As the discussions about the size our power cables rumble on in the background, I think we're about to face the first contentious issue of the build. The welders have been hard at it for about two weeks now and have finished the assembly work. The contractor and my architect reviewed the work last weekend. agreed on some welds that needed priming - in particular where the purlines are joined to the top of the rafters - and set tomorrow as the date when the tiling crew would start work. I had to be out all day and have returned home to find this hasn't been done and given that we went to lengths to do a good thorough job on the priming (closed sections were dipped rather than sprayed) it seems to me that these are pretty clearly vulnerable points for rust to develop.

Here's where I mean, and although the picture is pretty rubbish you get the idea.

Every joint is primed on the top but the bottom inside the C section they are left without protection.

What I suspect is going to happen is that the tiling people will turn up bright and early in the morning and I'll be forced to call the architect over and call a halt until it's sorted out. I have no qualms about doing that but I thought I'd like to get other opinions as to how critical priming these welds really is or whether you think I'm creating a storm in a teacup.

if corrosion is going to set in, it will be at those weld interfaces, in effect you have dissimilar materials ie the parent material and filler metal, so this could set up a galanvic cell if you have moisture.

you have spent the time and expense getting everything else protected from corrosion, so my opinion they need to prime these areas as well, and havent done it because they a lazy...

If it was me....I would make them do it properly...job half done IMHO

Thanks.

I can see why they don't want to do it - it's a miserable job because you have to get round into the C and up underneath the top part plus it looks next to impossible to be sure you've covered it. Couple that with the current weather and a MPR attitude.....

Grab a spray can of cold galvanise and give em a squirt.

Thanks.

I can see why they don't want to do it - it's a miserable job because you have to get round into the C and up underneath the top part plus it looks next to impossible to be sure you've covered it. Couple that with the current weather and a MPR attitude.....

Being a "miserable job" is irrelavant, as said above their lazy and doing 1/2 a job, if i was you i'd get it sorted and personally watch them do it till i was happy.

That would probably be the best way to do it, but I'm not climbing up there at my age.....

Maybe I'm looking at the pic wrong - but it appears they've used 3/4" box steel for your battens, and that they've forgotten about the reflective foil layer?

This is what we always use for battens, but foil goes down first:

This is then screwed onto the trusses, which also makes it removable again in the future (so in 20 years the reflective oil can be replaced, for example).

I've never seen a roof built that way here, but it's the way the SCG bolt together system works and, had I really understood the physics of radiant barriers, I would have had it done like that because it provides a constant air gap between the tiles and the foil. For some reason the box section steel is the standard purline although, given that it's heavier, probably more expensive and you can't place the foil underneath, I can't imagine why that might be. Trickier to fix the purlines once the foil is in place, perhaps?

When you say "we always", do you mean you personally or in the area/country you live?

Way too late to change that now but if there's a next time.....

I've never seen a roof built that way here, but it's the way the SCG bolt together system works and, had I really understood the physics of radiant barriers, I would have had it done like that because it provides a constant air gap between the tiles and the foil. For some reason the box section steel is the standard purline although, given that it's heavier, probably more expensive and you can't place the foil underneath, I can't imagine why that might be. Trickier to fix the purlines once the foil is in place, perhaps?

When you say "we always", do you mean you personally or in the area/country you live?

Way too late to change that now but if there's a next time.....

We Always = My family are property developers (I'm Thai)

I've never seen a roof built that way here, but it's the way the SCG bolt together system works and, had I really understood the physics of radiant barriers, I would have had it done like that because it provides a constant air gap between the tiles and the foil. For some reason the box section steel is the standard purline although, given that it's heavier, probably more expensive and you can't place the foil underneath, I can't imagine why that might be. Trickier to fix the purlines once the foil is in place, perhaps?

When you say "we always", do you mean you personally or in the area/country you live?

Way too late to change that now but if there's a next time.....

We Always = My family are property developers (I'm Thai)

Then your building standards are higher than most!

I'm told that that section is a CPAC product and more expensive using the type we have used. Is that correct?

I've never seen a roof built that way here, but it's the way the SCG bolt together system works and, had I really understood the physics of radiant barriers, I would have had it done like that because it provides a constant air gap between the tiles and the foil. For some reason the box section steel is the standard purline although, given that it's heavier, probably more expensive and you can't place the foil underneath, I can't imagine why that might be. Trickier to fix the purlines once the foil is in place, perhaps?

When you say "we always", do you mean you personally or in the area/country you live?

Way too late to change that now but if there's a next time.....

We Always = My family are property developers (I'm Thai)

Then your building standards are higher than most!

I'm told that that section is a CPAC product and more expensive using the type we have used. Is that correct?

CPAC (SCG) aren't the only manufacturer of this type of profile. I don't have any price lists to refer to, but can tell you that 3/4" box steel (assuming it's Mor Or Gor grade which I think starts at 2.3mm thickness) is a whole lot heavier than this type of C-line, so logically more expensive - either way, it's not expensive stuff.

Makes sense - I can't think why it's not used all the time.

The good news is that the main contractor sent a couple of his guys into the roof to do the touch up so it's about half way done (or will be by the end of the day). The less than good news is that I think they fell out with the steel sub-contractor whose job it should have been and there is at least another day's work to be done to finish the welding so they will be looking for someone else to complete the work. At least it won't hold the tiling up for a while as there must be several days of that to get on with.

In the meantime the plumbers arrived unannounced and I had to scramble to check the placement of the cold water pipes was all correct before they started hacking the newly completed brickwork to pieces. Also, the original plan was to fit multil point water heaters in three bathrooms and the kitchen but we're trying to cut back on the electricity loading so thinking again about regular boilers in at least two of them. I think I'm right in figuring that a rain shower needs a 9kW instant heater if you are running it through a mixer tap - anyone experience with a 6kW?

...but I'm not climbing up there at my age.....

Storm in a teacup...

Grab a spray can of cold galvanise and give em a squirt.

Where can we usually find that and what's the Thai name for it. TIA.

I think I'm right in figuring that a rain shower needs a 9kW instant heater if you are running it through a mixer tap - anyone experience with a 6kW?

That depends on what your typical inlet temps are - if using an above-ground water tank(s) and pumping your water in, 6kW should be OK for all but the most sadistic people most of the year, but could become marginal (only warm, not hot) if you live in a area that experiences colder winters.

9kW would be safer, but will make for expensive showers (1/2 hour @ 9kW twice daily = 36 Baht/day per person in electricity).

Have you considered solar hot water?

Grab a spray can of cold galvanise and give em a squirt.

Where can we usually find that and what's the Thai name for it. TIA.

I buy it from Hardware House and it is called Cold Galvanise on the label (in english).

We Always = My family are property developers (I'm Thai)

IMHO ... I see you now in a different light* ...

* Good thing

.

We Always = My family are property developers (I'm Thai)

IMHO ... I see you now in a different light* ...

* Good thing

.

Well, not so sure you should.. I hope my English is good enough that no-one needs to make too many allowances for me

Those welding points are always lumpy little blobs and unless ery well painted would always be prone to surface corrosion from atmospheric damp.

However would it ever get corroded deeper? Remember rust itself is an anti corrosion coating.

Grab a spray can of cold galvanise and give em a squirt.

Spray is the only way to be sure all surfaces are covered.

However, I doubt if most Thai houses have all the joints painted and they don't fall down for lack of it. More likely they have problems because the welding was done by someone that can't weld properly and either doesn't use a face shield or even just sunglasses, which means they can't see what they are doing.

In the end they sprayed all the places that needed it (with compressors and long lines, not cans) and I can't see any they've missed. On to the next challenge....