Hello,

From the photo it looks like the resin has "fish-eyed" off the surface due to the surface being slippery for the relative viscosity of the resin.  You could try a rougher surface finish or a slightly thicker resin.

Also be aware some surface contaminants or traces of release agents can cause the same issue.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Thank you very much for your answer. But I have another doubt about the process: How much time should I wait, after introducing the curing agent into the resin, before applying the mix onto the metal substrate? This is not mentioned in the TDS.

I will appreciate any recomendation about this issue.

Best regards

MJF

I agree with Warren. What is the application? I'm assuming something for corrosion testing if you are following that preparation standard? 

Thank you for your suggestions.

In fact, we are using this resin for anticorrosive tests. According to TDS this resin is suitable for this type of tests, should we try another one?

We are looking for a resin model without any additive to be used as anticorrosive primer. Do you have any other suggestion?




Thank you in advance.

MJF

My guess is you still have some form of contaminant / release agent / protective coating on the steel  Extract from the smooth-on website: http://www.smooth-on.com/pages.php?pID=43&cID=16 Preparation of Surfaces for Epoxy Adhesive Bonding

A clean, dry surface is a necessary prerequisite for adhesive bonding; and adhesives will either stick to the surface to which a bond is desired or to a film of extraneous material directly on that surface. Rarely can a structural adhesive penetrate through surface contaminants to provide an optimum bond on an unclean surface.  Porous materials are simple to bond to, providing they are dry. The surface should be sanded till clean and free from dust. Non-porous surfaces, as found on metal and plastic materials, should be degreased, dried, and roughened by sanding, sandblasting or chemical etching, the etching being required for certain surfaces.  In order to avoid contamination of these surfaces proper care must be taken prior to bonding. Handlers should wear clean cotton gloves to prevent body oils from contaminating the clean surfaces. Contamination can be caused by a fingerprint, not perfectly clean clothing, or through the use of substandard degreasing or chemical solutions.  For best results, surfaces can be prepared by three pretreatment procedures, which are listed by increasing effectiveness.  1. Degrease only.  2. Degrease, abrade, and degrease again.  3. Degrease and chemically pretreat.  Degrease, Abrade, and Chemical Pretreatment:  An optimum bonding surface is perfectly clean, free of oil and grease. Degreasing should be performed even when the bonding surface appears clean. 1. Suspend piece(s) in trichloroethylene or wipe bonding surfaces with clean cloth saturated with trichloroethylene. Allow piece(s) to thoroughly dry.  2. Abrade surface to allow for greater adhesion. Implements for abrading; sandblaster, wire brush, emery cloth, and or glass paper. Metal surfaces (Use grade 80-150 abrasives for steel and materials resistant to scoring. Use grade 300-600 abrasives for light alloys and  less resistant materials). Painted surfaces should be stripped prior to pretreatment for better adhesion.  3. For maximum strength a chemical or electrolytic pretreatment is required.  Note: Bonding of surfaces should be done as soon as possible upon completion of any pretreatment procedure.  ....... Ferrous Alloys other than Stainless  1. Degrease with trichloroethylene.  2. Sandblast, sand (100 grit) or etch in 15% aqueous hydrochloric acid (equal parts concentrated muriatic acid and water) for 10 minutes. Etched surfaces should be rinsed immediately and dried with hot air. Freshly sandblasted or etched steel begins to rust immediately; therefore, adhesive should be applied as soon as the surface has been prepared.  ........ Wrought iron and mild steel  1. Degrease with trichloroethylene.  2. Mechanically abrade (sand-blast or emery cloth).  3. Degrease.

Thank Chris for your contribution. Anyway I had it in consideration regarding the pre-treatment of ASTM where the chemical etching with Clark solution is included.

Best regards

MJF

If the substrate is prepared correcting with no contaminants and it has been etched correctly then it will break down the surface tension of the epoxy and you will not get this fisheye problem. Therefore it must still have something on the surface and it hasn't been prepared correctly.

Even the slightest trace of grease could cause that problem.  Also if the surface is too smooth it can happen, although in our experience, you shouldn't have any problems once the metal has a good key and is free from all contaminants.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant