Need Advice re Blister Re-lamination

[Bob Pitt]

I need the experts’ advice before I spend a lot of time and bucks and find that I almost got it right…

My ’72 B31, one that saw years of hard service as a VA Marine Police boat, developed extensive blisters and some delamination; the Commonwealth previously patched some blisters but had not solved the problem.

Approximately 1/6” or about 4mm of laminate has now been peeled from the original bottom which is only about 9mm thick (caliper readings at shaft logs and thru hulls) – this is a much “lighter” layup than some of the older B31s. After drying for a couple of years aided by vacuum bagging, it may now be close to the time to restore the bottom laminate with additional layers.

The hull is upside down to facilitate the work. I’ll clean off the residue by scrubbing with detergent and thoroughly flushing a couple of times, then ensure it’s dried before proceeding to re-glassing. The plan is to first fill the larger divots with glass/epoxy layers and smaller shallow depressions with filler (applying a “wetting” coat of epoxy first in hopes that capillary action will pull it beyond the actual depression border). MAS Low Viscosity epoxy resin will be used for this and to apply three layers of biaxial fabric with mat. Here are my questions:

1. Recommended filler/fairing compound to use? Alwfair/MAS w colloidal silica? (Yard suggests Alwfair, I prefer latter)
2. Best fabric orientation, lengthwise or widthwise ? (alternate layers as lengthwise/ widthwise/lengthwise? )
3. Suggested fabrics for the 3 layers? (Yard suggests 1208 biaxial; given the little thickness left, I think it should be 1708 biaxial – actually, I’d think that 1708/1808/1708 might be optimal since the 1708 is 45/45 and the 1808 is 0/90. Would the 1808’s axis be a worthwhile improvement to cover all directions? Would it be worthwhile to wrestle with 2408 biaxial as the first layer – the strakes might be a problem?
4. How far should the new laminate be carried up the hull? Cummins 6BTAs will be installed, and will lower the waterline but I’m guessing that it would still be not more than 1” above the chine at the stern, if that – stop at the chine?
5. Follow the 3 layer epoxy laminate with Interprotect 2000E epoxy barrier coat? (Other than their mica microplates, and a possible formulation difference, this sounds questionable to me – makes sense to put 10+ mils over polyester as a barrier coat, but the new laminate would already have considerably more than that in epoxy. However, after all of the above this would be a minor additional investment, so if it makes sense…)
6. Simply applying the fabric and mixing and applying the epoxy is going to be a logistics issue. Any suggestions on doing portions of the hull (and suffer a secondary bond with the subsequent portion)? My optimal notion of fabric application as lengthwise/widthwise/lengthwise wouldn’t allow doing just a portion so applying all three layers within tack time might not work out (or, depending on the hardener, I could be up all night!)
7. Before applying the laminates, how to be sure that the upside down hull is not twisted (since I assume the new laminate will lock in the current condition?
8. Estimating 90-100yds of 50” fabric (a full roll+ of 1708): lengthwise orientation would be 3 strips of 50” fabric @ 10yds = 30 linear yards; widthwise orientation would be 7.5 strips @ 4yds = 30 linear yards, so 90 linear yards for 3 layers plus 10% extra.
9. Estimating 45 gallons of mixed epoxy (30 resin + 15 hardener) as the max (this is the packaging break) with 30 gallons as the minimum.

Many thanks for your valued input!!

[CaptPatrick]

1. Recommended filler/fairing compound to use? Alwfair/MAS w colloidal silica? (Yard suggests Alwfair, I prefer latter)

"Awlfair is clearly marked "Not for use below water line"...

Cabosil, (colloidal silica), is a an additive used to increase bonding attributes and create a thixotropic, (non sagging), condition to a resin, but shouldn't be used alone.

Use two fillers: High Density Filler, (milled fiberglass), and colloidal silica. Ratio of these two fillers should be about 30% silica & 70% milled fiberglass. Mix with resin to the thickness you want.

The more filler you add to the resin, the less the shrinkage rate will be on large volume fills. Prime the area to be patched with unthickened resin/hardener mix. Be sure that the surface is fully wetted out, but pick up all excess resin. Allow this primer layer to tack up before adding the filler.

Mix your filler into a new batch of resin/hardener to the consistancy cookie dough. Carefully pack the void to slightly over fill. Lay a piece of wax paper over the patch and use a block of wood to press and iron the fill into the void. This will leave the fill very close to fair with the surounding surface. Leave the wax paper on until the resin cures.

2. Best fabric orientation, lengthwise or widthwise ? (alternate layers as lengthwise/ widthwise/lengthwise? )

Biaxle fabric is 45/45 weave, versus 0/90 weave for standard cloth. For maximum strength, orient multiple layers so that the weave is offset from the previous layer.

3. Suggested fabrics for the 3 layers? (Yard suggests 1208 biaxial; given the little thickness left, I think it should be 1708 biaxial – actually, I’d think that 1708/1808/1708 might be optimal since the 1708 is 45/45 and the 1808 is 0/90. Would the 1808’s axis be a worthwhile improvement to cover all directions? Would it be worthwhile to wrestle with 2408 biaxial as the first layer – the strakes might be a problem?

1208 will be easier to wet out, work with, and have a higher glass to resin ratio when properly applied. See http://bertram31.com/proj/tips/hole_patch.htm for patching info. Again, use wax paper and wood block to get a tighter and more fair patch.

4. How far should the new laminate be carried up the hull? Cummins 6BTAs will be installed, and will lower the waterline but I’m guessing that it would still be not more than 1” above the chine at the stern, if that – stop at the chine?
5. Follow the 3 layer epoxy laminate with Interprotect 2000E epoxy barrier coat? (Other than their mica microplates, and a possible formulation difference, this sounds questionable to me – makes sense to put 10+ mils over polyester as a barrier coat, but the new laminate would already have considerably more than that in epoxy. However, after all of the above this would be a minor additional investment, so if it makes sense…)
6. Simply applying the fabric and mixing and applying the epoxy is going to be a logistics issue. Any suggestions on doing portions of the hull (and suffer a secondary bond with the subsequent portion)? My optimal notion of fabric application as lengthwise/widthwise/lengthwise wouldn’t allow doing just a portion so applying all three layers within tack time might not work out (or, depending on the hardener, I could be up all night!)
7. Before applying the laminates, how to be sure that the upside down hull is not twisted (since I assume the new laminate will lock in the current condition?

DO NOT GLASS THE EXTERIOR OF THE HULL!

Wait, read that again:

DO NOT GLASS THE EXTERIOR OF THE HULL!


The hull was laid up in a mold and has the proper shape and design. Adding additional layers of fiberglass to the exterior is going to radically alter the designed hull surface and be a fairing nightmare. Only do the necessary repairs and fairing to the exterior of the hull as necessary to fill the blister areas.

After you have repaired, faired, and barrier coated the exterior of hull, all additional fiber glassing will be preformed on the interior of hull. This will give you a stronger hull because the additional glass will be on the tension side of the hull, (interior), rather than the compression side, (exterior).

It will also eliminate or greatly reduce the problem of glassing overly large sheets of fabric because you will be working within smaller sectional areas between stringers and chines. Additionally, you won't be faced with undo fairing & you'll use less fabric and less resin.

Two interior layers of 1208 biaxle fabric is all you need. Lay up with the mat side down and lay up both layers at the same time. Do not allow the first layer to cure before adding the second layer. Over lap the fabric up the stringers and other angle changes, but it's not necessary to cover the whole stringer.

While you're at it, re-do those crappy OEM strut pads! See: http://bertram31.com/proj/struts/strut_backing.htm

8. Estimating 90-100yds of 50” fabric (a full roll+ of 1708): lengthwise orientation would be 3 strips of 50” fabric @ 10yds = 30 linear yards; widthwise orientation would be 7.5 strips @ 4yds = 30 linear yards, so 90 linear yards for 3 layers plus 10% extra.
9. Estimating 45 gallons of mixed epoxy (30 resin + 15 hardener) as the max (this is the packaging break) with 30 gallons as the minimum.

Recalculate your materials for use with 1208 biaxle and two layers. This will reduce your material outlay by as much 50% - 60% while reducing labor and increasing strength.

Many thanks for your valued input!!

Spend some of the money you'll save using this schedule by sending the old capt a gratuity...

[Bob H.]

Bob, Thats quite the project your taking on I know the feeling...my 66 hull was alot thicker...I had some blister/gelcoat isuues as well. I media blasted the entire hull inside and out with corn to start with a nice clean base to work on. The media blasting exposed all the blisters, left the heat on in the barn for better part of a year to dry the hull out. Those blisters will weep for quite some time. Then I epoxied the entire hull, one half at a time with multiple coats, let one tack and add another, I worked past midnight on many a night.
The strut backers are a must, and Capt Pats tips section built my boat..he makes things look easy and shows you the right way to do things..I beefed up my hull from the inside as well..I retabbed the entire boat with one layer 1708, woven, 1708...bow to stern...I am running cummins 6btas as well and wanted to make sure the foundation was stout...persistence pays, keep at it...BH

[Bob Pitt]

Wow – talk about not knowing which end is up…

But, my plan wasn’t too far off: just applying too many layers of the wrong weight fabric on the wrong side of the hull, and maybe using unsuitable filler. Oh, and spending about half again as much as is needed and getting a worse result. Capt. Pat’s recommendations, aside from having the weight of expert experience behind them, are really just cheaper, easier, and more effective.

Thank God for the Capt. and his board; “almost got it right?” – nah – damn close to almost exactly wrong. As the GPS’s say, “Recalculating”; in the meantime, a check is in the mail! I believe I may have earned the position of poster boy for site support… THANKS, Patrick!!

The strut backings were replaced years ago now, back before the blister problem (hidden by numerous coats of bottom paint) became apparent; one of the few things that doesn’t still need to be done. Bob H., your work is inspirational and your tag line comforting (so I’m not the only one…) – appreciate your response and hope to be half as thorough!

[Raybo Marine NY]

awlfair lw is above and below the waterline filler

we had to do blister repair to a 72', I found a nice large tub of the interlux epoxy filler, good for like 3/4" thick and best thing is its easy 1:1 mixture, sands easy as well