Hi
Mate at work owns an MGTF so like us guys concerned about rust and becuase we sell Hammerite at work cheap he’s going to paint all the underneath of the car in Hammerite is this a bad thing over waxoyl etc and if so why…And yes it is a mate not me
I don’t think it will stick to underseal or waxoyl. Underseal can fall off, certainly in the case of the MX5, leaving untreated rust behind. I only use Hammerite on fresh metal
So if he can clear off al the old waxoyl back to bare rust potentially he could use Hammerite.
Would recommend treating with a rust convertor first before applying the protective paint coating . I’d go for POR15 instead of Hammerite , just my preference .
Your mate needs to put a little more effort into this if he wants reasonable results. I say this from my experience down here in salty Devon.
wire brush all loose rust and previous coatings away. Apply Hydrate 80 or similar rust converter product, paint with hammerite if you must:-) or more appropriate smoothrite or similar.
Finish with flexible underseal like finnegans with waxoil.
If done properly he can relax for 3 - 5 years
Clean and wire brush the underside. Then treat with a good quality rust treatment bilt hamber do good ones. Then I’d paint with POR 15 then cover with bilt hamber underbody wax.