UKH

Does anyone recommend best way of sealing under dish washer on mdf type worktop. Have new house and allergies triggering around dishwasher. (Will be the horrid glue in it)On inspection the silver sealant tape is damaged and mdf is slightly crumbly. We are drying it out and not using dishwasher for now. Doesn't appear to be any big structural damage. I have ordered some special silver adhesive tape. Local store recommends wood varnish. But you can get special mdf sealant online. Anyone any hints. Reluctant to change worktop as its very big. Thanks

"Wood Hardener" does what it says.  I'm not suggesting its better or worse than varnish, but this stuff really soaks in and dries hard - its waterproof too.

A lot of dishwashers come with a roll of thick, wide and very sticky clear tape a bit like the stuff used to protect the paint on mountain bikes. You're supposed to use it to prevent steam from when you open the door from damaging wood and composite worktops however, many people don't know what it's for and just chuck it in the bin. 

You could use a thin penetrating epoxy resin to stabilise the stuff that's there but it's not the nicest of stuff and it sounds like it's something you would want to avoid. Personally I think epoxies are ok as long as you mix them correctly and use PPE.

Thanks for the replies.ive ordered a strip of waterproof silver coloured proofing tape. Not sure of epoxy resins will agree with me but will look into it. 

exterior PVA?

It doesn't matter who disagrees with you.  Buy the tape!!