Etch Primers

[Adrian Harris]

I thought I'd start this as a separate topic, as it is one of those things which confuses the heck out of me.

The Phoenix Precision website (https://www.phoenix-paints.co.uk/etch-primer) states:

All Etch Primers need to be left for a minimum of 24 hours at a temperature of 18 - 20 degrees Celsius to dry properly.
Whilst this is the minimum it is advisable to allow significantly longer before applying topcoats.
More paint finishes are ruined by the application of paint over Etch Primer that is still drying than almost anything else.

Whereas the Kent Europe website (http://www.kenteurope.com/en/products/etch-primer) states:

You may then start with filling or painting already after a drying time of 10-20 minutes. However, the drying time may depend on the thickness, humidity and ambient temperature. To achieve best possible results, however, subsequent painting should be done within one hour.

Poles apart ?

Adrian.

[Stephen White]

Adrian,

Difficult to distinguish product data from marketing hype, I agree. Rustoleum guidance seems to hit the middle ground:

APPLICATION
Shake can vigorously for one minute after the mixing ball begins to rattle. If mixing ball fails to rattle DO NOT STRIKE CAN. Contact Rust-Oleum. Shake often during use. Hold can 12-16" from surface and spray in a steady back-and-forth motion, slightly overlapping each stroke. Keep the can the same distance from the surface and in motion while spraying. For best adhesion, apply 2 or 3 thin coats and allow each coat to dry for 2 minutes before applying the next coat. Allow the final coat of Self Etching Primer to dry for a minimum of 3-4 hours before dry sanding, or 15 minutes before wet sanding with #400 grit sandpaper. Do not use near open flame.
DRY & RECOAT
Dry and recoat times are based on 70°F (21°C) and 50% relative humidity. Allow more time at cooler temperatures. Dries to the touch in 10 minutes and to handle in 15-30 minutes. Apply a top coat after 30 minutes.

I’d suggest the guidance should be that etch prime is air dry in 30mins and safe after that to add a top coat but the curing process isn’t fully hardened off until 24 hours have elapsed. In other words, you can add coats very quickly but the coating won’t be robust until a day or so from application. That is born out by my experience. Any other views/understanding?

Stephen

[Greg Stephens]

I have a long history of applying finishes on wood and metal surfaces. I did a lot of work with catalyzed finishes when these first appeared in the early 80's. Many of them were specified to be quick dry. I have made a lot of costly mistakes by trying to rush things.

My experience has been it is best to wait 48 hours depending on temperature and humidity,and then lightly but thoroughly abrade the surface. Especially when switching between types of finish, i.e. oil to lacquer or acrylic, epoxy to polyurethane.


I have been using the Rust-oleum self etching primer and I already made the mistake of trying to use it as a filler primer on the mudguards I made for the Tiger I in order to hide some surface defects. It builds far quicker than it can dry very fast.

I had to strip it and re-coat VERY lightly. I took an half hour to prime the mud guards the first time.The last time I spaced three dust coats over three hours. I lightly sanded them the next day and dusted them again. It's still a bit heavy in places.

I would recommend applying roughly 1/5 of what you think you need with each pass and then letting it dry for at least 30 min before re-coating. It is very hard to restrain yourself with these rattle cans, they are really throwing out far more product than we need for our application. They were designed for home owners to re-finish lawn furniture and the like.

Your not going to hurt anything by applying less product than you think you need. It's easier to recoat than to strip the whole gummy mess of and start over.

Before I start air brushing the red primer I will sand with 600 grit wet sand paper and some oil free 0000 steel wool. Then a quick alcohol cleaning before proceeding.

[Brian Ostlind]

After going through around ten cans of etch primer sprayed onto my AT parts this is my conclusion. Sticks well! Otherwise, ick! I am not a fan. Several coats with wet sanding and non stop fumes I hate the thought of priming with it. I do believe that it is effective but I am moving on to Mission Models Primer now. They are a very high quality outfit and ensure that the primer is effective on metal and aluminum with only cleaning and scuff to prep. So excited to move away from the rustoleom

Edit; I am going back to rustoleum etch primer. The small bottles of mission model paints are just not practical.