LMF5000
Mechanical
- Dec 31, 2013
- 88
I'm having a storage floor (raft) installed beneath the roof of my garage, consisting of plywood sheets resting on mild-steel hollow square joists. The joists have welded right-angle flanges at the ends. The end flanges don't completely seal off the hollow section at the extremities, so air can still enter the hollow core of the joists. The flanges will rest in slots cut into the concrete/limestone walls of the garage. Each joist is in two parts, one sliding inside the other, so it will be extended in-situ to span the exact gap from one wall to the other, and a central bolt on the outer joist will be tightened to press onto the inner joist to stop it from sliding after installation.
The builder just delivered the material and it looks like mild steel, but seems to have a black surface to it. Pics here - . I've been advised to paint the outside of the steel to stop it rusting. My concern is the inside of the square hollow section - since it will be exposed to air, is it at risk of rusting? I am unable to paint the inside, the beams are 3 meters long and section is about 10cm x 5cm so barely big enough to insert a hand with a paintbrush.
Wall thickness is about 5mm - any idea how many years it would take for rust to appreciably weaken it? I live in Malta, the relative humidity reaches a peak of about 75% in winter. FWIW I'd estimate storing about 300kg of stuff on this structure. There are 4 joists in total. My structural calculations are a little rusty (pardon the pun) so I haven't calculated the factor of safety on this (I'm leaving it to the actual builder)
So, is there anything I can do to protect the interior? Should I try sealing the ends to the concrete walls with silicone caulk (once installed) and put extra paint or silicone on the joint between the inner and outer beams to prevent air entering as much as possible? Or does that trap moisture and make the problem worse? I enquired about galvanising but that's not an option in my region since the companies that do it have discontinued the service.
The builder just delivered the material and it looks like mild steel, but seems to have a black surface to it. Pics here - . I've been advised to paint the outside of the steel to stop it rusting. My concern is the inside of the square hollow section - since it will be exposed to air, is it at risk of rusting? I am unable to paint the inside, the beams are 3 meters long and section is about 10cm x 5cm so barely big enough to insert a hand with a paintbrush.
Wall thickness is about 5mm - any idea how many years it would take for rust to appreciably weaken it? I live in Malta, the relative humidity reaches a peak of about 75% in winter. FWIW I'd estimate storing about 300kg of stuff on this structure. There are 4 joists in total. My structural calculations are a little rusty (pardon the pun) so I haven't calculated the factor of safety on this (I'm leaving it to the actual builder)
So, is there anything I can do to protect the interior? Should I try sealing the ends to the concrete walls with silicone caulk (once installed) and put extra paint or silicone on the joint between the inner and outer beams to prevent air entering as much as possible? Or does that trap moisture and make the problem worse? I enquired about galvanising but that's not an option in my region since the companies that do it have discontinued the service.