You are asking a question that really needs to be a deeper and more complex question about reinforcing the floor joists properly. You need an engineer. The finished floor surface has little to nothing to do with the weight bearing capacity of the structure.

The finished floor is not what is supporting your tub I agree you better make sure the joists will do the job then put in what ever floor you want. I guess my question always is why cast iron when there are so many other beautiful choices for a tub.

Thanks for comments. I've already had a structural engineer look at floor & he's advised 18m ply or as an alternative engineered wood floor to spread the load. My question is really more about being able to paint the floor or not. Can you paint directly onto engineered wood?

thanks

The above is 100% correct. That being said, you can paint anything but it doesn't make it a good idea. Why on earth would you paint a floor? SMH

Why not get a sample floor board, paint it and seal it and see if it works?

The product normally called "engineered wood flooring" is simply boards that constitute the surface finish. Yes, it has some strength, but it is not rated for strength and hence references to how it affects load bearing capacity of the floor don't appear to make sense.

Perhaps your structural engineer was referring to the use of 18 mm (millimeter) plywood as a **subfloor**. That would make sense....plywood subflooring does provide strength. Along with correctly chosen or reinforced joists, it may be just what you need. Typically a flooring is out on top of the subfloor for better wear resistance, cleanability and improved look. However, sometimes people do simply choose an attractive subfloor, finish/seal it somehow, and use that as their finished floor. You could definitely work with the engineer to select a subfloor that will take paint and sealer.

The question in my mind is....why? If you want painted floorboards, just get the floor built and reinforced correctly (joists and subfloor), then put boards on top and paint. My 2c.

Thanks for comments - I have now found something that will work & is untreated so can paint. Cheers all.

Can you tell me what you did? I'm trying to paint my engineered hardwoods and I'm having trouble getting the primer to adhere. I've tried BIN odor/stain blocking primer in oil based and shellac based. I rented a big sander thing and sanded with 36 grit sandpaper and I tried using a stripper meant for urethanes. I can still rub off the primer with a damp towel. Painting the floor is my only option at the moment. We're going to replace all the flooring, but we haven't found anything we like yet. I have to paint them to get rid of super strong pet odors from my old tenants.

Well I did paint it & it looks great!

I was painting un-treated pine wood floor so it was a lot easier in the end. I've found Valspar trade paints to be v good

It sounds as though someone used a silicone type dusting product on the floor at one time. Or orange oil, or an oil soap. All of those things will retard adhesion of even shellac. The only solution is to 100% sand to bare wood and then try priming. I'd just try a small section, as if someone soaked it down into the spaces between the planks, the only option is going to be replacement.

I think you forgot floors are walked on. lets see how it looks in a few months. especially a high traffic area. Why would you waste money on hard wood just to cover it up? Pine isn't "hard" wood.