Sealing (screw) holes in FIbre glass

[bedouin]

We have a small but annoying leak into the cabin. Particularly annoying as it drips onto the chart table and can find its way into the drawer where the charts are stored. It is particularly difficult to track this down as the headlining is itself moulded GRP with a small gap to the deck - meaning water can be entering the void some way from where it finally drips.

The only way I can see this getting in is round the screws that hold the cover for the hatch garage - a sheet of ply screwed down to moulded GRP. As they are self tappers screwed into GRP and have been removed several times the threads are comparatively loose.

Is there an easy way to seal such holes? I was wondering about a butyl rubber washer that would seal the thread as it compresses - or maybe PTFE tape around the thread itself (doesn't sound too promising)

 

[Stemar]

Remove screw, blob of sealant in hole, replace screw and leave about 1/2 a turn loose. When the sealant's gone off, tighten down, but don't overtighten.

You really want to get everything dry if you can, if that isn't possible, use a sealant that works on damp surfaces.

 

[bedouin]

Remove screw, blob of sealant in hole, replace screw and leave about 1/2 a turn loose. When the sealant's gone off, tighten down, but don't overtighten.

You really want to get everything dry if you can, if that isn't possible, use a sealant that works on damp surfaces.

The trouble with sealant is that it doesn't last that long in the tube - so that means I need to buy a whole new tube just to use 6 blobs on the hatch

In fact this time I will do that as I am taking it off to run wires that will themselves need to be sealed where they go through the deck so can't avoid it - but I always get frustrated with the amount of sealant I waste. I wish they would sell it in small toothpaste sized single use tubes

 

[pvb]

The trouble with sealant is that it doesn't last that long in the tube - so that means I need to buy a whole new tube just to use 6 blobs on the hatch

In fact this time I will do that as I am taking it off to run wires that will themselves need to be sealed where they go through the deck so can't avoid it - but I always get frustrated with the amount of sealant I waste. I wish they would sell it in small toothpaste sized single use tubes

You can buy Sikaflex 291 in little 70ml tubes, which are ideal for small jobs. Seal the tube well and store in the freezer and it might be OK for another day.

 

[bedouin]

You can buy Sikaflex 291 in little 70ml tubes, which are ideal for small jobs. Seal the tube well and store in the freezer and it might be OK for another day.

Force 4 sell those for £8.75 compared to £9.95 for the 300ml version

Any idea how long you can keep an opened tube/ cartridge before it goes off?

 

[Tzu]

Maybe not for the purists but I've had some success with Milliput Fine in screw holes. Drop of oil on screw before its screwed home and it should be removable.

 

[pvb]

Force 4 sell those for £8.75 compared to £9.95 for the 300ml version

Any idea how long you can keep an opened tube/ cartridge before it goes off?

I bought one of the little tubes for use at home, because there wasn't enough access to use a conventional cartridge gun. I kept it in the freezer and used it again a few months later. You can do the same with cartridges, but you must seal them carefully.

 

[Poey50]

You can buy Sikaflex 291 in little 70ml tubes, which are ideal for small jobs. Seal the tube well and store in the freezer and it might be OK for another day.

I've kept one going for a season. After a while the main nozzle can harden but because is is squishy you can feel for the unhardened pools and access them through piercing the cover at that point. This hole then seals itself and on you go. A very good bit of kit to carry.

 

[Boathook]

The trouble with sealant is that it doesn't last that long in the tube - so that means I need to buy a whole new tube just to use 6 blobs on the hatch

In fact this time I will do that as I am taking it off to run wires that will themselves need to be sealed where they go through the deck so can't avoid it - but I always get frustrated with the amount of sealant I waste. I wish they would sell it in small toothpaste sized single use tubes

I use Arbomast BR which keeps for around a year if the tube end is sealed. It works well above and below water and being butyl doesn't set hard.

 

[Pavalijo]

I found my leak using an endoscope (Lidl special, £25 ish but amazing value). Poked it up through a downlighter hole in the inner lining. It was over 2m away from where it emerged.

 

[VicS]

Remove screw, blob of sealant in hole, replace screw and leave about 1/2 a turn loose. When the sealant's gone off, tighten down, but don't overtighten.
.

The trouble with doing that is that you risk breaking the seal again when tightening down

I would ( usually do ) use a small blob of Araldite on self tappers into GRP. Milliput is a good suggestion if you have any otherwise Araldite works well. If you dont clean the screw thread then it will easily be removable again if necessary. No need to specifically oil or grease the thread. This is the only thing I use Araldite Rapid for!

 

[andyj301]

Anywhere above the waterline you could try CT1 or one part polysulphide from Wickes. I've got a tube of each that were opened about three years ago, both are still good. I prefer the CT1 just cos it's available in clear.

 

[Pye_End]

If you use butyl tape then it would be worth using a countersink on the hole, so that when you tighten up the thread it squashes the butyl into the screw and hole rather than outside. Doesn't need to be that big. A butyl 'washer' will just end up squashed outside otherwise.

Presumably, although the screws are fairly loose, you can still get decent grip from them?

 

[lw395]

Remove screw, blob of sealant in hole, replace screw and leave about 1/2 a turn loose. When the sealant's gone off, tighten down, but don't overtighten.

....

That almost guarantees shearing the sealant.
It helps a lot to countersink the screw hole under the fitting or whatever else is being screwed down.
That way, a ring of sealant is left around the screw. This has a much better chance of surviving a little movement. Most sealants will stretch x% before failure. If the sealant is a very thin layer, x% of very thin is not very much, so slight movement = failure.

A better sealant may help, but bathroom silicone is keeping my dinghy airtight.

 

[bedouin]

If you use butyl tape then it would be worth using a countersink on the hole, so that when you tighten up the thread it squashes the butyl into the screw and hole rather than outside. Doesn't need to be that big. A butyl 'washer' will just end up squashed outside otherwise.

Presumably, although the screws are fairly loose, you can still get decent grip from them?

In this case I am screwing the plywood hatch down to the GRP moulding, and the danger of water ingress is through the GRP. Not sure if the water is getting there from on top of the wood (i.e. past the screw head) or from between. In the past I have tighted the screws down onto a dab of sealant but not particularly successful.

The screws are loose(ish) but as there is no force on them there is no need to do anything about it

 

[Hacker]

Get some strips of butyl tape and push it down the hole. When you screw in you should get a good collar of butyl under the screw head. You can get white as well as black. If you want to watch a video of it then find the Follow the Boat and look for their video series from the rebuild in Thailand

 

[LittleSister]

If you could find suitable size/material blind (internal) threaded inserts, these would probably be easier to fit firmly and in a way that is reliably waterproof. (I can't see self-tappers which pass right through grp ever being reliably watertight, especially if they are clamping a sheet of ply on top.)

 

[johnalison]

It is surprising how effective Capt. Tolley's stuff can be. Rainwater used to poor into our Sadler via a window until I sealed it. It seemed to last for years. Lazy? Moi?

 

[penberth3]

The trouble with doing that is that you risk breaking the seal again when tightening down

I would ( usually do ) use a small blob of Araldite on self tappers into GRP. Milliput is a good suggestion if you have any otherwise Araldite works well. If you dont clean the screw thread then it will easily be removable again if necessary. No need to specifically oil or grease the thread. This is the only thing I use Araldite Rapid for!

Would a gasket material work? Something like Hylomar or Hermetite is easy to find in small tubes at a sensible price.

 

[salar]

The trouble with sealant is that it doesn't last that long in the tube - so that means I need to buy a whole new tube just to use 6 blobs on the hatch

You can keep a large tube for multiple uses by stopping the nozzle with a four inch nail pushed right in and keeping it in the freezer between uses. The nail will need to be drawn out with pliers but being long there will still be a hole through any solidified portion at the nozzle end.