Refrigeration vacuum pump for drying out GRP

Discussion in 'Fiberglass and Composite Boat Building' started by WHumphreys, Jul 30, 2009.

  1. WHumphreys
    Joined: Jul 2009
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    WHumphreys Junior Member

    I was reading this on another forom looking for something un-related

    "Hi Buzz!
    Among the MANY things I have done with my E-37 over the 15 years I have lived aboard was to treat the BLISTERS! (Also I am a marine supply dealer, so have loads of info on epoxies, etc.) The bad news is that gouging out blisters, fairing them with epoxy, etc, will not solve the problem. The blisters indicate that your hull fiberglas roving is WET, saturated with water, which is collecting in air or solvent pockets and causing blisters. If you grind them out and refill them, you will only have to do it again next year, as more of the little ******** will pop up elsewhere as long as there is water in your glass. What you really should do is peel the hull and dry it out. The good news is that a friend of mine, an engineer, and I have come up with a great way to do this. Peel off the gelcoat and VACUUM BAG THE HULL! This can be done with a refrigeration vacuum pump (cost $200 or so) available at any commercial refrigeration supply house, and some plastic sheeting and cheap towels and duct tape all available at the local department store, and you can dry the whole hull out in 2-3 days instead of months and months. You can even re-sell the pump afterwards...I broke out even on mine.

    As far as barrier coats, if you barrier coat the hull WITHOUT drying it out, you will only compound the problem by trapping moisture IN the glass. I Learned that the hard way, believe me. 6 coats of Interprotect 2000 had to be REMOVED as they had trapped the moisture inside and made the blistering WORSE! West System is a fine product, but it is very expensive. Gougeon Bros does NOT manufacture it. It is made by Mobil or Shell or one of those major oil companies, as is almost all epoxy, and really is no better than any other epoxy for a barrier, and is more costly. Gougeon is kinda like the Frank Perdue of epoxy. If you want a really good material, try MAS EPOXY, from Phoenix Resins in New Jersey. West Sysyem was originally designed for making wind generator blades in Minnesota, and was never actually intended for use in the tropics...it can't handle heat well. MAS is stronger, less viscous, and the hardening speed can be "tuned" to your particular conditions, and it takes heat much better. And its more waterproof. Anmd less expensive...... go to www.masepoxies.com

    We vacuum bagged my hull here at Island Marine and got the moisture meter readings from 7's and 8's down to 2's and 3's in 48 hours...when the vacuum is at almost 30", the boiling point of water is something like 60 degrees BELOW ZERO, and it literally BOILED out of the hull!

    "

    Just wondered if anybody had tried this the theory does seem sound.
     
  2. WHumphreys
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    WHumphreys Junior Member

    I have spoke to a refrigeration and air conditioning friend of mine and he thinks it would work as well.


    Effects Of Pressure and Temperature on the Boiling Points of Water

    A high vacuum pump is capable of removing all moisture from a hermetic system by reducing internal system pressures to the boiling point of water at normal temperatures. For those being introduced here to high vacuum work, it should be stated that a vacuum pump does not "suck out" the liquid moisture, but rather causes it to boil in to a vapor state which can be harmlessly removed from the system and exhausted through the vacuum pump.

    The planet Earth is surrounded by matter in a gaseous state composed of about 78% nitrogen, 31% oxygen and 1% a mix of rare gases. Together they form our atmosphere, which extends approximately 600 miles above the earth and is held to the earth by gravity. Being a gas, the atmosphere has weight, and that weight is measured, as in any fluid whether liquid or gas, in pounds per square inch (psi).

    If you were to take a square inch column of the air extending six hundred miles above the earth, its weight and pressure exerted on the earth at sea level would be 14.7 lbs. This is called atmospheric pressure . Any pressure above atmospheric pressure is referred to as gauge pressure. Pressures below are referred to as vacuum.

    This same square inch column of air exerting 14.7 psi can support a one-inch square column of mercury (Hg) 29.92 inches high. This concept can best be understood by comparing it to a teeter-totter.

    When a one square inch column of Hg 29.92" high is placed on one end of the teeter-totter, and a 14.7 lb weight on the other end, the board will be balanced.

    Atmospheric pressure decreases at higher elevations. As stated, 600 miles of atmosphere at sea level is equivalent to 14.7 psi and/or 29.92 inch column of mercury (Hg). Going above sea level, to the summit of Mt. Whitney, for example, eliminates some of the 600 miles of atmosphere and, consequently, some of the pressure.

    Atmospheric pressure, therefore, governs the boiling point of water. At sea level, where atmospheric pressure is 14.7 psi (29.92" Hg), water boils at 212° F, but on Mt. Whitney, where atmospheric pressure is 8.32 psi (16.9: Hg), water boils at 184° F. The lower the atmospheric pressure is, the lower the boiling point of water. Therefore, if we can significantly reduce the atmospheric pressure inside a sealed refrigerant system, we can vaporize (or boil) moisture at even –90° F. This principle is illustrated in the chart below.

    Three ways exist to eliminate moisture from a refrigerant system by the boiling process:

    1. Transport the system to a higher elevation where the ambient temperature is sufficient to boil water at the existing psi.
    2. Apply heat to the system causing the moisture to boil.
    3. Employ a high vacuum pump to reduce the pressure and boiling point of water.

    The first two choices are impractical. Thus, a high vacuum pump is an essential aid to every service technician.
     

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  3. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    I have never heard of this, but I would love to know more abount the idea. Anyone have some thoughts?

    Edit: There is apparently a company named HotVac that makes a system to do exacally this. http://www.hotvac.com/

    While it looks impressive I still have my doubts. I am really curious if the vacuum really has any effect on what is occuring inside the panel, or if it just works on the top couple of layers. It wouldn't be hard to test, but I don't have any vacuum equipment, so here is an idea I have if someone could try it out I would appreciate it.

    Build two vacuum chambes seperated by a mock up piece of laminate with the exterior of the laminate bagged to prevent leakage. Then pull a vacuum on one side and measure if there is an appreciable drop in pressure in the second chamber. If the pressure in the second chamber drops then we know that the vaccum is pulling through the laminate, if not then it would be interesting to test thinner and thinner pieces until it is determined what the thickest layer of glass would be that the vacuum can pull through.
     
  4. WHumphreys
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    WHumphreys Junior Member

    As long as the moisture can escape and isnt sealed in I dont see why it wouldnt work. The vacuum pumps are normally used to remove all moisture from air conditioning systems.

    Ive have heard of the hotvac system but it isnt cheap. But surrounding your boat with what is basically a plastic bag and hiring or buying one of these pumps the cost is minimal.

    I suppose an easy test would be to take a small 1 meter ish square of osmosis ridden very wet GRP, remove the gelcoat, test the moisture content, wrap it in a sealed plastic and attach a vacuum pump. 48 hours later see what the moisture content of the grp is.
     
  5. WHumphreys
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    WHumphreys Junior Member

    I contacted the guy who made the original post and this is what he kindly responded.

    'Ahoy!
    yes, this address is still good.
    Essentially you need to dry the hull in sections, between the jackstands. Note that vacuum-bagging will NOT work if the gelcoat is still on the boat...it needs to be either peeled off or ground off first. Because of the jackstands, you need to do the boat in sections. You will need clean clear plastic sheeting (drop cloth type as sold in most hardware store paint departments ) with NO holes in it. lots of duct tape, some small-diameter clothesline-type rope, toweling or thick cloth, a small amount of weatherstripping "clay", and your vacuum pump. You can buy these pumps from any refrigeration supply company. CFM does not matter much, you just need to be able to draw down almost a total vacuum, 29 1/2" or more.
    Tape the rope to the hull in a zig-zag pattern, and then tape the toweling over the area you want to do. This will provide a "route" for the water vapor to get from the hull to the pump.
    Then tape the plastic sheet to the hull, after first cutting it to fit slightly larger than the towel-covered area. You need to seal ALL the edges all the way around. 3-M Duct tape is the best for this. Do NOT try to use masking tape or anything like that. This part is a big pain in the butt, as things want to fall off the hull, so you need to work fast, and preferably with some help.
    Cut a small hole in the plastic sheeting, where there is a rope passing under it, and insert the vacuum tube, taping it in place, and seal the hole around the tube with the weatherstripping. Then turn the pump on. The vacuum should quickly "plaster" the plastic to the hull, and you should see the vacuum guage on the pump start to rise. If it does not go high enough, you probably have a small leak somewhere, which you can fix without turning the pump off.
    Once you have hit 28-29" of vacuum, you should see water vapor start to come from the pump exhaust. This is water that was in your hull. At 29" of vacuum, the boiling point of water is 76 degrees F., so it's better if you can draw down 29 1/2" or more. Obviously you want to do this on a hot day if possible.
    Leave the pump running for at least 48 hours on each section. You will have to experiment with that to determine how fast your hull is drying. Once the moisture reading is below 3, you can go ahead and barrier-coat.
    After you remove the vacuum-bagging, rinse the hull off with fresh water (don't worry, it won't soak in!) and then wipe it down with acetone.
    We did our boat in 6 sections, so it took 12 days to dry out a 37' boat, and I saved a lot of "layup" time and money.
    Hope this is helpful.!!
    Cap'n Mike Miller
    S/V Seagull, E-37 #353"
     
  6. Stumble
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    Stumble Senior Member

    Sounds similar to what HotVac is doing, except they are using heating pads to both accellerate the drying proces and to act as a poor mans postcuring procedure for the hull itself.

    I still have doubts about the ability of the vacuum to effect what is going deep in the hull, and since I don't trust moisture meters....
     
  7. marshmat
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    marshmat Senior Member

    It certainly sounds like an avenue worthy of further exploration. The concept appears to be sound.

    I would advise against using an HVAC pump designed for depressurizing refrigeration loops. Many of these units are only rated for short duty cycles (<30min), and some will seize or burn up if run for hours on end; they're not worth the hassle. Continuous-duty pumps are readily available for only very slightly more money, and many will easily last for 40 years or more before needing rebuilding.

    The proposed procedure is not likely to restore the hull to its full original strength, but does sound like it should get it dry enough for a protection coat to work properly.
     
  8. Stumble
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    Stumble Senior Member

    Anyone happen to have a vacuum infusion rig they could run some tests with? I really would love to get some answers to this since I am looking at hauling my boat to dry at the end of the season.
     
  9. Ilan Voyager
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    Ilan Voyager Senior Member

    The concept is very interesting, and it is scientifically sound. Worth a trial.

    I agree with Marshmatt that a fridge pump is not a good idea; it's not rated for permanent use. It won't survive.

    I have used and made a lot a vacuum pumps and I suggests 2 possibilities of poor man vacuum pumps;

    - The beefy air conditioning pump for big car like the old Ram Charger. That works with a common industrial electric engine and can be found in a junkyard. If you take care of the oil it's very strong.

    - The big vacuum pump for milking station, the thick thing made of iron weighing a solid 50 pounds. Easy to find used at very low price in a farm. Very easy to maintain and fix. I made one in 1986 for my former shipyard and is always running after several thousands hours 23 years later. It looks like a Mad Max car, not very fancy but very useful. Not a very high vacuum but a big volume.
     
  10. apex1

    apex1 Guest

    I fully concur Ilan and like to add:
    Stumble must not doubt that the treatment does´nt go deep enough. Due to the fact that a gas is evaporated and not water (with its much larger molecules), you should get out all water that found it´s way in!
    The disadvantage of any other method was (is), that water molecules trapped in the laminate formed a chemical cocktail with the resin and glass treatment, often too large to find its way out again, even when the surface was opened.

    Regards
    Richard
     
  11. Stumble
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    Stumble Senior Member

    Apex,

    I understand what you are saying, and while I think it should work, in the back of my head I keep thinking that it taks years for this volume of moisture to collect through osmosis, it typically takes months if not a year to really dry a hull that is badly saturated, and this system is claiming to do the same job in about 24 hours (HotVac uses 2 pads for the boat that are slid down the hull once a day).

    The trick as I see it is that I could imagin that at the surface of the hull you will of course get whatever pressure your pump can lower the area too. However this will not be the case 5 inches deep into the hull (rediculously thick but I am using it for the example), as you penetrate deeper and deeper into the hull the vacuum pressure will have to decrease which will of course slow the effect of water boiling off. My question is how quickly will this occur?

    If you loose an inch of pressure for every layer of glass then it may not really be that good of a system, even though it will do an extrodinary job drying out the surface. If the pressure stays constant all the way through then the hull is acting like a permiable membrane and you could never get a vacuum in the first place.

    I have to assume that the real world is somewhere between these two extremes, so in part I am wondering how quickly the vacuum will migrate through the hull as it draws the water, and hopefully uncured resin pockets, out of the hull structure.
     
  12. fiberglass jack
    Joined: Dec 2005
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    fiberglass jack Senior Member

    I have a friend who has the hot vac system here in canda and it does work and work good,, after having a good look at the system working on a boat hull i tryed to rig a system myself and had good results heres what i did, took a couple of old wool blankets and duct taped them on the area of the hull i wanted to dry then taped a electric blanket over them the wool blankets act as a absorber,, then i used vac bagging tape over the piremeter and place some plastic film over the area,, i should also say that i also had some spiral tubing runing through the wool blankets as well, i used my vac pump the area was reading over 35% on my meter the max after 8 hours i had readings of 20 12 hours the reading was 15 after 24 hours i had the fiberglass down to 8% what i think that was the key was the electric blanket just a vac itself i dont think would cut it
     
  13. apex1

    apex1 Guest

    I think we have to wait until one of our professional boat restorers (PAR ?), gets his hands on that and tests a soaked layup from both sides. (first only one of course).

    Did I mention PAR ?
     
  14. Stumble
    Joined: Oct 2008
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    Location: New Orleans

    Stumble Senior Member

    Ya, where is Par when you need someone to do some thankless shop work for free that will only allow us to continue debating endlesly to no effect? :D:D:D
     

  15. apex1

    apex1 Guest

    what I say! Always just round the corner when we do´nt need him, but for some little field testing for free too lazy.:D
     
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