“Soaking” Epoxies – not so good
Generally the thinners based products were a precursor to the full high solids epoxy catastrophe (and I mean that in the most positive sense). The most common in Oz is the dear old Epicraft Everdure which we all used to seal the insides and underdecks and often under the paint of our racing dinghies in the seventies and very early 80s.
With racing dinghies weight is seen as somewhat critical – an extra pound or two is considered a catastrophe. Anyway, everdure was not particularly effective at keeping the water out of the timber – the boats would still put on weight – this could range from a pound or two up to about 5% of the hullweight. The reason as far as I have been able to gather is that the thinners are quite long complex molecules and as they come out of the epoxy matrix they leave holes behind.
As the thinners content of Everdure is very high – about 70 percent from memory the holes are very extensive.
Water molecules are somewhat smaller than the organic molecules so have little problem going up the same holes and into the wood.
As the graph below shows – the water uptake of timber treated with “penetrating” epoxy is about 5 times that of the Modern Epoxy solution below. A massive 35% compared to less than 8% for the “high solids” type.
The Modern Epoxies – a better solution
When WEST Epoxy first came on the scene (there were other good quality epoxies around at the same time – like the OZ Bote Cote and a few others ) it first gained popularity in the Tornado catamaran class, initially in America, where finally it was possible to build boats that took up very little weight during the sailing season. At the time it was very much preferred to build in plywood as it provide a much stiffer boat for the same weight compared to the solid fibreglass alternative that was allowed under the class rules. Later on foam/glass sandwich boats were allowed which can be built stiffer still in many cases.
The good quality epoxies are termed “high solids”. This basically means that there are almost no thinners added, so there are no wormholes from the exit of thinners from the matrix – so little opportunity for water to get in (and not even much exchange of air – no water, no air, no life – thus no rot if the job is done properly – (all surfaces sealed with ‘pox). This comes with a significant labour and materials cost, but has a good track record in general.
The objective in coating –
Timber is very unlikely to rot if the moisture content is down around 7 to 10 percent. From the graph above it is clear that the high solids epoxy – 105/205 in this case is excellent.
So we are left with the decision as to how much epoxy to use. Too much and you have wasted money – too little and it won’t seal the timber well enough.
In real life application it is considered that 3 coats are about right. The first coat will soak in to a large extent so may leave some areas a bit dry. The second coat may be absorbed into some areas and it is possible you may miss some. The third coat makes sure all the dry patches and missed patches are well covered.
Three coats may sound like a lot of work, but read the page on “Wet on Wet Epoxy Application” which gives the methods for saving heaps of labour in applying epoxy in different situations
Identifying High Solids Epoxies
One way to quickly test if your epoxy is high solids is to sniff it. There should be no intense thinners type smell. Usually the hardener has a slight ammonia smell, particularly if you have just taken the top off, but there should be nothing to make you gasp or that has a thinners type smell.
So West, Bote Cote, System 3 and some others are high solids. Many of the cheaper “Industrial” epoxies that are available have thinners added – so won’t keep the water out as effectively.
If you contact Epicraft and ask them about the best method to protect your boat from rot they will sell you their high solids epoxy system – because they know it is the most effective way of dealing with the problem. If you start talking about the expense they will be happy to sell you dear old Everdure and will wish you well as you depart.
High Solids Epoxies compared.
By virtue of being “high solids” quality boatbuilding epoxies are excellent moisture barriers. But do they differ in their physical properties?
The University of Queensland did mechanical testing about a decade ago on a wide range of the epoxies available at the time in Australia and it showed that in terms of tensile strength, impact resistance and work to fracture that you really do get what you pay for. The cheap epoxies are brittle and not capable of sustaining high loads, whereas the more expensive ones – Bote Cote, WEST, System 3 are a great deal better. It was certainly edifying seeing the results from the testing machines graphed. The good ones were not just 5 or 10 percent better, but often 40 or 50 percent than the cheaper ones.
Can you make a high solids epoxy soak in better?
WEST originally stood for Wood Epoxy Saturation Technique. But as all of us who build boats know – if you cut something that has been coated the epoxy only soaks in a very small distance – a mm or less. So now WEST stands for Wood Epoxy Stabilisation Technique – which is a much more accurate description.
However this does not mean that the system is less effective because it doesn’t soak in. WEST and BOTE COTE and other quality boatbuilding epoxy systems made their reputations because the stuff works. They provide an effective system for gluing and bonding timber. That effective system has never relied on soaking very far into the timber – it simply has to provide an effective bond.
You can thin epoxy to get it to soak in further for gluing purposes, but the thinners reduce the strength so much that you have made a large nett loss. They are generally not recommended for gluing applications. For coating they work, but (here we move very much more into the area of opinion – ie … mine) – I have hardly ever found them necessary.
There are thinners that you can add to a high solids epoxy that won’t evaporate. The one that Bote Cote do is called TPRDA – which links up with the epoxy matrix and becomes a permanent part of it. Some of the other brands have similar stuff.
One area where the TPRDA type thinners (whatever brand) are good is … back onto the thread … where a structural member or surface has a thin layer of rot. There the thinned epoxy can get in a little distance and help consolidate the area. However it does not make the timber as strong as it once was – so if the rot has compromised the structure then the strength has to be brought up to the original level. So, for example if you have a timber frame that is 50mm thick and there is a bit of rot 6mm deep on the bottom corner it MAY be OK to soak it. But if the frame is 30 or 50% rotten it needs to come out, or be sistered or a new section scarfed in.
Generally I use Bote Cote for my building, but one of the many good things that WEST have on offer is a wooden boat restoration booklet. It is really cheap – about 10 dollars and goes through all the techniques necessary to restore and repair older boats. One of the most useful things about it is that it helps you assess the structure to work out what you need to do.
Gosh it’s late – where did that time go!!!