Maybe you meant sodium carbonate. Sodium carbonate (washing soda) isn't just a filler. It softens hard water, binding up the calcium and magnesium so that detergents are not inactivated by them. And it adjusts the pH to a level effective for cleaning. I may try Ecover just because I'm kind of compulsive about trying lots of cleaning products. But in real-world conditions of hard water that is not scalding hot, I'd expect better results from OxiClean. I get a 15-pound box of OxiClean at Costco for I think about $12. Ecover around $4-5/lb is a lot more expensive. I'd have to get equal cleaning power from 1/5 the amount by weight to break even, costwise.

I was very pleased with 100% real tung oil, cut with Citrus Solvent. I have a parrot and 4 cats and was worried about toxic fumes - well, for the humans too! You don't get a shiney, glossy finish, but a warm matte one and it spills really do clean up well. You have to layer several coats, but it is worth it. It makes for a very "vintage" feel too, instead of that acrylic plastic look. Here is a link that might be useful: Real Tung Oil and Citrus Solvent

If it were me, I would sand well and use the acrylic primer. The reason is that even if I were to use an oil based primer, I would still sand, so what is the point? Do they want to skip the sanding entirely?

Milgard sent this pic. It is hinged on the top, it goes on a push out window and you have to swing it in to get to the latch and push the window open. Some companies won't make roto operators in small sizes. If I use push outs, the screens will hit things like the mattress and the kitchen faucet. In a little sleeping loft like this you'd have to push the mattress over, lie on the floor, open the screen toward your face or over your head and stick your arm out the window to operate the window! I can't reach to do that above the kitchen sink unless I jump on the counter, which I can do but.... In a regular or large house there would be room but it wouldn't matter as all the windows could be larger anyway. I can't have sliders in the awning locations as there needs to be some awnings so they can be opened in rain and wind as the house has no eves as the width required for eves won't be allowed on the road. Tiny houses have much tighter parameters. This is basically a stick built recreational vehicle and it needs to conform to RV codes. My compromise to avoid vinyl and push outs/hinged screens, appears to be getting the clad wood as those appear to be the only ones that anyone will make in all the sizes and styles called for if I put a casement in the slider location. Sierra Pacific uses a less fuming water based wood treatment but they don't want to make the casement in the size I need because it is a few inches short of egress code, even though I can fit through it easily. Loewen and possibly Marvin will make them but their wood treatment is solvent based. I didn't design this house but it is well designed and the operating types and sizes are proper for each location. Being a tiny house and already framed there is really not much room to change anything even if I could reframe it. All I can do is put a casement in the slider location, awning won't work because it has to be egress upstairs. If I was starting over I would design according to the sizes/types available in the least toxic window. I was lucky enough to find this custom tiny house builder who agreed to sub non toxic insulation, cabinets, paint, flooring, MC instead of Romex, etc., others weren't willing to customize anything. If I hadn't been made environmentally ill and chemically sensitive from a house with toxic mold, I wouldn't have to be so careful as to toxic materials but I was and the only way to detox from this is to avoid exposure to more chemicals and toxin exposure so as to allow my detox system to catch up and clear out accumulated toxins and that won't happen if one is accumulating more as would happen if living in an off-gassing house with a toxic encephalopathy headache daily. I am by far not alone with this issue as it is becoming more common everyday as buildings become older and moldy and materials and products become more toxic. I know of many, thousands, who are now having to build non toxic.