Roofing under a tent

[SteamyTea]

1.22 by 2.44 (8 by 4, the world is built from it).

The trouble with either just coating with resin, or putting up plain boards is that they will absorb some moisture.

So much safer to get them coated properly first.

It is hard to stress just how important keeping everything dry is.  It is not unusual for a boat to have the gelcoat stripped off because of problems (known as osmosis, but is actually a mismatch of materials), then the shell is stored in a shed for months to dry out.

[scottishjohn]

 resepectfully we will disagree here -- if boards screwed down in the dry then a good coat of resin --they will be sealed-as it will run in the joints 

not coated then screwed down 

[joe90]

  On 21/09/2020 at 15:11, Tony K said:

it now looks like a December job.

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my only worry is relative humidity at that time of year even if it’s not raining, @SteamyTea will correct me now ????.

[SteamyTea]

  On 21/09/2020 at 15:59, joe90 said:

relative humidity

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Would be my concern too if the whole job was to be done, and the low temperatures.

 

Build a decent shed, you know it makes sense.

[scottishjohn]

  On 21/09/2020 at 15:59, joe90 said:

my only worry is relative humidity at that time of year even if it’s not raining, @SteamyTea will correct me now ????.

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if the boards are stored in the damp ,then it will be the same how ever you do it ,even if you have a tent - proper treated roofing boards should be reasonably water proof as they come ,

 low temps - if dry just means more catalyst and or dif resin

 

Edited September 21, 2020 by scottishjohn

[Tony K]

  On 21/09/2020 at 15:41, scottishjohn said:

what about fitting a few boards to roof --then just coating in resin including joins  -  do that as weather allows and then come back sand and apply lay-up and top to a section at a time  that way boards are waterproofed ?

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If that works then it's probably the best of both worlds. Are you thinking of doing the final top coat on each section as I go along?

[SteamyTea]

Once the joints are layed up the final top coat could be done a few days later.

How big is this roof and how complicated a shape.

 

It is not to do with being waterproof, more to do with water absorption.

 

 

[Tony K]

  On 21/09/2020 at 16:24, SteamyTea said:

Once the joints are layed up the final top coat could be done a few days later.

How big is this roof and how complicated a shape.

 

It is not to do with being waterproof, more to do with water absorption.

 

 

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L shaped building with a split level roof, so basically two large separate rectangles each about 50m2.

 

Only other complications are a series of small rooflights. 

[SteamyTea]

  On 21/09/2020 at 16:27, Tony K said:

 

L shaped building with a split level roof, so basically two large separate rectangles each about 50m2.

 

Only other complications are a series of small rooflights. 

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Quite simple and not too large.

 

Have you thought of what you are going to do about finished edges (the ones you can see from the ground)?

[joe90]

https://www.fibreglassroofingkits.co.uk/blog/post/What are the best boards for a GRP flat roof/ Info

 

  On 21/09/2020 at 16:43, SteamyTea said:

finished edges

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I have always used pre formed angle, GRP to top surface, smooth finish to front, same with up stands (but other way up).

Edited September 21, 2020 by joe90

[Tony K]

  On 21/09/2020 at 16:43, SteamyTea said:

Have you thought of what you are going to do about finished edges (the ones you can see from the ground)?

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Here is the basic plan, nothing too complex. As @joe90 suggests, I was going to use pre-formed edges etc.

 

[scottishjohn]

  On 21/09/2020 at 16:24, SteamyTea said:

It is not to do with being waterproof, more to do with water absorption.

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thats why i say a coat of pure resin to start with --there is no absorption possible in pure resin ,that happens when fibre is added and its not  resin rich --eg  see through - not see through and there is space for water-as you well know

- so my proposed first layer of resin seals everything in one simple quick job -that can then wait for better weather to add next grp layers

that,s how osmosis happens - water gets in the fibre layers that are not fully wetted through  and does not want to come out without lots of heat and ventilation 

[SteamyTea]

  On 21/09/2020 at 18:11, scottishjohn said:

osmosis happens - water gets in the fibre layers that are not fully wetted through  and does not want to come out without lots of heat and ventilation 

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No it isn't.

The misnamed 'osmosis' is caused by the gelcoat failing. This is why the moved over to epoxy resins. The molecular crosslinking is greatly improved compared to modern polyester resins.

[scottishjohn]

  On 21/09/2020 at 18:16, SteamyTea said:

No it isn't.

The misnamed 'osmosis' is caused by the gelcoat failing. This is why the moved over to epoxy resins. The molecular crosslinking is greatly improved compared to modern polyester resins.

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half right -- if the grp behind gel coat was resin rich -then there would be no place for water to be and therefore no osmosis --or what ever you want to name it

,but I understand why its not resin rich it makes it brittle, heavy  and costs too much 

 I am familiar with epxoies having built an aircraft from it- a europa - blue foam wing cores sheathed in bidirectional cloth and using west expoxy system - all expoxy systems are resin rich  

so it does not occur 

same as pre-preg grp + kevlar -- its always see through --no air pockets ,

cut out the bits stick them together  in poly bag on the mould and evacuate it and autoclave it 

[SteamyTea]

  On 21/09/2020 at 18:28, scottishjohn said:

half right

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No, I am totally right.

If the resins are correctly proportioned and mixed with the hardener (misnamed catalyst, though it is really an oxidiser) then there is nothing for the water to react with (it is free hardener that causes the gelcoat to fail, when mixed with water the PH changes and dissolves the polyester molecules).

What you are describing is bad workmanship and will fail prematurely, even in the absence of water. Thermal expansion and contraction will see to that.

This is why prepreg was developed, it takes out the human element from it.

 

I developed, over 30 years ago, an 'ismosis' free system for high temperature and high humidity environments. The system is still for sale, but not cheap.  It is way over the top for a roof coating though.

Edited September 21, 2020 by SteamyTea

[Tony K]

Does anyone have any preference re tounge and groove or straight edge boards? 

[joe90]

  On 22/09/2020 at 08:47, Tony K said:

Does anyone have any preference re tounge and groove or straight edge boards? 

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If not using t+g best to use noggins under joins, also to leave 3mm gap between boards for expansion, best choice is t+g tho, writing side up leaves a small gap for resin to bond the joint.

Edited September 22, 2020 by joe90

[scottishjohn]

  On 22/09/2020 at 08:47, Tony K said:

Does anyone have any preference re tounge and groove or straight edge boards? 

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If you were going to lay them all and coat with just resin to waterproof them till later --then T+G must be better- 

 if going down rioute of pre grp each then maybe striaght edges could be easier -any resin in t+g slot would cause problems later

 maybe a talk with grp roof supplier is your next call

 

 

[Russell griffiths]

I did grp on my kitchen a couple of years ago in January, it was a bloody pain but came out very good with lots of hard work. 

 

I have a small small porch to do on the new house and won’t be using grp again, I will be using one of the liquid single component systems that uses a mat just like grp but cures with contact with moisture so removes all of those problems. 

 

Have a search around theres a few vids on you tube of companies changing to it from grp. 

[SteamyTea]

  On 22/09/2020 at 10:02, Russell griffiths said:

will be using one of the liquid single component systems

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I fancy having a play with some of those systems, I like polyurethanes.

If you have some left over, let me know.

[Tony K]

  On 22/09/2020 at 10:02, Russell griffiths said:

I will be using one of the liquid single component systems that uses a mat just like grp but cures with contact with moisture so removes all of those problems. 

 

 

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Is there a market leader I can start with that you know of at all, and is it as good as (properly done) GRP?

[Ferdinand]

If you want a work space, think about a further use for the storage container you are inevitably going to end up buying ?.

 

My dad built an entire house from fibreglass ("modular house"), and also used to make grp fake-pantile-panels for roofs, but I don't know enough to really get into this debate at a technical level.

 

I think there's a thread somewhere where a forum member built a tent over his grp roof that had only half worked, in order to do the recovery in semi comfort.

 

[Update. It was @andyscotland, and there are 2 threads:

 

Problems with GRP roof:

Scaffold tent to help recovery:

 

My suggestion: Play it safe or go for something like HDPE or corrugated tin if you won't play it safe. Don't mess with Mr In-Betweem on this.

 

Ferdinand

Edited September 22, 2020 by Ferdinand

[scottishjohn]

is this basically same stuf as they use as a tanking solution for basements .

is it hard when set 

is it crow and seagull peck proof ?

 

[Ferdinand]

It's quite possible that I have the wrong acronym, and could mean EPDM, but I mean the long lasting sheet that is used for the best pond liners and also used for roofs.

Someone will be along in a minute with the correct thing,

[scottishjohn]

  On 22/09/2020 at 13:15, Ferdinand said:

It's quite possible that I have the wrong acronym, and could mean EPDM, but I mean the long lasting sheet that is used for the best pond liners and also used for roofs.

Someone will be along in a minute with the correct thing,

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no dont, like them -- as i saw roof that crows had pecked holes in while trying to peck at food they brought up to flat roof to consume -

maybe not a common  problem -but a worry