Waterproofing MDF for bathroom cabinets...and should our builder have used Waterproof MDF? Should I complain?

[Needallthesleep]

We have had some major building work to the house recently. While our joiner was in we asked him to make some bathroom cabinets. He suggested he make them out of MDF which I agreed to.

It’s our job to paint them, and I’ve now realised that mdf isn’t great around water. It appears there is an mdf that is already waterproof, and I would have happily paid more for this. I feel like he has made these cabinets out of the wrong product.

My questions are...

How do I waterproof MDF? What are the best products?

Should I complain to the joiner and ask them to be redone? They also have the odd screw coming out of them (covered in wood filler so they aren’t a hazard, and they aren’t really visible, but still annoying).

You can waterproof it by painting a sealant on it. It will seal the mdf. Then add an undercoat and finish with something like eggshell paint for wood. That will definitely protect them.

If they are bespoke then it’s nice to have them made. If you could have just bought cabinets from someone like Duravit, I would have done so to save the effort of painting. Yes, there is waterproof mdf but is it worth changing them now?

Don't put glue on them. An oil-based paint will resist odd splashes and drips. If it is going to be persistently wet, for example under taps or basins, MDF is the wrong product. But it will be OK for wall cupboards.

A nominally water-resistant board is used for bathroom floors.

Thank you both so so much. Super helpful