How bad can the rust get? How much is acceptable/expected?

[(steven)]

Currently looking for a cheap track Mx5, so cars with a bit on body damage are par for the course.

Looked at a car today which mechanically was spot on but had serious rust on the front wings and the rear arches. (Sills didn't look to bad but one was covered in under sealant which suggested it had been repaired in the past).

Normally I wouldn't be too bothered however one rear wing was coming away in my hands. How bad can the rust get on these cars? I don't mind it being crusty round the edges (especially if can just sand back and rattle can the arches) however I don't want to sand the rust back and find there is no car underneath and find myself spending hundreds/thousands on replacement panels.

Do these cars just suffer surface rust or do they rust from within? How much rust is acceptable before the structure starts getting weak?

[franv8]

Rust can obviously occur anywhere on these cars, and some are almpst rust proof while others seem to show their age. And you have to figure in potential previous accident repairs.

Rear of the sills seems most popular place, although it's mostly sills in general. This si the most likely place that you'll also have concern for the structure. Normally it's a relatively straightforward repair that I think from other's on here previous experience is around a few hundred pounds a side for getting sorted by a pro.

[OnlyMX5ives]

Rusty sills and arches are common on UK cars.

Many imports are still rust free, for Mk1's:

If paying below £1,000 expect rust.

If paying over £2,000 there shouldn't be any really.

[MX-5 Lazza]

OnlyMX5ives said:

Rusty sills and arches are common on UK cars.

Many imports are still rust free

I think that's something that has been true but is becoming less true as time goes on as many Mk1 imports have been in this country 10-15 years now.