grimbo wrote:Don't seal it up as it will keep more crud in then t will keep out. it needs to be able o get high pressure water in behnd to keep it clean
Tend to dissagree with ya grimbo... reasons being ...
for "crud" to be flushed clear then a reasonable cavity/space would be needed, this inturn places more load on the method of attachment be it either popriverts or tek screws, further more with a larger cavity/space this would allow larger bits of crud to become lodged between the original sill and the new additional "bash sill".
surfaces which tend to rust out first are the areas which have a close relationship to another surface... IE: door skin to door frame joint, front 1/4 panel to sill, outer sill to inner sill joint. These close contact joints hold crud and moisture and lead to early rust, the problem is we dont see the rust untill it breakes through to the outer surface, at which point in time its too late to prevent.
popriverts are traditionally alloy but the need here for steel popriverts is obvious for strength reasons, these steel riverts are generaly electrically coated with a rust inhibitor, while this seems good they too also cause premature rusting..... works like this....
The higher quality material always corrodes the lesser quality material before it its self becomes victim to the corosion process it started in the first place.
Examples of this are
the lead we see on the keels of steel boats --- lead corrodes away first
lead on the bottom fin of an alloy outboard motor --- as above,
brass battery terminal to lead post --- brass corrodes away first,
I worked with a carpenter a few years back and got told off big time for putting the galv nails in my mouth ..... the saliva causes the galv nails to corrode, I thought he was full of it ....2 years later I had to replace the lattice work because the nails I had used har rotted away !!
With tek screws the same applys, they are electricly coated with a rust inhibitor. They cause corrosion through the same process as above.... they are the stronger material.
With these screws they drill their own hole and again this leaves unprotected steel shavings either inside the sill, or between the sill and "bash sill" again causing early corrosion.
Things that cause corrosion to steel....
minerals
such as salt, found in all soils/mud etc to varying degrees of amounts
water
usually where it tends to sit for long periods or between unpainted/protected areas of steel.
metal
the close proximity of a stronger/weaker material ( IE alloy/lead/brass/stainless steel/electro plated steels.
raw steel
unpainted steel placed in close proximity to either painted or unpainted steel
Any combination of 2 or more of the above causes an even more rapid corrosion process
If it were me doing this mod...
Press up 3mm checker plate ( steel ) to fit as close as possiable to the sill area I wished to protect,
Clean the original sill with steel wool or similar
Run a large bead of urathane around the outer edge of the bash sill aswell as several dollops along the middle line of the bash sill,
Coat the new bash sill's inner face with ARP ( a waxed based anti rust protection ) except on the urathane ofcourse
And then place it on the sill under load, IE : jack it, strap it, chain it, block it......
Leave it to cure for a day,
Paint the outer surface including the urathane.
but thats what I'd do
.... I'll just add that to my "padwhore" collection