Pilot Holes....

[Kai Morrison]

Hi all,

I’m going to have a go at putting up my solar kit on the next spell of good weather......have done some research on here and watched a few videos on YouTube.

The solar kit came with moulded plastic corner and side mounts which do not have holes cut.

I’ve got 6.3mm dia x 50mm long stainless steel self tapping screws....what size pilot holes should I drill through the plastic mounts and aluminium solar frame?

I will use Sikaflex to stick the mounts to the roof.

TIA,

Kai

 

[pappajohn]

I would drill the plastic feet to the same size, or slightly bigger, as the screws and a 5mm hole in the aluminium.
Drilling the two pieces the same size will lock the thread once it's tight in the plastic and prevent them pulling together.

 

[Kai Morrison]

Thanks pappajohn

 

[pappajohn]

Sorry, I read that as 6.8mm
Try a 4.5mm hole, you can always make it bigger if necessary.

 

[dunnah01]

I'd go 6.5mm through plastic with nothing through aluminium frame. Self driller will go through ally no problem with no pilot

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[Lenny HB]

I’ve got 6.3mm dia x 50mm long stainless steel self tapping screws....what size pilot holes should I drill through the plastic mounts and aluminium solar frame?

Never use stainless steel self tappers in aluminium due to galvanic corrosion which causes the aluminium to corrode away around the screw.
I use stainless steel nuts & bolts and smear the surfaces with silicon grease so there is no direct contact.

Also make sure you get the correct Sikaflex one or two of them are not suitable for plastic mounts.

 

[Kai Morrison]

Never use stainless steel self tappers in aluminium due to galvanic corrosion which causes the aluminium to corrode away around the screw.
I use stainless steel nuts & bolts and smear the surfaces with silicon grease so there is no direct contact.

Also make sure you get the correct Sikaflex one or two of them are not suitable for plastic mounts.

Hi Lenny HB

I have silicone grease....am I still taking a risk using self tapping screws smeared with silicone grease? My issue with using nuts and bolts is the potential difficulty in getting to the nuts if I ever wanted to remove the panel in future....however, I guess you’ll argue having self tappers come loose with corrosion is going to present a bigger issue...

If I’m going to use bolts with nuts should I use nuts with the plastic/nylon inners do you think?

I’m using Sikaflex 512 which others have suggested is ok.

 

[Kai Morrison]

I'd go 6.5mm through plastic with nothing through aluminium frame. Self driller will go through ally no problem with no pilot

Thanks dunnah01,

Have you used stainless steel self tapping screws in aluminium? and have you experienced the galvanic corrosion Lenny is warning me about?

 

[Lenny HB]

I wouldn't use ss self tappers, you could use pop rivets then its easy to drill them out to remove the panel. If worried about the strength of pop rivets use monel ones avalible from chandler's.

If using nuts & bolts yes nylock nuts are better as you don't need to use a spring or shake proof washer which would bite into the aluminium.

 

[Kai Morrison]

I wouldn't use ss self tappers, you could use pop rivets then its easy to drill them out to remove the panel. If worried about the strength of pop rivets use monel ones avalible from chandler's.

If using nuts & bolts yes nylock nuts are better as you don't need to use a spring or shake proof washer which would bite into the aluminium.

OK thanks for your advice ??

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[Gromett]

Just removed the panels off my van after 9 years.

They were held on with SS self tappers through aluminium angle.

The aluminium angle was sikaflexed to the roof and self tapped to make sure. The aluminium angles were self tapped to the panels themselves.

When removing them there was no sign of galvanic corrosion. They all unscrewed ok except for a couple which had rusted. Yes SS will rust eventually.

On the galvanic corrosion thing. It is in issue, but you can massively reduce the problem by removing access to electrolytes. Cover the screw head with some kind of sealant will prevent moisture and oxygen and slow the process down to a crawl.

I saw no evidence of galvanic corrosion on my install after 9 years of use.

 

[dunnah01]

Thanks dunnah01,

Have you used stainless steel self tapping screws in aluminium? and have you experienced the galvanic corrosion Lenny is warning me about?

I used galvanised self drillers which is close enough to aluminium to not have to worry about corrosion.

 

[dunnah01]

Hi Lenny HB

I have silicone grease....am I still taking a risk using self tapping screws smeared with silicone grease? My issue with using nuts and bolts is the potential difficulty in getting to the nuts if I ever wanted to remove the panel in future....however, I guess you’ll argue having self tappers come loose with corrosion is going to present a bigger issue...

If I’m going to use bolts with nuts should I use nuts with the plastic/nylon inners do you think?

I’m using Sikaflex 512 which others have suggested is ok.

I'd use a thread lock compound rather than a grease to provide insulation against galvanic corrosion whilst making sure the screws don't eventually work loose.

 

[Lenny HB]

Just removed the panels off my van after 9 years.

They were held on with SS self tappers through aluminium angle.

The aluminium angle was sikaflexed to the roof and self tapped to make sure. The aluminium angles were self tapped to the panels themselves.

When removing them there was no sign of galvanic corrosion. They all unscrewed ok except for a couple which had rusted. Yes SS will rust eventually.

On the galvanic corrosion thing. It is in issue, but you can massively reduce the problem by removing access to electrolytes. Cover the screw head with some kind of sealant will prevent moisture and oxygen and slow the process down to a crawl.

I saw no evidence of galvanic corrosion on my install after 9 years of use.

I think you have been lucky Karl, as you say you can take some protection.
Galvanic corrosion is most evident on boats as it is far worse in a salt atmosphere. It requires 3 things an Anode, a Cathode & an electrolyte. In this case the aluminum is the Anode the screw the Cathode and water the electrolyte, it is far worse if the Anode (which in this case it is)is a lot larger than the cathode and if saltwater is involved.
I live a couple of hundred yards from the sea no way I would risk it and having sailed for years I've seen the results on boats.

Might only be 1 in a 100 that corrodes badly but you don't want to be that one.

 

[Lenny HB]

I’m using Sikaflex 512 which others have suggested is ok.

Check with Sika it's one of the common ones that's not suitable, I can't remember which one a few Funsters panels have come adrift due to the wrong one being used.

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[MisterB]

Have you considered rawlnuts to secure the panels to the roof fixings

 

[Gromett]

I think you have been lucky Karl, as you say you can take some protection.
Galvanic corrosion is most evident on boats as it is far worse in a salt atmosphere. It requires 3 things an Anode, a Cathode & an electrolyte. In this case the aluminum is the Anode the screw the Cathode and water the electrolyte, it is far worse if the Anode (which in this case it is)is a lot larger than the cathode and if saltwater is involved.
I live a couple of hundred yards from the sea no way I would risk it and having sailed for years I've seen the results on boats.

Might only be 1 in a 100 that corrodes badly but you don't want to be that one.

For boats, or for underneath the van you are of course correct. But on the roof there is little access to salt. In addition once covered in either silicon or sika there is no access to oxygen.

As any one with a basic physics/chemistry or electronics background knows, water is a poor electrolyte. This is why you add a salt to it or an acid in batteries.

So in fresh water situations like on the roof of a van, the galvanic corrosion process is slow and even slower when protected from water and air. Underneath a van is a different matter as the roads are salted in the winter and accelerate the corrosion...

So I don't think I was lucky. I think it was perfectly normal.

 

[Lenny HB]

So in fresh water situations like on the roof of a van, the galvanic corrosion process is slow and even slower

Living where I live the air is constantly laden with salt, go outside on a winter day with a south westerly prevailing wind, particularly if there is moisture or light rain in the air after a few minutes you can feel & taste the salt in your hair.
A lot of Motorhomes camp by the sea when in use. Last October in Portugal after one night on the cliffs I had to find somewhere to wash the van it was completely covered in a layer of salt.

 

[Gromett]

Living where I live the air is constantly laden with salt, go outside on a winter day with a south westerly prevailing wind, particularly if there is moisture or light rain in the air after a few minutes you can feel & taste the salt in your hair.
A lot of Motorhomes camp by the sea when in use. Last October in Portugal after one night on the cliffs I had to find somewhere to wash the van it was completely covered in a layer of salt.

Last 4 years has been fulltime on the coast...

 

[Lenny HB]

Last 4 years has been fulltime on the coast...

You are inland compared to me.

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[Gromett]

You are inland compared to me.

Perhaps so. Half a mile from the beach. Can hear the sea at high tide...

 

[Kai Morrison]

Thanks for all your input people.....I contacted Sikaflex this morning and had a call back from a chap called Laurie. He confirmed that as a polyeurathane adhesive and sealant, 512 is suitable for mounting a solar panel in the way I described. He did make the point to ensure a sufficient bead of about 2mm and to leave it for 24/48 hours to cure....he said that people tend to put a 2mm bead on then squidge it down to something much less when fixing which could be why some have had problems. I'll use tile spacers to keep the recommended depth of Sika.

 

[Spriddler]

Oh, my mistake. I thought you meant Pilot holes

 

[Manic]

View attachment 385190

Oh, my mistake. I thought you meant Pilot holes

That not a pilot hole, surely that’s a gunners hole

 

[Gromett]

I think you have been lucky Karl, as you say you can take some protection.
Galvanic corrosion is most evident on boats as it is far worse in a salt atmosphere. It requires 3 things an Anode, a Cathode & an electrolyte. In this case the aluminum is the Anode the screw the Cathode and water the electrolyte, it is far worse if the Anode (which in this case it is)is a lot larger than the cathode and if saltwater is involved.
I live a couple of hundred yards from the sea no way I would risk it and having sailed for years I've seen the results on boats.

Might only be 1 in a 100 that corrodes badly but you don't want to be that one.

I thought that using aluminium and steel together underneath a vehicle would cause problems. But apparently not. It is common practice.

Check this little segment here. Aluminium extrusion with a steel cap riveted on in a structural element right next to the front wheels.

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