Any tips on using Coremat?

[pblanc]

If memory serves, a prior thread indicated that Muskrat, Alan Gage, and perhaps some others had some experience using Lantor Coremat. I am currently attempting to apply the thinnest variety of Coremat (1.4mm) to rebuild the bottom of a canoe and applied the first of three pieces yesterday. I would welcome any suggestions for its use from those who have used it, or similar microsphere-embedded, non-woven polyester core materials such as Spherocore.

In my application, the Coremat will be sandwiched between two layers of 4 ounce/square yard S-2 glass cut on different biases. I am working alone and the Coremat pieces are relatively large, 1 meter in length by up to 36 inches in maximal width. I am using West Systems epoxy (105/206). I do not feel it is possible to pre-saturate the Coremat prior to laying it in without creating a big mess, so what I did with the first piece was to apply a coat of epoxy, lay down the Coremat, and continue applying epoxy to the surface with a squeege until it seemed adequately saturated, then rolling it thoroughly with a grooved aluminum roller. I had hoped that this application method would be adequate due to the thinness of the material I am using.

I expected resin consumption to be considerable but it seemed to be a bit greater than I anticipated and I am still not entirely sure I completely saturated it, and I think I might have over-rolled it a bit given that it is somewhat compressible. Any suggestions regarding epoxy application and how to judge adequate resin saturation would be most welcome.

 

[Alan Gage]

No tips here, I've never use anything like it. But I am interested to hear what you learn from others and from personal experience.

Good luck!

Alan

 

[charlie wilson]

Bell used Coremat to build bottom thickness in their white/gold laminate, but with VE resin. 'Always an issue re resin draining out and the dang stuff seemed to kick hot and flatten the bottoms somewhat. But, like you, we rolled a splash of resin out, dropped the Coremat on top, rolled in more resin, then covered it with a Kevlar diagonal diamond and Kev inner blanket. The hulls were appropriate to their price point; rugged and reasonably light.

 

[Guest]

In my application, the Coremat will be sandwiched between two layers of 4 ounce/square yard S-2 glass cut on different biases. I am working alone and the Coremat pieces are relatively large, 1 meter in length by up to 36 inches in maximal width. I am using West Systems epoxy (105/206). I do not feel it is possible to pre-saturate the Coremat prior to laying it in without creating a big mess, so what I did with the first piece was to apply a coat of epoxy, lay down the Coremat, and continue applying epoxy to the surface with a squeege until it seemed adequately saturated, then rolling it thoroughly with a grooved aluminum roller.

Must be the Mistral with the rotted balsa core.

Pete, I give you mad props for even trying to resurrect the Mistral and fix that core issue. If successful your materials and process will be helpful to other early generation Mistral owners, and in any case the experiment should be a learning experience with Coremat.

How will the glass and Coremat be affixed to the notoriously hard to adhere Twintex hull?

 

[pblanc]

Yes, Mike. It is indeed that Satanic vessel.

After removing the interior layer of Twin-tex material that had covered the core in its entirety the hull bottom looked like the first photo:



Much of the balsa shown there that looks as if it was still semi-intact was waterlogged and the whole core was beyond savage, IMO. Besides, even if repaired it would still have been susceptible to rot.

After removing all the remaining core and cleaning up all the fragments, the hull bottom was given a thorough sanding and cleaned. I then bonded a series of fiberglass tapes to the hull bottom transversely and longitudinally, some of which will be visible in the next photo. This was done using G Flex epoxy after flame oxidation with a propane torch. Although the fiberglass tape strips restored only minimal stiffness to the hull bottom, it was a relatively inexpensive way to test the ability to bond glass to Twin-tex using G Flex. Some of these tape strips have now been in place more than a year and show no signs of delamination thus far. I have mechanically flexed the hull bottom a few thousand times to encourage them to break loose if they were going to.

I then filled in all the quadrangles between the tape strips with a layer of 4 ounce S-2 glass, again using G Flex after flame oxidation. After an additional waiting period I am now putting in the Coremat which will then be covered with a second layer of 4 oz S-2 glass cut on the bias. If that appears successful I will cover it with a layer of 5.5 oz , 2 x 2 twill weave carbon fiber.

The second photo shows the first two pieces of Coremat in with one more to go. You can see the outline of the fiberglass tape strips as well as the first layer of S-2 glass on the portion of the hull bottom that has not yet been covered with Coremat:


Conventional West System epoxy (105/206) is being used for the Coremat and all successive layers except for a 2 inch wide strip of fiberglass tape which I intend to use to cover and reinforce the seam between the rebuilt core and the adjacent Twin-tex hull. I will again use G Flex for that.

 

[Guest]

Yes, Mike. It is indeed that Satanic vessel.

After removing the interior layer of Twin-tex material that had covered the core in its entirety the hull bottom looked like the first photo


Much of the balsa shown there that looks as if it was still semi-intact was waterlogged and the whole core was beyond savage, IMO. Besides, even if repaired it would still have been susceptible to rot.

That bottom reveal reminds me of a bad parquet floor in a Filipino whorehouse. Um, er, I mean, gee it looks strange.

I then bonded a series of fiberglass tapes to the hull bottom transversely and longitudinally, some of which will be visible in the next photo. This was done using G Flex epoxy after flame oxidation with a propane torch. Although the fiberglass tape strips restored only minimal stiffness to the hull bottom, it was a relatively inexpensive way to test the ability to bond glass to Twin-tex using G Flex.

If G/flex and flame treatment will bond to Twintex that is huge. I’ve seen some Twintex hulls under repair or outfitting at BMO, but those all involved vacuum bagging and unknown adhesives.

Some of these tape strips have now been in place more than a year and show no signs of delamination thus far. I have mechanically flexed the hull bottom a few thousand times to encourage them to break loose if they were going to.

I like the “few thousand times”. And the “more than a year” as well. Slacker.

I then filled in all the quadrangles between the tape strips with a layer of 4 ounce S-2 glass, again using G Flex after flame oxidation. After an additional waiting period I am now putting in the Coremat which will then be covered with a second layer of 4 oz S-2 glass cut on the bias. If that appears successful I will cover it with a layer of 5.5 oz , 2 x 2 twill weave carbon fiber.



Conventional West System epoxy (105/206) is being used for the Coremat and all successive layers except for a 2 inch wide strip of fiberglass tape which I intend to use to cover and reinforce the seam between the rebuilt core and the adjacent Twin-tex hull. I will again use G Flex for that

Dayum. I recall your self-deprecatory description of “bullheadedness” in tackling repairs to the Satanic Mistral. Methinks you just enjoy a boatwork challenge, and if it all works I think you have the perfect moniker for the resurrected Mistral.

 

[pblanc]

The Esquif Zephyr is a whitewater solo canoe that is also made out of Twin-tex. Many cracked. I am aware of a few people who did repairs using G Flex and various fabrics. I am not entirely sure why it works or if it always works. I get the impression that thorough sanding of the surface is critical to getting a bond. It may be that the fiberglass fibers in Twin-tex need to be exposed in the polyolefin matrix material to allow the epoxy to bond to those.

 

[Jim Dodd]

Pete, just thinking out load, and wondering if you gave cedar strips a thought to replace the parquet Balsa ?

Jim

 

[Canotrouge]

I'm sure you know Shawn Alexander from Bomber bag/Fall Line canoe, I'm sure he could help you with that, he is some what of a genius at fixing boats!!

 

[pblanc]

Jim, I did consider using some other type epoxy-coated wood as a replacement core material but I would have had the same concerns regarding the adequacy of the bond of the wood to the underlying Twin-tex of the hull bottom. Obviously, the bond of that first layer is going to be critical to the short and long term durability of the entire repair. My thoughts were it would be a lot cheaper and easier to use fiberglass as a first layer rather than a fitted wood core which would have entailed considerably more effort, if in fact the whole thing was going to pop off. I also considered using wood ribs like hoops extending up to the gunwale line to hold down the rebuilt core and add additional bottom stiffness.

Canotrouge, I do know Shawn casually. Yes, he does appear to have a genius for canoe repair. A couple of years ago I was looking at a Zephyr he had patched and was selling. I briefly spoke with him about it and he told me he had used G Flex but I do not recall if we discussed the surface prep. More recently I saw a photo of a Zephyr on youtube which had been patched by Shawn with three large pieces of Kevlar applied to the hull exterior. Only one photo but the repair appeared to be holding and the boat had changed hands.

I sent a FB message to Shawn regarding the repair of that boat, but have not heard back from him as yet. Also spoke last year to the main canoe repair guy at Blue Mountain Outfitters in PA. The only experience they had with Twin-tex repair was using the thermal/vacuum bag repair device provided by Esquif. If I understand correctly, that basically melts a patch of Twin-tex material onto and into the damaged hull under vacuum. It would have been of no help for what I am doing.

 

[Muskrat]

Sorry I'm late to the party. I use coremat for ribs so I don't usually work with very large pieces. What you're doing already seems reasonable. The stuff does soak up more resin than you'd think. What I have always done is lay all my coremat ribs out on clear plastic drop cloth. Then I spread the resin on nice and thick. Let it soak in for a while and then squeegee around until its evenly distributed and squeeze out any extra. You could do the same by wetting it out first on plastic and then placing it in the bottom of the hull. I feel like doing it that way makes it easier to not use any extra resin since the coremat is already so thirsty.

 

[pblanc]

Thanks for the advice, Muskrat.

I already have the Coremat in at this point and it seems to have served its intended purpose. Since I was working with thin material (1.4mm thick) I think I was able to saturate it by first applying a coat of epoxy to the hull and then wetting it out from the top surface. But it would have been faster and easier had I been able to pre-saturate the material by applying epoxy to both sides on a plastic covered table before laying it in. I think for thicker material one would almost have to do this.

I didn't feel I could manage this working alone and using fairly big pieces of up to around 1 square meter. An option would have been to lay the material in, then turn half of it back on itself to apply epoxy to the bottom surface before turning it back down and applying more to the top surface. If I had it to do over again, that is what I would do.

I found the Coremat fairly easy to work with otherwise. It cuts very easily and conforms to shapes well and pieces can be butt jointed together fairly nicely. The material I bought was 1 meter in length (about 39 1/3") and I needed pieces 40 inches in length and I was able to stretch it a bit. As the material was stretched it tended to want to retract back until the epoxy started to get tacky but then it held well. It seemed to function very well as a print blocker. I think it is possible to compress this material by overworking it with a spatula or roller. The Coremat Xi is not recommended for vacuum application for this reason. I found that a grooved aluminum roller was nearly indispensable for working epoxy through the material and getting out air bubbles.

My only complaint is the substantial resin consumption. The 1.4 mm thick Coremat sandwiched between two layers of 4 oz/sq yd S glass has provided and impressive amount of stiffness to the hull bottom I am rebuilding.