New Mold Release agent

The standard for secondary bonding would be to use an industrial adhesive compatible with the substrate (epoxy or polyester) you are using. The theory is that in shear, only the resin (glue) is the only one holding the laminate together.

So for non critical parts, an epoxy or polyester resin reinforced with a light CSM (225 to 300 gr./m2) will do.

For critical bond, you need to use an industrial adhesive whose shear strength is greater than the resin. 3M makes an industry standard gray adhesive but there are other adhesive available in the market. Follow the manufacturers instructions.

Remember that adhesives strength are thickness sensitive so do not exceed the maximum thickness specified by the manufacturer for the bondline/glue line. For hard to reach areas, it can be temporarily bolted together or even blind riveted.

Next is surface area. The more surface area, the better the grip. 25 mm. wide for thin laminates, 50 mm. wide for thick (less that 5 mm.) laminates as a guide.

Surface preparation of the parts to be bonded is also critical to ensure it is free from oil or other contaminants. Degreasing with MEK, acetone, or other solvents comes first, then sanding lightly to remove surface gloss (but not enough to damage the underlying fibers). A previously peel plied surface makes work much simpler but light sanding it gives the best result.

Lastly, as an insurance, and overlay of of one to two layer of WR over and progressively wider than the bond width. This is to seal the bond and reduce edge/corner stress.

P.S.

That was for lap joint. Will continue with T joints

 

Hi Fgayford,
A quick explaination of silicon and wax. A) Wax is generally Curnubia wax and is a solid B) silicon is a liquid C) high temp waxes are generally a mixture of curnubia and silicon. Waxes stick to the mould and then the part and when you release the part the wax shears. Some sticks to the mould some to the part. This is why you need to rewax. Everytime you do a part you loss some of the wax. Silicon being a liquid sticks to both sides. Migration does occur and this needs to be cleaned off immediatly you release the part. I don't see how gelcoat etc could be affected unless it had a problem in the first place but silicon being liquid will transfer and ozze everywhere over time. Wax being a solid takes more to transfer and it definitley doesn't migrate unless its heated up eg in a post cure. tacky tape sticks to wax as its a solid, it won't stick to silicon because its just like having grease on the surface. Hope this helps... Peter s

 

please excuse me for my poor english
thanks for your guide
but about the time.what is the best time to connect the two pieces to make tee joint, from building them to curing,for example 8-10 days?
and about first lay?such as mat or woven roving?

 

Hi V1 - Buy a secondary bonding resin and follow the instructions. I prefer acylic adhesives (PMMA , Plexus, Weld on) they require minimal prep, some claim none, are easy to use and have great strength. Cheers Peter S

http://www.itwplexus.com/UserFiles/File/Guide_To_Bonding.pdf

 

Here is the second part of the T or L joint. A secondary bond is bonding two surfaces that is in an advanced stage of cure, that is, it is no longer tacky and can be sanded. This is usually 24 hours after lamination when the parts has fully cured.

The illustration attached is from LR and is a class standard. Most class have more or less the same pattern. If you want to tab the first layer with CSM, you can start with 225 gr/m2. This is a tie coat only and not considered structural grade by class. If you want it to form part of the structure, use 300 gr/m2 or heavier.

 

Unfortunately this shows the overlaps as being done short to long. It's now common practice to do it long to short. By doing it short to long you bend the fibers and this introduces weak spots. Plus with stiff laminates its hard to lay the long fabric across the short fabric and get it to drape properly. ie as drawn. To some the long to short method does not look attractive. If done neatly its very good to an engineers and laminators eye. If still unattractoive then a light covering cloth can be placed last to cover up all the exposed edges. Regards Peter S

 

How much practical exsperiance do you have with glassing . ?? always cover the edges of laminates !!! start short then get longer till the last layer completely covers everything and going over the layers if you peel ply its never a problem ! rolls down beautifully !! ok ?? if its now common practice its wrong bending fibres causeing weakness is cobblers !! where ever you found that information screw it !!

 

Hello Tunnels - fortunately or unfortunately I have been glassing for over 30 years. I'm sure if you go out a bit you would see these things. Peter

 

Ok I did boat and general fibreglass repairs for a while and during my time saw lots differant things and a few things that had been built differant ways by many differant people . you get to see what hold together and what lets go !! a very high percentage of cases parts joined were lapped both ways but the ones covered over stayed longer than the ones glassed with joins staggered over mainly stringers so i go with over not under and its the way i have shown lots other people to do there glassing . So thats the way i will keep doing it for ever more plus it makes a neater tidyer job specially when you use peel ply over the top . ripped glass usually tears from the edges .

 

Peter,

The purpose of the widest on top overlap is to expose only one ripped edge as tunnels is saying. The more exposed edges, the more like likely to delaminate. Overlaying with CSM is for cosmetic purpose only and an overkill if it is not part of the lam schedule. The only time you overlay with a mat is when you need to bond something to the stringers, a process required by class, or in some cases, class requires that the whole inner layer is resin rich CSM. A job that the structural designer should have foreseen.

The stagger overlap is to present a tapered edges, reducing stress points. Should not be a problem with regular tabbings. If it the edges keep lifting because the ply is thick, use peel ply.