Failed GRP Roof - Thoughts on replacement

[Temp]

1 hour ago, JSHarris said:

Replacing the roof with a properly installed GRP one would be my preferred choice, as it will last a lot longer than a felt roof.

 

That would be my choice. Find a 4-5 day slot in the 10 day weather forecast and get the lot done right.

 

 

[SteamyTea]

17 minutes ago, JSHarris said:

Any idiot can use a chopper gun, and as a consequence lots of boats were laid up by people who knew next to nothing about laminating properly

Too true, I met loads of them. The really sad but is that they don't save much time and tend to use more materials.

Even gelcoat spraying is a problem because of uneven thickness.

Mind you, gelcoats are a problem full stop.

[SteamyTea]

4 minutes ago, Temp said:

That would be my choice

Mine would be to pre-laminate sheets in a controlled environment, while weather is dry, then just laminate up the joints.

Cheaper, better, faster and nicer to do.

Edited July 30, 2019 by SteamyTea

[jack]

1 hour ago, epsilonGreedy said:

 

@JSHarris comprehended my point.

 

Of course he understood that you were talking about overheating. That is, however, a different point to moisture interfering with curing, which is the one you were making.

 

Goalposts moved.

[scottishjohn]

2 hours ago, Big Jimbo said:

Loads of fibreglass strips over the joints of the OSB3, before i could even start laying up the roof.

use t+g boards  meant for the job--not super cheap OSB --thats what proper grp roofers do+don,t forget to insulate the underside if it is likely to get condensation in the winter

and  if you must use 18mm  osb -then drop a coat of resin on it to water proof it if not doing complete job in one day 

https://www.aboutroofing.com/18mm-osb3-tongue-and-groove.html

read this

this boarding has a resin coat already on it

Edited July 30, 2019 by scottishjohn

[epsilonGreedy]

27 minutes ago, jack said:

Of course he understood that you were talking about overheating. That is, however, a different point to moisture interfering with curing, which is the one you were making.

 

 

I will explain in simple terms.

 

Having owned sailing yachts for most of my adult life I have picked up a lot if insight into grp hulls and their manufacture. I have never heard of moisture being a problem in a hull manufacturing plant. The patchy quality control, largely of British built yachts of the 1970 and early eighties has triggered much interest over decades as to what can go wrong when a grp hull is made.

 

@JSHarrisas claimed moisture it is a major recognized industry problem that even the lowly laminators on the production line will consider moisture the main enemy of good grp. It is odd that such a concern has never entered the consciousness of two generations of yacht owners given that osmotic blisters, the most common failure, lead to a £9k bill to fix. 

 

Given that an exothermic curing laminate will drive off moisture I find Jeremy's claim very odd.

 

I was once very interest in a fringe yacht design where the hulls were grp encapsulated plywood. After a decade or so it was recognized that once water got inside to the wood, the grp sheathing would progressively fracture as the wood swelled, this was a runaway process. I believe this is the root cause of the OP's roof failure and a more likely explanation than edge case science about moisture captured in grp during layup. It is a bit like saying if a shovel full of topsoil is thrown in a cement mixer to bulk up the load the house might fall down, well yes of-course but it is more constructive to discuss the probable than the unlikely.

[SteamyTea]

9 minutes ago, epsilonGreedy said:

It is odd that such a concern has never entered the consciousness of two generations of yacht owners given that osmotic blisters, the most common failure

Not odd to me.  Most yacht owners car very little about how the boat is actually made, same as most car owners don't know how a re is made, and most house owners too.

As I said earlier, the industry is not very professional.

12 minutes ago, epsilonGreedy said:

Given that an exothermic curing laminate will drive off moisture I find Jeremy's claim very odd.

What are you talking about, you seem to have no concept of the process at all, but you do seem to have a lot of opinion.

Apologies if that seems blunt.

[Jeremy Harris]

22 minutes ago, epsilonGreedy said:

 

I will explain in simple terms.

 

Having owned sailing yachts for most of my adult life I have picked up a lot if insight into grp hulls and their manufacture. I have never heard of moisture being a problem in a hull manufacturing plant. The patchy quality control, largely of British built yachts of the 1970 and early eighties has triggered much interest over decades as to what can go wrong when a grp hull is made.

 

@JSHarrisas claimed moisture it is a major recognized industry problem that even the lowly laminators on the production line will consider moisture the main enemy of good grp. It is odd that such a concern has never entered the consciousness of two generations of yacht owners given that osmotic blisters, the most common failure, lead to a £9k bill to fix. 

 

Given that an exothermic curing laminate will drive off moisture I find Jeremy's claim very odd.

 

I was once very interest in a fringe yacht design where the hulls were grp encapsulated plywood. After a decade or so it was recognized that once water got inside to the wood, the grp sheathing would progressively fracture as the wood swelled, this was a runaway process. I believe this is the root cause of the OP's roof failure and a more likely explanation than edge case science about moisture captured in grp during layup. It is a bit like saying if a shovel full of topsoil is thrown in a cement mixer to bulk up the load the house might fall down, well yes of-course but it is more constructive to discuss the probable than the unlikely.

 

 

You may well have owned boats for years, but it seems clear that you have a near-zero understanding of the mechanism by which polyester resins are catalysed by MEKP.  If you had, then the reason why even small quantities of moisture can inhibit resin curing will be blindingly obvious to you.  If you've spent any time in a good boat building workshop you will have seen the processes that have evolved to keep everything dry. 

 

Osmosis has nothing to do with moisture resin cure inhibition, it's a post-cure (more on that below*) phenomenon that only affects laminates that are immersed in water for long periods of time. 

 

The resin exothermic curing reaction is, as I've already mentioned, primarily a pot life concern, and rarely effects a laid-up laminate that's been manufactured by people who know what they are doing.  Again, this is pretty obvious, for the reason I gave earlier, the elephant and mouse problem.

 

Your final point about GRP encapsulated timber is a combination of poor encapsulation and simple mechanical failure resulting from the expansion of timber as it gets wet.

 

If you wish to seem authoritative, it's best to at least do some basic research to ensure that you understand the true nature of the subject, lest what you write makes you appear foolish.

 

* I mentioned post-cure, but there is some limited evidence ( @SteamyTea may know more, I've not used polyester for more than 20 years) that the issue may have been partly a consequence of tiny pockets of uncured, or poorly cured, resin within the layup (lots of reasons for this, given the ad hoc mixing methods used in lots of boat manufacturers years ago).  Osmosis then causes water to migrate slowly through to those pockets increasing their volume and causing the characteristic blisters.  If you've pierced osmotic blisters you will know that the liquid smells strongly of uncured resin.

[PeterW]

29 minutes ago, epsilonGreedy said:

Having owned sailing yachts for most of my adult life I have picked up a lot if insight into grp hulls and their manufacture.

 

Simple question - have you ever actually been involved in the process in a hands on way..?? 

 

There are a few people on here talking from hands on manufacturing experience which is different to talking to manufacturers about it (some of whom would rather you didn’t know what goes on...)

 

31 minutes ago, epsilonGreedy said:

Given that an exothermic curing laminate will drive off moisture I find Jeremy's claim very odd.

 

The exothermic reaction doesn’t reach a far high enough point to boil off all water vapour, and this would hence cause an issue. Keeping moisture out of big boat building sheds has always been an issue, they are not by design the driest of locations ....

[SteamyTea]

20 minutes ago, JSHarris said:

* I mentioned post-cure, but there is some limited evidence ( @SteamyTea may know more

It is similar to ordinary paint drying, it gets rid of any volatile.  Not really necessary for general purpose polyesters though, they are designed to cure properly at a much lower temperature.

[Jeremy Harris]

4 minutes ago, SteamyTea said:

It is similar to ordinary paint drying, it gets rid of any volatile.  Not really necessary for general purpose polyesters though, they are designed to cure properly at a much lower temperature.

 

Thanks, that was my understanding, that, over time, tiny pockets of monomer styrene remaining within the laminate attracted moisture through the osmotic membrane created by the gel coat and adjacent thin lay-up.  Certainly pierced blisters always seemed to exude liquid that smelled very strongly of styrene.

[scottishjohn]

bottom line is on a grp roof there will never be osmosis if it is rolled and compacted correctly .

 

 

[Jeremy Harris]

1 minute ago, scottishjohn said:

bottom line is on a grp roof there will never be osmosis if it is rolled and compacted correctly .

 

 

 

 

Bottom line is that there can never be osmosis unless the roof is immersed in water for a long period of time!  Heavy rain like that today doesn't really count...

[epsilonGreedy]

1 hour ago, PeterW said:

The exothermic reaction doesn’t reach a far high enough point to boil off all water vapour, and this would hence cause an issue. Keeping moisture out of big boat building sheds has always been an issue, they are not by design the driest of locations ....

 

 

This is easy to debunk.

 

How does a radiator running at 60 degrees dry cloths draped over it? Hint: look up a definition of evaporation.

 

Also Jeremy mentioned dew points which would be deterred by just a few degrees of exothermic temperature delta.

[Jeremy Harris]

11 minutes ago, epsilonGreedy said:

 

This is easy to debunk.

 

How does a radiator running at 60 degrees dry cloths draped over it? Hint: look up a definition of evaporation.

 

Also Jeremy mentioned dew points which would be deterred by just a few degrees of exothermic temperature delta.

 

The key point that seems to be being ignored is the elephant and mouse one. 

 

A GRP lay-up, be it a boat hull or a roof, has a very large surface area to volume ratio.  Heat loss rate for a given differential temperature is proportional to this ratio. 

 

The fact that the initial curing reaction is exothermic is relatively unimportant during the cure of a typical, fairly thin, lay-up, as the heat lost because of the high surface area will be significantly greater than the heat released by the initial curing reaction.  That's why it's perfectly possible for a still uncured lay-up to cool down to below dew point and so attract condensation, and the reason I had to spend a night in a smelly industrial unit in Penryn making sure that the laminate temperature didn't cool below local dew point overnight all those years ago.

[Ferdinand]

OP: Use whatever system you like but don’t put more on top of a bodge. Start again.

[Ferdinand]

Apart from that, enjoying the ping pong of debate on the thread.

 

 

 

[SteamyTea]

5 hours ago, Ferdinand said:

OP: Use whatever system you like but don’t put more on top of a bodge. Start again.

Too right.  And I know you know a lot more about it that most.

6 hours ago, epsilonGreedy said:

This is easy to debunk.

If you try to lay up onto something wet, it stops the exothermic reaction dead.  It just does not cure where it is damp.

I can see why the British boat building industry was so bad at one stage when nonsense like this is talked about as fact.

 

[Ferdinand]

.

 

Edited July 31, 2019 by Ferdinand

[epsilonGreedy]

19 hours ago, SteamyTea said:

Not odd to me.  Most yacht owners car very little about how the boat is actually made, same as most car owners don't know how a re is made, and most house owners too.

 

 

If you are referring to sailing yacht owners then you are very wrong. Self builders and yacht owners share a natural interest is how things are made.

 

In nearly 40 years of following yachting I have never heard a hint of a rumour that a brand or specific production run of yachts suffered from damp manufacturing conditions. Yacht owners can be highly partisan on internet forums and are not shy from criticizing other brands, yet in all the mud slinging never a mention of "that dodgy batch came out of that damp manufacturing plant". 

 

19 hours ago, SteamyTea said:

As I said earlier, the industry is not very professional.

 

 

A fair criticism of the British in the 70's and 80's, there is no volume British yacht brand left today. The original BBC Howards Way sailing drama portrayed the all too typical have a go yacht production enterprise of the time. From what @jsharris has posted here I infer he had a brief dalliance with underfunded yacht production decades ago.

 

My yacht popped out of its mouldings in Germany in 2004 at a truly massive manufacturing centre owned by a company valued at around a $ 1 billion at the time. The no.1 company is French and called Beneteau is worth £600 million. You and @JSHarrishave a dated perception of grp yacht production.

[Jeremy Harris]

12 minutes ago, epsilonGreedy said:

 From what @jsharris has posted here I infer he had a brief dalliance with underfunded yacht production decades ago.

 

The yacht I was working on was a one-off, custom built boat, that was being built by a company set up by the owner specifically to build his own yacht.  It's fair to say the owner had more money than sense, but he certainly didn't "under fund" the project.  Anything we wanted we could have, and the chap in charge of the lay-up was the one I learned pretty much everything about laminating from.  He'd been hired in from up-country specifically because of his skills and knowledge in custom yacht construction.

 

 

12 minutes ago, epsilonGreedy said:

You and @JSHarrishave a dated perception of grp yacht production.

 

No, @SteamyTea and I have a fair level of knowledge of some of the pitfalls that can arise when doing GRP work in general, not specifically related to GRP yacht production.  One of those pitfalls, directly relevant to this thread, is the very well-understood need to keep everything bone dry, because of resin cure inhibition caused by moisture.  Most of my composite work has been on aircraft components, rather than boats, although I did make one small boat from epoxy foam sandwich a few years ago. 

[joe90]

Well I have laid up a few flat roofs in my time and learnt from a course run by the material supplier, in essence they said if the OSB was wet or damp in any way IT WILL FAIL. They did not go into detail about how or why but said if the OSB got wet/damp, rip it off and do it again or you will be hauled back in the future to replace it. None of mine have failed.

[Onoff]

12 minutes ago, joe90 said:

Well I have laid up a few flat roofs in my time and learnt from a course run by the material supplier, in essence they said if the OSB was wet or damp in any way IT WILL FAIL. They did not go into detail about how or why but said if the OSB got wet/damp, rip it off and do it again or you will be hauled back in the future to replace it. None of mine have failed.

 

Presumably you could cover an OSB roof with a tarp thinking you were doing the right thing if it was going to say rain but then get screwed by condensation under the tarp making everything damp?

[SteamyTea]

1 minute ago, Onoff said:

condensation under the tarp making everything damp?

You don't need much moisture to ruin the layup.

I once spilled a few drops of tea in the mat cutting bench. Next person did not notice as they used it, long story short, a ruined moulding. But I managed to repair the damage. Would have been quicker to remake it though.

[joe90]

13 minutes ago, Onoff said:

 

Presumably you could cover an OSB roof with a tarp thinking you were doing the right thing if it was going to say rain but then get screwed by condensation under the tarp making everything damp?

 

Everyone on a building site knows tarps do not keep stuff dry, they stop most of the water but I am yet to see one keep anything dry.. also when it rains the air is full of “moisture “ which is enough to spoil GRP, only way to guarantee dry stuff during rain is indoors.