Strange OSB3 and fibreglass roofing

[Ollie78]

Hi

I just picked up a couple of boards of OSB3 from Wickes. I am going to use them as a roof deck for a combined bin/ log store next week.
This will have a fibreglass applied to it. The instructions for the fibreglass stuff says to have the "rough side " or the "printed side" up.
I didn`t notice at first but this OSB3 has no printing at all, usually its Norbord or Kronospan printed on it. There is no difference I can tell between the sides they are both really smooth there is a small label on one side with a barcode etc but thats it.
Should I sand it a bit to make sure its rough enough to key before applying fibreglass resin ?

Ollie

 

[Keith 66]

If you are fibreglass sheathing a roof (or deck of a boat) its worth remembering that Polyester resin is a pretty mediocre adhesive so often relies on a mechanical bond, Best way to scurf it up is with a coarse sanding disc on an angle grinder, 24 or 16 grit will score the surface well.
Second tip, If you apply the resin & glass at once the resin will cure in the glass first & is likely to come away from the wood. It is always best to apply a coat of primer resin to the wood first with a fairly high catalyst ratio, Allow it to start kicking off before you apply the glass & resin.
If its a mission critical job like a boat deck i would always use epoxy resin!

 

[Ollie78]

If you are fibreglass sheathing a roof (or deck of a boat) its worth remembering that Polyester resin is a pretty mediocre adhesive so often relies on a mechanical bond, Best way to scurf it up is with a coarse sanding disc on an angle grinder, 24 or 16 grit will score the surface well.
Second tip, If you apply the resin & glass at once the resin will cure in the glass first & is likely to come away from the wood. It is always best to apply a coat of primer resin to the wood first with a fairly high catalyst ratio, Allow it to start kicking off before you apply the glass & resin.
If its a mission critical job like a boat deck i would always use epoxy resin!

The stuff I have is a 2 part kit, instructions say fix the trims etc, cover the joints with the bandage and a bit of the resin, then fill in the rest with the glass matt and resin. Then a top coat of the er, topcoat.
I will be sure to give it a good sand before I start and a wipe with acetone. Not sure there is enough spare to do a priming coat as such.

Ollie

 

[baldkev]

Do you have a paddle roller? Years ago i used to do fibreglassing and a paddle roller helps to flatten the matt, get rid of air bubbles and squeeze out excess resin.
https://www.toolstation.com/big-boy...OxgSBLCr7S8wDLoSmwxoCGTIQAvD_BwE&gclsrc=aw.dsYou could pick that up for the extra resin.....

As keith said, poly isnt perfect, higher shrinkage and brittle, but it'll do the job.

 

[Jameshow]

You could try using a hardpoint saw to scrap the surface too.

Polyester is a cheap as chips resin!

 

[Keith 66]

Baldkev is right, Get yourself a paddle wheel roller, for a roofing job you need one at least 6" wide, It consolidates the wet mat & gets the air out making your resin go further. Without it you will use far more resin.

 

[Ollie78]

Do you have a paddle roller? Years ago i used to do fibreglassing and a paddle roller helps to flatten the matt, get rid of air bubbles and squeeze out excess resin.
https://www.toolstation.com/big-boy...OxgSBLCr7S8wDLoSmwxoCGTIQAvD_BwE&gclsrc=aw.dsYou could pick that up for the extra resin.....

As keith said, poly isnt perfect, higher shrinkage and brittle, but it'll do the job.

I have ordered a paddle roller with the kit, I already have normal rollers and disposable brushes. It seems a mechanical key is important here they recommend OSB over plywood for this reason. So its a bit annoying I managed to find the worlds smoothest OSB. I think I have some 60 grit sanding belts so will give it a going over with that first.

 

[baldkev]

Cool. I would think hand sanding it a radom fasion would be better than a belt sander, but keying it up either way will be good. Dont over think it, it'll be fine for a bin store, just pay attention to trying to get the matting flat..... when you top coat, you dont want bubbles, so do your best to work it ( the matting ) with the paddle. With epoxy, heat pops the bubbles very effectively but from memory poly didnt work so well with heat, it was more likely to start browning / burning.

 

[Scottbd]

Hi

I just picked up a couple of boards of OSB3 from Wickes. I am going to use them as a roof deck for a combined bin/ log store next week.
This will have a fibreglass applied to it. The instructions for the fibreglass stuff says to have the "rough side " or the "printed side" up.
I didn`t notice at first but this OSB3 has no printing at all, usually its Norbord or Kronospan printed on it. There is no difference I can tell between the sides they are both really smooth there is a small label on one side with a barcode etc but thats it.
Should I sand it a bit to make sure its rough enough to key before applying fibreglass resin ?

Ollie

 

[Scottbd]

Hi

I just picked up a couple of boards of OSB3 from Wickes. I am going to use them as a roof deck for a combined bin/ log store next week.
This will have a fibreglass applied to it. The instructions for the fibreglass stuff says to have the "rough side " or the "printed side" up.
I didn`t notice at first but this OSB3 has no printing at all, usually its Norbord or Kronospan printed on it. There is no difference I can tell between the sides they are both really smooth there is a small label on one side with a barcode etc but thats it.
Should I sand it a bit to make sure its rough enough to key before applying fibreglass resin ?

Ollie

Hi Ollie
I am having the same issue did you manage to find a solution at all ? Or did you sand them or just lay ontop ?

 

[Ollie78]

Hi Ollie
I am having the same issue did you manage to find a solution at all ? Or did you sand them or just lay ontop ?

I ran a belt sander over it once I had screwed it all down, 80g I think then wiped it over with acetone to remove the dust.
It stuck all right as far as I can tell.

 

[Scottbd]

Thanks for the speedy reply mate I am returning these now gona try and source some rougher ones didn't want to take the chance . Out of curiosity was it the writing side you laminated on ?

 

[Inspector]

There is OSB sold here about 11mm thick meant for roofs of houses. It has a side that has a pressed or rolled textured surface a little like corrugations. It is installed rough side up to provide some traction for those working on it. It is also printed with lines on a 16" and 24" grid to aid the framers. They can run their nail guns along them to hit the trusses underneath without having to think much. The resin instructions may have originated here if your construction industry uses different products. The other side of the OSB is smooth and we have other OSB sheets that are smooth on both sides. Roughing them for the resin to key into makes sense.

Pete

 

[Scottbd]

thanks very much I went fir the 18mm SMARTPLY type thanks all for your help