GRP Foam Sandwich roof – drill holes to ventilate underside?

[MYStargazer]

My cabin roof (pictured below) is made of a GRP foam sandwich, of 1973 vintage. It has numerous holes in it for exterior handrails, cable glands, etc, as well as a large (recovered) hole where the engines have been removed previously.

There has been rainwater ingress before, too.

I plan to remove all the fittings before refitting and resealing them.

My question is, is it worth, while the headlining is all off, drilling a matrix of small holes to let the underside of the foam sandwich ‘breath’? Or large holes? Or none?

Thanks for your thoughts.

 

[oldsaltoz]

My cabin roof (pictured below) is made of a GRP foam sandwich, of 1973 vintage. It has numerous holes in it for exterior handrails, cable glands, etc, as well as a large (recovered) hole where the engines have been removed previously.

There has been rainwater ingress before, too.

I plan to remove all the fittings before refitting and resealing them.

My question is, is it worth, while the headlining is all off, drilling a matrix of small holes to let the underside of the foam sandwich ‘breath’? Or large holes? Or none?

Thanks for your thoughts.

Drilling holes large or small will no achieve anything, If the foam core is wet it will be rubbish and needs to be replaced.

You can use a 6mm drill and drill holes on a grid pattern to find the total wet area, just inspect the material that the drill drops for moisture, mark any dry holes and you should end up with a shape representing the area/s that need treating.

Also check any existing holes for deck fittings to ensure they have drilled oversize and filled with a mix of epoxy resin and micro-fibres, then re drilled to the required size, this will prevent leaks into the core material.

Let us know how big the areas are and we take from there.

It is fixable.

Good luck and fair winds.

 

[pvb]

My question is, is it worth, while the headlining is all off, drilling a matrix of small holes to let the underside of the foam sandwich ‘breath’? Or large holes? Or none?

I wouldn't bother. Most headlining material isn't porous, anyway.

 

[MYStargazer]

Thanks for your thoughts, guys!

 

[Poignard]

No personal experience to offer but the subject is well covered in one of the WEST manuals.

http://www.westsystem.com/ss/assets/HowTo-Publications/Fiberglass-Boat-Repair-and-Maintenance.pdf

Section 5 refers.

 

[MYStargazer]

No personal experience to offer but the subject is well covered in one of the WEST manuals.

http://www.westsystem.com/ss/assets/HowTo-Publications/Fiberglass-Boat-Repair-and-Maintenance.pdf

Section 5 refers.

What a useful publication - hadn't come across it before - great call, thanks.