Hi, I am in the process of arranging for my fire doors to be upgtaded.

The joiner who does a lot of these told me the max 4mm gap is not possible as the door wouldnt close properly with the intumescent strips fitted.

Is that correct ?

Thanks

No, not if fitted properly - this is why a competent fire door contractor should be carrying out these works, I've seen thousands of pounds of wasted work on doors by well meaning joiners.

Thanks for that, Im trying to work out, how thick is the intumescent/ smoke strip ?

does the thickness vary as to whether its a self adhesive one that fits in the frame or a routered one in the door ?

thanks

There are various types of smoke seal including types that are separate from the intumescent strip.     https://www.lorientuk.com/products/architectural-seals/perimeter-seals 

So the 4mm maximum gap should not be an issue at all and make sure your fire door upgrading contractor has the necessary competence !!

thanks for that ?