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Old 14-08-2012, 12:52   #1
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Vacuum Pump Requirement for Drying Out Core-Cell

Looking for suggestions on the requirements of a 120v vacuum pump in order to attempt to dry wet coring. Looking at eBay, the Gast pumps seems to be popular, but not sure of the needed cfm, pressure, etc.

What do you call the "accumulator tank" which is needed to collect the water. One website mentions that you must use dry ice around it, so that water vapor doesn't enter the vacuum pump?

I know the customary method is to drill a series of holes into the hull from the outside & attach the vacuum tubes, but is there any reason why they couldn't be drilled from the bilge side? It seems especially with small (1/8"?) tubing, the water would still be sucked up.

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Old 14-08-2012, 13:20   #2
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Re: Vacuum pump requirement for drying out Core-Cell

I think the only effective cure is to slice the top fiberglass off, dig out the wet core, replace it and replace the fiberglass. Gotta be easier and cheaper and certainly a better fix.
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Old 14-08-2012, 18:43   #3
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Re: Vacuum pump requirement for drying out Core-Cell

How wet does Core-Cell get? Isn't it a closed cell foam? How far can water penetrate through it?

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Old 14-08-2012, 18:51   #4
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Re: Vacuum pump requirement for drying out Core-Cell

I dont know that it is really possible to get it dry enough to bond with epoxy etc filler....? humidity, condensation.... I dont think so... I had the partial coring on a hull fixed once, but the core was dry... just was not "fixed to the glass" on each side. An interesting thought occurred to me though.... if you were repairing a core that was damp, (ie: you have used high vacuum to pull the moisture out) why not inject one of the modern one part urethane glues? Three advantages: they LOVE water when curing, They expand when curing also instead of shrinking, and they are dirt cheap compared with Epoxy.... ?????
let's see... original question: I have seen two large shopvac's being used with taped on visqueen..... lower vacuum level but large volume....
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Old 15-08-2012, 05:36   #5
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Re: Vacuum pump requirement for drying out Core-Cell

The Gast pumps are good but pricey. A 5 or 6 CFM Robinair would do the job just as well. All the other parts you;ll need you can assemble from the hardware store.

This is my resin trap (white).



Nothing more than hardware store PVC sewer pipe, cap and end. The tubing is water supply line.

Although you won't need as an elaborate setup as this (for vacuum resin infusion) you can see the Robinair setup here....



A Robinair like this can be had from e-Bay for about $160.
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Old 15-08-2012, 14:10   #6
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Re: Vacuum pump requirement for drying out Core-Cell

Thanks all for your responses (so far).

Core-Cell apparently absorbs no/little water, but even with vacuum bagged construction, there seem to be many voids & "pathways". The wet area appears to be approx. 2' (down the middle of the hull) by approx. 5'. Neither the builder nor a surveyor have found the source of the water, though many of the thru-hulls weren't sealed (although the Core-Cell around them seemed dry). Also, many screws for bilge pumps, etc. were screwed thru the inner fiberglass with just some sealant, so they could have been a source. Unfortunately after those 2 items were corrected, the builder only attempted to vacuum the coring for one day, so the current water could be old or new. The 8 new holes they drilled from the bottom for the vacuum tubes could also be a source, as they were only filled with a "fiberglass putty" I believe they called it, along with a coat of barrier paint.

The coring is more than "moist"; several 3/4" holes drilled (carefully!) thru the inner fiberglass actually fill up with water. Water will continue to draw & re-fill the holes when sucking out with a shop vac.

The builder will come back for another look, but doesn't give any indication of doing what it will take to find the problem & properly dry the core. Hence, my appeal for help with the vacuum pump, etc. - I will look at ordering a Robinair pump this week & start purchasing the other parts needed.
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Old 15-08-2012, 17:52   #7
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Re: Vacuum pump requirement for drying out Core-Cell

Quote:
Originally Posted by Ortolan View Post
Thanks all for your responses (so far).

Core-Cell apparently absorbs no/little water, but even with vacuum bagged construction, there seem to be many voids & "pathways". The wet area appears to be approx. 2' (down the middle of the hull) by approx. 5'. Neither the builder nor a surveyor have found the source of the water, though many of the thru-hulls weren't sealed (although the Core-Cell around them seemed dry). Also, many screws for bilge pumps, etc. were screwed thru the inner fiberglass with just some sealant, so they could have been a source. Unfortunately after those 2 items were corrected, the builder only attempted to vacuum the coring for one day, so the current water could be old or new. The 8 new holes they drilled from the bottom for the vacuum tubes could also be a source, as they were only filled with a "fiberglass putty" I believe they called it, along with a coat of barrier paint.

The coring is more than "moist"; several 3/4" holes drilled (carefully!) thru the inner fiberglass actually fill up with water. Water will continue to draw & re-fill the holes when sucking out with a shop vac.

The builder will come back for another look, but doesn't give any indication of doing what it will take to find the problem & properly dry the core. Hence, my appeal for help with the vacuum pump, etc. - I will look at ordering a Robinair pump this week & start purchasing the other parts needed.

Core Cell is not a closed cell foam core material, it is more similar to Hexcell. It is mostly air and therefore can hold truly large quantities of water if compromised. On the other hand it is the only core material which can be quickly and easily dried in this fashion. Make sure to have air intake holes on the high side of the wet area and vacuum holes at the very bottom corner of the cored area to get all the water. Fairly simple repair. I use 5 gallon paint buckets for my resin/water trap, they seal great and are dirt cheap.
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Old 15-08-2012, 19:44   #8
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Re: Vacuum pump requirement for drying out Core-Cell

so.. just curious... after vacuum treatment.... is the core really dry, or just "no standing water"? does anyone know? ever cut a panel out after vacuum? or is the epoxy just filling the gaps but not bonding to wet core...?
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Old 16-08-2012, 10:07   #9
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

"What epoxy? Epoxy injecting core cell would be silly. Google hex cell to see what it looks like, it's a honeycomb core. You can get it surprisingly dry on the moisture meter usually."


I guess I'm just trying to understand what is being done... so you just suck the water out and forget it... no injecting epoxy or etc...? Seems like if the core was bonded to the fiberglass , the water couldnt migrate...? So if it's migrating it must be unbonded...?
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Old 16-08-2012, 10:20   #10
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

Quote:
Originally Posted by Cheechako View Post
I guess I'm just trying to understand what is being done... so you just suck the water out and forget it... no injecting epoxy or etc...? Seems like if the core was bonded to the fiberglass , the water couldnt migrate...? So if it's migrating it must be unbonded...?
If you pull a vacuum on the panels, the water will evaporate and be removed. I think the idea here is to remove the mass quantities of water and then dry out the core by pulling a vacuum on it, just like removing the moisture from an A/C system.
I could be wrong though
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Old 16-08-2012, 20:04   #11
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

I had thought Core-Cell was closed cell foam & unable to absorb water? But in any case, as I understand it, the Core-Cell used on curved surfaces comes micro-kerfed on both sides in order to bend to the hull shape. Here's where vacuum bagging comes in - to fill the micro-kerfs - in theory. In my case, they don't seem to be filled everywhere & I even have (at least one) joint between the pieces of Core-Cell with nearly a 3/16" gap extending several inches - with no resin at all. So, hopefully the Core-Cell is bonded to the fiberglass, but water is somewhat free to "roam around". This makes finding the source tougher too, as the water could be entering near the waterline, for example, then traveling & settling low in the hull.

I hope to find the source(s), then dry the coring as much as possible during a 2 - 3 week period (not 1 day as the builder did). Last year, after the 1 day of drying, my test holes thru the inner hull did seem to dry up somewhat - at least no standing water, but I epoxyed them within a couple of days so I don't know how long they stayed dry.

It may sound paranoid, but I am now ... I was thinking of leaving each inner hull with several threaded "inspection ports" so I can check for water intrusion without drilling holes. They would be epoxyed in & have plugs with thread sealant to avoid any bilge water from entering ... If my vacuuming from the inside of the hull is successful, I could easily perform any test or final drying in future haul-outs.
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Old 17-08-2012, 10:12   #12
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

Kinda begs the question... why not leave a multitude of holes on the inside and just leave them open...?...?
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Old 17-08-2012, 14:32   #13
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

Quote:
Originally Posted by Ortolan View Post
I had thought Core-Cell was closed cell foam & unable to absorb water? But in any case, as I understand it, the Core-Cell used on curved surfaces comes micro-kerfed on both sides in order to bend to the hull shape. Here's where vacuum bagging comes in - to fill the micro-kerfs - in theory. In my case, they don't seem to be filled everywhere & I even have (at least one) joint between the pieces of Core-Cell with nearly a 3/16" gap extending several inches - with no resin at all. So, hopefully the Core-Cell is bonded to the fiberglass, but water is somewhat free to "roam around". This makes finding the source tougher too, as the water could be entering near the waterline, for example, then traveling & settling low in the hull.

I hope to find the source(s), then dry the coring as much as possible during a 2 - 3 week period (not 1 day as the builder did). Last year, after the 1 day of drying, my test holes thru the inner hull did seem to dry up somewhat - at least no standing water, but I epoxyed them within a couple of days so I don't know how long they stayed dry.

It may sound paranoid, but I am now ... I was thinking of leaving each inner hull with several threaded "inspection ports" so I can check for water intrusion without drilling holes. They would be epoxyed in & have plugs with thread sealant to avoid any bilge water from entering ... If my vacuuming from the inside of the hull is successful, I could easily perform any test or final drying in future haul-outs.
Sorry I did some looking and I was confused as to your core product, it is not similar to hex cell at all but is closed cell like divinicell et al. The only way you will get acceptable moisture meter readings on this product will be to find a yard with a hotvac to dry it, or to remove and replace affected coring. You can also build a sort of home-made hotvac, if you are interested ask away. What you are considering already is half way there equipment wise. The basic idea is that the higher the vacuum you can pull on the area in question, the lower the boiling point of the water becomes. It is easy to pull enough vac to get the boiling point down to about 160-170F, at which point the water vaporizes and is removed through the vacuum hose. Instead of inspection ports consider buying a quality moisture meter, it will be cheaper and much more effective. Anyone who owns a cored boat should have one anyway.
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Old 18-08-2012, 08:16   #14
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

Yes, would be interested in making a hotvac type system. I already have a moisture meter which works quite well (especially using as David Pascoe recommends - from the inside of the hull). I was thinking of the inspection ports as I could/will probably have to continue the vacuum drying process multiple years, especially if I can't track down the source.

What is the proper method of sealing holes thru the hull on a cored boat? On my holes from the inside of the bilge, I have used a dremel to remove the coring from & around the hole, so that the filled epoxy has a larger contact area. A concern are the holes the builder drilled from the exterior for the vacuuming - he used "fiberglass putty?". There is also an un-used thru-hull he patched - not sure what he used there.

I'm aware of the patching method for solid fiberglass hull, tapering the area back a ways, layers of fiberglass cloth, etc. You can't really do that on a cored hull, as the outside layer is thin (- 1/4"). What is the proper method?
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Old 18-08-2012, 10:20   #15
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

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Originally Posted by Ortolan View Post
Yes, would be interested in making a hotvac type system. I already have a moisture meter which works quite well (especially using as David Pascoe recommends - from the inside of the hull). I was thinking of the inspection ports as I could/will probably have to continue the vacuum drying process multiple years, especially if I can't track down the source.

What is the proper method of sealing holes thru the hull on a cored boat? On my holes from the inside of the bilge, I have used a dremel to remove the coring from & around the hole, so that the filled epoxy has a larger contact area. A concern are the holes the builder drilled from the exterior for the vacuuming - he used "fiberglass putty?". There is also an un-used thru-hull he patched - not sure what he used there.

I'm aware of the patching method for solid fiberglass hull, tapering the area back a ways, layers of fiberglass cloth, etc. You can't really do that on a cored hull, as the outside layer is thin (- 1/4"). What is the proper method?
Oh, you can definitely grind and glass an exterior skin no problem. Any competent laminator should be able to knock that out for you in no time, 1/4" is actually plenty of meat. Just using filler on holes in a cored hull is unacceptable, make sure they get repaired properly.
Removing the core and filling with epoxy around all penetrations is just basics. I like a router bit on a cordless for this, does it super fast and clean.
If you were just using vacuum you probably would have to dry for multiple years. So let's talk home made hotvac. A commercial hotvac could dry the core in an area 2' by 5' in a couple of days, that is the size of one large pad. Our machine can run four large pads at once. The earliest versions were of course home made contraptions, and you can do the same for fairly cheap, though of course it will not work as well as a commercial model.
You need a vacuum pump, sucker feet, a vacuum gauge, bag film, 1/4" excelon tubing, a little bleeder material, a laser thermometer, and two or three electric blankets. Do it from the inside if there is enough access and it's not too much of a pain, outside would be easier but then you have to finish the holes you will drill. Drill a pattern of holes through whichever skin you are working on, for a patch that size you only need a dozen or so. Tape the electric blankets over the area in question, making sure to put the little wire fitting in the blanket that gets hot on with something underneath it or it may put a burn mark on your hull. Butyl tape the bag film over the blankets with plenty of pleats very carefully so that there are no leaks at all. If you have never vacuum bagged this will take some practice, unless the area in question is fairly flat. Make sure to use high temp bag film, not just any old plastic. Then install the sucker feet, try two equidistant on a patch this size. Put them on a bleeder pad to absorb any initial slug of water. Install your gauge in the bag. Then hook up tubing and fire up the pump. Make sure your bag is good and you are pulling good vacuum. I have seen a few extreme cases where a good vacuum couldn't be gotten because the entire core material was very heavily voided and connected to a hole somewhere that couldn't be found, probably sucking air on the other side of the boat somewhere. When you have a good bag, fire up the electric blankets. Carefully monitor the whole thing with the laser thermometer. You want to get it up to about 170F, but never more than 190-200, as you may damage the laminate at high temps (this really should require temps in excess of 250 but margin of error is good). Look carefully for hot spots, especially in the blanket wiring. Make sure the blankets are on a good breaker, if the initial water slug is big enough and they get wet they may short out. I think that covers it, run this setup for a few days to a week and you should have very dry core. The alternative is to remove saturated core and replace it. Depends on the area in question which way us more efficient. Ask away if I've missed anything obvious...
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