SEM Self Etching Primer and E z Coat products
Hi All,I'm in the earlier stages of building a RV8. Regarding priming, I was wondering if anyone has experience with SEM's E z Coat aeresol product? For the inside aluminum surfaces, I was considering using just the SEM Self Etching aerosol primer. However, after talking with the SEM Tech Rep, he suggested not using the Self Etching Primer. Instead, if just using a single product, he suggested using the SEM E z Coat product. Reason being, as many already understand, the Self Etching Primer, when used alone, does not offer optimum corrosion protection.Granted, using just the SEM Self Etching primer would be better than leaving the interior untreated. However, after my conversation with the SEM Tech Rep., it seems like their E z Coat product would be a better choice? If anyone has knowledge or experience with the above products, I welcome your toughts.Mike P.I would like to hear from anyone who has knowledge or experience with the above
I used to be involved in paint formulation, and the advice of the rep sounds good, although I don't have specific knowledge of these products.
The principle in paint formulation is to optimise the coating for its intended mission.
On aluminium, a hard oxide layer is quickly formed and this needs to be penetrated. An etch primer works by creating it's own key to the substrate by acidically attacking the oxide layer. However, optimising this etching requirement precludes the selection of the ingredients to provide the best barrier properties that are required for the best corrosion prevention. If the primer is designed to be overcoated, there is no need for barrier properties. I would expect that the second coating he recommended is a better compromise between best key and best corrosion resistance.
The accelerated test we used to do for corrosion testing involved placing scored and unscored coated panels in a salt spray chamber, and monitoring them periodically. It tests both the adhesion and corrosion properties, and I would ask the rep for the test values for the options he mentioned. The tests should have been carried out on aluminium. They may appear on the product data sheets.
I'm at an early stage of building a GlaStar and like you I have wondered about corrosion-resistance coatings for the insides of the aluminum surfaces. I did the rudder with Alumiprep, Alodine, and rattle-can zinc chromate but I really don't want to continue using these materials due to their toxicity. After a bit of internet researching and correspondence, I'm planning to use PreKote and Sherwin Williams GPB 988 self-etching primer on the next part. I found an article in which the author tested several of these primers that you may find useful: http://websites.expercraft.com/n51pw...ry&log_id=4863
The tech at the SW paint store pointed out to me that they can't make the rattle-can primers too acidic, as that would seriously cut into the shelf life as the acid worked on the inside of the cans. Whether one of these products would itself confer protection, I don't know. Seems appropriate to first remove oxides and other contaminants, which is how I've arrived at using the PreKote. I'd love to hear others' opinions on this matter.
As our esteemed "Hints for Homebuilders" speakers say: Good luck with your project!