Sopping wet glass fibre sandwich - what do I do??

[ChasB]

I've been stripping off the old lining carpeting inside my boat and discovered the primary cause of much water ingress.

On my aft deck (is that what it's called?) at the back in the centre a previous owner has drilled a hole down and through into the rear cabin to route some gas piping. His job is complete rubbish and has been allowing water to seep in for years! Up to now I thought several leaks were due to leaky safety rail fixings at the sides, but these turn out to be sound.

From 3" in from the edges the deck is constructed in three layers: two thick solid fibreglass layers sandwiching a 1.5" layer of wood. Water has got into the gas piping hole, and has seeped sideways inside (the deck curves gently to either side) until it's found places to exit elsewhere, such as where other fittings penetrate the lower glass fibre layer in the cabin.

I can only see into this construction by looking into the 2" hole made by the previous owner. Most of the wood for about an inch around this hole is rotten, but beyond that much appears sound, with rotten bits going off to either side where the water has followed gravity. But I can only poke in to investigate for a couple of inches.

The fibreglass layers appear to be solid and uncompromised, but between the layers (where the wood is) it is sopping wet. I could plug the hole, but then there would now no room for evaporation. In fact I can't se how this layer of wood can ever be dried out!

What should I do?

And how can I test if the fibreglass is sound (without hitting it with a hammer)?

 

[tinkicker0]

Prevent ant more water from entering the hole, get a localised heat source on the lines of a 100w bulb, put it under the hole and leave it going for a month or two so the sandwich gradually warms up.
Only time will dry it out, no quick fix.

 

[bikedaft]

the grp will be fine, but the wood may or may not be. sometimes the only way is to remove one of the grp layers to get at the wood. but the wood might be mostly ok... does the deck unduly flex etc where the wood/grp laminate is? is there cracks in the grp at all?

 

[ChasB]

No signs of anything untoward. Only cracks are the hairline ones you get on fibreglass decks around areas of strain, like the steps, but nothing where this double-thickness section is. It's built like a tank!

Guess I keep it warm over the winter, and keep the dehumidifier on...

Would pouring in a little anti-fungal solution be a really bad idea..?

 

[dmayes]

Cleaning out

You can bend a piece of steel rod into an "L" shape, then put it into a slow drill. Use this to cut out the balsa as far as you can. This will aid drying and remove the rotten wood. Use a vacuum cleaner to get rid of the swarf. Then, when dried out you could use a builders can of expanding foam to replace the wood before sealing the hole.

 

[PCUK]

The foam idea is good but don't use ordinary builders foam as this will soak up water quite soon. A product called 'Great Stuff' is a minimal expansion semi-closed cell foam which works very well in this situation. It can be found on-line or at some builders merchants and DIY stores.
There was an article on repairing a balsa cored deck in a recent issue of PBO.

 

[JasonClark]

depends how confident you are on your grp repair skills and access to all the right power tools etc, if you have access and are pretty handy i'd rip the whole lot out and replace it, sounds drastic but its the only way of a good solid non cowboy like repair job, that to me personally equals peace of mind. if you need to brush up on your fibreglass/gelcoat repair skills, there's tons of instructional videos on youtube done by experts for a totally invisible job. There is one video in particular done by some american company where they put a piece of flat shiny plastic over the gelcoat to get it flat and iron out the air pockets, i use this method all the time, it works wonders !

 

[TQA]

This is a very common problem with cored decks. To do a proper job you have to bite the bullet and cut out a patch either on top or the bottom of the deck. remove the rotted core, replace and reglass. There is a Plastic Classic forum with lots of advice on how to do this.

I helped someone do this and although messy it is easier once you get over the trauma of taking a circular saw to your deck. Remember to set the depth of cut to 3/16ths.

 

[oldsaltoz]

QUOTE
On my aft deck (is that what it's called?) at the back in the centre and water seeped in for years!
From 3" in from the edges the deck is constructed in three layers: two thick solid fibreglass layers sandwiching a 1.5" layer of wood. Water has got in and has seeped sideways inside until it's found places to exit cabin.
Most of the wood for about an inch around this hole is rotten, but beyond that much appears sound, with rotten bits going off to either side where the water has followed. !

What should I do?

Sorry to hear you have a problem.
When you say the wood is rotten, is this ply or balsa?

Regardless, if moisture has entered the wood and some has rotted you will have to ensure that All rotten material is removed and replaced with a suitable material.

The first stage is to establish the extent of the rot. The place to do this is on the underside of the deck, this will leave the aft deck in original condition. If this is not possible then the same method of finding the problem still applies.

Start by drilling a 4 or 5 mm holes through only one layer of the glass, 50 mm apart in a grid paten, not the material coming out of the hole and look for any trace of moisture. if wet or damp drill another alongside it till you get a dry hole, mark this with marker pen or pencil; continue this till you have established the total wet area.

To remove the layer of glass over the damp area I find a plunge router is easy to control and is quick, an alternative is an angle grinder with a thin cutting disc, rest the grinders safety guard on the glass to control the depth.

You may have to make a second cut in the wet area to remove the glass in two sections as the dry edge will be harder to remove. Try to keep the cut out section/s in one piece as you may be able to re use them later.

Next remove all the damp material, using an old alan key with the short end ground to a chisel and the long in a drill, clean out a ledge around the edge of the outer cut, check for any moisture as you go, if you find any extend the opening. It is most important that AKK DAMP material is removed.

Next, clean the remaining layer of fibreglass by first washing with Acetone then sanding, washing first will remove any contamination that will just be spread by sanding.

You should now have a clean layer of fibreglass and a ledge around the edge that has dry timber exposed.

Depending on the original material you now have a couple of options.
If you ar replacing ply.
Use a ply thin enough to bend to the required curve, this can can be thin layers laminated to the required depth as follows. Cut to shape and dry fit to ensure they will fit, drill 5 mm holes all over at 50 mm in a grid, the holes will allow air and excess clue to escape. Mix some epoxy resin (about a cup full) and mix the hardener then add one third of a cup of methylated spirits to the mix, this will thin the resin and assist penetration. Apply several coats wet on tacky (to avoid sanding between coats) to the ply sections paying particular to the edges and exposed end grain, it will soak up a lot more than the flat surface. Allow them to cure after they will take no more.

After curing give them a light sanding with a 200 grit, just to remove most of the high gloss, then clean with acetone.

Mix another batch of epoxy resin and add micro-fibres to about the thickness of peanut butter, spread a layer of this about 3 or 4 mm thick on the first sheet and press into the ho;e against the existing layer of glass, air and resin will come through the holes, repeat this till you have the required depth and place props or weights as required to ensure the curve is followed: then fill the void around the outer edge with more of the micro-fibres and resin mix. then let this cure for 24 hours. Then clean and sand as above.

The original sections cut out can now be reinstated provided they have been cleaned, sanded cleaned again and drilled as above and the edges ground to about 12 degrees to form a clean smooth wedge for glassing over. Also do this on the original remaining edge of the glass still in place.

If the original material was Balsa, you have a choice of replacing like with like, or Closed cell construction foam, the latter would be my choice. cut to shape then using s hand saw cut slots almost all the way through to allow it to form the required curve, dry fit to make sure before adding any filler the, fill the cuts with closed cell balloons or 'Q' cells and push into place wet side first, any excess will come out the ends of the cuts, prop or weight into the required position and fill the edge, after curing clean sand, clean and grind the edges off the original bit/s of glass removed to 12 degrees to provide a wedge to glass over. Also do this on the original remaining edge of the glass still in place.

I would also use epoxy resin and cloth (not chopped strand mat) to rejoin the original or replace the old material cover.

I hope this helps. Let us know how you go or if you have any further questions.

Avagoodweekend......

 

[ChasB]

Thanks, particularly to you Brian, for your replies. Feels a bit here like I'm thanking folks for sending condolences to a funeral! Man this looks bad...

I'm no expert on wood, but it's not ply and appears to be a soft wood, so that makes it balsa..?

Brian you appear to be a pro at this, so your approach would be a pro's and you wouldn't cut corners in the way I'm prepared to do. Also I'm really hoping the problem area is confined to a narrow strip. In unscrewing a number of items while re-carpeting I've not noticed wetness elsewhere, but maybe I've not been vigilant enough. I''l be looking more closely tomorrow. So first a few questions, then my tentative plan of action.

• 
  A: Is builders foam a reasonable substtitute for wood for a small area? How easy is it to finish off?
  
  B: If an area is wet but not rotten is it still doomed to rot? Is it worth attempting to dry a wet area out (though right now I don't see how without risking spreading the area of wetness!)?
  
  C: How important is it to thoroughly clean the space in-between before filling if one is using foam?
  
  D: what is a safe hole size and spacing in 3 below that wouldn't compromise strength?

And my proposed plan:

• 
  1) remove all heavy objects from deck and walk lightly till job complete!
  
  2) drill a series of test holes from beneath to find limits of rot and of wetness.
  
  3) make larger holes with circular saw type bit. Keep hold of drilled out chunks.
  
  4) scrape out bad wood
  
  5) leave to dry out while gently blowing warm air through (we're still having a last burst of summer here in the UK which should help)
  
  6) clean up to remove loose fragments
  
  7) plug up larger holes, replacing chunks from 3
  
  8) fill with foam using the smaller test holes
  
  9) fill remaining holes

How does that sound? Should have done this years ago, but I just didn't realise...

Been doing some internet research - a lot more to come I reckon. But thank God for the net! What would I have done some years back? Here's a pic of a badly rotten core (not mine) http://www.ramoak.com/yankee30/images/132.jpg Ouch. There's some interesting stuff on foam in the last post of this thread http://www.plasticclassicforum.com/viewtopic.php?f=4&t=2331 Anyone used the polyurethane glue he refers to?

 

[oldsaltoz]

QUOTE I'm no expert on wood, but it's not ply and appears to be a soft wood, so that makes it balsa..?
First a few questions, then my tentative plan of action.

A: Is builders foam a reasonable substtitute for wood for a small area? How easy is it to finish off?

No, it is not all closed cell so will soak up moisture and can turn into mush, you may also find it will not support weight applied from any direction.

B: If an area is wet but not rotten is it still doomed to rot? Is it worth attempting to dry a wet area out (though right now I don't see how without risking spreading the area of wetness!)?

Always better to remove all timber that contains any moisture

C: How important is it to thoroughly clean the space in-between before filling if one is using foam?

Critical if you don't want problems with the fibreglass skin de laminating from the core material.

D: what is a safe hole size and spacing in 3 below that wouldn't compromise strength?

The hole is not critical to carry out this repair, however using larger holes will result in more repair work so don't do it.
[/list]
And my proposed plan:

• 
  1) remove all heavy objects from deck and walk lightly till job complete!
  
  2) drill a series of test holes from beneath to find limits of rot and of wetness.
  
  3) make larger holes with circular saw type bit. Keep hold of drilled out chunks.
  See note above, nothing gained.
  
  4) scrape out bad wood Leaving only DRY material behind.
  
  5) leave to dry out while gently blowing warm air through (we're still having a last burst of summer here in the UK which should help)
  
  6) clean up to remove loose fragments
  
  7) plug up larger holes, replacing chunks from 3 see note above
  
  8) fill with foam using the smaller test holes. No, this implies using expanding foam, OK for buoyancy but not the best for structural work
  
  9) fill remaining holes. And re glass the cut away section/s after cleaning them and tapering the edges of both remaining structure and cut out/s

Hope this helps.

Avagoodweekend......

 

[srp]

If you're going to cut out large chunks of grp I can thoroughly recommend a Fein Multimaster (some pics on this page - http://corribee.org/technical/mast-beam/). Very thin saw kerf, very little mess and it doesn't get blown all over the place.
After you've finished the repair work, you'll find it useful for a million more jobs and wonder how you ever did without it. Buy the 'Top' kit as it includes all the accessories worth having.