Vacuum bagging.

[Jimmylovescake]

I have a couple of palm sized patches inside the bow, where after a bit of stripping it is clear that the very top layer of veneer in the ply is no good.
Being that I want to try to keep the inside entirely wood finish, and using techniques adopted from epoxy surfboard repair, I am intending on vacuum bagging a good piece of veneer from a left over piece of matching ply that I have routed to the last veneer.

Does anyone have any experience with this and what levels of success have been had?

[Obscured by clouds]

never tried it [I built my surfboards the old fashioned way ], but i can see that it would be a valuable and efficient way of repairing veneered hulls.

It would be very usefull for the rest of us if you photograph all the steps and create a record for the data base here

[Ed]

Yes, done it.....and it can work well.

But as with anything with vacuuming, you have to get the preparation right, which mainly means working out how you are going to use the bag or get a good seal around your vacuum area.

If you can put the whole item in a bag it is easy, but if you can't, then you have to use black-tack or other sealing strip around the place you want to pull down. If you are pulling down an outer veneer, then it can be hard to get a decent seal as you will be surprised how much air can pull through the wood, which of course can make it harder to get a decent vacuum.

But no, it is easy enough....go for it ....and do take some photos.

cheers

eib

[chris]

I use a vacuum bag for veneering and laminating but I haven't yet used it on a boat. One thing to think about if veneering a patch is that it is best to lay a scrap of thin material such as 1/16th ply, hardboard, stiff plastic sheet etc over the veneer patch to even out the pressure. Unless the ground is absolutely level and true, and the layer of glue is absolutely even you could otherwise end up with a few lumps in the veneer which you might sand through accidentally later. A hard surface added between the bag and the veneer with apply an evening-out pressure.
Don't forget to put a membrane over the scrap first so it does not also get glued down. I often use the brown parcel tape as nothing sticks to it but make sure is all nice and flat. A crease will leave an impression that is surprisingly hard to remove in the final work.

[Jimmylovescake]

As usual some really useful advice. Ed, I'm hoping I've solved the issue of air leaking through the wood having epoxied the bottom.

When Vac bagging does gravity still have much of an effect. I'm wanting to try and get a few bits done at the same time so just wondering on the importance of getting the repair surface level?

As far as membranes go Chris, I've been using acetate on some of the work I've already done with clamps, this peels off real easy and leaves a clean finish with no surface blush, not sure why; subsequently I do this when ever possible to avoid the whole cleaning the blush off before sanding.

Thanks again for your help folks.

[chris]

Gravity will only have an effect until the vacuum sucks unless you are gluing something really heavy.
You can hold things in place first with masking tape but this will leave an impression if its in veneer.

[Ed]

Don't think gravity will do much....against the power of the vacuum. It is hard to over-estimate the power of a decent vacuum. Just aim at getting all (or as much as possible of) the air out and that should be enough. Don't bother on pushing the vacuum up just for the heck of it as it can be kinda counter-productive and break or bend stuff.

just remember the golden rules:

No cavities, anywhere, anyhow.

Anything other than breather cloth/release film/peelply over the bit your are fixing will most probably leave a mark of some kind or damage it. Had a suck-tube once go over the bit I was laminating and just introduced a massive weak spot into my foil.

cheers

eib

[Jimmylovescake]

Well The wife finished early from work last Friday, and I'd borrowed a venturi vacuum fitting (from my good friend at Ding Devils surfboard repairers in North Devon) that simply fits onto a compressor (with an adjustable regulator) So I set to work repairing the veneers and by the end of the weekend they were all glued so borrowed equipment could be returned.

I had prepared for this by sanding the damaged areas, Filling with Epoxy and a combination of Filler additives which included a silica based one (to prevent run off), a fairing one (to aid sanding as silica goes really hard), and one for glueing (for added strength), plus added some sieved wood dust from sanding; I mixed only a little of the silica and used the wood dust more to tone the colour a bit better. I appreciated that this was never going to be invisible, but I didn't want the pinky red colour of the fairing additive to halo the finished veneer repairs; this was all mixed to a smooth peanut butter consistency.
Once the filling / fairing had gone off, I sanded it back with 60 Grit so it was smooth but keyed, with no bumps or edges that could leave any cavities behind the veneers.

I had made my veneers by using a router and a lot of patience with some of the left over good bits of ply that had been previously removed from the floor of the boat, taking it down as best I could, and finished by sanding carefully with some 60 Grit to get a good key down to the last ply veneer. I chose this option simply because a) I didn't want to pay for any, and b) The colour was guaranteed to be a lot closer to the original wood than anything I could find new due to the fact the boat was built in 1959.
I cut my veneers to shape with a Stanley knife (I wasn't going to spend out on a flash new veneer saw) taking great care not to split or separate the veneer as I did so.

Once all of the surfaces had been prepared I followed this process for each repair area...

I taped around the area with the double sided sealing tape. This stuff was really sticky and it felt a little like setting Mastick, but it made a good seal on the wood including around to bits where it had to go up onto the stringers.

I then cut pieces of the red release film and the breather fabric to fit within the taped area, and a section from a vacuum bag to fit over it.

Once I had everything prepared I warmed up the surface of the wood and the back of the veneer before applying a coat of epoxy with no additives. I left these for about 10 minutes before placing the veneer into position carefully and then covering first with the release film, and then with the breather fabric.
Before sealing all of this off with the vacuum bag I had to place the non-return valve base inside the repair area far enough from the veneer that it would not effect the end result, I then fitted the vacuum bag over the top before making a hole for the non-return valve and fitting the top part of the valve.

I ensured that the seam was as good as I could visibly see before then attaching the hose from the venturi pump to the non-return valve and switching on the compressor with the regulator turned all the way down.
As the compressor gained pressure I increased the vacuum pressure so it read a little over 4 psi on the regulator. This was enough to suck all of the air out of the bag and show up any leaks, I chased the leaks out by simply working the seal of the vacuum bag around the tape and then left everything on including a convection heater blowing warm (not hot) air onto the repair area.

Having left some of the left over resin in a cup within the same area, I had a good gauge as to how far the resin had kicked throughout this process. Despite being told that this would only need an hour, the resin in the cup took almost three hours to go hard. during the last hour I turned up the regulator to increase the pressure to 6psi.

After three hours I turned off the compressor and removed everything. The tape left a black residue in places that was easily removed with thinners, and the veneers appeared to stick firmly.
I did not touch any of the veneers for a further two days to ensure a full cure before I started to work on them.

After the two days I made a star at bringing the veneers flush by beginning with a series of different block planes and working from the centre outwards. once close I finished by using a sander at a low setting with some 80 Grit sand paper.

I was very happy with the results over all, and they look so much better than the alternative of using fibreglass an / or filler. There is an obvious halo of resin as a result of sanding them flush, but they look tidy enough, and the resin should hide a little more once varnish is applied.

I have added photos to the on-line album for anyone to see, here's the link:

https://plus.google.com/photos/11102597 ... Kvf3tjr1QE

...Please bear in mind that at some point I will remove a lot of these photos in time to come as there are duplicates (phone, camera, different settings etc). I will upload the vacuum bagging ones today so if you are able to search by date that should help, if not, they should be towards the end of the album.

I would like to say thank you to everyone who offered me some advice on here, to Lee at Ding Devils Surfboard repair in North Devon for further advice and the use of his venturi vacuum pump, to Mark at South West Dent and Scratch for the use of a compressor, and to the guys at East Coast Fibreglass Supplies who were also great with advice on materials friendly on the phone and really quick delivering my order.

I welcome further comments, questions or ideas on how I could have done this better; but in the mean time I would encourage anyone not to be put off by thinking that this is too complicated to do, it really isn't.

[Ed]

Great description! and well done.

Might just be me, but that link for the images didn't work for me and I would love to see them.

Anything that we can do to encourage people to try vacuuming is really worth it...I reckon.

I agree with you that it is not nearly as hard as people think and can work really well.

look forwards to seeing the images for real.

cheers

eib

[Jimmylovescake]

Great description! and well done.

Might just be me, but that link for the images didn't work for me and I would love to see them.

Anything that we can do to encourage people to try vacuuming is really worth it...I reckon.

I agree with you that it is not nearly as hard as people think and can work really well.

look forwards to seeing the images for real.

cheers

eib

Thank you for the feedback. You mail need a gmail account to view the pictures, I'm not sure; although I have just edited the link which didn't seem to work properly anyway.
I could upload them to the forum although I'm not sure of size limits and how many I can do.

[Ed]

I have a gmail account.

your link opened up the google pictures on my account, but it didn't contain your album......

but it does now!

Great photos.....and plenty of them too. Brilliant.

Well done,

Would you be up for re-writing it with a few images to show the process for our 'hints & tips' pages? If so, it would be great to have it.

cheers

eib

[Jimmylovescake]

I have a gmail account.

your link opened up the google pictures on my account, but it didn't contain your album......

but it does now!

Great photos.....and plenty of them too. Brilliant.

Well done,

Would you be up for re-writing it with a few images to show the process for our 'hints & tips' pages? If so, it would be great to have it.

cheers

eib

I would be more than happy to do something, although it will probably not happen until I have finished putting the boat together.
I do have to say that I am far from an expert on these things and have simply done my best using the advice and knowledge shared by others.
For anyone wanting to know more, the guys at East Coast Fibreglass supplies are a really helpful resource, I believe they even run short courses on the whole process, although probably not quite how I've done it.

It would be good if anyone else with experience in vac bagging could chip in with some feedback on how it could be done better, or even differently if it is to be as helpful as your varnishing guide.

[Ed]

Likewise I have had tons of help, advice and encouragement from Wizz Deas at Matrix Mouldings in Bristol. A great bloke!

Don't worry - most of us here are not experts, but are just willing to try and help others to get to the same level of knowledge as us, rather than trying to hide everything behind veils of mystery.

I just get a big kick when someone shows that some process that many think of as 'hard', 'impossible' or for the professional only, is in fact pretty easy to do with just a little help and information.

So thanks!

When you have time, please do write something and I will be delighted to add a few thoughts if it helps.

cheers

eib

[ent228]

ed said "most of us here are not experts"........I'm reminded of an kayaking definition of an expert....someone who got it right last time.

Perhaps a little cynical but to the point.

[Ed]

I like:

"If it is worth doing.....it is worth doing badly"




or (since I got this from Wiz mentioned earlier):

"We know this works in practice but not sure if it works in theory"


and since we see a fair amount here:

"....like trying to teach eggs to suck grandma"

Glad its Friday

eib