Is Sikaflex 512 man enough?

[Carpmart]

I’m fitting a metal bracket to the roof of my MoHo to secure a 4G antenna. Is 512 up to the job?

 

[DBK]

It depends how heavy and high the antenna is but 512 is widely used for sticking solar panels down.

Most of us who have fitted 4g antenna use models which lie flat and either bolted down or stuck with Sikaflex. I guess you are using something which has a mast?

 

[tonyidle]

Whether PU adhesive is appropriate or not depends entirely on the height of the antenna compared with the area of its base.

 

[Carpmart]

Hello DBK thanks for your reply - in short yes! It’s a high gain antenna and I want to fix it on the edge of the roof directly over the planned access and the cupboard the access will go into. Short cables to minimise loss etc.

 

[Carpmart]

Whether PU adhesive is appropriate or not depends entirely on the height of the antenna compared with the area of its base.

What’s the adhesive equation I need to use? Is it load (lateral) per square cm or something?

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[Carolyn and Kev]

.......Where's 596?

 

[Mikeco]

I used Sika 512 to stick my Puck 4g aerial down.

 

[DBK]

Hello DBK thanks for your reply - in short yes! It’s a high gain antenna and I want to fix it on the edge of the roof directly over the planned access and the cupboard the access will go into. Short cables to minimise loss etc.

I guess you have gone for a directional antenna? Omnidirectional are generally recommended for vehicles and they come in lower profiles which are easier to fit. But please give us feedback on how you get on.

With the reducing cost of broadband a broadband antenna may become standard soon.

 

[tonyidle]

What’s the adhesive equation I need to use? Is it load (lateral) per square cm or something?

No idea. I use intuition & experience that invariably means an over-engineered, overly-cautious, approach. My 1000 x 500 (approx) solar panel has aluminium angle brackets with a 50 x 150 footprint (six off) for example.

 

[The Wino]

I would have thought its a combination of the weight and the surface area facing the flow of air over your mh on the motorway vs the surface area its stuck down with. You could have an aerial that weighs very little but has a huge drag!. Maybe post a link to the aerial you intend to use for a few guesses!

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[autorouter]

What’s the adhesive equation I need to use? Is it load (lateral) per square cm or something?

On the Sika website there is a Technical Data Sheet which gives its tensile strength as 1.8N/mm^2. There is no information on peel strength between the substrate and the adhesive, presumably that is very dependent on conditions of use.

For tensile strength, an area of 50 x 150 mm is 7500mm^2, so tensile force is 7500 x 1.8 = 3500N. If you prefer force in kilograms-force (kgf) then at 9.81N per kgf, that's 3500/9.81 = 1376kgf.

Since there will be a rotational force from the wind resistance, you need to calculate the moments so that the tensile force is not exceeded at any point.

 

[Carpmart]

Thanks autorouter, The Wino, DBK, tonyidle, all very useful responses, much appreciated... ??

 

[tonyidle]

For tensile strength, an area of 50 x 150 mm is 7500mm^2, so tensile force is 7500 x 1.8 = 3500N. If you prefer force in kilograms-force (kgf) then at 9.81N per kgf, that's 3500/9.81 = 1376kgf.

No wonder it's hard to remove! Did I mention over-engineered?

 

[peterc10]

For tensile strength, an area of 50 x 150 mm is 7500mm^2, so tensile force is 7500 x 1.8 = 3500N. If you prefer force in kilograms-force (kgf) then at 9.81N per kgf, that's 3500/9.81 = 1376kgf.

I think you have got the maths wrong there. 3500 divided by 9.81 does not equal 1376. I usually just knock a nought off when converting ................ but then I am just a rough old civil engineer. IMHO trying to get it too accurate gives a veneer of accuracy that is simply not warranted when looking at the factors of safety involved.

Just noticed that the error is in the multiplication; 3500 should read 13500, so the end result is correct.

 

[Revolvor]

On the Sika website there is a Technical Data Sheet which gives its tensile strength as 1.8N/mm^2. There is no information on peel strength between the substrate and the adhesive, presumably that is very dependent on conditions of use.

For tensile strength, an area of 50 x 150 mm is 7500mm^2, so tensile force is 7500 x 1.8 = 3500N. If you prefer force in kilograms-force (kgf) then at 9.81N per kgf, that's 3500/9.81 = 1376kgf.

Since there will be a rotational force from the wind resistance, you need to calculate the moments so that the tensile force is not exceeded at any point.

When I contacted SIKA in 2018 asking for advice about fitting Solar Panels, I was advised to use SIKA 552. This has a greater Tensile Strength than 512, (3N/mm^2 versus 1.8N/mm^2) /and has less stringent surface preparation requirements.

I used it, and so far the panel is still attached!!

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[The Wino]

I think you have got the maths wrong there. 3500 divided by 9.81 does not equal 1376. I usually just knock a nought off when converting ................ but then I am just a rough old civil engineer. IMHO trying to get it too accurate gives a veneer of accuracy that is simply not warranted when looking at the factors of safety involved.

Just noticed that the error is in the multiplication; 3500 should read 13500, so the end result is correct.

So if the op came up with the shape of the aerial could you calculate if it will stick? It's beyond me but if it was on a reasonable base I'd just stick it on and see. That being said I probably wouldn't bother with an external aerial in the first place.

 

[Lenny HB]

If you want something stronger Sika 29i is a marine sealant adhesive and even stronger Sika 292i is a marine adhesive.
I used 291i for my solar panels & 292i for my sat dish.

 

[peterc10]

So if the op came up with the shape of the aerial could you calculate if it will stick? It's beyond me but if it was on a reasonable base I'd just stick it on and see. That being said I probably wouldn't bother with an external aerial in the first place.

The point of a calculation like this is not to determine if it will stick. It will. The point is to determine when it won't stick.

 

[peterc10]

So if the op came up with the shape of the aerial could you calculate if it will stick?

The answer is "yes" in theory.

But it would mean going up into the loft to find my uni notes and then applying 50 year old theories to come up with a figure as to what load would make it fail in certain assumed circumstances. Which would probably be useless because the theories are out of date, the circumstances will not apply and I would have to make too many assumptions about other variables.

And I am now getting too old to get up into the loft safely, let alone understanding the crap I was required to stuff into my brain just long enough to pass an exam all those years ago.

So the answer is "no" in reality.

Edit: and just to prove my point I have just noticed that I have answered the same post twice ....... I hate getting old (but I hate even more the only practical alternative on offer)

 

[tonyidle]

The answer is "yes" in theory.

But it would mean going up into the loft to find my uni notes and then applying 50 year old theories to come up with a figure as to what load would make it fail in certain assumed circumstances. Which would probably be useless because the theories are out of date, the circumstances will not apply and I would have to make too many assumptions about other variables.

And I am now getting too old to get up into the loft safely, let alone understanding the crap I was required to stuff into my brain just long enough to pass an exam all those years ago.

So the answer is "no" in reality.

Edit: and just to prove my point I have just noticed that I have answered the same post twice ....... I hate getting old (but I hate even more the only practical alternative on offer)

It isn't normally necessary to perform complex calculations to determine whether a non-critical application will be "strong enough". In industry careful calculation is normally used to determine how weak, or small, or minimal, or cheap one can go whilst remaining safe. In almost any casual use the user will over-engineer. We are all naturally over-cautious. A simple example came from a discussion I was involved in on a classic car forum. I described a method of lifting a V6 cast-iron engine and attached gearbox using the 4 studs that held the down-draught carburettor. These were 5/16 threaded studs and the engine and transmission together probably weighed upwards of 600Kg. A long discussion centred around the fact that most contributors didn't believe it was safe. When I finally looked at the tensile strength of a single stud it was more than capable of lifting the assembly on it's own. I was on safe ground anyway because my device was based on the Ford special tool that affixed to the same studs. But I too wouldn't have believed that less than using all four was safe or possible.

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[Carpmart]

The point of a calculation like this is not to determine if it will stick. It will. The point is to determine when it won't stick.

absolutely correct Sir! ?

 

[Landy Andy]

Having spent last weekend cutting off the 512 and having to redo a glue and fixing job, I won’t be using it again. Not impressed with it, and yes it was applied properly and all that. I’m used to sealing things for a living. 29i would be a better call.

 

[sallylillian]

After advice on here I used Sikaflex 252 to attach my 2 antenna to the roof.

 

[Revolvor]

It's worth noting that from the Data Sheets for the various Sika products, some are described as "Sealants" , some are "Adhesives" and others are "Adhesive/Sealants" !!

 

[Don Campbell]

Take a look at this article https://www.pbo.co.uk/gear/which-adhesive-sealant-is-best-20877

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[Chris CM]

I used Sikaflex 292i to fix the brackets for my solar panels, if they can hold a yacht keel on I reckoned they would hold the solar panels! Expensive though!

 

[Euro330]

Having spent last weekend cutting off the 512 and having to redo a glue and fixing job, I won’t be using it again. Not impressed with it, and yes it was applied properly and all that. I’m used to sealing things for a living. 29i would be a better call.

Landy, a question if you dont mind.
I have asked here before but none of the replies really answered my question.
I am changeing the external Thetford Storage/Locker doors, door No`s 3 + 4 + 5 and frames, Fresh water filler neck and EHU 240v external socket on my moho from original White to Black. What sealant/adhesives would you recommend? None of the changes are load/weight bearing or taking weight at all and all will be re-fitted to MoHo (Bailey Approach Advance 640 2016) useing original fixing points, all identical swap overs. Also I am fitting new GRP panels (Prima Leisure) into the Thetford doors. Again what would you recommend for sealing those and what best to use for cleaning excess sealant/adhesive away (White Spirit/Meths/soapy water/Rubbing alcohol)?
I have used Sikaflex EBT+ before for other jobs but thought it stayed a bit tacky!
You mentioned you use sealants for a living and I prefer asking advise from people in the know rather than peops with the best of intentions but not much of a proffessional idea.
Cheers. Graeme.

 

[Manic]

I used this from Toolstation to fix my mifi antenna

I
The stainless bracket is stuck onto a status aerial blanking plate.

 

[Max Enger]

No question, Sika products are top quality at a top price.
Bodywork professionals have been known to use Purfex instead. Top quality product at a third of the price. I’m not sure if is is trade only..
I’m only sayin’.....

 

[Sundowners]

Landy, a question if you dont mind.
I have asked here before but none of the replies really answered my question.
I am changeing the external Thetford Storage/Locker doors, door No`s 3 + 4 + 5 and frames, Fresh water filler neck and EHU 240v external socket on my moho from original White to Black. What sealant/adhesives would you recommend? None of the changes are load/weight bearing or taking weight at all and all will be re-fitted to MoHo (Bailey Approach Advance 640 2016) useing original fixing points, all identical swap overs. Also I am fitting new GRP panels (Prima Leisure) into the Thetford doors. Again what would you recommend for sealing those and what best to use for cleaning excess sealant/adhesive away (White Spirit/Meths/soapy water/Rubbing alcohol)?
I have used Sikaflex EBT+ before for other jobs but thought it stayed a bit tacky!
You mentioned you use sealants for a living and I prefer asking advise from people in the know rather than peops with the best of intentions but not much of a proffessional idea.
Cheers. Graeme.

Personally I would not use sikaflex or similar products to fit things like locker door frames----- it makes them extremely difficult to remove at a later date------ if sealant and screws are used I would definitely use a " putty type" tape that is designed for the job.

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