Needing some newbie advice - compatible primers underneath Emtech EM6500

[Phillip Mitchell]

I'm getting myself set up to spray waterborne finishes (1st time) and am having a hard time figuring out exactly how to proceed. I have a Fuji Mini Mite 4 gravity fed with 1.3 and 1.8mm tips.

I am doing some interior remodeling / custom woodworking for a client that involves installing 1x8 Nickel Gap T&G (planning on top coating w/ Emtech EM6500 pigmented laquer tinted to BM - Simply White) on some of the interior walls. I want all of this material to be pre-finished (sprayed off site) and consequently don't want any visible nail holes / no face nailing, which means nailing the tongue of the T&G only and, if necessary, using some type of construction adhesive on the back against the wall. The reasoning for no face nailing is that I don't want to have to do any finishing in the house once the material is installed, so pre-finishing 100% is my intention.

The only material that I've been able to source that fits my criteria of being a 1x8 Nickel Gap in tongue and groove (as opposed to ship lap, that I'd have to face nail) is a factory primed MDF. I initially thought I could source clear, raw wood SYP, but it turned out to be only available in Ship Lap and not T&G...

I have an order arriving tomorrow from Target Coatings that is a couple gallons of the HSF5000 and the tinted EM6500. I also have BIN white shellac-based primer.

The spraying will happen in a temporary spray booth in the back of a large shop with 2 open doors nearby and plenty of ventilation (large floor fans). From my research, this seems to be adequate for waterborne spraying but probably not for solvent based (shellac, etc.) It seems that I don't want to be spraying the BIN with this setup, plus the possible complication of cleaning my Fuji gun well enough and switching over to the waterborne Emtech without any contamination...maybe I'm being overly cautious on this point? I only have 1 gun.

Not knowing what the factory primer actually is on the MDF, (probably some type of latex primer?) can I re-prime over it with the HSF5000 (2 coats min?) then proceed with the top coat, or should I expect problems with this approach? I will try this on samples once all the materials arrive, but asking here in case anyone has actual experience.

If the above approach is flawed, is it any better to re-prime with BIN (then HSF5000? + top coat? or just top coat on top of BIN?) I'm apprehensive about spraying BIN with the setup I have, but it seems ludicrous to brush / roll on a coat of two of BIN primer if I'm going to spray the top coat. Seems like it would require a lot of extra sanding after priming to get the material back to as smooth as a sprayed primer application. Do I need to thin the BIN at all (with DNA?) if going on top with the Emtech? If so, what's a good starting point to thin?

Is there something else I should do instead of what I'm proposing?

What can I expect as far as grain raising on pre-primed MDF?

What tip(s) should I use for which products?

As you can see, I'm swimming up to my neck in questions and really just trying to do the right thing, but a lot of this is new to me. I initially thought pre-finishing (spraying) the nickel gap would be a time saver, a good opportunity for me to get setup for spraying, and result in a much better finish than brushed, and I'm sure it will once I get it done, but at this point I'm having a hard time working my way through the details, not having done a lot of this before now.

I'm also planning to spray an interior French door (clear pine) and a few small built-in type birch plywood cabinets (all with EM6500 as a top coat) just for reference, but those will both start as raw wood, which seems a bit more straight-forward to do, but I'm open to any suggestions there as well as far as primers, grain raising, etc...

Thanks for any help!

[John TenEyck]

First I would check with TC and see if the tinted EM6500 can be sprayed directly on the pre-primed MDF. If it can you will save time and money. If not, find out if their primer is compatible with the pre-primed MDF. If yes, that's what I'd use. If not, then I'd make some samples with the BIN shellac based primer to see if it's compatible with the tinted EM6500. TC claims there can be crazing problems over shellac, so you would need to satisfy yourself that's not the case.

I use mostly BIN shellac based primer under painted projects. It's really easy to spray. The viscosity is incredibly low and you would be able to spray it with 1.3 mm tip w/o thinning. I'm not sure about the 1.8 mm tip with the EM-6500 however. You may need to thin that.

The MDF is already primed so you should have no grain raising no matter what you put over it.

You will be fine if you end up spraying the BIN shellac based primer as long as you have the doors open and ventilation.

John

[Phillip Mitchell]

John, thanks for the reply.

I talked to Jeff at TC a few days ago (when I thought I was using raw yellow pine) and he strongly recommended BIN shellac primer as a seal coat (in order to prevent sap/tannin/knot bleed through), then the HSF 5000, then the EM6500. He did not specify whether to thin the BIN or not (and I didn't think to ask at that time), but I have read other comments online from folks who've talked to them that basically say to thin the shellac with DNA up to 50% under 6500 (and maybe the rest of their other finishes as well?)

He told me that I needed a 1.8mm tip for the 5000 and 6500, though I have read multiple times online of several folks using a 1.3mm tip spraying the 6500 with no problems. Mild confusion ensues, but I have both available.

Now that my material has changed potentially to pre primed MDF, I've got another message out for Jeff at TC and am awaiting a call back to check about the compatibility of 5000 and 6500.

I also just heard back from the building supply that raw Radiata pine (clear) is available in the size, T&G configuration I want (though it is nearly 50% more in cost than the pre primed MDF...) It seems to me that if I can spray over the primed MDF without much issue then that's the way to go from a cost/labor perspective.

When spraying BIN, do you just clean up with DNA and find it easy to get everything clean or is it more involved than that?

Thanks again

[John TenEyck]

Thinning BIN will give you less primer coverage. I assume TC is advising you to thin it out of concern of compatibility with their products. You definitely do not need to thin it for it to spray well. The viscosity is only about 35 seconds through a #4 Ford cup. All the WB clearcoats I use are higher. But now that you are using pre-primed MDF you may not even need the BIN.

When I had problems (big open pores that wouldn't close, and particles that looked like sawdust but wasn't) with EM-9300 (?) the first thing Jeff asked was what N/N I was using. I told him 1.0 and it sprayed fine in my pressure assisted HVLP, but he immediately told me to go to at least a 1.3 mm, and even higher would be better. His concern relates to shear breakdown of the emulsion, I think, rather than atomization. I've never had that kind of problem with GF's products, BTW.

If you want a dead smooth finish, go with the MDF. If you want to see grain, go with solid wood, but I wouldn't use anything with knots in it for paint grade work. If I wanted T&G solid wood and couldn't buy it, I'd mill my own from square stock. But for a nickel gap look I think I'd just mill a slot in both sides of the solid stock and use splines to hold them together. You can nail through the back half of the slot, just like you would with T&G, so it won't show when you insert the spline. MDF is dead stable, too, so the nickel gap is for show rather than necessity.

When I spray BIN I disconnect the air hose, dump out the gun, then put a couple of oz. of DNA in the cup and pull the trigger to let it flow through into a waste container. I wipe out the cup, too. Then I take it to the sink and pour a mixture of warm water, dish soap, and about 20% ammonia into the cup and let it flow through. Then I disassemble the gun and clean everything with more of the soapy water plus ammonia. Ammonia just eats up shellac. After I'm satisfied it's clean I reassemble the gun, dump an oz. of DNA into the cup and spray it out. If there are any stubborn deposits I soak them in DNA or lacquer thinner. It took about as long to write this as it does to do. 5 minutes, max. I use one gun for everything, too, and have never had any cross contamination problems. If you clean the gun well there won't be.

John