# Suitable filler for OSB joins - then paint?



## ColinK (Dec 13, 2018)

Suggestions for filler for OSB joints so that painted surface will not crack.

We have installed OSB boards over existing sound floorboards. The edges of most joints have no gaps other than what would naturally occur with the slightly textured edges of the boards from the manufacturer.

The boards have been screwed at approx 400mm widths into joists so there should be little movement.

Gaps around edges, up to skirting boards (which were not removed for a number of reasons) are obviously not so consistent

We intend to prime the floors and fairly uniquely add a large mural on the floor and seal with a strong transparent finish (will do another post on this). Aware that OSB is a textured surface - not an issue in this situation.

Please suggest a suitable filler for the main joints (where boards join) and same or different filler for edges at skirting boards.

For joins between boards what are peoples experience with eg a rigid filler like isopon, or something flexible like Silicone or a two part filer like Ronseal High Performance filler.

Same question for floor perimeter where gaps are larger and met the skirting boards.

Thanks ColinK


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## Woodco (Nov 19, 2016)

NOT SILICONE!!!!

No matter what you use, I see it cracking whether its the filler that cracks or the topcoats.


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## finishesbykevyn (Apr 14, 2010)

ColinK said:


> Suggestions for filler for OSB joints so that painted surface will not crack.
> 
> We have installed OSB boards over existing sound floorboards. The edges of most joints have no gaps other than what would naturally occur with the slightly textured edges of the boards from the manufacturer.
> 
> ...


 Why osb board?
If so, I would leave joins unfilled..Or just caulking..it will never look perfect..


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## Local paint pro (May 15, 2018)

flexseal.. it's a handyman in a can!


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## sayn3ver (Jan 9, 2010)

How large a floor? Tongue and groove osb vs butted square edges?

There is a reason an 1/8" gap is required for lost sheet goods. Expansion and contraction. Tongue and groove flooring provides this in the tongue and groove interface.

Your best bet would probably be thickened epoxy in the joint then fiberglass cloth and unthickened epoxy over the joint. Talking big $$$ and a strong guaranteed of the joints buckling or cracking still. 

If it's a busy mural I would have leave the 1/8" joints as is. 

If there was no consistency or care given at time of installation of the osb then that's on the installer. 

I would not want anything to do with this project.


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