Particle board must all be removed and replaced with the correct plywood build up. Particle board is not an accepted subfloor material for any flooring assembly. If you have major floor leveling issues, the joist structure may be insufficient and may also need reinforcing. You need to be able to assess that structure and be able to replace that plywood, properly.

As mentioned above, particle boards are not a approved subfloor material for your flooring, not solid enough. The product will swell and crumble once it gets wet. The good news, it is easy to remove. Your original subfloor is below it. Don't waste your time and money applying the feather finish over particle board. It will crack and crumble. Get down to the original subfloor and I can walk you through on how to screed and smooth out feather finish.

And just for fun, self leveling cement (SLC) is not self leveling. It has maximum and minimum requirements for thickness. The type of water you use, the temperature and the humidity in the home at the time it is mixed (and sometimes even altitude) will affect the work-ability of the SLC.

Let's just say you will have LOTS of learning ahead of you. While you are taking out the fibre board (yep...either take it out or lay down new plywood over top) someone can be practicing mixing batches and spreading it on random pieces of plywood (that you purchased extra off just so you can practice).

Some manufacturers allow their flooring to be installed on particle board. Check with the manufacturer...

Acceptable Subfloor Types • CD Exposure 1 plywood (grade stamped US PS1-95) • OSB Exposure 1subfloor panels • Underlayment grade particleboard • Concrete slab • Existing wood floors must be fastened to exisiting subfloors • Ceramic tile (must fill in grout lines with a compatible patch compound) • Resilient tile and sheet vinyl

https://www.calibamboo.com/content/installation/instructions/cali_bamboo_cali_vinyl_pro_flooring_install_guide.pdf

COREtec Installation Instructions

All other subfloors - Plywood, OSB, particleboard, chipboard, wafer board, etc. must be structurally sound and must be installed following their manufacturer’s recommendations.

https://pdmsview.shawinc.com/viewer/doc/5089

If you end up using self-leveling compound, be aware that many of these material are runny enough to flow significantly. If your floor is not fairly level to begin with, you could end up with a mess, with a pool of material at a low end.

Feather finish is not a self-leveling compound. You have to work the product smooth and flat. It's mainly used to fill in low spots.

I actually found this product and it says right on their packaging it's good for particle board floors

That is not the manufacturer saying that. That is akvr1986. How do you know Henry's allows it? What makes akvr1986 an authority on Henry's products?

Just wanted to come ask for an update or what you decided to do. We are in the same situation. I called the Henry/Ardex company myself and asked and they said they do not approve any of their products to be used on particleboard. For any future person coming across this thread. :(