin application of about .0001 to .0003 IN. The poured through material air dries to such a thick application that it cannot approach the heat coefficient of the corresponding part as the exhaust goes from 70 degrees (f) to as much as 1400 degrees (f) in as little as one minute. This radical change and radical expansion of the metal causes the ceramic to de-laminate and flake off.

It has been suggested that drawing a swab of foam rubber / sponge on the end of a wire could evenly distribute the ceramic material in an acceptable thickness.

You might want to try coating a drinking glass with this method before wasting your time trying it. The coating varies greatly and is of poor quality, displaying high and low areas that are not coated. The drinking glass test will show the transparency of this routine.

Needless to say: If you could see the interiors of the pipes that you're paying to be coated you'd quickly reject this coating if it were visible on the exterior surface of the pipe.

I'd love to hear how those that are charging you for coating the interiors of your headers are preparing them to bond the ceramic material.