What is the Slickest Most Adhesion Resistant Prep for Sodium Silicate Core Boxes?

In general, I rarely darken the door of Harbor Freight as their stuff is usually so poorly made. I do know there are exceptions. If you have experience with this gun and figure it’s plenty good for the purpose, why not? Like below?



Denis

 

So I bought the 17 dollar gun. And though it had a smaller than recommended tip, I did as DavidF suggested and reduced the fan to about 3” at 12” away and opened up the fluid flow to max and the stuff went on just fine. I am doing such a small part that a small fan and a small tip is not an issue. Now, if I were doing. 56 Buick hood, the small tip would make for slow going. By using the gravity feed gun I can mix up just 40 grams of paint and apply a coat. The siphon took more than that to have the suction tube fill.

This is good stuff.



Denis

 

I put the epoxy on the inside of the pattern. It laid in pretty nicely using the Rustoleum aerosol appliance epoxy. Now to let it cure for 24 hours and then see how it works for core making.



Denis

 

A little follow up on the epoxy. The epoxy seems to cure fairly slowly. I sprayed it Friday and have kept the pattern at or above 70 degrees since. Yesterday and the day before I set it out in the sun hoping the UV and warmth (probably only got to 85 degrees as it has been relatively cool outdors here) would hasten curing. I can still dent it with a fingernail and it will show a slight residual dent. I am surmising this formulation of epoxy is known to be somewhat slow curing as the application recommendations are to apply 2 or 3 coats with only 15 mins or less between coats and then to wait 1 full week before reapplying. That week wait time implies to me (no chemist by any wild stretch of the imagination) that the paint must be at some intermediate stage for that period of time.

On the other hand, a typical two-part epoxy like West System 105 resin plus 205 hardener will cure to "click" hard in 8 to 12 hours at 70.

I am keeping my fingers crossed that this epoxy will dry to a truly hard surface at some point. Otherwise I will work that sand may degrade the surface. Time will tell.

Otherwise, rather than use the spray epoxy for lining silicate core boxes I may go to brusing on conventional West system epoxy which will probably not lay out into a smooth a coat as does the spray.

Anyone have any insights on the Rustoleum epoxy cure?

Denis

 

My knowledge of epoxies is limited to general glue stuff: precise component ratios and thorough mixing is essential, there was a Ceiba Geigy Araldite glue that lost 50% of it's strength if there was a 3% variation in mixing ratios. Also heating almost always increases bond strength: you could get strong bonds to glass but only from 60 deg C/140 deg F upwards. You'd have to let most of the solvent flash off before heating an epoxy paint, the rule of thumb for chemistry is that every ten degrees C increases the chemical reaction rate by double, so curing rate is very temperature dependent.

 

With you 100% on the flash and chemical reaction with heating. I’ve also experienced reaction acceleration with UV exposure. That’s why I put the part out in the sun after a 24 hour flash-off. I think it is slowly curing harder.

This is one of those rare cases, David, where there is an epoxy that can be put in a can. It is an unusual type in that it is ketamine-catalyzed and is said to be a true epoxy. Tom Cobett advised me of its availability and that’s why I selected it. He knows that epoxy paints in particular are resistant to the action of sodium silicate binders.

I was aware of the availability of the type of epoxy paint in an aerosol cam that you mentioned. But because it is a one shot deal and quite expensive on that account, I also shied away from it and would not use it unless somehow I could utilize most of the can of paint per coat. That is not the case with this small part.

Indeed spraying the West System epoxy would be a very nice option. I will find out how much I can thin it with xylene and try that. That’s because that epoxy does cure very nicely to a very hard finish in fairly short order. I’m thinking on the order of six or eight hours at 70 to 75° F. I use a triple beam balance to measure out small amounts of epoxy components very accurately. That balance measures in tenths of a gram accurately. So I can mix up five or 10 g of epoxy at a time for various purposes when I have only a small area that needs attention.

Denis

 

West System instructions say you can do it either by volume with their pumps or by weight. See quote below with bolding added by me. And I've been doing it with their pumps for medium volumes, by graduated cylinder for larger volumes, and by weight for very small volumes and all with excellent and seemingly identical results. It may be that their product is somewhat forgiving of small error as well. A 3% precision requirement as someone mentioned above would require meticulouis measuring technique and very careful clearing of mixing containers and careful stirring etc. I am glad it is not that fussy.

"Dispensing without Mini Pumps (Weight/volume measure) – To measure 105 Resin and 205 Fast Hardener or 206 Slow Hardener by weight or volume, combine five parts resin with one part hardener. To measure 105 Resin and 207 Special Clear Hardener or 209 Extra Slow Hardener by volume, combine three parts epoxy resin with one part hardener (by weight, 3.5 parts resin-1 part hardener)."

When measuring on the balance-beam scale I place the mixing container on the scale and tare it, then I use the container pumps to make slow partial pumps to dispense the desired amount of resin and hardener as indicated by weight. That seems to be a neat no-drip no-slop method that is precise and quick. I am very careful to mix the combo using circular and cross strokes scraping the bottom and then doing mixing quality control by checking the eventually hardened residual in the mixing container to make sure there is no uncombined wet product laying under the cured button.

I today used some of the West System 105 and 205 to make some nice fillets in another pattern I am tuning up. It dried to click hardness in 5 hours sitting in the sun in 70 deg air temps. The pattern probably warmed to 90 F and the UV helped as well. I pop the bubbles in the wet epoxy with a super brief burst from my MAPP gas torch. The fillets are very level and fair and feather to an edge that is nearly impossible to feel. Using the epoxy resin makes a smoother and fairer fillet than I can make with bondo or similar manually-applied and sanded materials. And, best part, it takes a tiny fraction of the effort.

Denis

 

Exposure to UV doesn't always help with curing, the phenolic urethane no-bake resin for sand moulds has it's cure is inhibited by sunlight, I think this goes all the way back to the original Pepset by Aslin Croder in the 1980's. A possible reason is the crosslinker additive to accelerate the speed and hardness is light sensitive and the pure stuff was shipped in aluminium cans or dark brown bottles as it would break down to CO2 and water (I think from memory) with exposure to light and moisture. Crosslinkers get added to a lot of glues and paints to improve properties which is why some paints and glues have a use-by date.

 

West System has an interesting monograph on thinning their products. They have done significant testing. Here is the link.

https://www.epoxyworks.com/index.php/thinning-west-system-epoxy/

The bottom line is that for spray painting (not specifically discussed but alluded to as thin coat applications) thinning may be a reasonable option. That takes into account the possible loss of mechanical strength (not too important in a coating) that will accompany thinning. The good thing about using a volatile thinning agent in a thin-coat application is that, because the coat is thin, the volatile agent can evaporate before the epoxy cross-links. So, negative effects, in that scenario, may be minimized. I think I'll try it on some scrap and see what happens. For anyone interested in thinning epoxy I think the linked article is a worthwhile read.

Denis

 

Hmm, now I may have to try uncovered Evercoat. But, remember, I got on this epoxy kick at the recommendation of a bona-fide chemist and sodium silicate expert, Tom Cobett, who suggested using an epoxy coating for silicate cores as the epoxy is the most resists sodium silicate better than anything else. I intend to do my best to follow that approach until I either find a very practical and reasonably economical epoxy coating or give upo in frustration. Right now I am a long way from giving up. In fact, the only concern I have about the epoxy specifically recommended by Tom is its seemingly slow cure time.

That said, what is the viscosity of the Eastwood epoxy? I guess you know it to be designed for spraying and works well in that application. From what I found on the Eastwood site their spray epoxies are all listed as primers.

Denis

 

And matte or glossy?

 

One week later here is a little follow up on the Rustoleum Aerosol Epoxy cure. Rustoleum in its blurb about this epoxy coating says it is "Ultra-Hard." I think that may be a bit of an overstatement. It has become hard enough for my purposes as a silicate-resistant coating for core boxes. But, it certainly is not exceptionally hard. I can still make a visible dent in it with my fingernail, though it has a generally hard slick feel to it when simply holding it in your hand. But, for comparison, the Evercoat primer is rock-hard and became rock-hard in less than a day after application. And, compared to a conventional 2-part epoxy like the West System product I am using or the typical 5-minute epoxies, the aerosol coating is considerably softer as the 2-part epoxies also become rock hard in a few hours to 12 hours depending on curing temperature. Compared to a good quality enamel paint I rolled onto my kitchen cabinets a few years ago the aerosol is about the same hardness.

I also mentioned earlier in this thread possibly using a spray gun to apply 2-part epoxy to my silicate core boxes. After reading cautions on West System's website, if I do spray epoxy, I will be very careful to use a good organic filter on a facemask and to do it outside. It sounds like aerosolized epoxies are potentially potent sensitizers. I think I will simply brush on the West epoxy unless I find that impossible for some future core box.

Here is a link for those wishing to read what they have to say:

https://www.westsystem.com/safety/spraying-epoxy/

And, given the problems we have all encountered with links becoming deadends, I will quote the statement below.
"

Spraying Epoxy


Although it is possible to spray WEST SYSTEM® Epoxy, we strongly recommend against it. Leaving aside the practical difficulties, including equipment expense, the health and safety issues associated with spraying epoxy are enormous.

To effectively spray epoxy and obtain a desirable finish, it must be atomized. As epoxy leaves the spray gun nozzle, it is reduced to tiny droplets (spray mist). Most of the spray mist that doesn’t land on the surface that is being sprayed will remain airborne for some time before settling to the ground. While the mist is suspended in the air, it is likely to be inhaled, causing respiratory tract irritation or burns, sensitization, chemical pneumonia, and other serious health complications. Spray mist settling on unprotected skin or eyes can result in eye injury, skin sensitization, and allergic reactions. Spraying increases the amount of hazardous volatile components released from the epoxy, compared to other application methods.

In addition, using solvents to thin the epoxy so it can be sprayed poses equally dangerous health and safety risks. Solvent-related hazards would be similar to those of any spray painting operation and involve both health and explosion concerns.

If you are determined to spray epoxy, hazard control steps are crucial. Control of hazardous vapor or spray mist is best achieved with isolation and enclosure, such as a properly designed, ventilated and filtered spray booth. In any case, if you are spraying epoxy, use of an air-supplied respirator and full-body protective equipment is absolutely a must.—From “Spraying Epoxy is a Bad Idea” by Glenn House, Epoxyworks issue 6

For detailed safety information about specific epoxy products, visit our Safety Data Sheets page."

Denis