Reversing Fibreglass Osmosis :- Jabberwocky to GTR

Do you want to find out how we reversed moisture build up in our fibre glass boat hull for less than £100 ? 

Read on or click the play button to find out how we did it !

The biggest unknown in our rebuild project was our ability to ward off future osmosis stemming from the excess water which had seeped into the core of the hull over the years. The advice we had been given was that if it was not showing now and if we resealed the bottom of the boat with Epoxy that there was a good chance that it would not become a problem. While we trusted the expert opinion that we would be OK we decided to give some drying options a go.

So what is fibreglass Osmosis, how does it present, how do you know it is building up and most importantly what can you do about it ?

In this blog post we answer these questions, showing you how we tackled the drying process. Click the video link above to watch how we built our very own Hot Vacuum pump on a budget and read on to find out some of the more technical aspects of the drying process.

What is fibreglass Osmosis ?

The gel coat finish on the exterior of many fibreglass boats is reinforced plastic which is porous. As water is a solvent, when boat is afloat the water reacts with the fibreglass to create a weak solvent solution, usually with styrene. The process starts from the day the boat is launched, gradually increasing the longer the boat is in the water.

In the worst cases this reaction will soften the gel coat, over time the build up can combine with gas or fluid pressure which results in the external water getting sucked into the small pockets of space within the laminate. Filling the gaps in the fibre glass with water and soluble components left over from the build process. 

In the most extreme cases this buildup can present as an external blister on the surface of the boat. In simple terms if you leave your boat in the water for extended periods of time the chemical reaction can slowly suck moisture into the fibre glass and further into and reinforcement inside the hulls core (usually closed cell foam or wood). If enough water is sucked in the chemical reaction can produce enough pressure to create external blisters in your boats finish.

How do you know if moisture is building up in the core of your hull ?

The best way to find out if you have moisture in the core of your fibre glass hull is with a moisture meter. These devices penetrate the layers of glass with an electric field which emanates for an electrode which is coupled to a stable low frequency oscillator. The speed at which the electric current flow through the hull is then used to calculate the moisture level. 

 

How can you reduce the moisture levels in your hull ?

There are several ways to reduce the moisture levels in your hull, the simplest and cheapest approach is to pull your boat out of the water, storing it in a warm and dry place. The issue with this approach is it could take years to dry our depending on moisture levels and the temperatures in your storage area. While GTR was inside and dry the cold Belfast winter was not going to get us results.
The second approach many people use is stream treatment, this works by pushing steam into the small holes in the fibre glass. The stream heats up the moisture in the hull, if you can get the hull temperature above 100 degrees C the core moisture can boil. It will them force its way out of the hull taking the unwanted chemicals which create the blisters with it.

We gave steam treatment a go using a small home appliance and a plywood frame to keep in the heat. We managed to get some small reductions in the moisture levels but needed at more industrial sized machine to make the impact that we were looking for.

The final and most effective approach is to use a pressurised Hot Vac. This approach uses a combination of Heat and Pressure to boil the water and the unwanted chemicals out of your hull.

How does a Hot Vac work ?

Almost everyone knows that water boils at 100 degrees C, what many people don't know is that under vacuum pressure this number reduces. If you create enough pressure you can  boil water at temperatures below zero. With the average winter temperature in Belfast in the low single digits we need to create above 29.60 bars of HG Vacuum pressure to boil away the internal moisture, or heat up the hull to a level were we needed less pressure to achieve our goal.

How did we build our Hot Vac for less that £100 ?

To create our home made Hot Vac we acquired the more expensive items second hand via ebay or from contacts we had. We pulled it all together with item found in most tool kits. 


* Second hand moisture meter from ebay £40
* Vacuum pump free from unused dairy farm
* Electric blanket £25
* Heat proof rubber mat £20
* Tape and pipes $10

Close up of vacuum seal

If you liked this update make sure you watch the full story of Jabberwocky's transformation to GTR by clicking play on the window below.