Any GRP experts out there?

[Vernon B]

Does anyone know if GRP can become porous by how it has been formulated or by buffing off of the gell coat? I've a damp patch in the roof lining and its proving to be difficult to identify the source of the ingress (?) Vernon B

[richardoakley]

Hi Vernon B I know that grp boats can suffer from water seepage through the gel coat called osmisis and it is caused by the gel coat mix but I understand that modern mixes are less prone to this. What happens is that the water permiates the gel coat and the fibre mat capiliaries the water in. The 'cure' was to grind the gel coat off and recoat the surface with a waterproof coating ( I forget what is used but any boat yard will tell you). This process would look a bit messy and be a bit drastic! Another solution would be to spray the area with a two part paint (again from a boat yard) which is designed for boats and therefore waterproof! (lol) I hope that helps Richard ;-)

[Simon]

The problem with water is that it can move a long way within a structure before becoming visible. Are you sure that a seam is not leaking?

[RAA]

If the gel coat is damaged GRP may become porous. Nothing is completely water resistant but sound GRP lasts for years in boats. Some twenty or more years old. You might getaway with repairing with a GRP kit but once GRP has cured completely only a urathane compound can be relied on to adhere positively. Hope this helps.

[Vernon B]

Many thanks Richard I appreciate the information since it does suggest that this could be a cause of the problem ;-)

[Ranger]

Hi Vernon, without getting too technical, as it is the roof and presumably out of sight, give it a coat of underseal followed by a coat of aluminium paint to reflect the sun. Stops leaks and makes heavy rain fall much quieter..and will last as long as you want to keep the 'van I expect.