Vacuum bagging - ripples on finished piece ?

simo.b · 25 Apr 2016

Hi all
I've just purchased a vacuum bag set up and ran my first few test panels yesterday, pressing hpl sheet to 18mm birch ply using pva. The process went fine but i've got some slight ripples on the finished hpl surface. They're only visible at glancing angle. Probably made more visible as the test hpl is near black colour.

Any ideas what went wrong?

I applied the pva with a foam roller to the birch ply, layed the hpl on and placed faced down in the bag on an mdf baseboard. I ran breather fabric across the top as directed. The job was in the bag between 5-10 mins later.

I'm thinking it was something in my glue up, be it the choice of pva or uneven application perhaps. Perhaps i shoild have run over with a veneer roller before pressing to even out the surface?

Anyway, any tips from seasoned vac pressers would be much appreciated.

worn thumbs · 25 Apr 2016

I have no idea what hpl might be.I do have a fair bit of vacuum bagging experience and I would recommend using a pressure pad on the thinner material to eliminate ripples.Alternatively you can place the thinner material below the thicker piece and vacuum to a flat surface.In a bygone time I used to use a cast iron surface table for a base,but I recognise that not every workshop will have such a feature.

simo.b · 26 Apr 2016

Thanks for the reply and suggestions.

The hpl is high pressure laminate aka formica. I'm using an mdf baseboard inside the bag as a flat surface below the workpiece. I checked with Peter at Airpress who supplied the bag. They suggested its likely to be an issue with my glue application technique, maybe laying on a little thick. Seems like it's important to get the right amount on to stick, but not over saturated the wood.

Beau · 26 Apr 2016

Had similar problems myself and a presure pad does help.

Worst mistake I made was veneering both sides of a door and put this straight down onto the grooved base board. The veneer got sucked down into the grooves by some way. Now use a supporting both side of the build up. Corugated cardboard can also create some interesting patterns :lol:

Sawyer · 26 Apr 2016

I had a similar issue the first time I used mine. Then realised that I should have used a thin plywood caul on top of the veneer itself, which obviously, must be separated with a layer of paper. This solved the problem completely.

custard · 26 Apr 2016

Agree with the pressure pad suggestions, but if I read the OP right he loaded the job with the veneer/laminate facing down against the baseboard, so the baseboard in effect became the pressure pad.

I don't have much laminate experience but I do loads of vac bag veneering with wood, and loading the job face down is an effective (but slow) method of work. Was the baseboard grooved, (doesn't have to be by the way if you're using breather fabric and a top attaching pump hose), if so maybe the grooves are the explanation?