Soft Core and Mast Step Repair

[Peter T]

This post is long. I just spent over an hour doing it only to find that I had been timed out. I will start again but will do it in small bits and add to it. Wish me luck.

On my boat, I have bad cracks in the roof around the mast step area. This indicates a soft Core in the roof area. If that's the case, then water has been in there. Where can that come from I ask. Well, here are the possibilities.
1. The bolts holding the mast step can allow water in there if not sealed correctly.
2. The hand rails have been replaced by a previous owner. If when this was done, the old mounting holes have not been sealed, water can get in there.
3. If when fitting the new hand rails, no sealer was used to do this then water can leak in there.
4 there is an electrical plug fitted to the cabin roof just behind the mast. Water can leak in there if it is not sealed correctly.
5. Any other fitting in the roof such as the hinges for the hatch or a turning block are bolted on. If not sealed there water can also get in there.
On my boat all of the above were in fact the case. This is why I bang on about the right and wrong way of doing things on a boat.
All fittings on a boat need to be fitted by the following method.
Remove the fitting, over drill the bolt holes to double the size, use Gorilla tape ( about $30 per roll at Bunnings) on the inside and fully fill the hole with epoxy. Then drill the new mounting hole through the epoxy and re fit the fitting using a good sealer like Sikaflex. Never sylastic. A lot if work? Yes, but the more you do, the easier it is. And it is VERY WORTH WHILE.
Anyway, the core in my boat was soft as butter. There are two ways of fixing it. Cut the outer skin off, replace the core and then try to re fibreglass the skin back on again. A nightmare quite frankly.
Second method is what I did, try to determine the extent of the problem by tapping the roof with a hammer. You will hear the different sound on solid core or soft Core.
Remember that if the core is soft, then the chances are that it's also wet. This is where time comes into its own.
To inject an area, first you completely cover it with the best quality masking tape you can find. Use a measuring tape and a pencil and mark out in a square pattern where you are going to drill through the outer skin.
On mine, I did the whole roof. If it is hollow in there, you can use a compressor set to a low pressure, squirt air into one of the holes and it will blow out the others. If there is water in there, you will see it exiting. If this is the case, you need to work on it often, heat inside the boat, flush air through it often and do it over a long period of time to get it dry.
Once dry, it can be injected with epoxy.
When using epoxy for this job, I use winter hardener or slow hardener to give longer working time. Also, slow setting epoxy is stronger than fast cure.
Because the roof slopes forward and down at the sides, I made up little tapered plugs from a length of thin dowel in the lathe using a file to make it tapered. Then cut them off at about 30mm long. I made a couple of dozen of them. Using them stops the epoxy just running out of the lowest holes and then all over the cabin sides and deck. I removed them after a time before the epoxy had fully set. It needs to be non fluid to remove them but care is needed not to disturb the epoxy in the core.
I used a 60ml syringe and a small mixing cup to work easier and did a section at a time. If you are unable to get the epoxy to flow, that means that the core at that point is solid. If its hollow you will have no problem injecting. While it's taking on epoxy, keep it coming. The core needs to be full.
I mixed up about 4 pumps full of epoxy each time.

Here is the tools I used
The drill size needs to be the same size that you can just get the tip of the syringe to fit it firmly.
I purchased a small set if drill stops from "Wish" on line cheap as chips and used one that fitted the drill, tightened up the grub screw so the drill just went through the top layer of gibreglass.
Once the epoxy has set, the masking tape is removed and you are left with small holes every 50mm square. I then mixed up a small amount of epoxy and thickened it with filling fairing powder to a stiff tooth paste consistency, used an epoxy stirrer stick sharpened to a blunt point to allow a small dob of filler to each hole. Where the non skid sections are, its not too important to get a perfect finish as it's rough as it is and when you paint it with the rubberised non skid paint, you won't even see it.
Where it is on smooth fibreglass, over fill the holes slightly. Once it has been sanded , undercoated with 2 pack primer and sanded and final coated you won't see any evidence of it

This is mine, yet to be primed and painted

Now, to the Mast Step.
Once I knew that I had a soft Core, I also realised that the timber in the mast step would also be rotten.
I decided to cut the top out of the mast step leaving a small area of the top of it there to fibreglass on to later.
To understand the problem, I will explain the method of construction that I found out as I went deeper and deeper into it.
To make the cabin, the outer skin would be left in the mold. The core material ( plywood) put in place, a piece of around 20mm plywood shaped to fit in the top of the mast step. These materials were placed there while the fibreglass of the outer skin was still wet so it sticks there. As well as this, there is small pieces of timber placed in each of the hand rail mounts. Then one layer of fibreglass is layer over the ply of the mast step. Then it was two pieces of 2 x 1 inch timber notched out and fitted together in the shape of a cross was fitted to the mast step on the wet one layer of glass over the ply. Then the inner skin was layer up completing the cabin molding. So, we are left with four voids in each corner of the mast step on the inside in each corner of the mast step. Also we have voids around the small timbers in each of the eight hand rail mounts. These were later drilled and filled with epoxy as well as the roof core.
When I injected the roof, I worked towards the mast step and ended up injecting quite a lot of epoxy in that region ( due to the voids described earlier).
See photos below.

After chiselling out the wet 20mm plywood

Here you can see the 2 x 1 cross pieces. They were removed.

Here you can see the inside skin where the glass had stuck to the 2 x 1. Also note you can see some of the holes where I filled the core.
I then cut out a piece of about 5 or 6 mm marine ply to form a base from which to work. This was set in thickened epoxy to avoid getting any small voids in there. I had to use the mast step mount holes from the inside skin and gradually work them up through the ply inserts I fitted to get their location spot on. Where the bolt holes are, I bored out the holes through all pieces of ply to 1 inch, filled them with epoxy, then drilled them through the first piece from the inside. I also made an aluminium mold of the bolt holes to help me as I went. Very important to get the holes spot on otherwise the mast would end up out of alignment. Filling the bored out holes with epoxy is the only way of ensuring that water never gets back into the ply again once I started on 2nd and subsequent layers of ply, I had to cut them in half to maximise the amount of ply I could get in there. As I layer in each layer, I filled all around in there with epoxy so it eventually became one solid mass. Also, the epoxy also glued each piece together.

Layer 2

Once all but 1 layers of ply were fitted, I layer up 3 layers of double biaxle woven rovings ( super strong) which was also glassed on to the inside sides of the mast step molding

Last piece in place. As each layer of ply was fitted it was filled all around with epoxy

Then 5 layers of the same woven rovings were glassed on and trimmed

Then I used fibreglass tape to lay a fey layers over the top and down the sides of the mast step. Filled and faired ready to paint.

This has been an extremely time consuming job as well as a lot of time on old knees at an awkward angle, but I can guarantee you one thing. This is now the strongest roof and mast step on any Investigator anywhere.
If you have the same problems, then don't be afraid. Anyone can do this with a little guidance. I hope I have achieved that for you.
Cheers

[Ozzie]

Thank you Peter, a very comprehensive tutorial. I am now spurred on to get my tarp back on the boat asap.

[Peter T]

Thanks Ozzie, yes mate a tarp is so much easier than what I had to do.
Cheers

[Andrew]

Thanks Peter for the detailed construction analysis, photos, and how to repair it. Always wondered what's inside the deck and how it was built.

Also thanks for the detailed epoxy method, syringing through the drilled holes. Thanks for info voids could form where the ply cores under deck fittings might rot away if the bolts were not sealed properly. My boat has some of these issues too.

About the wood plugs for stopping epoxy coming out lower holes, could some good tape, or perhaps bluetack, seal the hole instead? Your method would definitely lead to strongest most sound boat out there, and be the longest lasting.

(I've read up on "Injecta deck" a USA structural foam product. It's not cheap but can bind with wet cores they claim...any thoughts on this approach? I'm currently leaning towards your method, stronger, better, probably cheaper too) Also too scaredy-cat to go ripping the top fibreglass layer off en-masse!)

Saw a video somewhere where the yachty used a rubber mallet to tap around his deck and the sound differences told him which areas were delaminating from the core (a duller thud and sound also depends on how far from the edges etc)

[Peter T]

Hi Andrew. I know nothing about injectadeck, sorry. I must do some research on it.
As for using tape instead of plugs, I fully understand where you are coming from. However, with the process I describe, the whole area is first covered with masking tape as the first step in the process. If you start at the front, or lowest point, which I believe you should, then as the core fills, the epoxy will flow out of the lowest holes when it is trying to find its own level, just like water would. If its allowed to flow, the epoxy will not be retained in the space of the core. If you tried to use tape to stop it, then because it is already wet with epoxy, there is no tape that will stick to wet epoxy and it would just end up in a horrible wet mess of epoxy. The danger of using plugs is that if you leave them in too long, they will glue themselves in there and the last thing you would need is small broken off bits of wood as your roof surface. If this was the case, you would then have to drill that wood out afterwards. My Idea is to remove the plugs after the epoxy has started to go off when it actually stops being liquid but before it sets hard. What you don't wantbto do is to disturb the epoxy that is in the core for fear of weakening it, so care must be taken. If you find a couple of the plugs break off leaving a bit in there, you can lightly drill it out because one of the steps in the process is to go over all the holes and put a small dab of thickened epoxy in there after the re coring has been done. What I did was to get an epoxy stirring stick and shape it to nearly a point to place the dabs of thickened in there. Then I just wiped it clean with a cloth as I went. Hope this helps.
With the mast step, I just want to say, remember that the whole weight of the boat is transferred down through the mast to convert the wind power in the sails to forward motion of the boat. That's why I did not want to leave any voids at all within the mast step and why I completely filled mine to a fully solid state so that the load at that point is distributed as far and as wide as I could make it
As for ripping off the outer skin and re fitting a new core, I too would not want to go there.
Cheers Andrew, hope this is of some help. Don't hesitate to ask anything you wish.

See here, I have injected my roof, and as it is now, it has grey epoxy primer on the non skid area and the white epoxy primer on the smooth areas has yet to be done.
As you can see, you just can't see where it's been done and as I said, the whole of this area was injected and is now as solid as a rock.
Cheers

[Watto]

Peter, good to see a full dissection of the mast foot.

Remember me trying to describe it you you with glass>wood>glass>air void followed buy the cabin roof.

[Peter T]

Yes Luke, exactly. Now we all know how it was built and how to repair if necessary. Cheers mate

[Andrew]

Thanks Peter, for the extra details which explain why that's the best.
I've not used epoxy, only fibreglass before.

Injectadeck costs $300 -$430 (USD?) for the small boat kit. Has 4 cartridges and a dual cartridge gun plus tips.. https://injectadeck.com/

Would epoxy costs be similar? How about WEST system epoxy, it's got a good reputation in boatbuilding.

[Peter T]

Hi Andrew, I use West System. I find it easy to use. The cost of it completely depends on how much you buy. You can get small amounts but the problem with that is getting accurate ratio's of epoxy to hardener. I use the 4 litre packs simply because you can get pumps to fit those size containers and it's a simple thing. Same number of pumps of both parts so it depends on how much you want to mix at a time. It might be 2 pumps of epoxy and 2 pumps of hardener or 1 pump of each. It's better to mix up smaller amounts and not to have a large amount in your mixing container because if you have a larger volume of mixed epoxy in a container, then the chemical reaction generates a lot more heat and it therefore goes off much faster. If you are mixing large amounts you need to have a larger flat mixing container rather than a smaller deeper one for the heat reason so only mix the amount you can use in a relative small amount of time.
If you need to make fairly small amounts, ie less than 1 pump of each component, it's best to use a syringe to get small amounts and accuracy of ratio's at the same time.
If you want, you can just use the syringe method and buy smaller amounts of epoxy at a time. For prices on differing amounts, look it up on the net or at a marine store but because I have had quite a bit to do, I am happy to get it in the 4 to 5 litre packs.
One thing to remember is that you can get fast and slow hardener. Also, chop strand matt is not the best to use with epoxy as it does not melt the fibres of chopstrand as well as it does with double bias woven rovings. Just make sure you get epoxy friendly Matt if you are fibreglassing with epoxy. Also, you can use epoxy over polyester but not the other way around. Once you have used epoxy over polyester, then to do more in the same area later, you then need to continue using epoxy.
Epoxy is far stronger than polyester and has a muck greater adhesive property as well as it being 100% impervious to water where polyester will take in a small percentage of moisture. That's why you get osmosis with polyester and not with epoxy.
I now use epoxy for everything as it is so versatile with all its additives you can get. Glue powder and different fillers all using the standard mix of epoxy.
I hope I have helped you and not confused you with all this. Let me know if I can help further.
As for cost, 105 West System epoxy can be purchased for aprox between $35 for 50mm up to $135 for the larger ones that I use, there abouts but you also need to buy the hardeners etc on top of that. Also, obviously, the larger amount you buy, the cheaper it is per quantit might pay to read my other posts re epoxy as well. Gloves are a must as continued exposure to the skin can cause dermatitis
Cheers

[Andrew]

Many thanks Peter for all the WEST system use info,

It's probably going to save allot of "learning the hard way" dramas later on
and to know what it can or can't do, it hasn't confused rather the opposite, it's really concise

I've got a screen shot of it to print out,